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.
