Abstract
One distinctive feature of Purkinje cells is that they have two types of discharge: in addition to simple spikes they fire complex spikes in response to input from the climbing fibers. These complex spikes have an initial rapid burst of spikes and spikelets followed by a sustained depolarization; in some models of cerebellar function this climbing fiber input supervises learning in Purkinje cells. On the other hand, synaptic plasticity is often thought to rely on the timing of pre-synaptic and post-synaptic spikes. It is suggested here that the period of depolarization following a complex spike, combined with a simple spike-timing-dependent plasticity rule, gives a mechanism for the climbing fiber to supervise learning in the Purkinje cell. This proposal is illustrated using a simple simulation in which it is seen that the climbing fiber succeeds in supervising the learning.
Highlights
In addition to weak inputs from parallel fibers and local inhibitory cells, a Purkinje cell receives a strong input from a single climbing fibre [1,2]
The simple spikes are similar to the spikes found throughout the nervous system whereas complex spikes have a distinctive structure with a leading spike followed by a series of partial spikes called spikelets and a sustained period of depolarization during which the cell is refractory [2,3,4,5,6]
The complex spike, in vivo, is generated by a broad dendritic depolarization mediated by the climbing fiber input
Summary
In addition to weak inputs from parallel fibers and local inhibitory cells, a Purkinje cell receives a strong input from a single climbing fibre [1,2]. The precise role of the cerebellum in movement is still debated; it is proposed, for example, that the cerebellum is a computational engine for deciding precise levels of muscle activation [17,18,19,20], or an organ of prediction, predicting the sensory consequence of movement [21,22,23,24] or that its has a role in proprioception [25,26]. These putative functions may co-exist, or may be co-dependent, but there is no definitive description of what the function of the cerebellum is and there certainly no theory of cerebellar function which would predict its distinctive structure
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