But how great was his apprehension, when he farther understood, that [the force of parturition] acting upon the very vertex of the head, not only injured the brain itself, or cerebrum—but that it necessarily squeezed and propelled the cerebrum towards the cerebellum, which was the immediate seat of the understanding!—Angels and ministers of grace defend us! Cried my father—can any soul withstand this shock?—No wonder the intellectual web is so rent and tattered as we see it; and that so many of our best heads are no better than a puzzled skein of silk,—all perplexity—all confusion within-side.
—Laurence Sterne (1713–1768)
The Life and Opinions of Tristram Shandy, Gentleman
I. FUNCTIONS OF THE CEREBELLUM
A. What the cerebellum does not do
Laurence Sterne correctly satirized the speculative neurophysiology of his time, which localized “the immediate seat of the understanding” to the cerebellum. Nevertheless, the cerebellum apparently participates in the regulation of cognition, emotion, and autonomic functions more than generally appreciated (Buckner, 2013). Cerebellar lesions can result in the cerebellar cognitive affective syndrome (CCAS) comprising a constellation of executive behavioral dysfunction, visual-spatial deficits, linguistic impairments, and behavioral-affective disturbances and a posterior fossa syndrome, presenting with similar symptoms but more often described in children after cerebellar tumor surgery. There is no general consensus with regard to assigning parts of the cerebellum to specific cognitive dysfunction, but it has been proposed that the anterior lobe and parts of medial lobule VI and lobule VIII of the posterior lobe contain the representation of the sensorimotor cerebellum; parts of lobule VI and lobule VII of the posterior lobe comprise the cognitive cerebellum; and the posterior vermis and the fastigial nucleus are the anatomical substrate for the limbic cerebellum (Buckner, 2013; De Smet et al, 2013).
The cerebellum has no clinically evident role in consciousness per se.
The cerebellum has no clinically evident role in the conscious appreciation of sensation, despite massive sensory connections. Holmes (Holmes, 1939; van Gijn, 2007) repeatedly stated that standard clinical tests did not reveal sensory deficits in cerebellar patients (Pts).
B. What the cerebellum does do
The most explicit function of the cerebellum for clinical testing is its role in coordinating willed muscular contractions. To coordinate means to adjust the rate, range, force, and sequence of willed muscular contractions. In so acting, the cerebellum belongs to a distributed sensorimotor network for coordination that includes the cerebral cortex, basal motor nuclei, thalamus, and reticular formation (De Smet et al, 2013).
As Hughling’s Jackson (1834–1911) stated, “It will not suffice to speak of coordination as a separate ‘faculty.’ Coordination is the function of the whole and every part of the nervous system.” Not the least are the sensory systems. Visual, tactile, and auditory systems send afferents to the cerebellum, but coordination pre-eminently requires proprioceptive input from joints, muscles, ...