How long term memory is stored

Information from the world around us is first stored by sensory memory, thus enabling the storage and future use of such information. Short-term memory or memory refers to information processed in a short period of time. Long-term memory allows us to store information for long periods of time, including information that can be retrieved consciously explicit memory or unconsciously implicit memory. A life full of unconnected events, of errors that do not lead to any lessons and of emotions without the ability to remember them is no life at all.

Memory is precisely the capacity that allows us to connect experiences, learn and make sense of our lives. In short, it allows us to build our story. This review attempts to provide a rigorous overview that permits anyone who wants to approach the latest scientific findings on memory to do so, as well as to understand them and properly order them.

We will focus on neuroanatomical, neurophysiological, and psychological mechanisms of the different types of memory. Although knowledge of molecular mechanisms is important for constructing a complete vision of memory models, in this article we can only point out general traits as summarized in this introduction [for more information see Kandel et al. In addition, knowledge gained from neuroimaging studies Binder and Desai, , as well as knowledge of the neural markers associated with memory Meneses, , will likely play a key role in future models of memory mechanisms, but in this review, as stated above, we focus mainly on neuroanatomical, neurophysiological, and psychological mechanisms.

We believe it is important to consider previous developments without which one cannot adequately understand the classifications of memories and the kinds of memory models that are now current in the scientific literature. The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory.

Information from the world around us begins to be stored by sensory memory, making it possible for this information to be accessible in the future. Short-term memory refers to the information processed by the individual in a short period of time.

Working memory performs this processing. Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously explicit memory or unconsciously implicit memory. As Squire points out, the first theoretical approaches relevant to current neuroscience come from the 19th century. The philosopher James, and his book The Principles of Psychology James, , is also especially worth highlighting.

Therein, James distinguishes between primary and secondary memory, thereby referring to short- and long-term memory, respectively. The importance of Pavlov and Fitts and Posner are especially noteworthy during the first two thirds of the 20th century. Unlike what followed, debates in this period were mainly philosophical or based on psychological intuition Ribot, ; Korsafoff, Beginning in the s, a series of experimental studies on how the brain stores information emerged, using animals and amnesic patients.

Within this decade, Milner, Atkinson, and Shiffrin were especially important researchers. The experimental modern era arguably began when Milner demonstrated, with HM experiments, that a seriously ill patient could acquire a new skill hand-eye coordination without any memory of having encountered the task before.

A few years later, Atkinson and Shiffrin proposed a modal model of memory that constitutes one of the most influential explanations for the existence of different components in the memory system. The importance of this model is such that it must be explained in the next section, but for now it should simply be mentioned that the modal model establishes the existence of short-term storage ACP , which receives sensory information that is processed by sensory and data storehouses within long-term memory.

This storage system can generate reasoning and new deductions from existing ones. Tulving first proposed the distinction between episodic memory and semantic memory. Baddeley and Hitch conducted research on the components of working memory. Both authors considered working memory as a limited capacity system that allows temporary storage and manipulation of information necessary to perform complex tasks such as understanding, learning, and reasoning. As explained later on, at first , they proposed the existence of three subsystems within the multi-storehouse model of short-term memory: the central executive, a phonological or articulatory loop and a visuospatial sketchpad.

Later, Baddeley included a fourth subsystem, the episodic buffer, which combines information from the subsystems in a form of temporal representation. Kandel proposed a model to explain the mechanism of operation in habituation and sensitization. To do this, he used the notion of non-associative memory, which, as we shall see, is one of the four types of non-declarative or implicit memory, like that which refers to new behaviors learned through repeated exposure to a single stimulus.

According to Kandel, new behaviors can be classified into two processes: sensitization and habituation. On the one hand, for habituation, acetylcholine is progressively consumed, decreasing the effectiveness of the stimulus and thereby the motor response. On the other hand, the presence of serotonin in sensitization, secreted by another sensory nerve terminal, causes an excess of acetylcholine.

An enhanced motor response thus emerges. In the s, the differences between declarative and non-declarative memories were consolidated and disseminated. This, together with contributions from Tulving and others, such as Di Lollo or Graf and Schacter, enabled a more precise classification of different types of memory.

As discussed in the next section, Di Lollo considered iconic memory a storage unit consisting of two components: the persistence of vision and information. This stems from the distinction that Tulving proposed between the aforementioned episodic memory and semantic memory both, as we will see, are currently included in declarative memory. In order to clarify its operation, Packard and McGaugh proposed that memory systems operate independently and in parallel. For example, an adverse event in childhood e.

