Cerebellar physiology: links between microcircuitry properties and sensorimotor functions

Abstract

Final sensorimotor command Sensory readout Movement commandAbstract Existing knowledge of the cerebellar microcircuitry structure and physiology allows a rather detailed description of what it in itself can and cannot do. Combined with a known mapping of different cerebellar regions to afferent systems and motor output target structures, there are several constraints that can be used to describe how specific components of the cerebellar microcircuitry may work during sensorimotor control. In fact, as described in this review, the major factor that hampers further progress in understanding cerebellar function is the limited insights into the circuitry-level function of the targeted motor output systems and the nature of the information in the mossy fiber afferents. The cerebellar circuitry in itself is here summarized Henrik Jörntell received his PhD degree in Neurophysiology from Lund University. He is currently employed as a senior lecturer at Lund University where he heads the lab 'Neural Basis for Sensorimotor Control' at the Department of Experimental Medical Science. His interests are the neurophysiological analysis of neuronal microcircuits involved in movement control, spanning cerebellar, spinal, brainstem and neocortical circuitry as well as models of how these structures interact during movement performance and motor learning. as a gigantic associative memory element, primarily consisting of the parallel fiber synapses, whereas most other circuitry components, including the climbing fiber system, primarily has the role of maintaining activity balance in the intracerebellar and extracerebellar circuitry. The review explores the consistency of this novel interpretational framework with multiple diverse observations at the synaptic and microcircuitry level within the cerebellum.(Received 9 May 2016; accepted after revision 29 June 2016; first published online 8 July 2016) Email: henrik.jorntell@med.lu.se Abstract figure legendThe cerebellar neuronal circuitry is here summarized as a gigantic associative memory, consisting of multiple functional subunits working in parallel, by which useful contingencies between diverse types of information can be stored. The sources of information are the multiple mossy fiber systems that inform the cerebellum about original motor commands/motor plans and sensorimotor information at different levels of abstraction. The output of each functional subunit of the cerebellum is refining the ongoing movement command by linking learnt appropriate sensorimotor functions for the particular context or state. Because of its size, the memory element can house the appropriate associations, translatable to synaptic weights, relevant for all contexts or states that the individual can be expected to experience during a lifetime. It follows that a key component necessary to further improve our understanding of cerebellar function is a precise knowledge of the types and formats of information that reaches the cerebellum via the vast variety of mossy fiber pathways, a subject area that has ...

Cerebellar–M1 Connectivity Changes Associated with Motor Learning Are Somatotopic Specific

“…Targets were displayed pseudorandomly such that every set of eight consecutive trials included one of each of the target positions. For each trial, subjects' performance was quantified as the angular end point error, which was defined as the angle between the starting position to the center of the target and the imaginary line connecting the starting position to the end point (Hadipour-Niktarash et al, 2007;Galea et al, 2011). Epochs were created by binning eight consecutive trials.…”

“…In Experiment 4, the CS intensity was set at 5% below the brainstem motor threshold to the cerebellum. This intensity was selected because cerebellar-M1 connections for the TA muscle show reduced inhibition compared with the FDI muscle (Jayaram et al, 2011).…”

“…The cerebellum is thought to be critical for learning error-based adaptation tasks (Martin et al, 1996;Diedrichsen et al, 2005;Chen et al, 2006) because patients with cerebellar degeneration show a marked impairment in such learning (Weiner et al, 1983;Martin et al, 1996;Smith and Shadmehr, 2005). In addition, acquisition of a visuomotor adaptation is enhanced when anodal transcranial direct current stimulation, a form of noninvasive excitatory stimulation, is applied over the cerebellum during training (Galea et al, 2011;Block and Celnik, 2013).…”

“…Therefore, this TMS technique is thought to measure the inhibitory projection from the cerebellar cortex to the dentate, which reduces M1 activity via the dentate-thalamus-cortical pathway (cerebellar inhibition; CBI). We have shown recently that the level of CBI to a leg muscle, the tibialis anterior (TA), decreases when healthy subjects learn a cerebellum-dependent locomotor adaptation task (Jayaram et al, 2011). Interestingly, those participants experiencing a larger magnitude of adaptation (i.e., greater degree of learning) expressed greater reduction in CBI.…”

“…Because this type of learning can transfer to untrained limbs (Sainburg and Wang, 2002;Criscimagna-Hemminger et al, 2003;Wang and Sainburg, 2004;Morton and Bastian, 2006;Savin and Morton, 2008;Balitsky Thompson and Henriques, 2010;Joiner et al, 2013), modulation of CBI in an untrained limb could be related to interlimb transfer (i.e., reflecting a somatotopy-specific plastic mechanism) or it could be a nonspecific response. Therefore, we also investigated CBI in the context of movement preparation in the absence of motor learning.…”