Episodic Memory Definition
Episodic memory is a kind of declarative, long-term memory that allows people to recall past personal events. The temporal lobe of the cerebrum contains all of the crucial elements engaged in episodic memory: the hippocampus, parahippocampus, entorhinal cortex, and perirhinal cortex. In addition, it contains the prefrontal cortex. The hippocampus activates episodic memory in response to environmental inputs that recall earlier events in relation to the present circumstance.
Once the hippocampus becomes active, other pathways become active, ultimately activating the prefrontal cortex. The prefrontal cortex then examines the memory and activates the motor cortex if it concludes, based on prior experience, that action is required. Episodic memory is interwoven with future episodic cognition so that remembering previous events might impact a person’s future goals.
Neurons and the Brain
The neural pathways in the brain enable episodic memory as a cognitive ability. Neurons (or nerve cells) comprise the nervous system’s cellular components. Using electrical impulses, they may rapidly excite nearby neurons and spread throughout the body very fast.
This occurs when one neuron forms a synapse with another, When an electrical impulse transforms into a chemical prior returning to an electrical signal at the next cell. Neurons encompass all components of the nervous system, which consists of the central nervous system (brain and spinal cord neurons) and the peripheral nervous system (nerve cells in the periphery) (neurons outside the brain and spinal cord).
Several brain regions have been investigated in connection to episodic memory. The brain is often divided into four major regions: the cerebrum (sometimes known as the cerebral cortex or simply cortex), the cerebellum, the diencephalon, and the brain stem.
Further subdivisions of the cerebrum include the frontal, parietal, temporal, and occipital lobes. Despite the fact that individual areas and lobes may be associated with particular tasks, many brain processes include linked neuronal pathways that span several brain structures and regions.
As will be explained further in this essay, episodic memory involves numerous brain areas. Primarily, the key structures for the integrity of episodic memory are located in the temporal lobe of the cerebrum. To understand the complete possibilities of episodic memory, researchers continue to examine alternate areas and less prominent lobes.
Memory is the retention of previously acquired knowledge. Memory is possible due to the plasticity of neurons. This enables them to recall and build new neural connections. There are two types of memory: temporary memory and permanent memory. Working memory (also known as short-term memory) is a temporary kind of memory that allows humans to execute activities. Although it does not necessarily use similar structures as permanent memory, researchers continue to examine their connections.
Declarative and non-declarative memory partition long-term memory (also known as explicit vs. implicit memory). The components of non-declarative memory include skills, routines, classical conditioning, and non-associative learning. In particular, this kind of “memory” does not need access to information held in memory.
Instead, it is the result of non-conscious skills with the power to influence behaviour. In contrast, declarative memory involves recalling events and information consciously. It is separated into semantic and episodic memory, the former reflecting conscious access to information and the latter conscious access to events.
In cognitive psychology, episodic memory refers to the capacity of humans to remember prior personal experiences. Similarly to semantic memory, it is a kind of declarative memory. Nevertheless, semantic memory might not require recalling emotional experiences. Semantic memory, on the other hand, is the ability to remember knowledge and concepts that are not necessarily personalised and are thus applicable in a number of circumstances.
Examples include knowing the number of feet in a mile and the colours that make up a flower. In particular, episodic memory has been nicknamed “mental time travel” because it enables humans to “reexperience” past events. Three factors must be present in the human intellect for this to occur: its own identity, the idea of time, and the fact that the event being remembered has already happened.
According to tradition, humans are the unique species susceptible to episodic memory, whereas some animals may possess episodic “like” memories. Recent research has shown that avian and rodent species are capable of episodic memory. This notion was derived from a comparison of the sizes and neuronal potentials of components reported to contribute to human episodic memory with several species of animals.
Associated Brain Structures in Episodic Memory
Numerous brain regions are being investigated as mental components of episodic memory. The hippocampus is generally regarded as the most important component in its maintenance. However, a number of cortical regions, including the parahippocampal region and prefrontal cortex, are acknowledged as significant structures.
