Responses in the inferior olive to stimulation of the cerebellar and cerebral cortices in the cat

Responses in the dorsal accessory olive of the cat to stimulation of hind limb afferents

1. Field potentials and single unit discharges were recorded in the dorsal accessory olive of the cat following stimulation of nerves of the contralateral hind limb.2. The largest field potentials were evoked when nerves were stimulated with brief trains at 200-300/sec. Responses were sometimes evoked from quadriceps nerve by volleys restricted to low threshold group I afferents, but responses were not usually evoked from other muscle nerves unless both group I and II afferents were excited.3. The spatial distributions of the field potentials evoked from different nerves were very similar and individual units were made to discharge by stimulation of each of a wide range of nerves including muscle, skin and joint nerves. Single units were also made to discharge by stimulation of both the ipsilateral and the contralateral quadriceps nerve.4. The latency of the field potentials evoked by stimulation of quadriceps nerve ranged from 14 to 23 msec in different preparations. The latency of responses evoked from various branches of the sciatic nerve was consistently longer and was usually between 20 and 30 msec.5. The activity was conveyed by a tract which, at the upper lumbar level of the spinal cord, lay in the ventral quadrant ipsilateral to the olive. In the upper cervical region the tract lay close to the ventral surface of the cord. Values between 24 and 30 m/sec were found for the conduction velocity of the tract.6. An excitatory response in the dorsal accessory olive was followed by a period of about 100 msec during which the amplitude of a second response was reduced.

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.

Inferior olive of the cat: intracellular recording

The action potential evoked from inferior olivary neurons of the cat by orthodromic, antidromic, or intracellular stimulation has a large prolonged depolarization, frequently with several superimposed smaller spikes. The all-or-nothing unitary response appears to be a property of the cell, and the later spikes are not secondary to synaptic excitation by recurrent axon collaterals.

Circuits in the cerebellar control of movement

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