Cerebellar motor learning versus cerebellar motor timing: the climbing fibre story

Abstract

Theories concerning the role of the climbing fibre system in motor learning, as opposed to those addressing the olivocerebellar system in the organization of motor timing, are briefly contrasted. The electrophysiological basis for the motor timing hypothesis in relation to the olivocerebellar system is treated in detail.

Figure 1. IO oscillations in voltage-sensitve imaging

Spontaneous oscillatory electrical activity was acquired simultaneously using optical voltage imaging and intracellular recording. The beginning of oscillatory sequence was defined as 0 ms. The upper panel superimposes the optical signal in red and intracellular voltage recording (asterisk) in black and demonstrates temporal waveform coherence. The lower panels illustrate the spatial distribution of voltage imaging at five different time points indicated by dots in the upper panel from two successive oscillation cycles averaged three times over the oscillatory sequence. Note that ensemble oscillations emanated from several fluorescent clusters of coherent activity, and that the spatial and temporal structure of the IO cluster activity is discernable directly from cluster distribution and size. Time voltage and spatial distribution are as indicated by the calibration bars. (Modified from Leznik & Llinas, 2005.)

Figure 2. Olivocerebellar conduction time is constant throughout the extent of the cerebellar cortex

A, diagram of the path for a single climbing fibre (red). Microelectrode recorded Purkinje cell complex spike latency (in ms) at different depths (red dots) is shown following IO electrical stimulation. B, tridimensional representation of climbing fibre length. The X and Z coordinates indicate, respectively, rostrocaudal and mediolateral climbing fibre localization in the different folia (indicated) and the Y coordinate the climbing fibre length. C, conduction time is plotted against climbing fibre length (4 ms (variance ± 500 μs)). D, conduction velocity related linearly to length. (Modified from Sugihara et al. 1993.)

Figure 3. Intracellular in vitro recording of spontaneous subthreshold oscillations and phase reset by an electrical extracellular stimulus

A, following an extracellular stimulation (marked with an arrowhead), the oscillations disappeared for 750 ms (boxed area) and then resumed. The membrane potential was –60 mV. B, superposition of intracellular recordings of spontaneous (dashed black line) and stimulus-evoked (continuous black line) oscillations in the same cell. Their corresponding power spectra are shown below. Note that extracellular stimulation only modified the phase of the spontaneous oscillations without affecting their amplitude or frequency. C, superposition of six individual intracellular traces of stimulus-evoked oscillations from the same cell. Each trace is shown in a different colour. Their corresponding power spectra are displayed below. Note that in each trace, the stimulation-induced shift in the cell's oscillatory rhythm is remarkably similar. Oscillations are seen clearly after the stimulus-induced reset but can barely be detected before the stimulation. Calibration bar: 1 mV 1 s. (Leznik, Makarenko & Llinas, 2002.)