Several authors Tulving et al. These studies show that severely amnesic patients can exhibit completely intact priming while performing memory tests that include conventional recognition of the same test items Squire, Thanks to the development of new 21st century technologies, researchers have been able to more accurately locate brain areas that are associated with different types of memory. Although this pertains to topics to be addressed in detail in the next section, there are two examples that we consider significant to the application of these new techniques and the significant progress made in understanding memory storage.

This process is closely related to the formation of episodic memory. Again, this will be explained in more detail in what follows. According to Lisman et al. With this brief historical and conceptual introduction laid out, we intend to delve into different types of memory in order to present the models that the scientific community has most accepted thus far.

In the last section, and before the glossary, we identify the likely directions for future research. Now we turn on to our main task, presenting an overview of the latest scientific findings on memory, classified according to different types and mechanisms.

There are three types of sensory memory: echoic memory, iconic memory, and haptic memory. Iconic memory retains information that is gathered through sight, echoic memory retains information gathered through auditory stimuli and haptic memory retains data acquired through touch. Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce. Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.

Iconic memory retains information from the sense of sight with an approximate duration of 1 s. This reservoir of information then passes to short-term vision memory which is analogous, as we shall see shortly, to the visuospatial sketchpad with which working memory operates. Therein, he considered iconic memory a storehouse constituted by two components: the persistence of vision and information.

It is sensitive to physical parameters, such that it depends on retinal photoreceptors rods and cones. It also depends on various cells in the visual system and on retinal ganglion cells M transition cells and P sustained cells. It concludes its representation in the primary visual cortex V1 of the occipital lobes. Iconic memory is a storehouse of information that lasts ms and that represents a codified and already categorized version of the visual image.

It plays the role of storehouse for post-categorical memory, which provides visual short-term memory with information to be consolidated. Sperling demonstrated this large capacity after presenting the results of his total and partial reports. On the other hand, in the partial report, subjects were directed to remember the characters in a row specifically assigned to them in the instructions. Regarding short-term, Sperling interpreted the results of the partial report as due to the rapid decline of the visual sign and reaffirmed this short duration by obtaining a decrease in the number of letters reported by the subject in delaying the audio signal for choosing a row to remember in the presentation.

After each letter, and in the same position, they showed a particular visual sign. When the visual sign appeared immediately after the letters, participants could correctly name the letter that occupied the position of the sign, however, as the presentation of the sign became more delayed, participant performance worsened.

These results also show the rapid decline of visual information. Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli.

Subsequently, evidence has been obtained that this system is not entirely pre-categorical Loftus et al. Short-term memory is the ability to keep a small amount of information available for a short period of time. The modal model establishes the existence of a short-term storehouse with limited capacity. The short-term storehouse receives sensory information processed by sensory storehouses and data in long-term memory.

In addition, the short-term storehouse can also send information to the structures involved in long-term memory. This storehouse can generate reasoning and new deductions from existing ones. This model implies that the short-term storehouse functions as a kind of working memory, a system to retain and manipulate information temporarily as part of a wide range of essential cognitive tasks such as learning, reasoning, and understanding.

They, in turn, give short-term storage central importance in the overall processing of information by attributing to it the role of controlling the executive system, responsible for the coordination and control of many complex subroutines in charge of acquiring new material and recovering old material in long-term storage. For example, this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage.

But studies like those of Tulving and Pearlstone and Craik and Watkins show that said relationship does not exist. Given these criticisms, new models began to appear to explain memory, such as those from Cowan , , and Goldman-Rakic As an introduction, it can be argued that Craik and Lockhart understood memory not as a process through which information is deepened at higher levels until it becomes part of long-term memory, but rather as a system of storehouses.

Despite an emphasis on information processing instead of structure , they continued to accept the existence of short-term memory as independent from long-term memory. At first , they proposed the existence of three subsystems within the multi-storehouse model of short-term memory: the central executive, a phonological or articulatory loop and a visuospatial sketchpad.

The latter two sub-memory systems are equivalent to verbal and visual short-term memory systems, respectively. They compared two genetic syndromes Williams and Down with different brain morphology. Williams syndrome patients, despite having widespread mental handicaps, preserve their language skills, while Down syndrome patients preserve more partial capacities, but have very limited language skills.

