This article presents the neuropsychological contribution to origin and development of the working memory model. A matter for current investigation and discussion was a model established originally by Baddeley and Hitch. Within a large working memory system, they proposed three subcomponents: the central executive, the phonological loop, and the visuospatial sketchpad. Later, a fourth component was proposed, the episodic buffer, which is assumed to be purely mnemonic in character. The goal of this paper is to clarify the neural and cognitive determinants of these systems, as well as to show explanatory value and limitations of the working memory model. Current interest focuses most strongly both on the link between subcomponents of memory, and between working memory and other cognitive processes. Neuroanatomical correlates were taken into account as well. It was emphasized that working memory has a rather widespread representation in the brain, which involves both prefrontal and non-frontal structures. The original concept of working memory seems controversial and simplified, mostly because it underestimates the role of complex language processes in memory functioning, and a close relationship between memory and posterior parts of the brain.
The study aimed at evaluating of verbal fluency in right hemisphere-damaged patients. Forty-six vascular right hemisphere-damaged (RHD) and 30 control subjects were submitted to a verbal fluency task for which criteria were either phonemic or semantic. The strategies that the participants used spontaneously in order to maximize word production, namely clustering (CL) and switching (SW) techniques, were evaluated. Results showed (a) that RHD subjects do show a significant reduction of verbal fluency as compared to controls, (b) that this reduction is more prominent for the phonetic criterion, and (c) that verbal fluency impairment in the RHD subjects is predominantly a consequence of dysfunction to the frontal cortex and subcortical nuclei (i.e. striatum and thalamus). Both CL and SW strategies were related to total word production on both tasks. These results tend to agree with a general theory on a right-hemisphere contribution to lexical processing, and more specifically, to its phonological aspects, as well as to executive component of verbal fluency.
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