UNCOUPLING COGNITIVE WORKLOAD AND PREFRONTAL CORTICAL PHYSIOLOGY - A PET RCBF STUDY

Working memory is a fundamental cognitive building block, involved in the short-term maintenance and transformation of information. In neuro psychological studies, working memory has been shown to be of limited capacity; however, the neurophysiological concomitants of this capacit y limitation have not been explored. In this study we used the [O-15]w ater PET rCBF technique and statistical parametric mapping to examine normal subjects while they performed two cognitive basks, both individ ually and simultaneously, One task was the Wisconsin Card Sorting Test , a complex reasoning task involving working memory, and the other was a rapidly paced auditory verbal shadowing task. When both tasks were performed simultaneously, there were significant decrements in perform ance compared with the individual task performance scores, indicating that cognitive workload had been increased. Analysis of the rCBF maps showed that when the two tasks were performed together, in contrast to when they were performed separately, there was less prefrontal activa tion. These results suggest that increases in cognitive workload do no t necessarily recruit and then sustain cortical neurophysiological res ources to a maximum, but rather may actually be accompanied by a dimin ution in cortical activity. (C) 1998 Academic Press.