Cerebrocerebellar Connections

In the cerebral peduncle, prefrontal fibers are most medial, sensorimotor fibers intermediate, and fibers from the parietal, temporal, and occipital lobes are lateral. In the monkey, terminations in the pons from motor and association areas are topographically arranged. The caudal pons preferentially receives sensorimotor inputs and projects mostly to the cerebellar anterior lobe and lobule VIII, containing primary and secondary sensorimotor representations, respectively. Dorsolateral pons projects to visual areas in the vermal and hemispheric lobule IX. Medial parts of the rostral pons project to crus I. Medial, anterior, and lateral pons project to crus II. By way of these projections, lobules III through V of the anterior lobe and lobule VIII receive sensorimotor afferents. In contrast, much of lobule VI, crus I and crus II of lobule VIIA, and lobule VIIB receive inputs from association areas and limbic-related regions of the cerebral cortex.

Clinicopathologic studies in patients show that speech is represented medially in the rostral pons, hand coordination medially and anteriorly in the rostral and midpons, the arm anteriorly and laterally to the hand, leg coordination mostly laterally in the caudal pons, and gait is distributed in medial and lateral locations throughout.

In the feedback system, primary motor cortex receives projections via thalamus from dorsal parts of the dentate nucleus and caudal portions of the anterior interpositus nucleus, where neurons activate with arm movement. Premotor cortex receives input from midrostrocaudal dentate nucleus. Frontal eye field–projecting neurons are in the caudal third of the dentate nucleus activated by saccadic eye movements. The dorsolateral prefrontal cortex (areas 46 and 9 lateral) receives projections from the ventral dentate. Projections to parietal, temporal, and cingulate association areas also appear to arise in ventral and lateral parts of the dentate nucleus. Fastigial nucleus projections to intralaminar thalamic nuclei appear to have widespread influence on the cerebral hemisphere.

These connectional patterns are matched by magnetic resonance imaging studies in humans using resting state functional connectivity and experiments performed while subjects are actively engaged in tasks. The cerebellum, like the cerebral cortex, is topographically arranged into functional domains. The primary sensorimotor cerebellum is in lobules III, IV, and V of the anterior lobe and adjacent parts of lobule VI; the secondary sensorimotor representation is in lobule VIII. The motor cerebellum is functionally coupled with sensorimotor cerebral areas and engaged in motor tasks: leg and foot are in lobules II, III, and VIII; hand representation in lobules IV, V, and VIII; and orofacial movements in paravermal anterior lobe and medial lobule VI. The supramodal, or cognitive, cerebellum is linked with cerebral association cortices but not with sensorimotor areas. These posterior lobe regions are lobule VI, lobule VIIA at the vermis and in crus I and crus II in the hemispheres, and lobule VIIB. The cognitive cerebellum is differentially linked with the various subdivisions of the prefrontal cortex and other cerebral association areas. Lobules VI, crus I and crus II, and lobule IX also correlate with an executive control network in the cerebral hemispheres; lobule VI with a salience network; and lobule IX with the default network. Working memory and executive functions engage lobules VI and VII, language recruits posterolateral cerebellum on the right, and spatial tasks recruit it on the left. Affective/emotional processing and pain and autonomic functions involve lobules VI and VII in the vermis more than the hemispheres. The anterior lobe is not engaged in cognitive tasks; the posterior lobe is not involved in motor tasks, with the exception of parts of lobule VI and the second sensorimotor representation in lobule VIII.

These anatomic and imaging findings demonstrate a high degree of functional topography in cerebrocerebellar loops, and they provide the anatomic and functional foundations for the cerebellar modulation of sensorimotor, cognitive, and limbic domains.

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