Sensorimotor Integration and Amplification of Reflexive Whisking by Well-Timed Spiking in the Cerebellar Corticonuclear Circuit.

To test how cerebellar crus I/II Purkinje cells and their targets in the lateral cerebellar nuclei (CbN) integrate sensory and motor-related inputs and contribute to reflexive movements, we recorded extracellularly in awake, head-fixed mice during non-contact whisking. Ipsilateral or contralateral air puffs elicited changes in population Purkinje simple spike rates that matched whisking kinematics (∼1 Hz/1° protraction). Responses remained relatively unaffected when ipsilateral sensory feedback was removed by lidocaine but were reduced by optogenetically inhibiting the reticular nuclei. Optogenetically silencing cerebellar output suppressed movements. During puff-evoked whisks, both Purkinje and CbN cells generated well-timed spikes in sequential 2- to 4-ms windows at response onset, such that they alternately elevated their firing rates just before protraction. With spontaneous whisks, which were smaller than puff-evoked whisks, well-timed spikes were absent and CbN cells were inhibited. Thus, sensory input can facilitate millisecond-scale, well-timed spiking in Purkinje and CbN cells and amplify reflexive whisker movements.