Response characteristics and vestibular receptor convergence of frog cerebellar purkinje cells. A natural stimulation study.

1. The horizontal sinusoidal frequency response and the problem of vestibular receptor convergence in Purkinje cells (P-cells) of the auriculum, dorsal rim and corpus cerebelli were studied in curarized frogs with natural stimulation. 2. Primarily "simple" but also "complex" spikes were evoked by sinusoidal stimulation of the horizontal canals. P-cell "simple" spike activity could be grouped into types I-IV. Type I and II responses were directionally sensitive and thus were evoked at the stimulus frequency. Type III (and IV) cells, on the other hand, had response waveforms double that of the input frequency, with peak increases (or decreases) in discharge inphase with head velocity in the mid-frequency range. Except in the cerebellar midline regions where type III response waveforms were symmetrical, ipsilateral sinusoidal responses were larger in magnitude than those evoked during contralateral rotation. Despite the differences in magnitudes, ipsi- and contralateral response phase angles for one cell were approximately equal. "Complex" spikes were evoked with ipsi (type I) or contralateral (type II) horizontal rotation. Generally only 1-2 spikes were evoked per cycle with short (0-60 degrees) or long (120-150 degrees) phase-lags following acceleration. 3. A Bode analysis of type I "simple" spike activity in yaw indicates a slightly greater phase-lag and a 10-15 fold smaller P-cell gain in the range 0.05-0.5 Hz when compared to peripheral horizontal canal neurons. 4. Stimulation of the vertical canals and otolith organs also evoked "simple" and, to a lesser extent, "complex" P-cell spikes. "Simple" spikes were in most cases (85%) evoked by stimulation of several canal and/or otolithic receptors thus demonstrating a high degree of receptor convergence. "Complex" spikes, however, were only evoked by stimulation of one canal or otolith receptor. 5. Otolithic input to P-cells, examined statically and with low level constant velocity rolls, was mainly phasic or phasic-tonic in nature.