Cerebellar Contribution to Motor and Non-Motor Behaviour: From simple to complex levels

Abstract

The cerebellum, Latin for ‘little brain’, is located in the posterior cranial fossa underneath the larger cerebral cortex. Anatomically, it is superimposed onto the pons and classified as a part of the metencephalon (figure 1.1). The central, most medial part of the cerebellum is called the vermis from which on both sides the cerebellar hemispheres extend. Macroanatomical, the cerebellum is subdivided into several lobules divided by fissures in the transversal plane. Each fissure contains a large number of sulci, packing the surface of the cerebellar gray matter into a much smaller volume. Of the cerebellar cortex, 86% is packed in fissures. Unpacked, the human cerebellar cortex consists of a surface of 550 cm2 packed into an anatomical space of 70 cm3 (Henery and Mayhew, 1989). Cell-wise, the cerebellum contains 80% of all neurons, packed within 10% of the total brain mass (Lent et al., 2012). For every neuron in the cerebral cortex, there are 3.6 neurons in the cerebellum. The cerebellum is connected with the rest of the brain through the cerebellar peduncles composed of white matter. The largest middle cerebellar peduncle is the most important afferent system for the cerebellum. It contains fibres from the pontine nuclei including the nucleus reticularis tegmenti ponti. Besides the middle cerebellar peduncle, information is transmitted to the cerebellum through the inferior cerebellar peduncle containing the spinocerebellar tract from the spinal cord and the olivocerebellar tract arising from the contralateral inferior olive. The main output runs through the superior cerebellar peduncle originating in the deep cerebellar nuclei and projecting to the brain stem and thalamus (see figure 1.1). Packed inside the cerebellar white matter are the four deep cerebellar nuclei. Together with the vestibular nuclei in the brainstem, these nuclei form the output of the cerebellar cortex. In humans the four cerebellar nuclei are called (from medial to lateral) the fastigial nucleus, globose nucleus, emboliform nucleus and the dentate nucleus.