Responses to a spino-olivo-cerebellar pathway in the cat.

1. Surface potentials, similar to those found by earlier workers, have been recorded from the vermis of the anterior lobe of the cerebellum following stimulation of muscular, cutaneous and articular nerves of the ipsilateral hind limb. The most conspicuous component of the response consisted of a positive potential succeeded by a smaller negative potential.2. Micro-electrode recordings showed that this component coincided both with climbing fibre responses in individual Purkinje cells, and with extracellular field potentials within the cerebellar cortex which closely resembled those found by Eccles, Llinás & Sasaki (1966) following electrical stimulation of the inferior olive.3. Stimulation of the cerebellar surface, in the region where the responses to limb nerve stimulation were largest, led to antidromic invasion of neurones of the contralateral inferior olive. The antidromic action potentials were sometimes followed by up to three orthodromic spikes. Histological techniques were used to show that these neurones were located in the caudal parts of the dorsal and medial accessory olives.4. Stimulation of nerves of the hind limb evoked discharges of the same neurones of the dorsal accessory olive which were antidromically invaded from the vermis of the anterior lobe. The nerves used (quadriceps, gastrocnemius-soleus, sural and the posterior nerve to the knee joint) were shown to excite heavily overlapping populations of neurones.5. Those neurones of the medial accessory olive, which were identified antidromically from the anterior lobe vermis, were not discharged by stimulation of hind limb nerves.6. Simultaneous recording from the surface of the anterior lobe and from the dorsal accessory olive showed that the onset of olive cell discharges occurred about 5 msec before the onset of the positive potential at the cerebellar surface.