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How Stress Affect Memory?

Posted on September 30, 2013 by 6s79T

Stress can be chronic or acute. They both induce chemical changes in the body and brain. Excess stress – chronic or acute – both adversely affect memory function (working memory and long term memory), especially the explicit or declarative long-term memory. The level of stress hormones increase upon exposure to extrinsic or intrinsic stress. The part of the brain that was found to be affected by stress hormones are the hippocampus, prefrontal cortex and the amygdala – all of which are important and involved in memory function. Cortisol (or Hydrocortisone) is the stress hormone produced in the body during stress. It belongs to a group of steroid hormone known as glucocorticoid produced by adrenal cortex. Mild stress does not appear to severely impair memory probably because of body’s natural defense response under stress. The release of cortisol in stress response also activates anti-stress and anti-inflammatory pathways which may mitigate the potential adverse effects on health including memory and cognitive functions. The effect of stress on memory has been implicated to be an inverted U shaped effect. Cortisol was found as a common mediating mechanism for both the facilitating and impairing effects of stress during different memory phases. The difference in effect may be due to how cortisol impacts glucocorticoid receptors in the hippocampus and prefrontal cortex.

Effect of Acute Stress

When does stress facilitate memorization instead of impairing it? The stress will only facilitate memorization when the stress is originated in the context and around the time of event that needs to be remembered and when the stress hormones and neurotransmitters (some stress hormones are neurotransmitters themselves) activate the same circuits as those activated by the situation. The more relevant the context in which stress is experienced, the easier the events will be hard encoded by brain. Enhanced memories resulting from stressful learning situations can be due to the effect of stress on memory acquisition and consolidation phase through enhancing attention, sensory perception, motor function.

Is there a difference for extrinsic or intrinsic stress in terms of their effect on memory? It is hypothesized that intrinsic (psychological)stress facilitates learning and memory processes whereas extrinsic stress normally will impair memorization or memory retrieval. Some intrinsic stress tend to enhance memory consolidation. But the role of extrinsic stress in memory consolidation seems to be quite heterogeneous. The controllability and predictability of the stressors make a difference. Uncontrolled stressors tend to be more deleterious.

Is there different effects for different memorization phases ? Based on the review of results presented in the scientific literatures, scientists has proposed the opposing effects by stress. Stress appear to facilitate memory consolidation while impair the retrieval of information, but only generally. Acute extrinsic stress has been revealed to be more efficient to disturb memory retrieval.

Is there different effects on the type of things to be remembered (types of memory)? Whether it is declarative implicit memory or nondeclarative explicit memory? It appears that declarative memory is more vulnerable to stressors. Studies has shown that both intrinsic and extrinsic stress enhances classical conditioning (a type of nondelarative implicit memory; see post “examples of Examples And Types of Nondeclarative Implicit Memory). But experiencing an acute, highly stressful external event can interfere with retrieval of previously stored declarative memory (facts, events, knowledge).

Effect of Chronic Stress

Chronic stress occurs when the body experience stressors (environmental or psychological) with sustained frequency and intensity to such an extent that the body’s natural anti-stress (relaxation) response can not be activated or be suppressed. Chronic stress induce what is know as fight-or-flight response during which stress hormone epinephrine (or adrenalin) and norepinephrine (or noradrenaline) are produced by adrenal along with other hormones such as cortisol. Epinephrine and norepinephrine are not only hormones but also neurotransmitters belong to the categories of neurotransmitter known as catecholamine. Other member of catecholamine include dopamine. Epinephrine, norepinephrine and dopamine comprise the most abundant catecholamine in the human body. Moderate level of epinephrine is actually positive for memory function, it has been found to help create the type of autobiographical long term memory known as flashbulb memory.

Chronic high intensity stressors seem to facilitate classical conditioning whereas it impairs explicit declarative memory. Hippocampus was the main target of cortisol.Cortisol has been found to shrink the size of hippocampus – the central unit of the brain that transfer short-term memory to long-term storage for later retrieval. It is not yet known whether this shrinking is reversible. It is believed that structural and molecular alternations induced by chronic stress in this brain area account for impairment of hippocampus dependent memory types i.e explicit declarative memory (episodic and semantic memory). Stress induced high glucocorticoid levels can suppress neurogenesis in the dentate gyrus and compromise neuron survival.

Increasing evidence suggests parallel alternations in the prefrontal lobe as well – a region of brain important for working memory function induced by chronic stress. Major neuronal structural alteration occurs in the medial part as a consequence of chronic stress or prolonged treatment of glucocorticoid in vitro including dendritic atrophy. Prefrontal cortex is very sensitive to changes in the neuromodulatory inputs it receives from norepinephrine (NE) and dopamine (DA) systems and that this sensitivity can result in marked alteration in the working memory functions of the PFC. Very high levels of catecholamine release during exposure to uncontrollable stress disrupt the cognitive functions of prefrontal cortex.

The Role of Attention For Working Memory

Posted on September 25, 2013 by 6s79T

In cognitive psychology, “attention” is the terminology refer to the capacity of selectively concentrating on the focused items while ignoring other things. In the post “what is working memory?”, a multi-component model of working memory was presented where the concept of “central executive controller” was formulated as a functional area in the brain for processing and manipulation of attentional selected information for short-term memory as well as long term storage afterwards. One of the major capacity of the executive controller is the attention control including the process of selection and inhibition (filter out irrelevant information).

Attention is one of the most studied area in cognitive neurobiology and cognitive psychology. The concept of attention is essential in understanding how memory works. The theories of attention form the basis on how to improve memory, prevent memory decline with age through attention control training. Patients with Adult ADHD (attention-deficit hyperactive disease) display such symptoms as

disorganization
extreme distractibility
difficulty in following instructions or apparently not listening
difficulty relaxing
difficulty starting a task
chronic lateness
angry outburst
mis-prioritize obligations (spending long time on insignificant things, but forgetting important things or tasks)

Attention can be functionally or clinically divided into several types: focused attention, selective attention, sustained attention, alternating attention and divided attention – in the order of increasing level of difficulty. The model is based on the observation in the recovering of attention processes in brain-damaged patients after coma. The clinical classification of attention or the clinical model of attention has its application in evaluating attention in patients with various pathologies corresponding to different daily difficulties and is particularly helpful for designing attention training programs and rehabilitation programs.

Focused attention is the ability to respond discretely to specific visual, auditory or tactile stimuli. Selective attention involves a selection process for focusing on a specific perception while ignoring others. Selective attention measures the ability to maintain a cognitive set in the presence of distracting or competing stimuli. The selected attention can be voluntary attentions. They can be unconscious or automatic as well (in a photo with a background, the focused image will receive attention initially). The “cocktail party effect” refers to that selective auditory attention (one only attend to one voice) with the background noises and other conversations in the room being ignored. The selective visual attention is sometime also called “attentional spotlight” where the spotlight scene will receive attention selectively which suggests visual attention can be focused on a small portion of the environment.

