Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Neuroscience

Supervisor

Dr. Stefan Everling

Abstract

Cognitive control enables us to guide our behaviour in an appropriate, context-dependent manner. This behavioral flexibility is probed by task-switching paradigms, which require working memory to maintain relevant rules and flexibility to switch between rules. The dorsolateral prefrontal cortex (DLPFC) has been implicated in rule maintenance by neuroimaging and electrophysiological studies. While these studies have identified a correlation between DLPFC activity and rule maintenance, deactivation studies allow us to establish a causal relationship. Here we have examined the effect of bilateral deactivation of areas 46 and 9/46d on rule maintenance, while a monkey (Macacca mulatta) performed blocks of pro- and anti-saccades.

Areas 46 and 9/46d were deactivated by pumping chilled methanol through bilaterally implanted cryoloops. Rule maintenance was tested while monkeys performed blocks of pro- and anti-saccades with and without instruction cues. Monkeys had to look toward the stimulus on pro-saccade trials and away from the stimulus to its mirror location on anti-saccade trials. After 15-25 correct responses, the task switched (e.g. from pro-saccades to anti-saccades) without any explicit signal to the monkey.

Bilateral area 46 deactivation impaired performance throughout both blocks, while bilateral area 9/46d deactivation did not affect performance. Surprisingly, bilateral deactivation of both areas (46 and 9/46d) impaired performance on anti-saccade trials but recovered performance on pro-saccade trials. These results present a causal relationship between area 46 and rule maintenance and provide evidence for functional dissociation between subregions in the dorsolateral PFC for rule-guided behavior.

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