Complex Spike Wars: a New Hope

Abstract

The climbing fiber–Purkinje cell circuit is one of the most powerful and highly conserved in the central nervous system. Climbing fibers exert a powerful excitatory action that results in a complex spike in Purkinje cells and normal functioning of the cerebellum depends on the integrity of climbing fiber–Purkinje cell synapse. Over the last 50 years, multiple hypotheses have been put forward on the role of the climbing fibers and complex spikes in cerebellar information processing and motor control. Central to these theories is the nature of the interaction between the low-frequency complex spike discharge and the high-frequency simple spike firing of Purkinje cells. This review examines the major hypotheses surrounding the action of the climbing fiber–Purkinje cell projection, discussing both supporting and conflicting findings. The review describes newer findings establishing that climbing fibers and complex spikes provide predictive signals about movement parameters and that climbing fiber input controls the encoding of behavioral information in the simple spike firing of Purkinje cells. Finally, we propose the dynamic encoding hypothesis for complex spike function that strives to integrate established and newer findings.

Pogz deficiency leads to transcription dysregulation and impaired cerebellar activity underlying autism-like behavior in mice

“…Not only that mutations in Pogz resulted in a profound alteration in gene expression in the cerebellum, we also observed in Pogz-deficient mice abnormal motor coordination and learning and decreased firing rates of simple and complex spikes of cerebellar PCs. Although both firing modes are known to participate in motor performance as well as in motor learning [52][53][54][55][56][57][58][59][60] , the mechanism is still debated. Regardless of the exact mechanism of motor performance or motor learning, it is clear that a reduction in simple spike activities in the Pogz-deficient mice is bound to affect motor learning.…”

A Revised Computational Neuroanatomy for Motor Control

“…A final alternative is that reward signals in the cerebellum are found more laterally in the cerebellum and thus reflect internal modelling of reward that is not directly connected to movement (Heffley and Hull, 2019;Sendhilnathan et al, 2020;Tsutsumi et al, 2019). Considering other recent results showing that climbing fibers provide predictive signals about movement parameters (Streng et al, 2018) the canonical view is still widely accepted (Apps et al, 2018;Sokolov et al, 2017).…”

Motor context dominates output from Purkinje cell functional regions during reflexive visuomotor behaviours

“…There is great debate about whether climbing fiber signals convey error, predictive, or novelty signals (see Simpson et al, 1996 andStreng et al, 2018 for reviews). The error hypothesis would suggest that the visually-evoked responses we observe here signal unexpected events or "negative 1030 sensory events to be avoided" such as retinal slip (Lang et al, 2017).…”