The hippocampus is a structure of the brain present in various animals and located in the inner temporal lobe. It comprises the subiculum, the dentate gyrus, and the cornu Ammonis areas. The entorhinal cortex of the temporal lobe provides many connections to the hippocampus. Additionally, the hippocampus is linked to the septum of the forebrain, which is located near the brain’s midline. Functionally, the hippocampus is essential for spatial memory maintenance.
The parahippocampus, entorhinal cortex, and perirhinal cortex (the whole temporal lobe) are significant structures that link the hippocampus to the surrounding cortex. The parahippocampal area comprises two information-sending routes. These consist of the “what” and “where” pathways. The “what” route is essential for the processing of characteristics and objects. This route uses all of the body’s senses, facilitating the formation of object-related memories. This circuit includes the perirhinal cortex and the lateral entorhinal cortex.
In the meantime, the “where” route analyses visuospatial information, enabling a person to recall space and position. As a common mechanism preserved in several animal species, this has proven evolutionarily significant for locating oneself within an environment. The parahippocampal/perirhinal cortex and medial entorhinal cortex make up this route.
The prefrontal cortex receives data via cortical regions and is connected to both cortical and subcortical motor areas. It has direct communication between the hippocampus and lateral communication with the parahippocampal regions. Working memory, inference, as well as judgement are all facilitated by the prefrontal cortex.
According to its linkages with the motor cortex, it is considered that the prefrontal cortex has a substantial impact on action efficiency. As a result, it is hypothesised that the prefrontal cortex is essential for linking an individual’s views to their past experiences and prompting them to engage in appropriate responses.
Connections Between Structures
Episodic memory is initiated by the direct transmission of the sensory integration of taste, touch, sound, and sight to the thalamic nuclei (found in the cerebral cortex). This data is sent to the neocortex’s primary sensors. Now, the data is split according to its degree of complexity and transported towards the hippocampus and also parahippocampal areas. The hippocampus separates data about specific objects and impulses from context knowledge. This is the place in the brain where “what” and “where” become distinct.
In addition, the brain must filter information on “when” as a second dimension. Despite the fact that this mechanism is poorly defined, it is crucial to comprehend given the function of episodic memory in separating previous experiences from current self-awareness. The cortex and subcortical areas, like the striatum, are thought to be involved in this function.
Recalling Episodic Memory
When a person remembers a particular experience in relation to the present, episodic memory is engaged. This function is provided only via the hippocampus. While the hippocampus is engaged, the parahippocampal areas and prefrontal cortex may become active as well.
The hippocampus may stimulate the prefrontal cortex either directly or indirectly through the parahippocampal areas. In reaction to the recollection, the prefrontal cortex then mainly directs the individual’s activities. If the prefrontal cortex determines the relevance of a recalled event, it may transmit messages to the motor complex and initiate an appropriate physical response.
Future Episodic Thought
Numerous connecting routes and overlapping portions have been discovered between episodic memory and future planning and forecasting. This talent is referred to as “future episodic cognition,” and it is unique to humans owing to our capacity to generate potential future situations. Episodic memory facilitates these stimuli by evaluating, based on prior experiences, which consequences are conceivable. Consequently, the person may make appropriate plans.
In 2018, a teenage woman enjoyed one week at the beach. She packed plenty of shorts, t-shirts, and beachwear in anticipation of daily temperatures of 80 degrees Fahrenheit. However, since she was unaware of the substantial drop in temperature at night at the beach, she did not bring any lightweight clothing. Based on her prior experience, she included a lightweight sweater and a pair of long trousers in her 2019 beach holiday luggage.
It is uncertain if this capacity extends beyond humans to other animals, but researchers are now examining plausible ideas.
Disorders Involving Episodic Memory
Typically, age diminishes episodic memory, with cognitive ageing being characterised by a decline in higher thought and reduced mental function. Despite its importance to episodic memory, the hippocampus often declines with age. Specifically, investigations conducted on rats revealed that older people had identical hippocampus neuronal firings in both familiar and unfamiliar environments.
