Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Prefrontal Cortex and Working Memory

(paraphrase of Eichenbaum, Cognitive Neuroscience of Memory, 311ff)

The prefrontal cortex performs a critical role in "working-with-memory" in rodents, monkeys, and humans. Most investigators regard its role as critical to working memory, the capacity to hold items and manipulate them in consciousness. The prefrontal cortex is parcellated into several distinct areas that have different inputs and whose functions can be dissoci­ated according to different modalities of stimulus processing. However, they share common higher-order function in working memory and strate­gic processing, reflected in perseveration and other common strategic dis­orders following damage to any of the subdivisions.

Correspondingly, prefrontal neurons encode all events during working memory task performance, and large numbers of prefrontal cells are in­volved in maintaining item memories for brief periods and in encoding stimuli and events in accordance with acquired task rules. Prefrontal sub­divisions are highly connected with one another and with posterior areas of the cortex to operate as a complex and widespread network for con­scious control over memory and other intellectual functions.

While the entire cerebral cortex is involved in memory processing, the chief brain area that mediates these processes is the prefrontal cortex, the area in the frontal lobe whose functions are not fully understood but clearly involve strategic mechanisms of the sort that work with memory as a major part of its function. The role of the prefrontal cortex is generally viewed as mediating working memory. Working memory involves a combination of storing new incoming information, plus some type of cognitive manipulation, during a brief period in consciousness.

We perform tasks that demand working memory in almost all of the activities of our conscious lives, from checking off the jobs accomplished in our morning routine, to keeping track of the flow of information in reading a text chapter, to solving the many complex problems we en­counter during our work. Working memory is considered a form of de­clarative memory because this sort of processing goes on in consciousness and involves relational organization and inferential judgments, and is ac­cessible to explicit forms of expression. However, the short term mechanisms of working memory are distinctly differ­ent from the mechanisms of long term declarative memory and procedural memory.

Alan Baddeley and his colleagues first realized the importance of distinguishing the cognitive and storage processes in short term memory, and replaced the concept of a unitary short term memory with a mul­tiple component conception of working memory. The multiple component model was inspired by findings from experiments in which they found an unexpected low degree of interference in the capacity for storing lists of visual patterns or word items when people performed cognitive tasks simultaneously. So, in their model of working memory they proposed the existence of a set of specialized subsystems that mediates the storage process, and a distinct "central executive" that controls the subsystems and performs the mental "work" of controlling the slave subsystems and forming strategies. Corresponding to the materials involved in Baddeley's studies, the model involved two distinct subsystems, a "visuospatial sketch pad" that could maintain nonverbal images and a "phonological loop" that mediated speech perception and subvocal rehearsal of verbal materials. These should be considered just examples of the full range of specialized subsystems available to the central executive.

Because this kind of conceptual model of working memory involves multiple types of cognitive processing combined with a range of stored material, it will come as no surprise that working memory relies on a wide­spread network of brain structures. Indeed, there is considerable evidence that the brain network for working memory is large and can be subdivided into a central executive with multiple subsystems. Considerable evidence points to the prefrontal cortex as the locus of the central executive, and to a variety of other cortical areas as the mediators of subsystem processes.

(end of paraphrase)



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