The results of investigations across different disciplines in neuroscience indicate that there is a level of organization in the cerebellum such that sensorimotor control is topographically separate from cognitive and emotional regulation. This new understanding of the cerebellum represents a major departure from conventional wisdom. Given the available evidence, we conclude that the anterior lobe and parts of medial lobule VI, together with lobule VIII of the posterior lobe and the interpositus nuclei constitute the sensorimotor cerebellum
. Lobule VII and parts of lobule VI, which together with the ventral part of the dentate nucleus has expanded massively in the human, constitute the anatomical substrate of the cognitive cerebellum
. The limbic cerebellum
appears to have an anatomical signature in the fastigial nucleus and the cerebellar vermis, particularly the posterior vermis. Little is known of the possible cognitive role of lobule IX, although early fcMRI data provide some insights into its potential incorporation into the default mode network (Habas et al., 2009
). Lobule X remains an essential node in the vestibular system. This functional heterogeneity, determined by functional imaging, physiological/behavioral studies, and clinical observations, is matched by the intricate connectional heterogeneity between different cerebellar regions and the spinal cord, brainstem and cerebral cortex. Further identification of the precise arrangement within the cerebellum of the multiple different aspects of cognitive and emotional processing is the focus of ongoing investigations.
This wider role of the cerebellum in cognition, emotion, social intelligence and mental health may be viewed within the context of the anatomical substrates that constitute the distributed neural circuits subserving all domains of neurological function. The demonstration across modalities that the cerebellum is incorporated into the neural circuits governing many behaviors, and not only motor control, begs the question as to what it is the cerebellum contributes to these behaviors. This important question is discussed elsewhere (see Schmahmann, 1997
; Schmahmann and Pandya, 2008
), but the question itself is predicated on the focus of the present report, namely, the recognition that there are indeed distinct cerebrocerebellar loops linked with motor, cognitive, and emotion circuits, and that this anatomical arrangement leads to organization within the cerebellum that is functionally and clinically relevant.
A number of avenues of investigation are available to test the hypothesis that there are separate, topographically-organized cerebellar subsystems involved in processing sensorimotor, cognitive and affective information. Advances in imaging technologies hold promise for defining the structural and functional anatomy of the cerebrocerebellar loops in humans. For example, diffusion tensor imaging (Ramnani et al., 2006
) and diffusion spectrum imaging (Granziera et al., 2009
) have the potential to elucidate details of these cerebrocerebellar pathways. Functional connectivity analyses (Allen et al., 2005
; Booth et al., 2007
; Habas et al., 2009
; Honey et al., 2005
; Krienen and Buckner, 2009
) and magnetoencephalograpy (Kujala et al., 2007
) make it possible to examine functional relationships between cerebellar and cerebral cortical activity; already these techniques suggest that the cerebellum contributes to the functional networks underlying cognitive tasks such as reading (Kujala et al., 2007
). Functional MRI can be used to examine topography within the cerebellum by studying cerebellar activation during a range of different tasks within individuals to determine whether the motor-nonmotor dichotomy, and the patterns of activity suggested by previous studies, can be seen at an individual level.