On the other hand, younger rats, on the other hand, when introduced to a new environment, the organisms’ firing frequencies change. This demonstrates that elderly individuals’ decreased ability to view unfamiliar surroundings as unique events, hence hampering the hippocampus’s capacity to remember a particular event when necessary.
(Note: Although episodic memory loss cannot be reversed, individuals may practise activities to enhance their existing episodic memory!)
As a result of this understanding, certain disorders as well as illnesses that are frequent among the elderly are more prone to be associated with a deterioration in episodic memory. This is particularly noticeable in conditions when forgetfulness is the major indication, like Alzheimer’s disease, hippocampal sclerosis, and also temporal lobe epilepsy.
Alzheimer’s disease is the very common form of neurodegeneration, with symptoms including loss of memory, impairment in judging and diminished visuospatial and linguistic ability. Scientists have always been unsure as to how individuals get the disease. However, it is recognised that amyloid-beta (A) accumulation is critical to the pathophysiology of the disease.
The hippocampus is one of the primary regions affected by Alzheimer’s disease. However, those with mild Alzheimer’s disease have fast shrinkage of other regions required for episodic memory. The variety of indications is also impacted by the damaged components and pathways.
Alzheimer’s disease is often characterised by an inability to appropriately retain new knowledge. Patients cannot thus “extract” these memories as required. Additional complications develop when people are unable to notice the symptoms themselves.
Initially, it was assumed that the capacity to stay “familiar” with an item or event remained intact, but the capacity to “recall” stored knowledge diminished. However, it is now established that both recognition and memory are impaired in Alzheimer’s patients. This lack of ability to distinguish between new and old items and experiences results in “false memories.”
It is also fascinating to note that various stimuli may induce distinct neuronal firing patterns in Alzheimer’s patients’ memory store regions. Specifically, visual stimuli (such as displaying images and objects) may result in enhanced memory recall compared to verbal stimuli. This is likely due to the fact that people recall visuals better than words describing images.
As its name implies, hippocampal sclerosis is a neurodegenerative illness in which the hippocampus’s formation declines. Compared to Alzheimer’s disease, much less research has been conducted. similar to Alzheimer’s disease but more prevalent in older adults and those with dementia symptoms. The occurrence of asymmetric hippocampus and ipsilateral mammillary body degeneration in individuals with hippocampal sclerosis may serve as a diagnostic indicator. It is also often accompanied by tumescent lesions and frontotemporal degeneration.
Temporal Lobe Epilepsy
Abnormal electrical activity in the brain, resulting in convulsions and loss of consciousness, characterises epilepsy. It is a well-known fact that people with temporal lobe epilepsy have memory impairment. Epilepsy of the temporal lobe primarily affects adults and typically involves the hippocampus formation and cortical areas. Intriguingly, people with epilepsy of the temporal lobe are more prone to suffering from object-specific memory impairments.
This is believed to result from verbal memory impairment. Notably, impairments in verbal memory tend to occur in the dominant hemisphere (where speech and mathematical abilities are found). In the non-dominant hemisphere, visual and visuospatial memory impairments are seen (where creativity is found).
Patients with epilepsy may exhibit other kinds of forgetfulness, including temporary epileptic amnesia. This kind of amnesia often affects middle-aged and older people, manifesting as brief, recurrent memory gaps. In addition to transient epileptic amnesia, rapid long-term forgetting and distant memory impairment may also be present.
Accelerated long-term forgetting entails the usual capacity to acquire and recall information in a short period of time, followed by the fast loss of this knowledge over the following days to weeks. In contrast, remote memory impairment is the impairment of distant semantic memory relative to more recent experiences.
Episodic memory is a kind of declarative long-term memory that enables people to remember past personal events. The hippocampus, parahippocampus, and prefrontal cortex are all necessary for recovering memories in response to current inputs. They may also trigger motor responses as necessary.
Humans with episodic memory may have future episodic thoughts, allowing them to prepare for future occurrences based on recent personal experiences. Alzheimer’s disease, hippocampal sclerosis, and temporal lobe epilepsy may all have a significant impact on episodic memory.
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