Thach et al. (1992, see attached figure): The return loop of the cerebellar maps to the motor cortex via the cerebellar nuclei is from the fastigial nucleus (connected to the anterior lobe of cerebellum), the interpositus nucleus (connected to the posterior lobe of cerebellum), and the dentate nucleus (connected to the mediolateral lobe of cerebellum). Damage to the cerebellum or M1 abolishes the playing of musical instruments (Holmes 1922), which are highly automated acts (supporting a very high information transfer rate of 40 bits per second, Tehovnik and Chen 2015). Even though the establishment of an efference-copy signal occurs in the cerebellum (Bell et al. 1997; De Zeeuw 2021; Loyola et al. 2019; Shadmehr 2020; Tehovnik et al. 2021; Wang et al. 2023), the execution of an automated act depends on an intact neocortex to respond to a specific sensory context that triggers the act. Following such a trigger, a minimal number of synapses is utilized to shorten the response latency (Tehovnik, Hasanbegović, Chen 2024).
As suggested by the figure, M1 is considered part of the efference-copy loop; indeed, M1 receives a robust visual input (Tehovnik et al. 2013) that can trigger the discharge of its neurons to evoke body movements. On this point, it has been known for over 100 years that electrical stimulation of V1 paired with the electrical stimulation of M1 can condition a response such that V1 stimulation alone evokes muscle contractions (Doty 1969). This is a clear example of Hebbian learning and an early example of efference-copy development, but there was no linkage to the cerebellum at this time which harbors the circuitry for the efference-copy encoding for automaticity to be realized.
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