Neurophysiological measures of working memory and individual differences in cognitive ability and cognitive style.

The capacity to deliberately control attention in order to hold and manipulate information in working memory is critical to higher cognitive functions. This suggests that between-subject differences in general cognitive ability might be related to observable differences in the activity of brain systems that support working memory and attention control. To test this notion, electroencephalograms were recorded from 80 healthy young adults during spatial working memory tasks. Measures of task-related neurophysiological and behavioral variables were derived from these data and compared to scores on a test battery commonly used to assess general cognitive ability (the WAIS-R). Subjects who scored high on the psychometric test also tended to respond faster in the experimental tasks without any loss of accuracy. The amplitude of the late positive component of the event-related potential was larger in high-ability subjects, and the frontal midline theta component of the EEG signal was also selectively enhanced in this group under conditions of sustained performance and high working memory load. These results suggest that subjects who scored high on the WAIS-R were better able to focus and sustain attention to task performance. Changes in the EEG alpha rhythm in response to manipulations of task practice and load were also examined and compared between frontal and parietal regions. The results indicated that high-ability subjects developed strategies that made relatively greater use of parietal regions, whereas low-ability subjects relied more exclusively on frontal regions. Other analyses indicated that hemispheric asymmetries in alpha band measures distinguish between individuals with relatively high verbal aptitude and those with relatively high nonverbal aptitude. In particular, subjects with a verbal cognitive style tended to make greater use of the left parietal region during task performance, and subjects with a nonverbal style tended to make greater use of the right parietal region. These results help clarify relationships between task-related brain activity and individual differences in cognitive ability and style.