It is now believed that prior to any gain change by Purkinje neurons, they are anchored to either a high spontaneous spike rate (Z- neurons), a low spontaneous spike rate (Z+ neurons), or an intermediate spontaneous spike rate (non-Z neurons: Zhou, De Zeeuw 2014; De Zeeuw 2021; Hasabegović 2024; see Footnote 1). This arrangement allows for bidirectional changes to the gain of Purkinje firing which is regulated by the presence or absence of complex spikes produced by climbing fibre input, such that one climbing fibre controls one Purkinje neuron and the presence of complex spikes lowers the simple spike rate, and the absence of complex spikes increases the simple spike rate (Bell et al. 1997; De Zeeuw 2021; Gallistel et al. 2022; Giovannucci et al. 2017; Loyola et al. 2019; Shadmehr 2020; Tehovnik et al. 2021; Wang et al. 2023). It is suspected that the gain changes are under neocortical control via projections to the inferior olive which supplies the climbing fibres (De Zeeuw 2021; Hasanbegović 2024; Zhou, De Zeeuw 2014).
When looking closely at the distribution of Z- and Z+ Purkinje neurons it is revealed that the lobules I to VI (including the vermis) contain a preponderance of Z- Purkinje neurons, whereas the extreme posterior portions of cerebellum, including lobules IX and X and the flocculus (which contains vestibular circuits) have many Z+ Purkinje neurons. Crus I and II including the vermis include a mixture of Z- and Z+ Purkinje neurons. So, what could this mean?
1. Lobules I to VI control skeletomotor and ocular responses mediated by S1, M1, and the frontal eye fields (Tehovnik, Patel, Tolias et al. 2021). These areas discharge to contract the muscles for the evocation of skeletal and ocular movements. This would require that the discharge of Purkinje neurons be dropped (Z-) to facilitate the elicitation of muscle contractions, causing an eyeblink, a saccade, a reaching response, or a locomotor response.
2. Lobules Crus I and II control body part coordination to dribble a ball or to give a speech (Tehovnik, Patel, Tolias et al. 2021). This region contains both Z- and Z+ Purkinje neurons; this allows for bidirectional control of the muscles for precision.
3. The posterior lobules of cerebellum (IX, X, and flocculus) contain a preponderance of Z+ neurons which are biased toward reducing the contractive strength of muscles. Perhaps, the retinal slip response for VOR is really a release from movement with respect to the head, thereby requiring that the ocular muscles be relaxed with respect to the head.
4. Throughout the cerebellum exist Purkinje neurons that are neither of the Z- nor Z+ type, but are bidirectional gain controllers (Hasanbegović 2024). This bidirectional control would be useful in specifying precise changes in posture which has long been known to be central to cerebellar function and it is postural preparation that shortens the latency to any behavioral response (Hasanbegović 2024; Mao, Sultan et al. 2023). Such preparation would require that the posture of the body be in ready (preparatory) mode, such as when Usain Bolt starts a 200-meter race: before the start gun goes off, all the skeletal muscle lengths must remain in a fixed position at a moderate (but not too extreme) tension, so that once summoned by the neurons and the musculature, Bolt’s body is propelled forward toward the finish line—with minimal sensory feedback at maximal efference-copy control—like a bullet from a gun. Propelling the body forward likely depends on anterior cerebellum along with S1 and M1 (Tehovnik, Patel, Tolias et al. 2021; also see Hasanbegović 2024).
Footnote 1: The Z- and Z+ Purkinje neurons are discriminated by a genetic label and found the be differentially active such that the simple spikes of the Z- neurons spontaneously discharge at a high rate, whereas the simple spikes of the Z+ neurons spontaneously discharge at a low rate, permitting for gain changes in contrary directions: down for Z- neurons and up for Z+ neurons (Zhou, De Zeeuw et al. 2014).
Yes, the cerebellum plays a crucial role in coordinating skeletal muscle action. It's responsible for fine-tuning movements, maintaining balance, and ensuring smooth coordination between muscles. While it may not exhibit intelligence in the same way as cognitive processes, its function in motor control is essential for skilled and efficient movement.
Edward J Tehovnik, I agree with Seyed Reza Samaei. - - But, just 30+ years ago we recognized the complex language and social lives of whales and dolphins. True to ourselves, we now say they possess intelligence. I’m not sure we are capable of recognizing “intelligence” at any level.