A Passage-of-time Model of the Cerebellar Purkinje Cell

TL;DR

This paper proposes an internal passage-of-time model for cerebellar Purkinje cells that learns and reproduces timing in classical conditioning without relying on synaptic strength changes, addressing limitations of previous models.

Contribution

The model demonstrates an internal timing mechanism within Purkinje cells that is invariant to probe structure, challenging traditional synaptic depression theories.

Findings

Model accurately simulates Purkinje cell learning behavior

Predicts electrophysiological responses for experimental validation

Shows timing reproduction without synaptic strength modifications

Abstract

The cerebellar Purkinje cell controlling eyeblinks can learn, remember and reproduce the interstimulus interval in a classical conditioning paradigm. Given temporally separated inputs, the cerebellar Purkinje cell learns to pause its tonic inhibition of a motor pathway with high temporal precision so that an overt blink occurs at the right time. Most models relegate the Purkinje cell's passage-of-time representation to afferent granule cells, a subpopulation of which is supposedly selected for synaptic depression in order to make the Purkinje cell pause. However, granule cell models have recently faced two crucial challenges: 1) bypassing granule cells and directly stimulating the Purkinje cell's pre-synaptic fibers during training still produces a well-timed pause, and 2) the Purkinje cell can reproduce the learned pause, invariant to the temporal structure of probe stimulation. Here, we present a passage-of-time model which is internal to the Purkinje cell and is invariant to probe structure. The model accurately simulates the Purkinje cell learning mechanism and makes testable electrophysiological predictions. Importantly, the model is a numerical proof-of-principle for a biological learning mechanism which does not rely on changes of synaptic strength.