Hostname: page-component-7c8c6479df-fqc5m Total loading time: 0 Render date: 2024-03-18T10:12:49.140Z Has data issue: false hasContentIssue false

Working memory retention systems: A state of activated long-term memory

Published online by Cambridge University Press:  01 December 2003

Daniel S. Ruchkin*
Affiliation:
Department of Physiology, Program in Neurosciences, University of Maryland School of Medicine, Baltimore, MD21201
Jordan Grafman*
Affiliation:
National Institutes of Health, Cognitive Neuroscience Section, NINDS, Bethesda, MD20892http://intra.ninds.hih.gov/Lab.asp?Org_ID=83
Katherine Cameron*
Affiliation:
Department of Psychology, Washington College, Chestertown, MD21620http://faculty.washcoll.edu/bios/cameron_katherine.html
Rita S. Berndt*
Affiliation:
Department of Neurology, Program in Neurosciences, University of Maryland School of Medicine, Baltimore, MD21201http://neuroscience.umaryland.edu/faculty.asp?FacultyID=4

Abstract:

High temporal resolution event-related brain potential and electroencephalographic coherence studies of the neural substrate of short-term storage in working memory indicate that the sustained coactivation of both prefrontal cortex and the posterior cortical systems that participate in the initial perception and comprehension of the retained information are involved in its storage. These studies further show that short-term storage mechanisms involve an increase in neural synchrony between prefrontal cortex and posterior cortex and the enhanced activation of long-term memory representations of material held in short-term memory. This activation begins during the encoding/comprehension phase and evidently is prolonged into the retention phase by attentional drive from prefrontal cortex control systems. A parsimonious interpretation of these findings is that the long-term memory systems associated with the posterior cortical processors provide the necessary representational basis for working memory, with the property of short-term memory decay being primarily due to the posterior system. In this view, there is no reason to posit specialized neural systems whose functions are limited to those of short-term storage buffers. Prefrontal cortex provides the attentional pointer system for maintaining activation in the appropriate posterior processing systems. Short-term memory capacity and phenomena such as displacement of information in short-term memory are determined by limitations on the number of pointers that can be sustained by the prefrontal control systems.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2004

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Note

1. The coherence function provides a measure of the degree of correlation between a pair of signals as a function of frequency. For EEGs, the signals are recordings from a pair of electrode sites. The coherence between a pair of signals at a given frequency is approximately equivalent to (i) filtering each signal with a very narrowband filter with a passband centered about the given frequency, and (ii) then computing the squared correlation coefficient of the filtered signals. The amplitude of a coherence function can range from a minimum of zero to a maximum of 11.0. Coherence functions are useful in the study of neural signals and cognitive behavior because systematic relationships have been found between mental states and the frequency composition of concomitant neuroelectric activity (Klimesch 1999). For a concise, cogent review of the application of coherence functions to EEGs, see von Stein and Sarnthein (2000).

Coherence values can be statistically analyzed with the same types of designs as employed for ERP amplitudes and behavioral variables. However, because the probability distribution of coherence values is very different from a Gaussian probability distribution, it is best to use nonparametric tests for evaluating the statistical significance of experimental effects.