What term refers to the process by which material in memory is located route to awareness and used?

Conclusions

Episodic memory has played, and continues to play, an important role in memory research. Over time, the emphasis in research has expanded from an emphasis on the content of personal experiences to include tasks that assess the context and awareness associated with memory retrieval. Episodic memory continues to be used in a heuristic sense to refer to certain kinds of tasks, but the more important use of the term is theoretical, where episodic memory refers to a type of memory system. Although a good deal of cognitive research continues to explore the nature of episodic memory, the newest areas of research have added the study of the brain to cognitive tasks.

Abstract

Episodic memory is a past-oriented memory system that allows reexperiencing previous events. Episodic memory is composed of a number of distinct but interacting component processes. Retrieval from episodic memory is subserved by a widely distributed network of brain regions, including temporal, parietal, and frontal cortices; diencephalon; and the cerebellum. This network overlaps partly with those subserving other systems, but specific interactions among regions uniquely define episodic retrieval. Episodic retrieval structures are not static but are affected by factors such as ways of probing episodic memory, practice, and individual differences in genetic makeup and experience.

Abstract

Episodic memories are consciously recollected memories related to personally experienced events. Episodic remembering is a dynamic process that draws upon mnemonic and non-mnemonic cognitive abilities in order to mentally reconstruct past experiences from retrieval cues. The neural substrates of these abilities represent a distributed set of functionally-specific nervous system structures that operate in concert. The profound anterograde amnesia observed in patient HM demonstrated that the medial temporal lobes are critically involved in the formation of episodic memories, while more recent research highlights the role of other brain regions, including prefrontal and parietal cortex, in episodic memory.

Episodic memory refers to a neurocognitive system that renders possible the conscious recollection of events as they were previously experienced. The term is closely related, but not identical, to autobiographical memory, which refers to memory for and about a person's own life. The defining characteristic of episodic memory is its dependence on a special kind of conscious awareness called autonoetic awareness. An individual with autonoetic (or ‘self-knowing’) awareness is capable of roaming at will in subjective time, by recollecting aspects of past experiences, or imagining possible future experiences. It can be contrasted with semantic memory, or the neurocognitive system that makes possible the acquisition, retention, and use of factual information whose retrieval is accompanied by noetic awareness. Research in cognitive neuroscience has identified two brain regions, the medial temporal lobes and the prefrontal cortex, which are critical for the normal operations of episodic and autobiographical memory. The former area is necessary for the establishment of episodic and autobiographical memories, and also participates in their retrieval for a limited time following encoding. The latter area underlies the ability to become autonoetically aware of the personal past and future, and is especially important in episodic memory.

Definition

Episodic memory is currently described as the memory system in charge of the encoding, storage, and retrieval of personally experienced events, associated with a precise spatial and temporal context of encoding. Episodic memory allows the conscious recollection of happenings and events from one's personal past and the mental projection of anticipated events into one's subjective future (Wheeler et al., 1997). Recollection of episodic events includes autonoetic awareness, which is the impression of re-experiencing or reliving the past and mentally traveling back in subjective time (Tulving, 2001). Of the many components of memory, episodic memory is hierarchically the highest memory system (Fig. 13.1) – the most sophisticated but also the most sensitive to pathology, trauma, and toxicity.

Episodic Memory

Episodic memory is concerned with personal experiences (hence also called autobiographical) –the breakfast you had that morning, the suit you wore for last night’s party – such episodic events are important for day-to-day activities. The duration of its storage largely depends on the attention an individual gives to it – you may remember the sumptuous dinner eaten at your friend’s house for years, yet you may forget other details (like your friend’s son’s name) that are associated with the event. Hippocampus is fundamental in recording episodic memory (see ‘Mechanism of LTM formation’, below).

Amnesia is a condition in which a person fails to recollect episodic memory. A peculiar sort of anterograde amnesia called Korsakoff’s psychosis (see ‘The Papez circuit’, below) occurs in some persons with chronic alcoholism (with vitamin B1 deficiency), rendering them unable to store episodic memory – the person can remember all past memories but new memories are not recorded.

67.3 Episodic Memory

Episodic memory (and the related notion of autobiographical memory) refers to memory for specific experiences, usually associated with a time, place, and emotion (Tulving, 1984). Tulving (2002) likened the capacity of remembering specific episodes to “mental time travel,” as if the individual is able to re-experience individual events. This type of memory is commonly associated with the subjective mental experience that requires a sense of self and an awareness that this event happened in the past. For example, recalling a birthday party that you attended, who was there, where it occurred, and your own personal interactions there, reflects your episodic memory of that event. In this way, episodic memories represent one-time episodes (i.e., one-trial learning) and rely heavily on the hippocampus. Similarly, the first exposure to a new vocabulary word will be encoded as an episodic memory and be associated with the context in which it was learned.

