Neural Basis of Saccade Preparation

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DESCRIPTION (provided by applicant): The oculomotor repertoire is governed by alternating activity patterns in competing networks that generate saccades and preserve fixation. When the operation between the two networks is properly maintained, eye movement function is normal. A bias in the balance of activity, however, can lead to dysfunction. For example, decreasing the efficacy of the fixation network or enhancing the activity of the saccade generation network compromises the ability to delay or inhibit movements. This proposal seeks to examine the activity of neural elements in these networks and the consequence on behavior during a perturbation that alters the balance between the two. The focus is specifically on the superior colliculus, whose rostral pole is involved in preserving fixation and caudal region is essential fo generating saccades. The perturbation of choice is to induce a blink by delivering an air-puff to an eye as subjects perform various oculomotor tasks. Blinks have been shown to compromise the integrity of the saccadic inhibition network at the level of the pons, and if the blink is triggered after presentation of the saccade target (and permission to initiate the movement), the goal-directed movement accompanies the blink at a reduced latency. Specific Aim 1 examines the effects of a blink on the fixation and saccade generation networks in the superior colliculus. It specifically tests the hypothesis that blinks suppress activity in the fixation network (rostral region) and increases the excitability of the saccade generation network (caudal region). Specific Aim 2 examines whether the underlying neural activity at the time of prematurely triggered saccades encodes premotor information. It will specifically test the threshold principle of the motor preparation hypothesis and whether spatial attention and motor preparation can be dissociated. We anticipate that the combination of behavioral and neurophysiological approaches will provide insights into neural mechanisms that are altered in neuropsychiatric disorders (e.g., ADHD, schizophrenia) characterized by an inability to suppress reflexive movements.