[Afferents from a single muscle of the forelimbs and fastigial neurons of the cerebellum].

Responses of neurons in the medial nucleus of cerebellum (CBM) were studied on stimulation of ipsilateral and contralateral homonymous muscles, in decerebrated cats. The aim was to find out to what extent information from homonymous muscles of the forelimbs converge on the same CBM neurons and whether the probability of such a convergence depends on location (axial, proximal, distal) or function (flexor, extensor) of the tested muscles. The analysis was limited to the neurons belonging to the rostral part of the nucleus which is known to control the ipsilateral muscle periphery. Neuronal activity was recorded extracellularly using tungsten microelectrodes (5-12 M omega) and muscle stimulation was performed by bipolar coated steel electrodes, with the exception of the tip. At least 6 pairs of homonymous muscles were generally stimulated: two axial, two proximal and two distal in both forelimbs. Care was taken that, when a muscle was stimulated, the others were not activated either directly or in a reflex way. Out of the 65 neurons studied, 60 (92%) were responsive to muscle stimulation. It was specifically observed that a high percentage of cells reacted to stimulation of distal muscles (74% to ipsilateral and 71% to contralateral ones). More than half (55%) of the neurons were responsive to activation of a pair of homonymous distal muscles and about one third of them (31%) to both the pairs of distal muscles. On the contrary the percentage of responses to proximal muscles was reduced foremost in the ipsilateral ones (23%) and only an exiquous percentage of cells (15%) received information from the homonymous proximal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)