Sustained attention is the ability to direct and focus cognitive activity on specific stimuli for a duration of time. Sustained attention measures the vigilance capacity – the ability to maintain a consistent behavioral response during continuous and repetitive activities. A distraction can interrupt and consequently interfere in sustained attention as well. When a person has difficulty in sustained attention, they often showing difficulty in adapting to environmental demands or modify behavior.

Alternating attention (task-switching) measure the ability in shifting focus of attention between tasks having different cognitive requirements. Divided attention is the most difficult level of attention. It measures the ability to respond simultaneously to multiple tasks.

An individual’s working memory capacity is closely linked to their attentional control capacity. Attentional control allow simultaneous information being filtered and selected and gain access or entry into working memory for evaluation, manipulation and for forming behavioral decisions. The model described here explains how information across different domains (environmental stimuli: sensory or motor; stored memory, internal state) are competitively selected and transduced to the working memory through the attention system . Four processes or components are fundamental to attention: working memory, top-down sensitivity control, competitive selection, and automatic bottom-up filtering for salient stimuli (i.e. salient filter). Each process makes a distinct and essential contribution to attention. The model depicts both voluntary (endogenous attention) and involuntary attention (exogenous attention, automatic attention).

Involuntary attention or exogenous attention is the bottom-up process to capture and competitively select relevant important information (i.e salient stimuli) from external (sensory or motor) environment and filter out the irrelevant or unimportant information. Salient stimuli are those stimuli standing out from the background as in the examples of “cocktail party effect” and photo mentioned in the post. Involuntary attention involve the three processes: from automatic salience filter to the competitive selection which selects the information that gains access to the circuitry for working memory. What the salience filter does is to modulate the neural electrochemical signal strength of those competing representations of exogenous information. The competitive selection procedure determines what information will be allowed to gain access to working memory by comparing the relative signal strengths of competing representations of information.

Voluntary attention (or endogenous attention) process is a top-down goal-directed process in that the attention originates from within one’s own knowledge (stored memory or internal state). Voluntary control of attention involves the three processes from working memory to top-down sensitivity control and then going through the “competitive selection” procedure which allow new neural representations of information enter into working memory for re-processing. This loop completes the voluntary attention process. The top-down sensitivity control is the process during which signal strength representing endogenous information are modulated and increased in intensity. The responsiveness to these signals are enhanced in the brain. The endogenous signals are said to be biased because they are based on the decisions made in working memory and are derived from goal and task demand. The voluntary (endogenous) attention sometimes can be overwritten or distracted away by involuntary external stimuli if they are sufficiently salient to capture the attention.

The proposed conceptual framework for attention process suggests that attention does not consolidate information or make decisions. It is the working memory where information are further analyzed, manipulated and where decisions are made. The information subject to competitive selection are across all the domains (endogenous or exogenous). These information can be from outside environment (sensory perception, motor responses) or from internal state of the mind such as ongoing thoughts, motivations, moods as well as stored memories. Research has shown that both top-down and bottom-up control of attention requires frontal and parietal cortices. It appears that prefrontal neurons signal first during top-down voluntary attention whereas parietal neurons are activated earlier during bottom-up automatic attention.

Many factors can affect an individual’s attention control capacity including :fatigue, stress, substance use, age. Both the clinical model and conceptual model described are necessary in designing attention improvement and attention training programs such as mixed attention training, working memory training.

What Is Working Memory? The Effect of Aging

Posted on September 20, 2013 by 6s79T

Working memory is more of a theoretical concept representing the theoretical framework that explains our cognitive functions – the limited capacity for the temporary storage and manipulation of information for a wide range of cognitive tasks -comprehension, reasoning, learning – beyond the simple retention and recall of information . The term working memory has been used interchangeably with short-term memory historically. The presentation of the framework of how working memory functions has to begin with the comparison of the subtle difference in the terminology of “working memory” and “short-term term”. Generally speaking, short -term memory refers to the passive storage of bits of information (or items) temporarily, in this sense, short-term memory is only the storage component of working memory that does not involve information manipulation or consolidation. Memory encoding and consolidation are not passive processes of temporarily holding bits of items in the brain (see post “memory process”). The capacity the short-term (working) memory – the number of items that can be temporarily held is about 7+/-2. Working memory emphasize the executive control function of the information manipulation process for cognitive tasks which is an active process with integration of the effect of attention.

The development of the concept of working memory is closely linked with lines of researches that lead to the proposals of several working memory models which form the theoretical framework in this area. Among them, the multi-component model perhaps is the most cited accepted working memory model that dominate the explanation of how working memory works. The model functionally divided the working memory into a “central executive controller” and temporary storage (or called “buffer”). The temporary storage was further divided functionally into three different types of storage buffer:

visuo-spatial sketch-pad to store visuo-spatial representations;
phonological loop to temporary store speech or language related auditory-verbal or acoustic-verbal information;
episodic buffer is the temporary storage for episodic memory items (autobiographical facts and events)

multi-component model of working memory

These functional components (the 4-component model) interact with each other; and interact with their corresponding long term memory (LTM), forming a system to explain cognitive memory processes. (see figure). Despite very different theoretical methods and models adopted by researchers, there is general consensus or agreement among neuropsychologists and neurobiologists on the existence of a functional area known as “central executive controller” with limited attentional capacity. The parts of the brain believed to be involved in working memory function include (pre)frontal lobe (cortex), parietal lobe (cortex), anterior cingulate, and parts of basal ganglia.

The central executive controller is located in the frontal lobe of the brain. It is an attentional control system for the control and regulation of cognitive functions. Central executive controller manipulate information in short-term memory storage as well as information retrieved form long-term memory. The executive control component of the working memory comprises an integrated network of processes including:

the capacity to focus attention
to divide attention among two or more tasks simultaneously
binding information from multiple sources into a single episodic experience
coordinate the interaction between visuo-spatial sketch-pad, phonological loop and episodic buffer
the ability to filter out irrelevant information (the selective inhibition functionality)
and control access to long-term memory.

The executive functioning of the working memory has been studied extensively for patients who suffered from dysexecutvie syndrome – a deficit in working memory capacity due to the damage in the frontal lobe of the brain. Patients with dysexecutive syndrome have problems or impairments in the ability to control or focus attention, maintain goal-directed information retention against distraction. Sometimes, the patient exhibit symptoms of confabulation resulting from inappropriate association of past memory with new information. The inability to associate recalled long-term memory with new incoming information could sometimes lead to totally false memories. ADHD (The attention-deficit/hyperactivity disorder) is the medical condition associated with the problem in working memory where a set of attention and executive functioning are impaired.

