Author: Jeevitha Ramesh
From our previous blog, we have understood the basics of memory and its various types. In this blog, we will understand the biological basis of memory and the processes involved in memory formation.
Although memory begins with perception, it is encoded and stored using an electrochemical pathway. Nerve cells connect with each other at a junction called synapse, which passes chemical electrical signals from one neuron to another. The electrical firing of a pulse across the gap triggers the discharge of chemical messengers called neurotransmitters. As one brain cell sends signals to another, the synapse between the two gets stronger, called Long-term potentiation (LTP).
LTP is a molecular basis for the formation and storage of memories. In LTP, when two neurons continuously and simultaneously become activated, the connection between them is strengthened. This synaptic strengthening is commonly referred to as ‘cells that fire together, wire together.’
Thus, on a rudimentary level, the relative strength of the connections between neurons reveals memory’s nature. A network whose connections are very strong are often thought of as a strong memory. In contrast, those with weaker connections require more synchronized activation to become an enduring memory (which gives rise to the old saying that practice (or repetition) makes perfect).
Next, we will understand the process of memory formation.
During memory formation, the information gets to our brains through encoding, which is the act of taking in information and transforming it into a usable mental form.
Once we receive sensory information from the environment, the brain processes and organizes this information (i.e., what should be attended to, and can be passed on to later memory systems). Then it is stored and retrieved when needed. For example, Zara while driving sees a poster of an upcoming movie (visual sensory information), she comes home and thinks about watching it (information processing). This information about the movie gets stored in Zara’s brain and is retrieved when she starts watching the movie.
Process of memory formation
Encoding is a crucial process in creating a memory. It is a biological phenomenon, rooted within the senses, and begins with perceiving
objects. Attentional processes allow categorizing information for further prioritizing information and allocating them into short-term memory stores.
Types of encoding
Encoding takes place in various forms. For instance, visual encoding is the encoding of images; acoustic encoding is the encoding of sounds (words in particular); semantic coding is the encoding of words and their meaning; and tactile encoding is the encoding of something’s texture. The semantically encoded information is remembered more often than words encoded visually or acoustically, suggesting a deeper level of processing in semantic encoding.
These separate sensations move to the hippocampus (responsible for memory), integrating these perceptions as they were occurring into one single experience. Hippocampus, along with the frontal lobe cortex (responsible for planning and decision-making), analyzes these sensory inputs and decides if they’re worth remembering. If they are, they are stored and may become part of long-term memory.
Once memory gets encoded, the next step is the storage of this information. Storage refers to how, where, how much, and how long encoded information is retained within the system of memory. The encoded information is first stored in short term memory (STM) then, if need be, is stored in long term memory (LTM).
Lapse of time and inattention causes forgetting of information stored in STM. This is because STM only lasts between 15 and 30 seconds. Additionally, STM only holds between five and nine items of data. In this context, the term “items” refers to any piece of information. However, long-term memory has immense storage capacity, and information stored within LTM is often stored indefinitely. Information that is encoded semantically is primarily stored in LTM. It also holds visually- and acoustically-encoded information.
Once information is stored within LTM or STM, individuals should recall or retrieve the information to use the said information. It is the retrieval process that often determines how well students perform on assignments designed to check recall. The conscious repetition of information is referred to as rehearsal, allowing information to move from the temporary short-term memory store into long-term memory, a process known as memory consolidation. When you want to recollect something, you retrieve the knowledge on an unconscious level, bringing it into your conscious mind at will.
After encoding and storage in the memory formation process, we have retrieval. Retrieval is the process through which individuals access stored information. The action of getting information out from memory storage, into our conscious awareness is known as retrieval. This would be almost like finding and opening a document you had previously saved on your computer’s disk drive. Now it’s back on your desktop, and you can work with it again.
Our ability to retrieve information from LTM is significant to our everyday functioning. You retrieve information to do everything from knowing how to brush your hair and teeth, to driving, to know how to perform at your job.
You can retrieve information out of your long-term memory storage system in two ways: recall, recognition.
Recall means you’ll access information without cues. For example, you’d use recall for an essay test. Recognition happens once you identify information that you simply have previously learned after re-encountering it. It involves a process of comparison. When you take a multiple-choice test, you’re counting on recognition to help you select the right answer. If you’ve forgotten something, it’s because you didn’t encode it very effectively.
We now know how memory works, the process of its formation, and stages. In the next blog, we will see about forgetting, its type, memory deficits, and how we can enhance our memory.
References
Duman RS, Heninger GR, Nestler EJ. A molecular and cellular theory of memory. Arch Gen Psychiatry. 1997;54:597–606.
The neurobiological bases of memory formation: from physiological conditions to psychopathology Reto Bisaz, Alessio Travaglia, and Cristina M. Alberini, Psychopathology. Author manuscript; available in PMC 2015 Oct 3.
Lamprecht R, Farb CR, Rodrigues SM, LeDoux JE. Fear conditioning drives profiling into amygdala dendritic spines. Nat Neurosci. 2006;9:481–483.
Alberini CM. The role of protein synthesis during the labile phases of memory: Revisiting the skepticism. Neurobiol Learn Mem. 2008;89:234–246.
Suzuki A, Josselyn SA, Frankland PW, Masushige S, Silva AJ, Kida S. Memory reconsolidation and extinction have distinct temporal and biochemical signatures. J Neurosci. 2004;24:4787–4795.
Alberini CM. Transcription factors in long-term memory and synaptic plasticity. Physiol Rev. 2009;89:121–145.
McGaugh JL. Memory–a century of consolidation. Science. 2000;287:248–251.