TOPOGRAPHICAL ANALYSIS OF CORTICAL EVOKED ACTIVITY DURING A VARIABLE DEMAND SPATIAL PROCESSING TASK

This experiment studied changes in brain activity as subjects performe d a variable demand spatial rotation task. The task involved the seque ntial presentation of a template histogram and a spatially rotated com parison histogram. Task difficulty was manipulated by varying the numb er of bars and the degree of rotation. Topographical analysis of the b rain event-related activity data indicated the presence of negative co mponents that were maximal at the vertex within 80 ms and bilaterally in the temporal lobes within 140 ms of stimulus onset rind that appear ed to be insensitive to changes in task difficulty. Demand-sensitive p otentials were recorded, however. Positive components corresponding to P200 and P300 activity were recorded symmetrically around site PZ. Th e P200 component declined in amplitude, but showed no changes in laten cy as task demand increased. P300 activity declined in both amplitude and latency as the task became more difficult. Finally, a positive com ponent was recorded over right central cortex approximately 490 ms aft er stimulus onset. This component declined in amplitude but increased in latency as task difficulty increased.