An EEG study of the functional organisation of working memory

Dehkan, Leila (1990) An EEG study of the functional organisation of working memory. University of Southampton, Doctoral Thesis.

Abstract

On the basis of previous work both on memory and the EEG, a working memory model of processes in serial digit recall was proposed, based on the original model put forward by Baddeley and Hitch (1974), but including several sources of arousal which can affect performance. Two major experiments were designed to investigate the relationship between brain activity and performance in a serial digit recall task and to detect EEG characteristics that relate to different components of the proposed model. Subjects were required to recall in order, nine-digit sequences immediately after presentation. EEG was recorded from eight locations and eight frequency bands before and during the task, and the results were analysed by MANOVA, correlational, discriminant and multiple regression analyses. In Experiment One, digits were presented auditorily to male participants. There was a general increase in EEG activation as a function of serial position, showing different patterns for low and high frequencies. Overall, EEG activation decreased however, as a function of time, as subjects performed more trials and as performance improved. Main effects of hemisphere were found in different locations and in opposite directions during the task and at pre-task rest, suggesting differential involvement of cortical areas and hemispheres before and during task performance. Within subjects, good trials were associated with lower EEG activation. Higher EEG activation in the alpha frequencies prior to the task was however associated with better subsequent performance. There was some, although not extensive, evidence of individual differences in performance and EEG, with good and poor recallers often showing different patterns of cortical activity. In Experiment Two, digits were presented visually to participants of both sexes. Overall performance was superior to that in Experiment One. Male subjects performed better and showed higher EEG activation than females. Once again, EEG activation increased as a function of serial position. However, unlike Experiment One, a general increase in EEG activation was found as subjects did more trials and as performance improved. Further evidence was found for different functional significance of low and high frequencies during and before the task, and for differential activity of the two hemispheres and various locations depending on modality and whether subjects were resting or performing the task. There were a number of significant main effects for performance and gender which also showed interaction effects with other variables in the study. Good performance was associated with higher EEG activation both between and within subjects. There were also several interaction effects. All findings are discussed in relation to the proposed model and previous research, and links with neuropsychological evidence (in particular, work with frontal lobe patients) are examined. Finally, recommendations are made for future research.

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