How Your Memory Works

By: Michael Maina

Memory is one of the most critical functions of the brain. Contrary to popular belief, memory is not only useful for recalling information for tests and remembering where we placed something that we lost. Walking, driving, texting, reciting the days of the week, knowing what chocolate tastes like and playing an instrument are just a few instances where memory is required. Without your memory, you would completely lose your individuality since every activity in our daily lives requires the use of memory in one way or another.

What Is Memory?

Memory pertains to the cognitive processes used in the acquiring, storage, retention and retrieval of information. These cognitive processes include encoding, storage and retrieval.

1.   Encoding

This is the first process in memory formation. Sensory organs (such as the eyes) pick up raw information from the environment. These pieces of raw information are referred to as stimuli. Encoding is the process of transducing (converting) stimuli into a form that is more suitable to be stored in the brain. Stimuli have first to be transduced into electrical signals. Electricity and neurotransmitters (brain chemicals) constitute the language of the nervous system. They are responsible for the transportation and processing of information in the brain.

Neurons (nerve cells) are connected with each other at junctions called synapses. Electrical signals of significant voltage lead the neurons to release neurotransmitters into the synapse. The neurotransmitter attaches to and activates the next neuron, thus propagating the electrical activity. This process is the principle behind memory encoding and communication in the brain.

An individual neuron can make thousands of synaptic connections with other functionally similar neurons. Scientists estimate the number of brain synapses to be close to a quadrillion (1000 trillion). Connections between neurons strengthen over time with use. Every experience you have causes your brain to rewire its structure slightly. This ability to change and strengthen the brain’s connections throughout life is called neuroplasticity.

The amount of information detected by the senses is so colossal that if your brain stored everything, there would be an overload. In the simple act of looking for a book on a table; your eyes pick up the shape, color, size, patterns and writings on every single object on that table; including the scratches, stains and the design of the table down to its most delicate details. Consequently, the brain has to screen stimuli and allow only the relevant information is encoded. The criterion used in this screening process is attentiveness. The brain prioritizes information that you pay attention and encodes it, whereas information of little importance is lost.

2.   Storage

In 1968, Atkinson and Shiffrin came up with a theory – the multi-store model – stating that memory storage is divided into three parts: sensory memory, short-term memory and long-term memory.

i.                   Sensory Memory

This is the component of memory that deals with storing information detected by the body senses (such as sight, smell, pressure). The brain stores this information for the briefest moment: half a second for visual stimuli and 3-4 seconds for auditory stimuli. This information is stored in the temporal lobe of the brain. Intentionally focusing on sensory information causes it to move on to the short-term memory.

ii.                Short-Term Memory

The short-term memory entails the information that we are currently conscious of and thinking about. The limbic system (hippocampus, hypothalamus, amygdala) and the frontal lobe are responsible for storing this type of memory. Information stored here is generally limited to an average of seven items and is typically retained for 18-20 seconds. Nevertheless, information can be retained for more extended periods by actively rehearsing the information. Rehearsal resets the memory time limit. Memorizing items on a grocery list illustrates the workings of the short-term memory.

iii.               Long-Term Memory

Significant information ends up in the long-term memory. The storage of long-term memory is complex and occurs at various parts of the cerebral cortex. Repetition increases the chance of information being stored here. Furthermore, information associated with intense emotion is more likely to be committed to the long-term memory. This explains why you can remember your first kiss in great detail. Long-term memory is stored for an unlimited period and is not restricted in capacity. These memories are stored unconsciously and are called upon when needed. However, some long-term memories are retrieved more easily than others.

Classification of Long-Term Memory

Long-term memory is primarily classified into two main categories: implicit and explicit memory. Implicit memory does not necessitate conscious thought to retrieve the memory. It is also known as automatic/unconscious memory. Explicit memory requires a conscious effort for the memory to be retrieved. When you recite the alphabet, you are using your implicit memory. On the other hand, reciting the alphabet backward makes use of your explicit memory.

Explained below are the sub-classes of long-term memory. Some are subsets of the classification mentioned above while others are derivatives of minor classifications.

Procedural Memory

Procedural memory is a subclass of implicit memory that involves motor skills. It is also known as muscle memory. Examples include riding a bike and playing a musical instrument.

Semantic Memory

This type of memory enables us to remember basic facts and common knowledge, such as the color of grass or the name of a loved one.

Episodic Memory

This is the subset of explicit memory that is associated with personal experiences. Some of the details memorized include your feelings at the time of the events, the time the event took place, the location, the surrounding environment and the people involved.

Autobiographical Memory

Autobiographical memory involves the consolidation of episodic and semantic memory to come up with a system regarding all of your personal information and experiences.

Retrospective Memory

This subset of long-term memory, along with prospective memory, is derived from the temporal classification of memory. It involves information and occurrences that took place in the past. Retrospective memory can be either implicit or explicit.

