We are taught in elementary statistics that a correlation does not prove causation. Nevertheless, given that the number of neurons in the neocortex scales at the slope of one with respect to the number of neurons in the cerebellum of mammals (Fig. 9B of Herculano-Houzel et al. 2014), one is apt to conclude that these two structures, at the very least, are developmentally related. Furthermore, the amount of energy consumed per neuron is 20 times greater (on average) for the neocortex than the cerebellum (Fig. 1), and this consumption for the neocortex has been attributed to maintaining a steady stream of consciousness during wakefulness (Herculano-Houzel 2011; James 1890). The neocortex subserves the storage (and retrieval) of declarative/sensory memories (Penfield and Roberts 1966; Scoville and Milner 1957; Squire 1992), whereas the cerebellum is believed to mediate the storage (and retrieval) of motor routines that have been automated (Tehovnik, Hasanbegović, Chen 2024). It is common for cognitive processing to be studied separately from motor processing such that when studying a cognitive variable, such as learning, great effort is made to rule out the effect of movement (e.g., Swain et al. 2011; also see Sendhilnathan, Goldberg et al. 2020a). This functional apartheid can be attributed to the notion that cognition is a human quality that depends on a neocortex specialized for thinking and language (e.g., Chomsky 2012), whereas sensorimotor routines are shared between humans and non-humans, a topic of biology. Pure cognitive psychologists have traditionally been contemptuous of cognitive conclusions arising from brain research based on nonhuman subjects (e.g., Chomsky 2007/8, MIT seminar).
So, what about that correlation at the slope of one between the number of neocortical neurons and the number of cerebellar neurons (Fig. 9B of Herculano-Houzel et al. 2014)? What this indicates is that the massive projection between the neocortex and the cerebellum via the middle cerebellar peduncle should not be underestimated (Hasanbegović 2024; Tehovnik et al. 2021), and it should remind us that all cognition is ultimately expressed as a motor act even if one spends a year deliberating whether (or not) to storm the Capitol (James 1890). Those who insist on studying the brain divorced from its motor output risk never figuring out how the brain works, as evidenced by the billion-dollar effort of failure by the Human Brain Project of Lausanne, Switzerland to reverse engineer the brain in the absence of behavior, i.e., body movements (Abbott 2020).
Figure 1: The illustration is modified from figure 1b of Herculano-Houzel (2011).
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