It was therefore assumed that the former would be better at verbal tasks related to operative memory, and that the latter would be better at visuospatial tasks related to operative memory. As expected, subjects with Williams syndrome performed better at phonological tasks, while subjects with Down syndrome, in turn, performed better at spatial tasks. Later, Baddeley included a fourth subsystem, the episodic buffer Figure 2 , which combines information from the different subsystems in a kind of temporal representation.

The central executive is a system of attention control with limited processing capacity. Baddeley adopted a model originally proposed by Norman and Shallice , in which actions are controlled in two ways. Processes that are not recognized as habitual are controlled by a second system, the supervisory attention system. This system uses long-term knowledge to propose novel behavioral solutions and to weigh options before deciding on a response.

In its original version, the central executive was considered an overall system capable of processing and storing. However, Baddeley and Logie proposed that it only has attention capacity.

Baddeley and Logie understand the central executive as the result of the integration of several processes: the ability to focus attention, the ability to divide attention between two or more tasks, and the ability to control long-term memory access Baddeley et al. The way to accomplish this may be with one or more types of inhibition Engle et al. It has been shown that spatial tasks such as driving a car can interfere with spatial skills, while exclusively visual tasks, such as watching a series of images or colored shapes, can interfere with the recall of objects or shapes Logie, ; Klauer and Zhao, These patterns of interference, together with cases of brain-damaged patients that show a deficit in one kind of task but not the other Della Sala and Logie, , suggest that spatial information and visual characteristics can be stored separately.

On the one hand, it contains a visual component that reflects the processing and storage of objects and their visual features. On the other hand, it contains a second parietal area, presumably involved in spatial aspects.

It can be argued that the phonological buffer supports language acquisition by providing the ability to store new words, while they are consolidated into long-term memory Baddeley et al. Within this phonological loop, two basic sub-processes emerge: a short-term acoustic storehouse and a subvocal articulatory rehearsal process. On the other hand if several trials are given to learn a longer list of say 10 words, meaning becomes all-important and sound loses it power, consistent with different systems for short-term and long-term storage Baddeley, a , b.

Evidence for the importance of rehearsal comes from the word length effect, whereby immediate recall of long words e. Baddeley and Hitch proposed that retention of items in the short-term storehouse quickly fade, but can be maintained by repeating them. The verbal and visual systems within the conventional model of working memory may explain many aspects, but Baddeley points out that evidence from patients with short-term memory deficits— who resist memorizing prose with a verbal span much higher than that of isolated words and resist serial memory of articulatory suppression— leads to supposing that a storehouse of additional support exists.

This is seen in the existence of a new mechanism that combines information from multiple subsystems into a form of temporal representation. Baddeley proposed the term episodic buffer for this new kind of representation.

The episodic buffer is thus a temporary storage system capable of integrating information from different sources, likely controlled by the central executive. It can be preserved in patients with advanced amnesia and severe impairment of long-term episodic memory. With that said, it is possible to consider the episodic buffer as conceptual short-term memory.

Studies to date do not specify activity in a specific area. Long-term memory refers to unlimited storage information to be maintained for long periods, even for life. There are two types of long-term memory: declarative or explicit memory and non-declarative or implicit memory.

Explicit memory refers to information that can be consciously evoked. There are two types of declarative memory: episodic memory and semantic memory. For its part, implicit memory encompasses all unconscious memories, such as certain abilities or skills. There are four types of implicit memory, including procedural, associative, non-associative, and priming.

Explicit memory refers to information that can be evoked consciously. As shown below, episodic memory stores personal experiences and semantic memory stores information about facts. These memories typically include information about the time and place of an event, as well as detailed information about the event itself. There are a number of neural components that are closely related to the proper functioning of episodic memory, which include the following: the cortex near the hippocampus [as discussed below, the perirhinal cortex PRC , the entorhinal cortex, and the parahippocampal cortex PHC ], cortical and subcortical structures, and the circuits within the medial temporal lobe and hippocampus.

The cortices near the hippocampus extensively interact with a number of cortical and subcortical structures; cortical components have key roles in various aspects of perception and cognition, while the medial temporal lobe structures mediate the organization and the persistence of the memory network, whose data is stored in these cortical areas Dickerson and Eichenbaum, The structures directly related to the hippocampus include the entorhinal, the parahippocampal, and the perirhinal cortices.