Prospective Memory

This is the part of memory related to information that you plan to recall in the future. It serves as your intrinsic to-do list and reminder. A cue, such as a place or time, usually triggers the prospective memory. Calling someone at noon or buying your spouse a present when you stop at the gas station are excellent examples of this.

Prospective memory is partially dependent on retrospective memory when remembering to do something that involves past events. Nevertheless, retrospective memory is not dependent on prospective memory.

3.         Retrieval

Retrieval is the remembering of information that is stored in the long-term memory. Various factors affect memory retrieval such as the duration of time since you last retrieved the information and other information learned during that period. To improve the probability of remembering a concept, it is advisable to practice retrieving it frequently. This occurrence is most commonly observed when studying for tests, thus its name: the testing phenomenon. Moreover, information that is studied repeatedly spaced over a period is more likely to be retrieved than that which is studied all in one sitting.

Types of Memory Retrieval

·        Recall: the retrieval of information directly from the long-term memories without a cue. Recall operates two times faster than blinking. Fill in the blank and open-ended questions require the use of recall.

·        Recognition: this is the retrieval of information with the help of a familiar external stimulus. An example is remembering to send an e-mail after seeing/touching your phone.

·        Recollection: it involves using partial memories, logical structures, cues or narratives to reconstruct a memory. For instance, when writing an essay, you first remember part of the information then use this partial knowledge to restructure the rest of the information.

·        Relearning: the learning of information repeatedly to make future retrieval easier. The testing effect exemplifies relearning.

Patterns of Retrieval

i.                   Serial Recall

This is the tendency to remember memories in chronological order. You can use the events that occurred first as a cue to recall later events. When recalling items on a list, you are more likely to recall the items at the beginning more easily. This phenomenon is referred to as the primacy effect. It is attributed to the individual having more time to rehearse said items in the short-term memory. Furthermore, it is also easier to recall the last items on the list, possibly because they are still fresh in the short-term memory – the recency effect.

ii.                 Free Recall

Free recall is the pattern of retrieval used when recalling events or items in no particular order. It is also subject to the recency and primacy effects.

iii.               Cued Recall

A cue is a stimulus that triggers the memory. The process of remembering something with the aid of a cue is cued recall. For a cue to be effective, it should have an active link to the memory.

Interference

The interplay between newly learned and previously learned material might interfere with the retrieval of either type of information. Interference is more likely to occur when both pieces of information are similar and were learned in almost similar contexts.

Proactive interference is when previously learned information causes you to forget the newly learned material. This explains why you sometimes struggle to remember your new passwords since the previous one is still stuck in your memory.

Retroactive interference happens when freshly learned material hinders the retrieval of previously learned material. An instance of this is when people mistakenly refer to their exes by the name of their current partners.

Retrieval Failure

Occasionally, we are unable to access memories that have been encoded and stored. This may occur due to neural decay (where like a muscle, disuse of memory causes neural connections to decline), distractions when remembering the information and the lack of strong enough cues. Other times, forgetting is a result of not paying attention while performing an action. Attentiveness is a prerequisite for memory encoding; therefore, the information to be retrieved in this case was never encoded in the first place.

The tip-of-the-tongue phenomenon is a common type of retrieval failure. This is when a person fails to remember a word but recalls some information related to the word such as its first letter or other words similar to it in meaning or sound.

Recent Discoveries in Memory

Neuroscientists keep on making numerous discoveries on the working of memory as time elapses. Some of these findings negate previous knowledge and open up realms of possibilities in the field of neuroscience. It was recently discovered that the long-term memory is capable of storing up to 2.5 petabytes (2,500,000 gigabytes) of information. This approximates to the entire capacity of the World Wide Web! Have you ever walked into a room, only to forget what you wanted to do there? It turns out that scientists have shown that walking through doorways is linked to forgetfulness!

Other discoveries establish previously held assumptions. Research conducted at the University of California has demonstrated that our memories learn to prioritize the retrieval of information that may lead to a reward in the future. A different study has shown that sleep not only helps in memory consolidation, but also reconfigures our memories to create new innovative ideas. This finding affirms the commonly held belief that sleep helps in overcoming creative blocks.

The Future of Research in Memory

Neuroscientists have recently shed light on a state of memory that was previously unknown — the part of the memory that acts as a bridge between short-term and long-term memory. This finding will lead to changes in the perception of learning. It may then be possible to speed up the process of converting short-term memory to long-term memory.

Furthermore, there is much ongoing research attempting to locate the precise sites and synapses where specific information is stored. This brings about the possibility of erasing undesirable memories without altering the rest of the memory. Some scientists suggest that after a prodigious amount of research has been done, it might be possible to input information directly into the brain and even transfer information from one brain to another just like we do with computers.

In conclusion, we are nowhere close to understanding the complete workings of the memory. “The human brain,” according to the Nobel Prize winner Gerald Edelman, “is the most physically complex object in the known universe.” There is still so much left shrouded in mystery. The uncovering of these secrets will lead to significant scientific breakthroughs that will completely revolutionize the way we live.