Changing plans: a high density electrical mapping study of cortical control.

High density electrical mapping was used to index event-related brain activity in subjects performing parametric variations of the "AX"-type continuous performance task (AX-CPT) that differentially challenge control, and informative control conditions. In the AX-CPT, subjects must use context, created by a cue stimulus, to guide response to a target. Diseases such as schizophrenia and attention deficit hyperactivity disorder (ADHD) are associated with impaired AX-CPT performance. Event-related potentials (ERP) were analyzed as a function of both global and local stimulus context. The topographical analysis revealed that well-defined ERP are elicited under conditions where subjects must override a prepotent response. Activation patterns related to overriding a prepotent response (Go to No-Go) differed markedly from those associated with overriding a prepotent non-response (No-Go to Go). Dipole source mapping suggested that withholding a prepotent response is reflected primarily in anterior cingulate/dorsolateral prefrontal cortex activity during the 350-450 ms latency range following presentation of the No-Go. In contrast, preparing to respond is reflected in parietal (including area BA 40) activity during the same latency range, followed by a prolonged frontal negativity (contingent negative variation; CNV). Similar patterns of activation were observed whether the changes in preparation were triggered by cue or target stimuli, though target-elicited potentials peaked earlier.