UNIT DISCHARGES RECORDED FROM DORSAL PORTION OF MEDULLA RESPONDING TO ADEQUATE EXTEROCEPTIVE AND PROPRIOCEPTIVE STIMULATION IN CATS

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Abstract
In a series of intercollicular decerebrate and decerebellate cats, the dorsal part of the lower medulla was explored in search of the modality and topographical arrangement of the spinal afferents, employing microelectrodes inserted freehand. All the responses were produced by mechanical deformation of peripheral tissues and were obtained ipsilaterally. The responses observed were classified into three groups: (a) unit discharges responding to stimulation of deep tissues, showing slow adaptation (proprioceptive afferent); (b) unit discharges to movement of hairs or light touch on the skin, showing quick adaptation (tactile afferents); and (c) unit discharges driven by pressure upon the skin, showing slow adaptation (pressure afferents). The tactile afferents were most frequently encountered in the gracile nucleus, while the proprioceptive afferents from deep structures were the commonest pattern in the cuneate nucleus. In the restiform body, the responses to hind limb stimulation were the commonest pattern. For any part of the body, the proprioceptive, pressure and tactile afferents were found in the decreasing order of occurrence. The paraalar area resembled the restiform body in the modalities of the afferents projecting thereto. The major component of the fibers terminating in the paraalar area were from the hind limb via the dorsolateral funiculus. The proprioceptive afferents were the commonest pattern, but occurrence of the pressure afferents was relatively high.