The Study of Task-Level Control Signals Using fMRI

Washington University, Saint Louis MO

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Abstract

DESCRIPTION (provided by applicant): A major issue in cognitive neuroscience is how specific neural pathways are organized for task performance. The major hypothesis of this proposal is that task-level control is implemented, in part, by activity sustained across task trials, and can be studied using fMRI. This hypothesis is addressed through 3 Specific Aims. Specific Aim 1: To refine paradigm designs and analysis methods for separating sustained and transient fMRI signals. The main hypothesis is that the mixed block/event related paradigm can be optimized for the accurate and sensitive identification of sustained "control" signals from transient "trial-related" fMRI signals. Specific Aim 2: To characterize the functional attributes of different regions exhibiting sustained activity across trials. Three general hypotheses will be tested: 1) Some regions will exhibit sustained activity across a wide range of tasks, implicating them in general control functions; 2) In spite of this commonality, manipulation of separable aspects of control (e.g., input or response selection) will differentially affect specific subsets of these regions; 3) Some regions will show sustained activity related to specific task domains, implicating them as sources of domain specific control, or as sites at which control signals affect ongoing trial-related processing. Specific Aim 3: To use properties of sustained signals to address issues specific to memory retrieval. Several episodic retrieval studies have shown activation of right frontal regions, and it has been proposed that this activity may be related to "retrieval mode". Two related hypotheses are tested: 1) Right frontal sustained activity will be found across conditions that demand "re-collective effort" or "re-collective mode"; 2) The right frontal sustained activity will not be specific to "recollection", but will also be present when complex retrieval constraints are placed at "intermediate levels" between recollection and familiarity. As a group, these studies should improve our understanding of task control processes in the brain. Several psychiatric and neurological diseases (e.g., Tourette's syndrome, frontal lobe strokes) have been related to deficits of control; a deeper understanding of the neural mechanisms related to control processes may allow more specific diagnostic, prognostic, or rehabilitative approaches to these difficulties than currently exist.