Anatomical and physiological foundations of cerebellar information processing

Abstract

A coordinated movement is easy to recognize, but we know little about how it is achieved. In search of the neural basis of coordination, we present a model of spinocerebellar interactions in which the structure-functional organizing principle is a division of the cerebellum into discrete microcomplexes. Each microcomplex is the recipient of a specific motor error signal - that is, a signal that conveys information about an inappropriate movement. These signals are encoded by spinal reflex circuits and conveyed to the cerebellar cortex through climbing fibre afferents. This organization reveals salient features of cerebellar information processing, but also highlights the importance of systems level analysis for a fuller understanding of the neural mechanisms that underlie behaviour.

Selective Impairment of the Cerebellar C1 Module Involved in Rat Hind Limb Control Reduces Step-Dependent Modulation of Cutaneous Reflexes

“…In line with this observation, input and output pathways to and from the paravermal parts of the cerebellum of the cat seem to be modulated during locomotion (Arshavsky et al, 1986;Apps and Lee, 1999). Therefore, the cerebellar paravermis, which involves the C-modules, would seem to be an ideal candidate to monitor and adjust these reflexes in a learning-dependent way, especially because they have been implicated to be involved in controlling withdrawal reflexes (Kolb et al, 1997;Bracha et al, 1999;Apps and Garwicz, 2005). Indeed, the present results show that a selective impairment of the hindlimb-related C1 zone reduces the depth of modulation of these reflexes.…”

“…Especially studies on eye blink conditioning have demonstrated that the cerebellum, apart from facilitating the newly acquired response, is also involved in controlling the timing and amplitude of the conditioned reflex, thereby aiding in both motor learning and motor performance (Koekkoek et al, 2003). With respect to cerebellar involvement to voluntary movements and locomotion, we have only just begun to appreciate and pinpoint more precisely its modulatory actions (Bracha et al, 1999;Apps and Garwicz, 2005). For example, recent studies with human cerebellar patients indicated that the cerebellum is involved in the timing of withdrawal reflexes (Kolb et al, 2007).…”

“…Furthermore, many climbing fibers collateralize to reach both the COP as well as the anterior lobe parts of this module (Voogd et al, 2003;. Purkinje cells of all these related cortical regions project to the medial part of the AIN (Apps and Garwicz, 2005;Pijpers et al, 2005). Hence, these cortical zones together with the caudolateral part of vfDAO and the medial AIN are considered to constitute the C1/C3 hindlimb module.…”

“…A module consists of one or several functionally related strips, or zones, of Purkinje cells that (1) project to a specific part of the cerebellar nuclei, (2) receive their climbing fibers from a well defined subnucleus of the inferior olive, (3) have specific receptive field characteristics, and (4) differ in their chemical characteristics from adjacent modules (Voogd and Glickstein, 1998). As such, modules are thought to represent functional cerebellar units (Apps and Garwicz, 2005). However, although cerebellar functions are usually described in terms of motor control, coordination, and motor learning, it is not known whether and how individual modules contribute to specific aspects of these functions.…”

Besides Purkinje cells and granule neurons: an appraisal of the cell biology of the interneurons of the cerebellar cortex

“…In contrast, genetic and molecular means to identify, characterize, or manipulate basket, stellate and Golgi cells, candelabrum neurons, Lugaro cells or unipolar brush cells have been largely elusive. It is not surprising, then, that these cells are typically not considered even in recent integrative views of cerebellar function (e.g., Apps and Garwicz 2005;Porrill et al 2004;Boyden et al 2004); at best, the more prominent Lugaro cells and unipolar brush cells are mentioned, and rather in passing (e.g., Ito 2008;Millen and Gleeson 2008).…”