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Scientific Understanding of Consciousness |
Cognitive Control
Science 9 June 2000: Vol. 288. no. 5472, pp. 1835 - 1838 Dissociating the Role of the Dorsolateral Prefrontal and Anterior Cingulate Cortex in Cognitive Control Angus W. MacDonald , III, 1 Jonathan D. Cohen, 2, 4 V. Andrew Stenger, 3 Cameron S. Carter 1, 2 1 Department of Psychology, University of Pittsburgh, Pittsburgh, PA 15260, USA. (paraphrase) Theories of the regulation of cognition suggest a system with two necessary components: one to implement control and another to monitor performance and signal when adjustments in control are needed. Event-related functional magnetic resonance imaging and a task-switching version of the Stroop task were used to examine whether these components of cognitive control have distinct neural bases in the human brain. A double dissociation was found. During task preparation, the left dorsolateral prefrontal cortex (Brodmann's area 9) was more active for color naming than for word reading, consistent with a role in the implementation of control. In contrast, the anterior cingulate cortex (Brodmann's areas 24 and 32) was more active when responding to incongruent stimuli, consistent with a role in performance monitoring. Cognitive control has long attracted the attention of philosophers and psychologists interested in how the human brain carries out the higher functions of awareness, memory, and language. The concept of control generally refers to a resource-limited system that guides voluntary, complex actions. Solving difficult, novel, or complex tasks, overcoming habitual responses, and correcting errors all require a high degree of cognitive control. Cognitive control has frequently been operationalized as the provision of top-down support for task-relevant processes; for example, a representation of the attentional demands of the task can be used to bias processing in favor of task-relevant stimuli and responses and thereby establish the appropriate stimulus-response mapping. Other work suggests that a second component is required to provide ongoing feedback indicating whether control is being allocated effectively. Studies using functional neuroimaging techniques have related cognitive control to activity in the dorsolateral prefrontal cortex (DLPFC) [Brodmann's area (BA) 9 and BA 46] and the anterior cingulate cortex (ACC) (BA 24 and BA 32). For example, both the DLPFC and ACC activate when participants are required to hold increasingly long sequences of items in working memory or when two tasks are performed at once, compared to when they are performed one at a time. A number of neuroimaging studies have reported relative dissociations for these regions. DLPFC activity in the absence of ACC activity has been found for tasks that require maintenance and manipulation of information in working memory. These relative dissociations led us to hypothesize that the DLPFC may be involved in representing and maintaining the attentional demands of the task. In contrast, the ACC may be involved in evaluative processes, such as monitoring the occurrence of errors or the presence of response conflict, which occurs when two incompatible responses are both compelling. To test for a hypothesized double dissociation between the functions of the DLPFC and ACC, we used a modified version of the Stroop paradigm. These data suggest that cognitive control is a dynamic process implemented in the brain by a distributed network that involves closely interacting, but nevertheless anatomically dissociable, components. Within this system, the DLPFC provides top-down support of task-appropriate behaviors, whereas other components, such as the ACC, are likely to be involved in evaluative processes indicating when control needs to be more strongly engaged. (end of paraphrase)
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