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Abstract
The cerebellum is increasingly recognized as a structure that regulates cognitive and emotional functioning in much the same way that it modulates motor activity. Reciprocal connections with prefrontal and temporoparietal association cortices facilitate cerebellar modulation of implicit learning and executive functions, while connections with paralimbic regions allow for cerebellar regulation of emotional responses. Furthermore, recent evidence indicates that the cerebellum is reciprocally connected with the basal ganglia, forming an interconnected subcortical network with an extensive influence on cortical processing. In this review, we first discuss the neuroanatomical basis of the cerebellum's role in implicit learning and executive functioning. Next, we examine evidence of cerebellar contributions to executive dysfunction in select neurological and psychiatric illnesses. We conclude with a brief discussion regarding potential treatments targeting the cerebellum.
Keywords: cerebellum, executive function, emotion, implicit learning
1. Introduction
The essential function of the cerebellum was long considered to be the coordination of voluntary movement. Early observations of patients with cerebellar lesions described fragmentation of normal motor sequences (dysynergia) and of rapid alternating movements (dysdiadochokinesia), as well as deficits in the rate, range, and force of movement resulting in the overshooting or undershooting of intended targets (dysmetria) (Babinski, 1899; Holmes, 1939; Ropper and Samuels, 2009). The classical view of cerebrocerebellar connections is that the cerebellum receives input from select regions of the neocortex and projects this information back through the ventrolateral nucleus of the thalamus to the primary motor cortex. According to this view, cerebellar output influenced motor control and abnormal activity in this circuit would lead to purely motor deficits.
In the past several decades, the role of the cerebellum in the implicit learning and homeostatic regulation of both motor and non-motor information has been emphasized. Ito (2010) has argued that the cerebellum is involved in the adaptive control of activities that are performed outside of a person's conscious awareness, such as when a behavior becomes more refined due to practice. Importantly, this role was extended to cognitive processes. Specifically, he asserts that repetitious thoughts and mental plans become more implicit over time, that is, they require less and less conscious effort as the cerebellum forms an internal representation of the cortical mental model (Ito, 2010). Schmahmann (2000) proposed a universal cerebellar transform to describe...