The component “phonological loop”is assumed to have two basic subcomponents -a temporary speech-related/acoustic store and a subvocal articulatory rehearsal process. The speech-auditory store hold sound memory traces (when one reads the words) which are subject to rapid time decay and is a passive storage unit. The articulatory rehearsal component (or articulatory loop) is used to recall the sound memory trace via rehearsal (when one reads the words repetitively to prevent the decay). Visually presented verbal information is transformed into auditory (phonological) code by reading the word to oneself (silent articulation).

The visuospatial sketchpad is where information what we see was stored. Spatial and visual information are temporarily stored in the sketch pad where they can be manipulated by the central executive controller such as combining the shape and color of the objects, the location and speed of a moving object in space. The visuospatial component of the working memory can be divided into separate visual, spatial and possibly kinesthetic (moving) subcomponents. This conclusion was derived from the fact that brain-damage patients who showed one deficit but not the other .

The episodic buffer is where information across different domains of storage (visual-spatial, verbal-auditory, and LTM) can be collated and combined. Integrated units of visual, spatial and verbal information with chronological sequences are stored. Semantic meaning of the information is also assumed to be linked to the episodic buffer.

The framework of working memory has been implicated in the development of rehearsal strategies. Age is a factor that influence the working memory capacity. It is believed that this cognitive functional part of the brain – the working memory is most sensitive to the aging process. Aging people tend to have slower processing, manipulation and integration ability of the central executive controller. This would lead to more time-dependent decay of the information and less efficient for transferring short-term memory to long-term memory. Not only the speed declines, the capacity of the working memory also declines – less items can be held in the temporary storage for integration. Attentional control system are less efficient. Another theory of the age-dependent working memory decline is the capacity to filter out irrelevant information in inhibition function, making the memory being cluttered with interfering irrelevant information. The multi-tasking function also tend to decrease with age, making the task completing capacity vulnerable to environmental disruptions or distractions.

Examples And Types of Nondeclarative Implicit Memory

Posted on September 15, 2013 by 6s79T

Nondeclarative memory (or implicit memory) is one of the two categories of long term memory. Declarative memory or explicit memory are those long-term memory (LTM) related to autobiographical facts and events or experience (episodic memory) and contextual knowledge (semantic memory) (see.post “types of memory” for more detail about declarative memory). Nondeclarative memory distinguish from explicit memory in three ways:

nondeclarative or implicit memory operates outside of awareness i.e. it does not require consciousness and focused attention as being emphasized by declarative memory;
the retrieval and influence are implicit, usually only observable by changes in behavior or habits;
functionally independent of declarative memory and the medial temporal lobe is not involved.

types of memory

The most easily understood and perhaps most widely studied nondeclarative implicit memory is procedural memory – the type of memory give us the skill for “procedural (motor) tasks” such as how to play music instruments or how to do surfing or diving. Procedural memories are affected by the part of the brain known as striatum (the subcortical part of the forebrain, the major input station of the basal ganglia system) and cerebellum. There are several other nondeclarative memories with unique characteristics and depends on different and specific brain circuits.

Priming defines a category of implicit memory that is associated with the same or related stimuli we encountered before. Basically, priming is the ability to constitute an unconscious response to the information with increased speed and accuracy to which we have been encountered before. There are a few forms of priming. Two main categories are perceptual priming and conceptual priming. Perceptual priming refer to the priming for different kinds of sensory perceptions (visual, auditory and etc.). They are mediated by the corresponding cortex of the brain for each specific sensory type. Conceptual priming facilitates processing of the meaning of a stimulus or enhances the access to a concept. One example of priming is: if a person was shown study list of words including the word “table”, and then is asked to complete a word starting with “tab”, the probability that he or she will answer “table” is greater than if they are not shown (primed) the study list. In the research field, the “perceptual identification task” is used to identify and evaluate the perceptual priming. The participant was exposed to a series of words on the computer screen for a flash of 34 milliseconds, then the participant is asked to identify each flashed words. Then the result is compared to that of the participants or same individual who was first shown a list of words containing the flashed words before the “perceptual identification task”. The probability or accuracy of identifying the flashed words increases if the participants was shown the word list before, even though they themselves report that they were simply guessing the flashed words. This suggests that the participant are not aware of the influence by the study list. Similar phenomenon can be observed for semantic representations. Conceptual priming (facilitated processing of the meaning of a word) can be demonstrated by “category exemplar generation task” which will not be detailed here.

Habit memory is a type of nondeclarative implicit memory belong to the category of non-associative learning. With habit memory we have the capacity to learn and retain new information unconsciously, retaining so-called habit memory even when conscious or declarative memory is absent. This type of memory require reflex pathways as well as basal ganglia for function which give us the ability to respond to habitualized stimuli formed through habitual repetition and slow accumulation of knowledge between a stimuli and a response in the past. The acquisition and retrieval of habit memory can be identified and evaluated using “probabilistic classification task” – an experimental test procedure designed to measure the habit memory. Combined with the techniques of neuroimaging which can measure what part of the brain in activated during “probabilistic classification task”, researchers has observed the increased basal ganglia activation and decreased medial temporal lobe activities, a result consistent with the conclusion that implicit memories are functionally separated and independent of explicit memory which is an active “learning process” instead of “passive learning”. For this reason, habit memory may be a trainable technique for helping people whose conscious explicit learning or declarative memories are impaired. The process by which new behaviors become automatic is habit formation. Real life examples of habit memory include those classified as nervous habits such as nail-biting, sniffling.

In contrast to non-associative learning (habit memory), associative learning (conditioned association) form another category of nondeclarative implicit memory. A brief definition for associative learning is the process of acquisition, retention and expression of a response or behavior through association between two stimuli (for classical conditioning) or between a behavior and a stimulus which is the consequence of such behavior (for operant conditioning). The two forms of associative learning are classical conditioning and operant conditioning. Classical conditioning (or respondent conditioning) is the learning of an involuntary reflexive response to a neutral stimuli through association of this neutral stimuli or so called conditioned stimuli with its natural stimuli (also called unconditioned stimuli). Classical conditioning is the most basic and simplest form of associative learning first described by behavioral psychologist Pavlov. A simple example of classical conditioning is the eyeblink response. Eyeblink response to air puff (the unconditioned stimuli) occurs naturally and automatically, When the participant was presented each time before air puff with a tone sound (the conditioned stimuli), then human has the ability to acquire or learn to respond (the “learned blink” or “conditioned response”) to the tone sound in the absence of the unconditioned stimuli (the air puff) eventually.

