221 13 13 4 4 R. Llinás W. Precht M. Clarke Division of Neurobiology, Dept. of Physiology and Biophysics University of Iowa Iowa City USA Dept. of Neurobiology Max-Planck-Institut für Hirnforschung Frankfurt West Germany Summary The electrical activity of single Purkinje cells was studied in the auricular lobe and in the vestibular cerebellum of Rana catesbeiana during horizontal angular acceleration. This form of physiological stimulation allowed the Purkinje cells to be categorized into four main classes, depending on the general properties of their responses. 1. Type I Purkinje cells responded to ipsilateral horizontal acceleration. Their discharge was blocked during contralateral rotation. Within this group, individual Purkinje cell responses to a protracted acceleration varied from purely phasic to purely tonic discharge. 2. Type II Purkinje cells were characterized by their activation following contralateral horizontal acceleration and by lack of response to the ipsilateral rotation. Both type I and II Purkinje cells were encountered mainly in the auricular lobe. 3. Type III, the most common form of Purkinje cell response, was activated by rotation in either ipsi- or contralateral direction. Their response, as that of type I, could vary from a purely phasic to a purely tonic discharge. The study of field potentials and unitary responses evoked by electrical stimulation of the vestibular nerve demonstrated that type III Purkinje cell response was evoked via a polysynaptic pathway different from that which activated Purkinje cells in the auricular lobe. 4. Type IV Purkinje cells were characterized by the reduction of spontaneous firing during acceleration in either ipsi- or contralateral directions. 5. A comparison of the responses evoked by type III Purkinje cells in the cerebellar cortex demonstrated that neighboring Purkinje cells may respond in different fashions to the same vestibular input. Furthermore, the tonic or phasic character of a given Purkinje cell was very similar for ipsi- and contralateral rotation, suggesting that the subtle differences between responses in neighboring Purkinje cells may be related to differences in their dynamic properties rather than differences in the types of afferents received. 6. Climbing fiber activation of Purkinje cells during horizontal rotation was clearly demonstrated in five cells. These responses are considerred to be mediated through the saccular or utricular systems rather than through the semi-circular canals. The conclusion is derived that the semi-circular canal input to the cerebellum is subserved mainly by mossy fiber input. 7. The possible functional meaning of the different types of Purkinje cell response is discussed.
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