Each one is discussed in detail below. The entorhinal cortex is the main interface between the hippocampus and neocortex, thus it is associated with the distribution of information to and from the hippocampus. The surface layers II and III of the entorhinal cortex project out toward the dentate gyrus and hippocampus.

While layer II mainly projects out toward the dentate gyrus and the CA3 region of the hippocampus, layer III mainly projects out toward the hippocampal CA1 region and the subiculum. These layers receive input signals from other cortical areas, particularly the association cortices, the PRC and the parahippocampal gyrus, as well as the prefrontal cortex.

Layers II and III receive highly processed inputs from each sensory modality, and inputs related to ongoing cognitive processes.

Deep layers, particularly layer V, receive one of the three output signals from the hippocampus and, in turn, exchange connections with other cortical areas that project out toward the superficial entorhinal cortex.

The PRC has a role in visual object recognition, while the PHC is involved in the perception of the local environment and processing information related to that place. Thus, fMRI studies indicate that the PHC becomes very active when human subjects receive topographical stimuli such as landscapes or rooms. Finally the hippocampus is responsible for the formation and retrieval of memories.

That is, the information that the three cortices described above process reach the hippocampus where new memories are generated and from which they can later be retrieved. Episodic memory recall involves a spatial and temporal context of specific experiences.

For further review of the mechanisms of memory formation see Craver The rats were presented with a sample of an odor in one specific place along the edge of a large open field. Subsequently, as a way of testing their memory, they were presented with a choice between two arbitrarily selected odors in their original locations. The results of the test showed that normal rats use a combination of where and what information to judge the timing of the events, while rats with a damaged hippocampus cannot manage to effectively combine what, when, and where information in order to form a recovered memory.

Three years later Eichenbaum et al. These streams converge in the hippocampus, which represents items in the context in which they were experienced. It should be noted that memory of faces is typically associated with activity in the perirhinal and hippocampus rostral regions, while memory of objects is typically associated with wider-ranging activity Preston et al.

Both results concerning functional an anatomic and characterizations in animal models are consistent with the hypothesis that is guided by anatomic criteria about the functional organization of the hippocampal system Dickerson and Eichenbaum, As noted, in the context of long-term memory, there were two types of memory, corresponding to declarative and non-declarative memory.

Within declarative memory, we find both episodic memory, as discussed above, and semantic memory, as discussed below. Human beings have the ability to represent concepts in language.

This ability allows us not only to disseminate conceptual knowledge to others, but also to manipulate, associate, and combine these concepts. Activities such as reasoning, planning for the future or reminiscing about the past depend on the activation of concepts stored in semantic memory Mahon and Caramazza, Binder and Desai showed two striking results related to neuroimaging research: on the one hand, the participation of the specific sensory, motor and emotional modality in understanding language and, on the other hand, the existence of large regions of the brain the inferior parietal lobe and a large part of the temporal lobe involved in tasks related to understanding.

These latter regions converge on the many currents involved in perception processing, and these convergences allow supramodal representations of perceptual experience that support a variety of conceptual functions, including language, social cognition, object recognition, and the extraordinary human ability to remember the past and imagine the future Binder and Desai, Therefore, accepting their argument, semantic memory consists of two representations: a specific modality and supramodal modality.

In this regard, Binder and Desai found several objections. A not inconsiderable one is that activations observed in imaging experiments could be an epiphenomenon rather than causally related to understanding. Therefore, the involvement of the motor system for processing a text would contribute to understanding and is not a mere product.

Another critical point is the possibility of interpreting that collected activations represent images after understanding takes place. Although it is often overlooked in reviews of embodied cognition, emotion is as much a modality of experience as sensory and motor processing Vigliocco et al. Following Binder and Desai, brain appears to use supramodal abstract representations for conceptual tasks.

A second argument supporting the hypothesis that the brain appears to use supramodal abstract representations during conceptual work comes from patients with damage to the lower and lateral temporal lobe.

The clinical profile of semantic dementia is marked by progressive atrophy in the temporal lobe and loss of multimodal semantic memory Hodges et al. Patients with semantic dementia is characterized by a loss of conceptual knowledge, and this loss may reflect the disruption of a central semantic hub or the degeneration of a temporosylvian language network for verbal concepts Irish et al.