Operant conditioning (or instrumental conditioning) is distinguished from classical conditioning in that operant conditioning deals with the modification (increase or decrease) of “voluntary behavior” or operant behavior. The terminology was coined by behavioral psychologist B.F. Skinner. In the case of operant conditioning, the association of the learning occurs between the behavior itself and the consequence of such behavior. When the consequence of the behavior is associated with behavior, such behavior or the probability or frequency of the behavior is either increased or decreased. The increase of the behavior as a result of operant conditioning is called “reinforcement” while the decrease of the behavior is called “punishment”. Examples in experimental and real-world setting help to clarify the concept. One simple example of operant conditioning is in the classroom setting: each time a student raise hand to ask a question, he or she receives a praise from the teacher. Such association of “raise hand and ask question” with the consequence of “receiving praise” will reinforce or increase the frequency of student’s behavior of “raise hand and ask a question”. Under certain situations, in order to reduce or remove an undesired behavior, association can be made between the behavior and the “punishment”. For example, if the student will be told and punished with losing their good grades if they talk out of turn or interrupt in the class. This consequence of the behavior acts as the stimuli to a decrease potential disruptive behavior.

The classical and operant conditioning are applicable to many areas of real life situations. Two major areas of application of classical and operant conditioning is in the skeletal musculature reflex responses and the emotional responses such as phobia (fear), anxieties. These two functional aspects of classical conditioning are medicated by the different areas of brain during the acquisition stage. Amygdala has the role in forming conditioned associative learning related to emotional responses. Cerebellum is required for acquiring classical conditioning of skeletal musculature reflex responses. Patients with cerebellar lesion failed to acquire new conditioned eyeblink response. Cerebellar circuits are not essential for the storage and expression of the acquired conditioned responses, however.

How Memory Works? Amnesia Cases of H.M, M.S, C.W, E.P

Posted on September 12, 2013 by 6s79T

How Memory Works? Much of what we know today comes from the stories and real cases of amnesia (memory loss) patients result from brain damage under various different situations. Human memories have different types corresponding to the encoding, storage and retrieval of different types of information, sensual stimulation, and experience. For example, episodic memory are those used to store autobiographical facts and events, semantic memory handle the information which has contextual meanings that are part of the knowledge. Procedural memory record information how an individuals can remember to complete certain tasks such as play piano or how to do surfing (motor tasks, skills). For details of different types of memory, refer to the table in this post at the end or to the post “Types of Memory”. Different parts of the brain get involved and are responsible for the formation and retrieval of different memory types. Much of what neurobiologist and neuropsychologist know about how memory works comes from their casebooks of real life amnesia (memory loss) patients. This post describes 4 of them which is considered as the most well-known with significant value in the research studies conducted by neurobiologists.

H.M is the initial for Henry Molaiso. H.M amnesia case has identified hippocampus as the most important brain structure responsible for new memory creation, the transfer from short-term memory into long-term memory for storage. This memorization process or memory process involves 3 phases as encoding (acquisition, consolidation) (the step to transform information into biological electrochemical signal that have the corresponding pattern that can be stored, accessed and retrieved later), storage, and retrieval. See post “memory process” for more detail. Individuals with damage to hippocampus can not form new memory which implies that they have anterograde amnesia (inability to create new memory, especially recent events after the onset of amnesia). (For different types of amnesia, see post “memory loss diseases”). H.M amnesia case is by far the most prominent case whose hippocampus was completely removed due to the surgery operation trying to treat his year’s epileptic seizures. Before H.M’s surgery operation, no one know the importance of hippocampus in the memory formation. Both of Henry Molaiso’s hippocampus within each temporal lobe was skillfully removed. Although the surgery successfully reduced Henry’s seizures, he was left with severe global memory loss in that he can not create new conscious memories after his operation, he also suffered some retrograde amnesia for a span of 11 years of past memory before his surgery operation. His retrograde amnesia does not appear to be caused by the removal of his hippocampus, instead the complication of retrograde amnesia (can not remember past experience) may be a consequence of his chronic and large use of medications – the antiepileptic drugs which affect the other area of the brain that is responsible for memory storage and recall function. His procedural memory retain intact so that he can normally perform various motor tasks and other skilled procedural tasks as before. Since then, Henry Molaiso has been participating in numerous scientific experiments and researches led by teams of neuropsychologists and H.M became the most cited amnesia cases in the literature.

C.W is the initial for Clive Wearing. His case identified the difference between short-term and long-term memory. Clive Wearing has only short-term memory but no long-term memory (particularly the declarative or explicit memory). His procedural memory -one of the main implicit long-term memory – is till intact though. Procedural memory is affected by the region of brain that form the striatum and cerebellum. Long-term declarative memory are medicated mainly by the medial temporal lobe (hippocampus and associated cortices). Hippocampus is responsible for the transfer of information from short-term memory after being encoded and consolidate to the long-term storage in the cortex. Short-term memory is affected by angular gyrus. Clive Wearing can create new short-term memory, but the formed short-term memory can not be transferred to long-term memory. His memory only lasts between 7 and 30 seconds. Wearing still remembers how to play the piano and conduct a choir (he is a musician) which uses his intact procedural memory, but quickly forgets that he has just played piano. His hippocampus was damaged due to encephalitis (infection of the brain). Some of the temporal lobe and some of the frontal lobe in the cerebral cortex were damaged. These damage of temporal lobe cortex wiped out some of his past stored information (past long-term memory – explicit memory) made him suffer both long-term anterograde amnesia and some degree of retrograde amnesia. He has also been showing some physical signs (shake spasmodically) of impairment in controlling memory related to emotional thoughts (e.g. some outburst of anger). These appear to be linked to the lesion in his frontal lobe cortex.

M.S’s amnesia is a very distinct case. His amnesia identified the importance of the regions of brain that store long-term visual memory as well as for visual perceptual priming. M.S suffered from sever visual perceptual priming deficit – the visual memory deficit amnesia – a distinct amnesia presentation and etiology. Visual priming is the type of implicit memory that does not require conscious effort. Visual perceptual priming refer to the ability of an individual to spontaneously increase the speed and accuracy of response (process of visual information) to a visual stimuli that he has been exposed to in the past. Visual priming require the visual-specific cortex region of the brain that also responsible for the storage and retrieval of the visual memory. He can copy images but can not recognize them later, he also can not recognize faces and many other common objects. He can not manipulate visual images including those involve color, people. The associative nature of the (visual) perceptual priming suggests that activation of past stored same or similar visual information may be involved or required in this implicit memory function. At the same time of his long-term visual memory loss, he also suffered from some semantic memory impairment. M.S manifests both a severe retrograde amnesia and moderate anterograde amnesia. The lesion in his brain was caused by infection of herpes encephalitis. Neuroimaging techniques revealed extensive damage to his occipital lobes on both sides. This is what responsible for his long-term storage problem for visual information and visual priming deficit. In addition, part of his hippocampus was damaged which made him difficult to form new memories (moderate anterograde amnesia). Part of his parietal white matter was also destroyed but the parietal lobe cortex is intact. His loss of autobiographical memory (episodic memory) is believed to be linked to his sever long-term loss of past visual memory and visual priming. The loss of visual memory storage region in the brain appear to disrupt and impair the activation in retrieval of autobiographical information.