Episodic memory impairment is the hallmark symptom of amnesic patients. For example, patient H.M. was unable to recall any events from his daily life after his hippocampal resection (Corkin, 2002). Although the formation and retention of new episodic memories is clearly impaired in amnesia, the preservation of older episodic memories is less clear. It is clear that even in cases of extensive medial temporal lobe damage including the hippocampus, old autobiographical memories are typically still present. For example, H.M. was able to produce well-formed autobiographical memories from ages 16 years and younger (Corkin, 1984). Other amnesic patients have also produced rich autobiographical memories from earlier years prior to their amnesic episodes (Bayley, Hopkins, & Squire, 2006; Kirwan, Bayley, Galvan, & Squire, 2008). However, there is still debate regarding whether these memories are truly episodic and contain the same recollective detail found in healthy individuals (Gilboa et al., 2006; Moscovitch, Nadel, Winocur, Gilboa, & Rosenbaum, 2006). Whether the hippocampus is required to truly reexperience an event retrieved from memory (as suggested by Multiple Trace Theory, see below), it is clear that damage to this system would have profound effects on the learning and memory processes used in language (which need not be truly episodic).

There is debate in the literature regarding whether animals also possess episodic memory. Because episodic memory is defined as having insight into the memory, to travel back in time and re-experience a memory, it is nearly impossible to test in animals. Therefore, based on this definition, Tulving (2002) argues that episodic memory is unique to humans and may be one of the factors that make humans unique from other animals. However, an alternative theory of episodic memory proposes that there is shared neural history between animals and humans, focusing on memory for events in context (Allen & Fortin, 2013). Episodic memories can instead be defined by the unique characteristics of their what, where, and when components. Utilizing this definition, Clayton and Dickinson (1998) demonstrated that scrub jays could remember what food they stored (worms or peanuts), as well as where (the location of the cage) and when (4 or 124 h ago) it was cached. This information can be updated and used flexibly (Clayton & Dickinson, 1999; Clayton, Yu, & Dickinson, 2003) and expressed spontaneously (Singer & Zentall, 2007), and it has been demonstrated in other species, such as rats (Eacott, Easton, & Zinkivskay, 2005; Ergorul & Eichenbaum, 2004), mice (Dere, Huston, & De Souza Silva, 2005), and nonhuman primates (Hoffman, Beran, & Washburn, 2009), much like the definition applied to episodic memories.

1.02.4.2.1 Episodic Memory

Episodic memory refers to memory for particular events situated in space and time, as well as the underlying cognitive processes and neural mechanisms involved in remembering those events. A key ingredient of episodic memory that distinguishes it from other forms of memory is the retrieval of information regarding the spatial and/or temporal context in which the remembered event occurred. As previously mentioned, episodic memory is also associated with autonoetic consciousness, considered by some researchers to be an evolutionarily advanced, unique human capacity (e.g., Wheeler, 2000; Tulving, 2002, 2005). On the other hand, research with infrahuman animals has pointed to “episodic-like” behavior, and so some researchers dispute the claim that only humans have episodic memory.

One can point to a wide variety of examples of episodic memory, ranging from remembering what a friend wore at a party the night before to individual words studied in a list moments ago. In most contexts, episodic memory is synonymous with explicit memory, although the former term is usually used to represent a memory system and the latter term to designate types of tests that are used. Many tests have been designed to measure certain aspects of episodic memory in the lab, including free recall (recall of a set of material in any order), serial recall (recall of events in order), cued recall (recall of events given specific cues), recognition judgments (recognizing studied material intermixed with nonstudied material), source judgments (recognizing the source of presented material, such as whether it was presented auditorily or visually). Subjects may also be asked to make judgments of the recency of an event, its frequency of occurrence, or of some other quality. In addition, subjects can be asked to make metamemory judgments, or judgments about their memories. For example, a student might be asked to rate how confident he/she is in the accuracy of his/her recollections. Similarly, individuals might be asked to judge whether they can remember the moment an event occurred or the context in which it occurred or whether they only just know that they were previously encountered but cannot remember the context (Tulving, 1985). These remember/know judgments (with remember judgments reflecting episodic recollection) have been much studied. Episodic memory (as well as working memory) tends to decline with age.

Episodic Memory

Episodic memory captures individual experiences of particular times and places. Episodic memory associates what, when, and where, and is the basis for cognition, because the animal that remembers episodes can use them to recall previous events, or to project forward, predicting future events. These are key elements of mental time travel. For example, if an animal has previously forded a rapidly running stream, it might reflect on that experience and form a plan for fording a newly encountered stream. Sometimes reference to an occurrence at a specific time is useful, as in time–place learning (see the following section on time–place learning). While humans seem to refer to specific times during the circadian cycle (the time of day that an event happened), rats measure the time elapsed since the event happened.40 Either approach is useful in cognitive processes. Experiments designed to test for cognition in animals focus on episodic memory.

Parietal Lobes

Although episodic memory has traditionally been conceptualized as a medial temporal- and frontal lobe-driven process, the advent of functional neuroimaging has shown that the parietal lobes play a key role in these processes. Posterior and lateral parietal regions, particularly the posterior cingulate, precuneus, and retrosplenial gyrus, have received increasing recognition for their role in harnessing attention and working memory processes during encoding and recall of episodic memories. Thus, although parietal lobe lesions are rarely associated with frank episodic memory deficits, these regions contribute important attentional resources to episodic learning that results in more efficient encoding of verbal and visual material.