Rhythmic Properties of Climbing Fiber Afferent Responses to Peripheral Stimuli
An intriguing property of inferior olivary neurons is their tendency to discharge rhythmically at frequencies from 5–12 Hz (Armstrong 1974, Llinas 1981). This report focuses on the rhythmicity in the responses of Purkinje cells to climbing fiber inputs evoked by natural forepaw stimuli. In decereberate, unanesthetized cats the complex spike (CS) activity of Purkinje cells evoked by a forepaw displacement was averaged in post-stimulus time histograms (PSTH), and the autocorrelogram of the PSTH was calculated. The surgical procedures, recording techniques and peripheral input are described elsewhere (Ebner and Bloedel 1981, Ebner et al. 1983, Bloedel and Ebner 1984). Rhythmicity was defined as a minimum of three equally spaced peaks of complex spike activity, observed either in the PSTH or autocorrelogram. In 220 Purkinje cells with a complex spike response to the forepaw tap, 105 responded with a periodic discharge, the majority exhibiting a periodicity ranging from 100 to 160 ms. In 10 of 25 pairs of simultaneously recorded Purkinje cells the forepaw stimulus evoked periodicity in the complex spike discharge at a similar frequency. For some cells exhibiting only two peaks of CS activity, altering the stimulus duration did not alter the timing of the second peak of the CS response suggesting that the second peak of CS activity was due to a rhythmic activation of the climbing fiber afferent rather than a response to the “of” phase of the stimulus.
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