Episodic Memory

Episodic memory is the memory of every day events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred at particular times and places; for example, the party on one's 7th birthday. Along with semantic memory, it comprises the category of explicit memory, one of the two major divisions of long-term memory (the other being implicit memory).

The term "episodic memory" was coined by Endel Tulving in 1972, referring to the distinction between knowing and remembering: knowing is factual recollection (semantic) whereas remembering is a feeling that is located in the past (episodic).

Episodic memory emerges at approximately 3 to 4 years of age. Activation of specific brain areas (mostly the hippocampus) seems to be different between younger (aged 2339) and older people (aged 67-80) upon episodic memory retrieval. Older people tend to activate both their left and right hippocampus, while younger people activate only the left one.

The relationship between emotion and memory is complex, but generally, emotion tends to increase the likelihood that an event will be remembered later and that it will be remembered vividly. Flashbulb memory is one example of this. An example of this would be an experience such as a close family member dying or the Christmas that you got the exact toy you wanted as a kid. The experience holds so much emotional significance that it is encoded as an extremely vivid, almost picture-perfect memory. However, whether the vividness of the flashbulb memory is due to a virtual "flash" that occurs because of the emotional experience has been hotly contested. Flashbulb memories may occur because of our propensity to rehearse and retell those highly emotional events, which strengthens the memory.

One of the main components of episodic memory is the process of recollection, which elicits the retrieval of contextual information pertaining to a specific event or experience that has occurred. Tulving seminally defined three key properties of episodic memory recollection as:

Aside from Tulving, others named additional aspects of recollection, including visual imagery, narrative structure, retrieval of semantic information and feelings of familiarity.

Events that are recorded into episodic memory may trigger episodic learning, i.e. a change in behavior that occurs as a result of an event, such as a fear of dogs after being bitten by a dog.

There are essentially nine properties of episodic memory that collectively distinguish it from other types of memory. Other types of memory may exhibit a few of these properties, but only episodic memory has all nine ...

The formation of new episodic memories requires the medial temporal lobe, a structure that includes the hippocampus. Without the medial temporal lobe, one is able to form new procedural memories (such as playing the piano) but cannot remember the events during which they happened.

The prefrontal cortex (and in particular the right hemisphere) is also involved in the formation of new episodic memories (also known as episodic encoding). Patients with damage to the prefrontal cortex can learn new information, but tend to do so in a disordered fashion. For example, they might show normal recognition of an object they had seen in the past, but fail to recollect when or where it had been viewed.

Some researchers believe that the prefrontal cortex helps organize information for more efficient storage, drawing upon its role in executive function. Others believe that the prefrontal cortex underlies semantic strategies which enhance encoding, such as thinking about the meaning of the study material or rehearsing it in working memory.

Other work has shown that portions of the inferior parietal lobe play a role in episodic memory, potentially acting as an accumulator to support the subjective feeling that something is 'old', or perhaps supporting mental imagery which allows you a sense of the vividness of memories. Indeed, bilateral damage to the inferior parietal lobe results in episodic memory that is largely intact, however it lacks details and lesion patients report low levels of confidence in their memories.

Researchers do not agree about how long episodic memories are stored in the hippocampus. Some researchers believe that episodic memories always rely on the hippocampus. Others believe the hippocampus only stores episodic memories for a short time, after which the memories are consolidated to the neocortex. The latter view is strengthened by recent evidence that neurogenesis in the adult hippocampus may ease the removal of old memories and increase the efficiency of forming new memories.

Endel Tulving originally described episodic memory as a record of a person's experience that held temporally dated information and spatio-temporal relations. A feature of episodic memory that Tulving later elaborates on is that it allows an agent to imagine traveling back in time. A current situation may cue retrieval of a previous episode, so that context that colors the previous episode is experienced at the immediate moment.

The agent is provided with a means of associating previous feelings with current situations. Semantic memory, on the other hand, is a structured record of facts, concepts, and skills that we have acquired. Semantic information is derived from accumulated episodic memory. Episodic memory can be thought of as a "map" that ties together items in semantic memory. For example, all encounters with how a "dog" looks and sounds will make up the semantic representation of that word. All episodic memories concerning a dog will then reference this single semantic representation of "dog" and, likewise, all new experiences with the dog will modify the single semantic representation of that dog. Together, semantic and episodic memory make up our declarative memory. They each represent different parts of context to form a complete picture. As such, something that affects episodic memory can also affect semantic memory. For example, anterograde amnesia, from damage of the medial temporal lobe, is an impairment of declarative memory that affects both episodic and semantic memory operations.

Originally, Tulving proposed that episodic and semantic memory were separate systems that competed with each other in retrieval. However, this theory was rejected when Howard and Kahana completed experiments on latent semantic analysis (LSA) that supported the opposite. Instead of an increase in semantic similarity when there was a decrease in the strength of temporal associations, the two worked together so semantic cues on retrieval were strongest when episodic cues were strong as well.

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Episodic Memory: Why Some Memories Seem Like Movies: 'Time Cells' Discovered In Human Brains   NPR - November 11, 2020
If you fall off a bike, you'll probably end up with a cinematic memory of the experience: the wind in your hair, the pebble on the road, then the pain. That's known as an episodic memory. And now researchers have identified cells in the human brain that make this sort of memory possible. The cells are called time cells, and they place a sort of time stamp on memories as they are being formed. That allows us to recall sequences of events or experiences in the right order.

Why'd I Come in Here? A Brain Zap Could Boost That Fuzzy Memory   Live Science - June 5, 2019
Fuzzy memories can be frustrating, whether you're at the grocery store trying to recall if you finished the last bit of milk or in court giving eye-witness testimony. Now, a new study finds that zapping the brain might boost that memory. After receiving stimulation in a certain part of the brain, study participants were 15.4% better at recalling memories. Specifically, these subjects were better at recalling episodic memories, those that involve a specific time and a place. In an episodic memory, you have contextual detail.

Simulation Hypothesis - Holographic Universe Theory