The inferior olive, the source of climbing fiber input to cerebellum, is implicated in the control of learned movement, but its specific function remains poorly understood. Recently we initiated microelectrode studies of this nucleus in anesthetized and intact cats. The results indicate that somatosensory information is strongly represented in the olive, and single cells have properties suggestive of a role in somatic event detection. We propose a combination of microelectrode, neuroanatomical and behavioral studies designed to explore further the properties and functions of olivary neurons. Preliminary work suggests that responsiveness of cutaneous neurons is gated on and off during movement. We will study this phenomenon by delivering tactile stimuli during different phases of movement and as a cue for movement. A lesion study will test for gating via a cerebellar pathway. We will evaluate the directional preferences of proprioceptive neurons and determine their topographical distribution in olivary subnuclei. Passive velocity sensitivity will be studied by applying ramp displacements to the limb, and active velocity sensitivity will be evaluated during tracking. We will also evaluate responsiveness to perturbations applied in the course of movement. We will map the face zone of the dorsal accessory olive. Our previous work indicates that other portions of this subnucleus contain detailed cutaneous maps of contralateral body parts. We will study the fine topography of the olivocerebellar connections to and from physiologically identified regions of the olive using small injections of WGA-HRP. Discrete unilateral lesions will be placed at physiologically identified olivary sites using pressure injections of ibotenic acid. The animals will then be tested in a set of tasks designed to demonstrate deficits either in sensorimotor processing or in the adaptive modification of sensorimotor linkages. These studies should improve our understanding of the control of limb movements and their adaptation to new environments. The same adaptive mechanisms are likely to play an important role in the recovery of function following head injury or other types of brain lesions.