E.P’s story is strikingly similar to the well-known case of H.M. His amnesia was also a result of encephalitis. His disease result in extensive damage to medial temporal lobe where hippocampus resides. Crucial structures – among them the amygdala and hippocampus – were eliminated. Additionally, other brain regions had atrophied. Therefore E.P does not have new memories too. In addition, he also has modest impairment in his semantic knowledge. (memories about contextual concepts, words). E.P was subject to continued study which include hundreds of different assessment and tests regarding his cognitive and memory functions. E.P’s case provides new and surprising twists in understanding how memory functions and the difference between types of amnesia. One twists is the fact that E.P does not have any residual capacity in learning anything subconsciously. Scientists has believed that besides hippocampus, there may be some other ways information can get in. E.P’s learning ability is absolutely zero, this is attributed to the fact of a total damage of all specific memory-linked brain structures. A second twist from E.P case is to identify the different areas of brain cortex that stores episodic and semantic memory. It appears that some adjacent areas of the medial temporal lobe, not just the medial temporal lobe alone, are responsible for semantic memory storage. Finally, E.P’s retrograde amnesia is very different from other cases. His retrograde amnesia extending back 40-50 years compared to a few months or years of the past memory loss of other amnesia cases. Scientists said this effect probably is the result of lateral temporal lobe damage caused as a secondary consequence of the initial encephalitis-induced brain damage.

Types of Memory

Type And Time Frame	Subtype	Region of Brain	Items Can Be Held	Other Properties
Sensory Memory milliseconds to seconds	iconic memory (visual sense) echoic memory (hearing) haptic memory (touch) smell taste		many
Short-Term (Working) Memory seconds to minutes	short-term memory working memory	frontal cortex, parietal cortex, anterior cingulate, parts of basal ganglia	7+/-2	disrupted by distractor recency effect
Long-Term Memory - Declarative Memory (days, decades, up to lifetime)	Episodic Memory (autobiographical, facts, events)	medial temporal lobe (hippocampus) and associated cortex	unlimited	rehearsal facilitates storage many types of LTM mediated by different brain region
	Semantic Memory (contextual meaning, knowledge)	medial temporal lobe (hippocampus) and associated cortex
Long-Term Memory: Nondeclarative Memory (days, decades, up to lifetime)	Procedural Memory (motor tasks, skills)	striatum and cerebellum		operate outside of awareness (consciousness)
	Priming	cortex		operate outside of awareness (consciousness)

How Do We Remember: Memory Acquisition, Consolidation And Retrieval

Posted on September 7, 2013 by 6s79T

This post explains the 3 stages of memorization process (or 3 phases of memory process):

memory acquisition (sensory memory), memory encoding
consolidation (working memory) and storage (long-term memory)
memory retrieval.

memory process

Memory Acquisition and Memory Encoding

The first stage of the memory process is the perception and acquisition of streams of information and experiences (facts and events) from around the external environment as well as from an individual’s internal thought process. Memory acquisition involve both conscious and unconscious effort. Most of the information and stimuli are acquired unconsciously where much of them are simply ignored because brain can not constantly filter the information it receives unconsciously. Conscious attention facilitates the brain’s ability to acquire and filter the various information it receives. During the process of acquisition, chunks of information and perceptions are being encoded to prepare them to be committed to a long-term storage at one area of brain.

As the first step in creating a memory, encoding begins with perception. Because information are of various types, memory encoding allows the perceived item of interest to be converted into a construct that can be stored within the brain, and then retrieved later from short-term or long-term memory. Memory encoding for different types of information are not the same. Sensation encoding converts visual, acoustic perceptions and perceptions for other senses. Semantic encoding is the processing and encoding of inputs that have particular meaning and can be linked to a context. Brain’s memory function are associative in that new information is better recorded if they can be related to existing memories in the brain. Elaborative encoding is the process in the brain that can actively associate new information to those already in the brain. In other word, how we remember depends at least partially on what is already recorded. Studies have shown that long-term memory can be enhanced through elaborative encoding. Another type of memory encoding is organizational encoding which refer to the encoding process of categorizing information according to the relationships among a series of items.

The part of the brain responsible for memory encoding and memory acquisition process is hippocampus (deep within the medial temporal lobe of the brain) and the frontal lobe of the cerebral cortex. Basically, various inputs of perception and information traveled to the hippocampus, where these perceptions are integrated and combined into one single experience. On the molecular level, memory encoding are neurobiochemical processes. This is a complex process that is not yet understood well. The process could involve the modification of neural synapses, proteins, creation of new synapses, activation of gene expression and protein synthesis. Basically, memory encoding involves the electrochemical transmissions of information between networks of neurons through the action of neurotransmitters at the synapses (the structure connecting nerve cells). The engram or memory trace is the term used to define the pattern of integrated bits of information encoded in the language of bio-electrochemical changes in the brain at which time memory consolidation becomes possible.

Memory Consolidation And Memory Storage

Generally speaking, memory consolidation is the process of stabilizing “memory engram” or “memory trace” – the chunks of information encoded in the language of electrochemical signaling. Memory consolidation is divided into two specific processes based on the timeline: synaptic consolidation which occurs within the first few hours after learning or encoding and system consolidations define those consolidation processes which could span over a period of weeks to years or even decades.

A basic mechanism describes (synaptic) consolidation is the phenomenon known as long-term potentiation – a model of synaptic plasticity (the ability of synapses to strengthen or weaken over time) which allows a synapse to increase in strength as increasing numbers of signals are transmitted between the two neurons. LTP explains the importance of repetition or association in the process of “learning”. By enhancing the intensity and strength of synaptic transmission. Information are better organized and transferred into different parts of the brain and better retained (stored) in the long-term memory storage of the brain.

System consolidation is a slow dynamic process for stabilizing engram toward storage. Two steps of system consolidation can be defined – the hippocampus dependent stage and the hippocampus independent stage, known as the standard model of system consolidation proposed by Squire and Alvarez (1995). New memories are initially encoded in hippocampus and retained there for up to one week. This initial “learning” represented the hippocampus-dependent stage where memories are temporarily stored. After one week and beyond the initial learning experience , the memories are slowly and gradually transferred to the neo-cortex (where it becomes both permanently stored and hippocampus-independent). Neo-cortex is part of the cerebral cortex – cortical parts of the limbic system – involved in cognitive functions including sensory perception, memory, reasoning, thinking and language. System consolidation is therefore the process whereby the hippocampus activates the neocortex continually leading to strong connections between the two.

