Abstract
While research on the cerebellar cortex is crystallizing our understanding of its function in learning behavior, many questions surrounding its downstream targets remain. Here, we evaluate the dynamics of cerebellar interpositus nucleus (IpN) neurons over the course of Pavlovian eyeblink conditioning. A diverse range of learning-induced neuronal responses was observed, including increases and decreases in activity during the generation of conditioned blinks. Trial-by-trial correlational analysis and optogenetic manipulation demonstrate that facilitation in the IpN drives the eyelid movements. Adaptive facilitatory responses are often preceded by acquired transient inhibition of IpN activity that, based on latency and effect, appear to be driven by complex spikes in cerebellar cortical Purkinje cells. Likewise, during reflexive blinks to periocular stimulation, IpN cells show excitation-suppression patterns that suggest a contribution of climbing fibers and their collaterals. These findings highlight the integrative properties of subcortical neurons at the cerebellar output stage mediating conditioned behavior.
Highlights
The cerebellar cortex, like the neocortex, is well suited for establishing new associations required during memory formation
Classical Pavlovian eyeblink conditioning has proven an ideal model for studying the neural mechanisms underlying associative learning, and offers a suitable paradigm to address the question of how the cerebellar nuclei integrate their cerebellar cortical and extra-cerebellar input
We collected 270 recordings of interpositus nucleus (IpN) cells that were located below Purkinje cell layers at depths between 1500–3000 mm (Figure 1B), that were recorded during at least 10 valid CS-US trials, and that showed modulation in their firing rate in response to the CS and/or US
Summary
The cerebellar cortex, like the neocortex, is well suited for establishing new associations required during memory formation. As a simple and quintessential behavioral manifestation of learning and memory, eyeblink conditioning depends on the cerebellar cortex and nuclei (McCormick et al, 1982; McCormick and Thompson, 1984; Yeo et al, 1985a1985, 1985b), which are known to facilitate processes that require precise timing (Ivry and Keele, 1989; Breska and Ivry, 2016). Lobule HVI of the cerebellar cortex and its downstream target, the interposed nucleus (IpN), are essential for the manifestation of this conditioned eyelid behavior
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