Sensorimotor loops in vibrissa somatosensation

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DESCRIPTION (provided by applicant): We address active sensation in the context of tactile localization of objects accomplished by exploratory whisking movements of the rat vibrissae. Our guiding hypothesis is that neural representations that span closed sensorimotor loops underlie the localization of objects by actively moving sensors. Past work has established two forms of vibrissa sensorimotor signals that, in principle, can be used by the rat for computing contact and object localization in head-centered coordinates. One is a contact-independent reference signal that codes for vibrissa angle as animals actively whisk. The second form is a contact-based signal whose cortical representation during whisking, as opposed to the representation for primary neurons, remains to be characterized in awake behaving animals. We propose to probe the convergence of sensor position and sensor contact information. This serves to delineate the computation of active vibrissa touch in head-centered coordinates and the subsequent motor control of the vibrissae. Our program is conducted at two levels: that of the brainstem sensorimotor loop and that of cortical signaling. We ask: What is the role of feedback at the level of the brainstem, which provides relatively fast signaling, in directing the motion of the vibrissae? This feedback will necessarily change the nature of a touch signal this is processed by higher-order brain areas. How does the rat fuse signals of vibrissa position with those of touch in vibrissa primary sensory (S1) cortex as it palpates a target? This inquiry can establish the neural representation of contact in head- centered coordinates. How is vibrissa position represented by spike trains in primary motor (M1) cortex and further, does M1 control vibrissa motion? These concurrent inquiries can establish the transformation of sensory feedback into motor control. What is the nature of signaling between vibrissa S1 and M1 cortices during exploratory whisking and touch? Investigations of sensorimotor control are fundamental to the understanding dystonias, i.e., disorders of motor function. The nested, closed loop structure of the vibrissa system parallels other architectures, such as the trigeminal loop involved in the cranial dystonia blepharospam and the corticostriatal loops involved in Parkinsonian tremors. Thus the vibrissa system provides an experimentally accessible computational test- bed for fundamental concepts in neuromuscular control.