Distribution of spinocerebellar Purkinje cell responses to passive forelimb movements in the rat

Abstract

We recorded Purkinje cell activity throughout the spinocerebellum of anaesthetized rats while imposing circular passive movements to the unrestrained forelimb. The aim was to understand the type of processing of sensory information occurring at the level of the cerebellar cortex, on the basis that precerebellar sensory neurons have been shown to represent whole limb movement parameters better than single joint movements. We observed that neurons representing sensory aspects of arm movements were scattered throughout the spinocerebellar cortex without a distinct segregation from those that did not respond, albeit the relative density of responsive and unresponsive neurons was quite variable and depended on the area of the cortex. Furthermore, Purkinje cells that responded significantly to the arm movement cycles all showed the same response pattern consisting of a firing rate increase during the downward extension of the arm. These results are discussed as suggesting a coordinate framework for the representation of proprioceptive information in the cerebellum congruent to that observed for encoding motor parameters.

Representation of Movement Velocity in the Rat's Interpositus Nucleus During Passive Forelimb Movements

“…In order to analyze the histological data across animals, we had to account for size differences in individual rat cerebella. For this purpose, we used a procedure described in detail in Bosco et al [2]: first, we matched the histological section morphology to the corresponding section of Paxinos and Watson's atlas [28] and then we applied a normalization algorithm (for details, see Bosco et al [2]) to rescale the dimensions of any given rat section to those of the matching atlas sections.…”

“…As a matter of fact, sensory signals generated by passive limb movements strongly modulate the activity of Purkinje cells in the intermediate zone and this activity modulation appears to be related to kinematic parameters, such as forepaw position and movement velocity [1][2][3][4]. Similarly, neurons belonging to the external cuneate nucleus and to the dorsal spinocerebellar tract, which convey a significant fraction of the somatosensory signals to the cerebellar cortex and to the IN, show firing activities related to the same kinematic parameters [5][6][7].…”