Because memories have different types including declarative memory (episodic or semantic memory), non-declarative memory (procedural memory) (see post “Classification of Memory – Types of Memory”), system consolidation can be further distinguished based on these different types of memories. Episodic memory consolidation rely significantly on the hippocampus system but semantic memories consolidation can be established in structures beyond hippocampus – the neo-cortex. This is because semantic memories could involve the extraction and abstraction of the meanings from episodic facts or events. This distinction between this two major types of declarative memory lead to the proposal of the multiple trace theory which is formulated to try to explain the distinction in processing the semantic and episodic memory.

Procedural memories differ from declarative memory in that it is implicit rather than explicit . Consolidation of procedural memory relies primarily on the motor area of the neo-cortex. Memories related to emotion and stress are encoded and consolidated in the area of the brain known as amygdala located deep within the medial temporal lobes of the brain. The consolidation process of this type of memory appear to require stress hormone such as epinephrine. Not only consolidation can occur under consciousness. Nonconscious spontaneous consolidation have been thought of part of the essential mechanism of memory processes.

Memory reconsolidation has recently been described as a third category of memory consolidation. The concept of reconsolidation is consistent with the understanding of the associative property of memory function. Memory reconsolidation actively reconsolidate and integrate with new inputs or previously consolidated memory after the initial retrieval or recall of existing memory. Reconsolidation strengthens and modifies old memories. This post-retrieval stabilization is believed to be a different and distinct form of consolidation. It is part of the memory retrieval process too as is discussed next.

Memory Retrieval

Memory retrieval or recall or recollection answers the question “how do we remember” in a narrow sense, that is – how stored memory is re-accessed later. There are three main types of recall: free recall, cued recall and serial recall. Serial recall is the ability to recall items or events in the order in which they occurred. Some scientists distinguish the memory retrieval as:

recall (free recall or direct retrieval): being able to access the information without being cued
recollection: involve reconstruction of memory using logical connections, or clues, this applies to semantic memory where information is arranged in a contextual way.
recognition: identify information from and after accessing what is stored. (see two-stage theory of memory retrieval below)
relearning: retrieve and relearn the information

There are two main theories about memory retrieval

two-stage theory of memory retrieval: stage 1: is a search and retrieval process, stage 2 is the decision or recognition step where the correct information is chosen from what has been retrieved
theory of encoding specificity (proposed by Endel Tulving in the 1980s): When memories are accessed and retrieved, not just the information stored is reactivated, Under what environment the memory is accessed also affect what end up as”remembering”.

The framework of memory acquisition, consolidation, storage, and retrieval provides the basis for developing memory improvement strategies such as mnemonics which use the concept of elaborative encoding and the associative nature of memory. Mnemonics utilizes verbal, visual, or auditory associations with other easy to remember constructs to facilitate the remembering.

Why We Forget -Theories And Mechanisms Behind Normal Forgetfulness

Posted on September 5, 2013 by 6s79T

Why do we forget? To understand the reasons (theories) behind forgetfulness which is a normal memory problem, it is necessary to give forgetfulness or memory lapses a scientific definition as well as to obtain an understanding of the basic memorization process (memory processes). Memory process basically consist of three stages or steps -the transmission of perceived information (stimuli) from sensory memory to short-term memory via working memory to the long-term memory. See post “Classification of Memory – Types of Memory” for difference between sensory, short-term and long-term memory and the distinction between short-term versus working memory. This three stages process of memory formation (memorization) are separated as 1) memory acquisition, encoding 2) memory consolidation (via working memory) 3) long-term memory storage. A fourth step involves the retrieval of these stored memory and this is equivalent to what we say “remember” “recall the memory” and “recollection of the memory”. (see post “How Do We Remember: Memory Acquisition, Consolidation And Retrieval” for more detail and in depth discussion).

Forgetfulness (memory lapses) is the term used to define normal memory retention loss (the apparent loss of information already encoded and stored in an individual’s long term memory) that could occur at any age. As we age, forgetfulness may become more frequent, but this is still a normal part of aging process as long as the memory lapses issue or problems not severe or frustrating enough to interfere daily life. (see post “Age-Related Memory Loss Diseases – Amnesia With Age” for abnormal memory failure problems). Broadly speaking, forgetfulness (the memory loss issue termed as memory lapses) can refer to any disruption on the chain of the three stages of memory process described above. But strictly or narrowly speaking, forgetfulness is the problem on the linkage between “long-term memory storage” and memory recollection (memory retrieval). Either the stored information is lost from long-term memory storage (known as decay theory) over time, especially there is no memory rehearsal or repetition; or the ability to retrieve and recall memory is impaired at the fourth step. Either disruption will cause people to “forget”. Broadly, any loss of information at the sensory memory or short-term memory stage can be thought of “forgetfulness” too. Because the information never gets encoded or consolidated and to be processed for further long-term storage, there is nothing to retrieve. The information lost at the sensory memory stage is normal if no attention or focus is exerted when stimuli was perceived. The impairment or disruption on memory encoding or memory consolidation will prevent information from being transferred from short-term memory to long-term memory.

There are minor differences in the manifestation of forgetfulness. The symptoms of forgetfulness can be categorized into several major types such as transience, blocking, absent-mindedness, misattribution, suggestibility, bias, scrambling, multi-task inefficiency (see post “types of forgetfulness). Next presented is 4 basic theories (mechanisms) of forgetfulness to explain why do we forget:

Decay theory of forgetfulness

Decay theory of forgetfulness states that memory fades (retention loss) occurs over time. The Theory appears to apply to both short-term and long-term memory storage. Over time, if without rehearsal or recollection, stored information may lost and no longer available for later retrieval. Memory strength could wear away. Actively rehearsing information is believed to be a major factor counteracting this temporal decline. It is known that neurons die off gradually as we age although new brain cell can be created at any age. This partially explains why aged people are more easier to forget things. One observation is that some long-term memory are more resistant to time decay. People sometimes remember events or experiences long time ago with accuracy. This fact suggests that time decay is not the only factor that contribute to memory fades.

Interference theory of forgetfulness

Interference theory implies that memory information can be competing and interfering with each other if the stored information is very similar to the new information. Proactive interference is the case that a similar past memory make the new information difficult to remember. Retroactive interference is the case that a new information make it difficult to remember a similar past experience or learned information. The basic assumption is that the stored memory is intact but during the process of retrieval, information could be distorted by the newly acquired (learned) material due to similarity and competition. Interference theory explains the observation of multi-task inefficiency, especially in elder people. This is termed as Dual Task Interference. The efficiency for people to do multiple tasks decreases if they try to complete them at the same time.

