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RESEARCH

Cognitive Control: Prefrontal Cortex

In one line of research, lab co-director Todd Braver and collegues have suggested that PFC actively maintains representations of context information in working memory (Braver, Cohen and Servan-Schreiber, 1995; Cohen, Braver and O'Reilly, 1996; O'Reilly, Braver, and Cohen, 1999). These context representations serve as a "top-down" source of excitatory activation that biases the local competitive interactions between mutually incompatible thoughts or actions (e.g., between two alternative response options or between two alternative perceptual interpretations of a stimulus). These internally maintained context representations are especially critical in situations in which a dominant, but inappropriate, response must be inhibited (e.g., the Stroop task). Context representations can be thought of as being similar to goal representations (e.g., task instructions), but may also represent more specific information (e.g., the information provided by a previous stimulus). This theory has motivated a series of functional neuroimaging studies (using fMRI methods). These studies have demonstrated a consistent pattern of PFC activity during performance of working memory tasks that suggests a role in actively maintaining context (Cohen et al., 1994; Cohen et al., 1997; Braver et al., 1997; Barch, Braver et al., 1997). Most recently, the CCP Lab conducted an extensive series of studies using a simple cognitive control paradigm (the AX-CPT), that demonstrates the power of the theory to specifically predict and explain the results of: 1) behavioral studies involving healthy subjects under normal and interference conditions, and under conditions of pharmacological challenge; 2) studies with schizophrenia patients; and 3) neuroimaging studies examining the dynamics of PFC activity under normal and interference conditions.