These patients manifesting in striking alterations in naming and comprehension Irish et al. Basically, these deficits do not seem to be categorical, constituting further evidence that semantic impairment does not imply strongly modal representations and, therefore, the modular and supramodal systems are presented as an interactive continuum of hierarchically ordered neuronal combinations, supporting representations that are progressively more idealized and combined Binder and Desai, In addition to bottom-up input within their associated modality, each system receives top-down input from other modal and attention systems.

These systems are modal in the sense that their output is a analogic or isomorphic representation of the information that they receive bottom-up within their associated modality Barsalou, a. One function of these high-level convergences is to bind representations from two or more modalities, such as the sound and visual appearance of an animal, or the visual representation and action knowledge associated with a hand tool Wernicke, ; Damasio, ; Barsalou, b ; Patterson et al.

More generally, supramodal representations allow the efficient manipulation of abstract, schematic conceptual knowledge that characterizes natural language, social cognition, and other forms of highly creative thinking Dove, ; Diefenbach et al. As noted, long-term memory refers to unlimited information storage that can be maintained for long periods, even for life.

There are two types of long-term memory: declarative or explicit memory and non-declarative or implied memory. Implicit memory encompasses all unconscious memories, as well as certain abilities or skills. There are four types of implicit memory: procedural, associative, non-associative, and priming.

Each one is detailed below. Procedural memory is the part of memory that participates in recalling motor and executive skills that are necessary to perform a task. It is an executive system that guides activity and usually works at an unconscious level. When necessary, procedural memories are retrieved automatically for use in the implementation of complex procedures related to motor and intellectual skills.

Development of these rote capacities occurs through procedural learning, that is, by systematically repeating a complex activity until acquiring and automatizing the capacity of all neural systems involved in performing the task to work together. The acquisition of skills requires practice.

However, the simple repetition of a task does not ensure skill acquisition. A skill is thought to be acquired when behavior changes as a result of experience or practice. This is known as learning and it is not a directly observable phenomenon.

Here we will discuss two models for acquiring skills. These scientists propose an explanatory model of skill acquisition, based on the idea of learning as a process in three phases:. At this point, the psychological process of attention is important. The skill to be acquired must be broken down into its basic components and one must understand how these components are combined to form a whole in the correct execution of the task Fitts, ; Fitts and Posner, As one progresses through this point, the actions that are important for the implementation of a skill are learned and become automated, just as any superfluous or ineffective actions disappears.

The individual sensory system acquires the exact symbolic and spatial data required for the appropriate execution of the skill Fitts, ; Fitts and Posner, Optimally encoded memories last much longer than shallow processed memories. Another factor is the retrieval of memory. The number of times a specific memory is accessed plays an important role in the strengthening of memory. This is probably the reason for better retrieval of information that is repeated and practiced again and again.

Giving attention and focus to the information makes it stick to the brain for a relatively long time. The capacity of long-term memory is thought to have no limits.

According to some studies, the upper bound on the size of visual and acoustic long-term memory has not been reached. We may find it difficult to encode the details of many events but under certain conditions, a person succeeds when he focuses and tries to encode the information.

Long-term memories are not permanently stored in their original condition. Memories are susceptible to change, interference, and also misinformation. Memories are transformed every time they are pulled up. In the process of encoding, the neurons first encode memories in the hippocampus and brain cortices.

Whenever a memory is retrieved, it is re-encoded by similar neurons, but not identical to previous ones. Re-encoding of memories have a great impact on their storage. Details of the memory may change due to re-encoding.

Certain aspects of long-term memory may strengthen or weakened depending upon the types of neurons activated. These memories are susceptible to inaccuracies because people sometimes miss details of events. The brain then fabricates the details to fill in the missing gaps. In some cases, old memories may affect the formation of new memories.

This may lead to the change in memories or encoding of false memories. Previously, it was believed that only the cortex of the brain stores long-term information. Now we know that they are stored in different regions throughout the brain and other parts of the nervous system depending upon their type. Memories are not somewhat localized but stored through circuitry.

Some types of memories may be stored throughout the body because receptors for chemicals in the brain are found everywhere.

When neurotransmitters are activated in the brain, a process called chemotaxis communicates the message to every part of the body. This communication is done basically through blood and cerebrospinal fluid. In this way, some memory may also get stored in muscles. People with organ transplants have reported the emotional reactions and feeling to certain events that they never had before. Long-term memory loss refers to the difficulty in recalling the information. It can also be a sign of some serious problems such as dementia.

There are many causes of long-term memory loss. These causes can be classified into reversible and irreversible causes.

