Cerebellum controls timing of periaqueductal grey encoding of fear memory and expression of fear conditioned behaviour

The pivotal role of the periaqueductal grey (PAG) in fear learning is reinforced by the identification of neurons in rat ventral (vPAG) that encode fear memory through signalling the onset and offset of an auditory conditioned stimulus during retrieval. Within this framework, understanding of cerebellar contributions to survival circuits is advanced by the discovery that: (i) reversible inactivation of the medial cerebellar nucleus (MCN) during fear consolidation (a) reduces the temporal precision of vPAG offset, but not onset responses and (b) increases rearing behaviour during retrieval, and (ii) chemogenetic inhibition of the MCN-vPAG projection during fear acquisition (a) reduces the emission of fear-related ultrasonic vocalisations and (b) slows the extinction rate of fear-related freezing. These findings show that the cerebellum regulates fear memory processes at multiple timescales and in multiple ways. The current findings indicate that dysfunctional interactions in the cerebellar-survival network may underlie fear-related disorders and comorbidities.