Abstract
Climbing fiber inputs to the cerebellum encode error signals that instruct learning. Recently, evidence has accumulated to suggest that the cerebellum is also involved in the processing of reward. To study how rewarding events are encoded, we recorded the activity of climbing fibers when monkeys were engaged in an eye movement task. At the beginning of each trial, the monkeys were cued to the size of the reward that would be delivered upon successful completion of the trial. Climbing fiber activity increased when the monkeys were presented with a cue indicating a large reward, but not a small reward. Reward size did not modulate activity at reward delivery or during eye movements. Comparison between climbing fiber and simple spike activity indicated different interactions for coding of movement and reward. These results indicate that climbing fibers encode the expected reward size and suggest a general role of the cerebellum in associative learning beyond error correction.
Highlights
Computational, anatomical, and functional evidence support the theory that the cerebellar cortex performs error correcting supervised motor learning (Albus, 1971; Gilbert and Thach, 1977; Marr, 1969; Nguyen-Vu et al, 2013; Stone and Lisberger, 1990; Suvrathan et al, 2016)
We found that many Purkinje cells (40 out of 220) had different complex spikes (Cspks) rates in the different reward conditions
Complex spike coding of target motion does not depend on reward size. These results indicate that the Cspk rate differentiates between reward sizes when reward information is first made available, but not during delivery
Summary
Computational, anatomical, and functional evidence support the theory that the cerebellar cortex performs error correcting supervised motor learning (Albus, 1971; Gilbert and Thach, 1977; Marr, 1969; Nguyen-Vu et al, 2013; Stone and Lisberger, 1990; Suvrathan et al, 2016). Cspks are thought to represent instructive error signals triggered by movement errors These error signals adjust the Sspk response of the Purkinje cell to parallel fiber input, resulting in improvement in subsequent movements. This hypothesized role of the Cspks in learning was broadened when it was shown that the Cspk rate increases in response to cues that are predictive of undesired successive stimuli (Ohmae and Medina, 2015). The Cspk signal is well-suited for driving associative learning based on motor errors that drive avoidance of aversive stimuli
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