Reversible causes can be treated. Examples of these causes include:. In some cases, loss of long-term memory may be a result of brain injury. Dementia is also a big problem in developed countries. Its first symptom is short-term memory loss which is then followed by long-term memory loss. Taking the history of patients is the first step in diagnosing long-term memory loss.

This history should cover medical history, family history, and history of medication. The second step in diagnosing this condition is a physical exam. The physical exam may include checking for muscle weakness, brain damage, and vitamin deficiencies. Some times complex neuropsychological testing is done to diagnose this condition. There are various treatments for this condition depending upon the underlying cause. If the underlying cause can be removed easily, then it is removed.

Regular exercise, adequate sleep, and a healthy diet may also help in some cases. Attention is an important requirement to improve long-term memory. Actively attend the information being presented to make it a part of long-term memory. Students should stay away from distractions such as television, music, smartphones. Quality sleep is known to optimize the neural processes of the brain.

Slow-wave sleep has shown an important role in the consolidation of long-term memories. Sleep deprivation impairs the ability of the brain to encode new memories during the daytime. Optimal sleep of hours a day is always recommended. Exercise is known to activate the muscles and keep the heart working properly, which has a positive impact on brainpower.

Exercise enhances the chemical and neurotransmitters that empowers the brain to grasp concepts and make them part of long-term memory. Retrieval is known to be one of the best strategies to convert short-term memories into long-term memories.

Retrieving information taking tests is an amazing strategy for students to score more in the exam. Retrieving allows the information to be processed at a much deeper level than the processing of short-term memory. Memories that are not retrieved and recalled weaken and are sometimes replaced by other information. Imagination and visualization refer to an association of images with words to improve neuronal connection strength. Students benefit greatly from visualizing the concepts and information.

This association leads to a great improvement in the storage and retrieval of long-term memories. Long-term memory formation requires the synthesis of new messenger RNA Ribonucleic acid. There is an increased expression of some genes during and after the learning process. Transcription factors and signal transduction mechanisms that guide the process of formation of mRNA have been identified. Epigenetic modifications are critical for memory storage because they play a role in the regulation of transcription.

Memory formation also requires molecular processes for the regulation of neuronal transcription. Drugs of abuse like cocaine and marijuana damage neurons to a great extent. Sedative drugs and benzodiazepines which are mind relaxers and stimulants also exert bad effects on memory. Some drugs are used as memory supplements. These drugs improve cognitive and storage abilities of an individual. These are used as powerful boosters to improve cognition.

Alcoholic consumptions are mainly associated with the destruction of the hippocampus and the nerve cells. The nerve cells responsible for memory encoding, storage, and retrieval are destroyed. An excessive amount of alcohol affects the stomach lining which causes ulcers and other gastrointestinal problems. Alcohol also interferes in many ways with thiamine.

Firstly, it impairs proper thiamine intake as alcoholics more often skip meals. Thiamine converts certain carbohydrates to glucose. Episodic memories are autobiographical memories from specific events in our lives, like the coffee we had with a friend last week. How do we know this? In , a patient named Henry Molaison had his hippocampus surgically removed during an operation in the United States to treat his epilepsy.

His epilepsy was cured, and Molaison lived a further 55 healthy years. However, after the surgery he was only able to form episodic memories that lasted a matter of minutes; he was completely unable to permanently store new information.

He was, however, still able to improve his performance on various motor tasks, even though he had no memory of ever encountering or practising them. The study of Henry Molaison was revolutionary because it showed that multiple types of memory existed. We now know that rather than relying on the hippocampus, implicit motor learning occurs in other brain areas — the basal ganglia and cerebellum.

The neocortex is the largest part of the cerebral cortex, the sheet of neural tissue that forms the outside surface of the brain, distinctive in higher mammals for its wrinkly appearance. In humans, the neocortex is involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning and language. Over time, information from certain memories that are temporarily stored in the hippocampus can be transferred to the neocortex as general knowledge — things like knowing that coffee provides a pick-me-up.

Researchers think this transfer from hippocampus to neocortex happens as we sleep. This is particularly important because strong emotional memories e.

The amygdala doesn't just modify the strength and emotional content of memories; it also plays a key role in forming new memories specifically related to fear. Fearful memories are able to be formed after only a few repetitions. Understanding how the amygdala processes fear is important because of its relevance to post-traumatic stress disorder PTSD , which affects many of our veterans as well as police, paramedics and others exposed to trauma.