8: Examination for Cerebellar Dysfunction

INTRODUCTION

I. FUNCTIONS OF THE CEREBELLUM

A. What the cerebellum does not do

1. 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 (Schmahmann, 2001). Cerebellar lesions can result in the cerebellar cognitive syndrome comprising a constellation of executive, visual spatial, linguistic impairments, and affective dysregulation. A topographical organization has been proposed such that the anterior lobe, 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. (Stoodley and Schmahmann, 2010)

2. The cerebellum has no clinically evident role in consciousness per se.

3. The cerebellum has no clinically evident role in the conscious appreciation of sensation, despite massive sensory connections. Holmes (1917, 1939) repeatedly stated that standard clinical tests did not reveal sensory deficits in cerebellar patients (Pts).

B. What the cerebellum does do

1. 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 (Giron and Koller, 1993).

2. As Hughlings 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 preeminently requires proprioceptive input from joints, muscles, and vestibular system. (See page 404 for a full definition of proprioception).

3. To make a movement, the brain must know where the body part starts from to orchestrate the sequence, rate, and force of muscular contractions required to get the part from point A to point B. Musculoskeletal proprioceptors and other senses ...