Fail to retrieve (memory recall problem)

Fail to retrieve (memory retrieval and recollection problem) explains the problem associated with the memory recollection and retrieval step. There are three main types of memory recall used in studies: free memory recall, cued memory recall and serial recall. Serial recall measure and individual’s ability to recall items or events in the order in which they occurred. This mechanism of forgetfulness is less associated with normal people. Aging people or people with amnesia are easily found with impairment of memory retrieval due to disease, injury.

Failure to Store (encoding failure )

Encoding failure (fail to store) is associated with the impairment of memorization process when short-term memory failed to enter into long-term memory storage. Sometimes information is not encoded simply because attention and focus is not exerted, and was ignored by the brain. This is normal and with common sense, if one does not pay attention and concentrate, many details of the perception simply slipped away. Amnesia patients or aging people may have encoding failure due to the changes in their brain structure that are involved in the biochemical process of memory encoding and consolidation. An impaired working memory function will reduce an individual’s ability to process and synthesize perceived information including properly store them in the appropriate areas of brain (not all memory are stored in one area of the brain).

Motivated forgetting

This is to cope with the persistence in remembering traumatic events or experiences; Motivated forgetting describes the practice to forget those traumatic or disturbing events or experience. Suppression and repression are the two basic forms of motivated forgetting.

Age-Related Memory Loss Diseases – Amnesia With Age

Posted on September 4, 2013 by 6s79T

Amnesia (abnormal memory loss conditions): an abnormal degree of forgetfulness; i.e. inability to retrieve old memories and/or inability to create new memories.

Amnesia is the abnormal memory loss caused by brain damage, disease, or psychological trauma that can occur at any age. Amnesia can be broadly categorized as organic or functional . Organic amnesia are the memory loss result from damage to brain due to infection, degenerative (brain) diseases, stroke or direct brain injury (for the influence of lifestyle factors, also see post ” Intrinsic and Extrinsic Causes of Age-Related Memory Loss”). Functional (or psychogenic) amnesia occurs as a result of traumatic psychological experience. An Alternative way to classify amnesia is based on the area of brain that are damaged or affected. Some major types of amnesia conditions are listed below:

Transient global amnesia: rare, temporary, complete loss of all memory.
Anterograde amnesia: inability to create new memory, especially recent events after the onset of amnesia
Retrograde amnesia: inability to remember events preceding a trauma
Dissociative amnesia (functional amnesia:psychogenic amnesia): the memory loss caused by psychological problems instead of direct brain injury

This list is not conclusive. There are also many rarer instances (types) of amnesia such as Wernike-Korsakoff’s psychosis (alcohol induced memory loss), Hysterical (fugue) amnesia (forget one’s identity), source amnesia (can not remember when and where they got the information), Prosopamnesia (can not identify face). Moreover, Combinations of anterograde amnesia and retrograde amnesia could occur in the same individual.

How do we tell the difference between amnesia symptoms and those of regular memory lapses and forgetfulness? More specifically, what is the distinction between amnesia and the memory problems we face as we age? How amnesia is linked to aging? While we all could forget something or have trouble recalling information from time to time. Particularly fatigue or stress can momentarily interrupt memory retrieval or memorization process. Normal memory interruptions i.e general memory lapses or forgetfulness are usually minor, temporary and will not interfere with day to day activities. This post “Normal Age-Related Memory Loss Types – Types of Forgetfulness or Memory Lapses” listed and discussed various types or phenomenons of regular or normal forgetfulness. Amnesia is a more complete memory loss. Amnesia of or caused by other age-related (degenerative brain) diseases tends to have a more lasting effect on short term and/or long-term memory. The most typical symptoms of amnesia are:

difficulty or inability to learn new information (anterograde amnesia)
difficulty or inability to recall past stuff
false memories: either completely invented or misattributed
confusion or disorientation
partial or complete loss of memory
fail to identify face and places
vulnerable to interruption, can not resume a task if interrupted.

Some age-related (degenerative) brain disease or conditions of cognitive decline are associated with severe amnesia. These include Alzheimer’s disease, dementia and other cognitive decline or degenerative brain conditions. Alzheimer’s disease, dementia are important triggers and manifestations of severe Amnesia. Dementia categorizes a group of brain problems as a result of progressive deterioration in cognitive function (memory, language, problem solving and attention) associated with aging. Symptoms may involve changes in personality, mood, and behavior in addition to declining cognitive functionality. Dementia develops when the parts of the brain responsible for learning, memory, decision-making, and language are affected by injury or disease. (lifestyle habits can exacerbate or accelerate this process. see post “Intrinsic and Extrinsic Causes of Age-Related Memory Loss”)

Alzheimer’s is the most common type of dementia that causes problems with memory, thinking and behavior. The disease is progressive, symptoms develop over time and gets worse and worse. The characteristic symptoms are the gradual loss of memory and other intellectual abilities serious enough to interfere with daily life. With late-stage Alzheimer’s, individuals can not start a conversation and respond to environment stimuli. Current treatment of Alzheimer’s treatments cannot cure the disease, however, they can temporarily slow the worsening of symptoms. The most prominent early signs of Alzheimer’s disease is the difficulty in remembering newly exposed information.

Mild Cognitive Impairment (MCI) defines a transitional state between cognitive changes of normal aging and Alzheimer’s disease. People with MCI could have memory problems more frequent than average of the individuals within the same age group. People with MCI still can carryout normal activities and their symptoms are not as severe as that of Alzheimer’s disease. Studies have indicated that MCI individuals are at an increased risk for developing Alzheimer’s disease.

Many different types of dementia, although less common than Alzheimer’s disease, can be caused by many other causes (diseases). Dementia can be categorized by underlying causes or they can be divided into two categories based on the region of brain affected – cortical and subcortical dementias. Alzheimer’s disease if a form of cortical dementia. Dementias which sometimes caused by Parkinson’s disease are subcortical dementias.

Vascular Dementia (impairment in drive blood flow to the brain) (e,g, stroke induced dementia and memory problem)
Mixed Dementia (multiple causes)
Dementia with Lewy Bodies (DLB) (abnormal protein deposits -Lewy bodies – in nerve cells in the brain stem)
Parkinson’s Disease Dementia (PDD)
Frontotemporal Dementia
Creutzfeldt-Jacob Dementia (CJD)
Normal Pressure Hydrocephalus (NPH)
Huntington’s Disease Dementia
Wernicke-Korsakoff Syndrome
Mild Cognitive Impairment (MCI)

Some forms of dementia may improve greatly or can be completely cured when the underlying cause is treated. Non-curable causes of dementia include: Alzheimer’s disease, Vascular dementia, Dementias associated with Parkinson’s disease and similar disorders, AIDS dementia complex, Creutzfeldt-Jakob disease. Best way to prevent age-related amnesia is to eliminate those lifestyle habits that may accelerated the brain aging process and exacerbates the situation if early signs of cognitive decline start showing up. Maintain a healthy lifestyle habits are crucial not just to prevent age-associated memory loss problem, but is important for healthy aging and overall wellness.

