Control of whisking amplitude and positioning.

University Of California, San Diego, La Jolla CA

Investigators

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Abstract

? DESCRIPTION (provided by applicant): Rodents actively scan and position their whiskers (vibrissae) in order to probe their surroundings. The amplitude and setpoint of whisker movement determine the region explored. Control of this motor behavior is an accessible model to dissect the mechanisms by which movement is directed for sensory exploration. Fast rhythmic movement of vibrissae is driven by a central pattern generator (CPG) in the brainstem, but the mechanisms by which the amplitude and setpoint of whisker movement are set are unknown. The whisker motor cortex (vM1) has been postulated to control these slow parameters by providing both input through both direct and oligosynaptic projections to the facial motor nucleus (FN). This study will determine the role of major descending pathways from vM1 in controlling the amplitude and setpoint of rhythmic whisking driven by the brainstem CPG. I will test the behavioral role of areas in the midbrain and brainstem which receive prominent projections from the whisker motor cortex, and send input to the FN and are thus likely to be involved in control of whisking. In aim 1 I will use electrolytic, chemical and viral lesions to dissect the behavioral role of candidate descending pathways from vM1 cortex on whisking amplitude and setpoint. Preliminary results show that whisking amplitude and setpoint are altered after lesions to superior colliculus and whisker motor cortex. In follow up experiments I will use viral lesions to test the role of speci¿c pathways in target areas and con¿rm their rolein controlling whisking amplitude and setpoint. In order to guide selective viral lesion experiments, I use pharmacological injections in the facial motor nucleus to test the role of glutamatergic and cholinergic pathways. In aim 2 I will determine whether vM1 cortex modulates amplitude and setpoint of ongoing whisking that is generated by the whisking CPG. I use global stimulation of vM1 in conjunction with pharmacological activation of the whisking CPG to test the role of vM1 in modulating whisking driven by the CPG. Preliminary results show that vM1 stimulation at a high frequency potentiates amplitude and setpoint of whisking. Further experiments will address the effect on whisker movement driven by the CPG of stimulating descending pathways from vM1 identified in Aim 1. The proposed experiments will establish the role of descending projections from vM1 in modulating amplitude and setpoint of rhythmic whisking driven by a CPG. This is a critical step to determine the role of vM1 in orchestrating whisking behavior. Thus, this study will provide an understanding of how a cortical motor area interacts with premotor areas in the midbrain and brainstem. Determining the mechanisms by which cortical motor commands modulate ongoing stereotyped movement is critical to understanding how exploratory movement is controlled in sensorimotor systems.