A couple of months ago I came across a ten years old article Deconstructing Episodic Memory with Construction by Demis Hassabis and Eleanor A. Maguire published in Trends in Cognitive Sciences. The article dealt with episodic memory that was the area of my interest then but the name of one of the authors — Demis Hassabis attracted my attention even more. I got my hands on the article when everyone was talking about successes of chess playing AI algorithm Alpha Zero developed by DeepMind, a part of Google’s Alphabet group. Demis Hassabis is a co-founder and CEO of DeepMind now.

In the article Demis and his colleague made an attempt to deconstruct episodic memory with scene construction. They wanted this way to support a hypothesis that not only episodic memory but many cognitive functions dealing with past, present and future are related because they all critically depend on scene construction. In this post I just tried to put together a number of articles addressing the issue of encoding and retrieval of episodic memory that may play a crucial role in the development of human-like AI.

The Entropic Brain

In this article a hypothesis is presented that human brain has a primary entropic consciousness state and that entropy is suppressed by normal waking consciousness state that makes us self aware.

“The psychedelic state is considered an exemplar of a primitive or primary state of consciousness that preceded the development of modern, adult, human, normal waking consciousness. Based on neuroimaging data with psilocybin, a classic psychedelic drug, it is argued that the defining feature of “primary states” is elevated entropy in certain aspects of brain function, such as the repertoire of functional connectivity motifs that form and fragment across time. Indeed, since there is a greater repertoire of connectivity motifs in the psychedelic state than in normal waking consciousness, this implies that primary states may exhibit “criticality,” i.e., the property of being poised at a “critical” point in a transition zone between order and disorder where certain phenomena such as power-law scaling appear. Moreover, if primary states are critical, then this suggests that entropy is suppressed in normal waking consciousness, meaning that the brain operates just below criticality. It is argued that this entropy suppression furnishes normal waking consciousness with a constrained quality and associated metacognitive functions, including reality-testing and self-awareness. It is also proposed that entry into primary states depends on a collapse of the normally highly organized activity within the default-mode network (DMN) and a decoupling between the DMN and the medial temporal lobes (which are normally significantly coupled).” More info…

The Episodic Memory

This is a classic article about the episodic memory that is our memory about ourselves. It, actually, enables us to constantly remember who we are.

“The three clues — sense of subjective time, autonoetic awareness, and self — point to three central components of a neurocognitive (mind/brain) system that makes mental time travel possible.”

“Episodic memory is about happenings in particular places at particular times, or about “what,” “where,” and “when.”

“Episodic memory is a recently evolved, late-developing, and early-deteriorating past-oriented memory system, more vulnerable than other memory systems to neuronal dysfunction, and probably unique to humans.”

http://www.annualreviews.org/doi/10.1146/annurev.psych.53.100901.135114

An Episode

This article explains what is an episode in the episodic memory and how our brain separates one episode from the other.

“Event-segmentation theory (EST) proposes that continuous actions are parsed, or segmented, into events. EST also suggests that the perception and understanding of everyday experiences is mediated by a system that uses mental models to make predictions about how those experiences should unfold. Event models are proposed to be active representations that incorporate the perceptual details of the current experience with semantic knowledge of similar past experiences, as long as the current experience is congruent with the active mental model. When perceptual details become incongruent with the active model (e.g., when one activity is finished and another is begun), EST proposes that the event model is updated to accommodate these changes. The points at which these updates are proposed to occur are called event boundaries.

“Perhaps because mental models are also prominent in theories of narrative comprehension, much of the evidence supporting EST has come from the narrative domain. Researchers have shown that spatial and temporal shifts in narratives tend to be identified as event boundaries.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4451827/

Scene Construction

This is the article by Hassabis et al. It explains how scenes in which episodes are played is constructed.

“We define scene construction as the process of mentally generating and maintaining a complex and coherent scene or event. This is achieved by the retrieval and integration of relevant informational components, stored in their modality-specific cortical areas, the product of which has a coherent spatial context, and can then later be manipulated and visualized. The full recollective experience of richly recalling an episodic memory.”

“Scene construction provides the stage on which the remembered event is played or the ‘where’ for the ‘what’ to occur in, using Tulving’s ‘what, where, when’ taxonomy of episodic memory. Moreover, we argue that scene construction is an excellent candidate for a common core process that underpins a host of related cognitive functions including navigation and imagination.”