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 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.