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1. The input from cutaneous nociceptors to climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe was examined in barbiturate‐anaesthetized cats. Climbing fibre responses were simultaneously recorded in single Purkinje cells and as field potentials from the cerebellar surface close to these cells. 2. The cutaneous receptive field of the climbing fibres studied were located on the ipsilateral forelimb. All climbing fibres were activated by both non‐noxious tactile stimulation and noxious pinch of the skin. The location of the receptive field and the distribution of sensitivity in the receptive field appeared to be identical for noxious and tactile stimuli. 3. A phasic response in the climbing fibres was evoked by either short‐ or long‐lasting non‐noxious pressure applied to their cutaneous receptive field. By contrast, all climbing fibres studied were strongly and tonically activated (up to 4‐11 Hz for the duration of the stimulation) by sustained noxious pinch in the most sensitive area of their receptive fields. 4. Experiments with anodal block of impulse conduction in myelinated fibres indicated that a major input to climbing fibres during sustained noxious pinch originates from nociceptive C fibres. 5. Sustained noxious pinch of the skin evoked large field potentials on the cerebellar surface. These field potentials were evoked simultaneously with climbing fibre responses in single Purkinje cells and were due to synchronous activation of many climbing fibres. These field potentials and discharges in single climbing fibres were elicited from the same area of the skin suggesting that many of the synchronously discharging climbing fibres have the same receptive field on the skin.

1. Climbing fibre responses evoked on stimulation of the ipsilateral superficial radial nerve were examined in the forelimb area of the C3 zone in the barbiturate‐anaesthetized cat. Climbing fibre responses were recorded in sixty‐five Purkinje cells and as field potentials from the surface of the cerebellum. 2. In addition to the previously described A beta‐fibre‐evoked climbing fibre response, late climbing fibre responses were consistently evoked in all Purkinje cells studied when C fibres were stimulated. The latencies of the A beta‐ and C‐fibre‐evoked climbing fibre responses were 11‐20 ms and 110‐220 ms, respectively. In most experiments climbing fibre responses with an intermediate latency (20‐30 ms) were evoked. It was demonstrated that this response depended on A delta fibres. 3. The long‐latency climbing fibre response generated by electrical stimulation at C‐fibre strength was evoked also during selective anodal block of conduction in A fibres (Brown & Hamman, 1972). Hence, impulses in C fibres were sufficient for generation of climbing fibre responses. 4. The distribution within the forelimb area of the C3 zone of the A beta‐ and C‐fibre‐evoked climbing fibre field potential was similar. No climbing fibre response was evoked in this area of the C3 zone by stimulation of A and C fibres in the contralateral superficial radial nerve or in the plantar nerves of the hind limbs. 5. It can be concluded that climbing fibres projecting to the forelimb area of the C3 zone in the cerebellum receive a somatotopically organized input from both A beta and C fibres.

1. Responses evoked in Purkinje cell dendrites by impulses in climbing fibres were studied by recording from the cat cerebellar cortex. Intra‐ and extracellular responses from dendrites of single Purkinje cells were recorded, as well as field responses from the intact cerebellar surface. The intracellular responses were presumably recorded from relatively proximal dendrites. The resting potential usually was 20‐40 mV. The responses consisted of an initial spike‐like component (amplitude 10‐30 mV) followed by a plateau‐like component (amplitude 2‐12 mV) with a duration of about 100 ms. The duration of consecutive responses varied little. 3. The extracellular unitary responses were recorded from more distal dendrites. These responses were negative deflexions consisting of an initial component followed by a plateau‐like component (amplitude 5‐15 mV). The duration of consecutive responses varied widely from about 25 ms to more than 1 s. The negative deflexions are assumed to correspond to dendritic depolarizations. 4. The field responses recorded from the cerebellar surface consisted of a positivity followed by a negativity lasting several hundred milliseconds. The positivity signals the e.p.s.p.s generated by the climbing fibre synapses which do not extend to the most distal dendrites. The negativity presumably signals the plateau‐like dendritic depolarizations which would involve also the most distal dendrites. 5. The nature and significance of the plateau‐like depolarizations evoked by climbing fibre impulses in the purkinje cell dendrites are discussed.

Responses evoked in Purkinje cell dendrites by parallel fibre volleys and climbing fibre impulses were investigated by intra‐ and extracellular recording from cat cerebellar cortex. The depth distribution of recording sites suggested that the intracellular recordings were predominantly from proximal dendrites whereas the extracellular recordings were predominantly from distal dendrites. Parallel fibre stimulation evoked monosynaptic excitation and disynaptic inhibition in the dendrites and, at higher strength, prolonged plateau‐like responses in distal dendrites but only rarely in proximal dendrites. However, when the inhibitory synapses were blocked with topically applied picrotoxin, parallel fibre volleys evoked plateau potentials also in proximal dendrites. The duration of the parallel‐fibre‐evoked plateau potentials in distal dendrites was prolonged by increasing the intensity of the eliciting stimulus or by increasing the number of stimuli. A similar prolongation in the duration of climbing‐fibre‐evoked plateau potentials was observed when brief repetitive stimulation was applied to the inferior olive. The investigation provided evidence that under physiological conditions plateau potentials in Purkinje cell dendrites are exclusively evoked by climbing fibre impulses.

1. Pathways ascending in the lateral funiculus of the spinal cord and terminating as climbing fibres in the anterior lobe of the cerebellum have been investigated in decerebrate cats with the cord partially transected in the third cervical segment, sparing only part of the left lateral funiculus. The climbing fibre responses evoked in Purkinje cells by electrical stimulation of peripheral nerves were studied by recording from single cells and by recording the mass activity at the cerebellar surface.

1. A pathway ascending in the lateral funiculus of the spinal cord and terminating as climbing fibres in the cerebellar anterior lobe has been investigated in decerebrate cats with the cord partially transected in the third cervical segment sparing only part of the left lateral funiculus. The climbing fibre responses evoked in Purkinje cells were studied by recording from single cells and by recording the mass activity at the cerebellar surface.

1. Neurones in the Group I projection area of the first sensori‐motor cortex were investigated with extra‐ and intracellular technique.

1. The potentials evoked in the first sensorimotor area on stimulation of muscle and skin nerves in the contralateral forelimb were recorded in preparations with either the dorsal funiculus (DF) or the spinocervical tract (SCT) interrupted.