Normal Age-Related Memory Loss Types – Types of Forgetfulness or Memory Lapses

Posted on September 3, 2013 by 6s79T

Everyone forget things from time to time. As we age, the frequency of the occurrence of forgetfulness or memory lapses increases. Age-related memory loss is part of the normal aging process. How much memory loss is too much which may show the early signs and symptoms of age-related memory problems (diseases) such as Alzheimer’s or other memory impairments? The key issue is whether such memory lapses or further cognitive changes are extreme and persistent enough to interfere with the daily life with frustration.

Harvard University Health Publication (www.health.harvard.edu) has a publication which identified 7 types of forgetfulness (memory lapses) that people could experience at any age. Some of them become more pronounce with age. “The Seven Sins of Memory: How the Mind Forgets and Remembers – a book by Daniel Schacter describes these normal memory problems in more detail. The list in this post includes the original 7 types of forgetfulness (memory lapses) and some more types of memory loss were included from other sources.

transience: the tendency to forget facts or events over time
- negative: appear to be an indicator of deteriorated episodic memory (one of the declarative memory) (see “Classification of Memory – Types of Memory”)
- positive: brain scientists believe that transience, on the other hand, clears the brain of unused memory information, making room for new or more useful information to be stored and processed. This property of the memory system is also known as “fade out” which is normal at all ages.
absentmindedness: it is very easy to forget what is perceived if attention or focus is lacking. This applies to retrospective (perception or past experience) and prospective memories such as forget a scheduled event.
blocking: refer to the temporary or sudden inability to recall a memory (the temporary inaccessibility of stored information. e.g. a name, a place)
misattribution: remember some facts partially and forget the details
suggestibility: this memory failure refer to the fact that people sometimes accepts untrue suggestions from others as the recollection of memory when they actually are not elements of past experience.
bias: an individual’s current feelings or views world distort memory of past facts or events.
persistence: refer to the symptom of persistently recalling unwanted memory (disturbing information or traumatic experience)
scrambling: the individual remembers most of the event or chunks of information but forgets the important details
muddled multitasking (demitasking): the decreased ability to do several tasks at the same time because multitasking make the focus difficult and less efficient.

What types of forgetfulness (memory lapses) or memory failure (memory loss) are most commonly seen with aging people?

Memory blocks are more common with age. Elders are having more trouble remembering people’s names. Misattribution is also more sever with aging population. Elders are less efficient in concentrating and processing information; and usually acquiring fewer details. As we age, the brain has to exert more effort to maintain focus, the ability on multitasking reduces. Further, it takes longer time to resume an task after an interruption. Short-term memory loss and encoding failure are also more common with aging people in that information either can not get to the next stage of memorization process – long-term memory or very easily lost from the short-term storage. Interference problem is very common with aging people, usually associated with impairing visuospatial working memory functionality.

Classification of Memory – Types of Memory

Posted on September 1, 2013 by 6s79T

Memory can be broadly categorized as: sensory memory, short-term memory, long-term memory. Working memory is a concept derived from and related to short-term memory. The different types of memory constitute the sequence of three stages or steps of the memorization process – from sensory to short-term and working memory to long-term memory.

Sensory Memory (Ultra Short-Term Memory) (< 1 sec)

Sensory memory is a very brief recall of a sensory experience at the end of the original sensory stimuli, and is often considered as part of the process of perception that does not require conscious attention. In other words, sensory memory is an automatic response outside the brain’s cognitive control. For the sensory perceived information to be extracted by short-term memory and processed by working memory, conscious attention is necessary. The brain is created to only process and store those of information that gets attention and are useful at a later time and the rest being ignored and not stored in short-term memory and processed by working memory. Each of the main physiological senses should have a corresponding memory storage:

iconic memory (visual sense)
echoic memory (hearing)
haptic memory (touch)
smell
taste

Short-term (working) memory (< 1 min)

Short-term memory holds a small amount of information (typically around 7 items +/- 2) in mind in an active, available state and is a necessary step toward the next stage of information retention – long-term memory. Is there a distinction between the terminology of short-term memory and working memory? The two concepts although distinctive, but overlaps. Short-term memory emphasizes the ability to store information without rehearsal (repeating) while working memory emphasize the brain’s ability to actively process, manipulates, and controls the information. It is the gateway memory function to consolidate short-term memory into long-term memory where memories can last a lifetime. The time span defined for working memory can be longer (range from less than 1 min to a few days) and is sometimes referred to as intermediate memory.

Long-Term memory (range from a few days to decades and life-time)

Long-term memory is an important component of cognitive function of the brain. Associations of perceived information items are stored. Two major divisions of long-term memory are: explicit memory (declarative memory) and implicit memory (procedural memory):

Explicit memory or declarative memory are those stored information about facts and events that can be retrieved under conscious control. Explicit memory can be further divided into:

episodic memory: are autobiographical memories that record facts of experiences and episodes of events.
semantic memory: are memories about knowledge, concepts learned in the past such as the meaning of the words.

Based on the temporal direction of the memories, sometimes declarative memory can be classified alternatively as:

retrospective memory
prospective memory

Implicit (non-declarative) memory refer to the ability to perform a task or skilled task using previously stored information of prior experience or knowledge without conscious awareness. Procedural memory and priming belong to implicit memory:

procedural memory: is the type of memory responsible for the performance of particular actions or tasks. it is automatically retrieved without the need for conscious control. Procedural memory are accessed and used for the carryout of the procedures and tasks that require both cognitive skill and motor skill.
priming memory: refer to the effect of prior experience on the (increased) responsiveness to future exposure to same or similar stimuli. Priming memory is believed to be retrieved outside of conscious awareness.

The brain’s memory function ages and deteriorates with the normal aging process. Many factors contribute to the age-related memory loss. (see post “Intrinsic and Extrinsic Causes of Age-Related Memory Loss”). Understanding the distinctions among types of memory and how they together forming the sequential stages of memorization process as well as how brain retrieves and uses the stored information for cognitive and motor tasks will help to combat and prevent aging memory loss and diseases. Different memory strategies are developed for strengthen the short-term vs. the long-term memory function. Short-term memory strategies adopt focus, concentration, awareness, attention training. Long-term memory strategies include those such as repetition, paying attention, association, attaching meaning and visualization.