ReviewBrain stimulation studies of non-motor cerebellar function: A systematic review
Introduction
The cerebellum has traditionally been viewed as a brain structure involved in the implementation of motor behaviour. Early clinical studies e.g. (Luciani, 1891) suggested that damage to the cerebellum resulted in a loss of muscle tone, disorganisation of movement and loss of balance. Several early investigators also noted cognitive and psychiatric changes in patients who had suffered cerebellar injury (reviewed in Schmahmann, 2010). These suggestions of non-motor cerebellar function were largely ignored in subsequent investigations as the reported effects were often subtle, contradictory and overshadowed by the effects of cerebral damage. Consideration of cerebellar contributions to non-motor behaviour was not part of mainstream research for several decades. In recent years, however, there has been renewed interest in the possibility of the cerebellum playing a role in autonomic, affective and cognitive functions with findings derived from newly available technologies. It is the purpose of this systematic review to examine the use of several recently developed brain stimulation techniques in the investigation of cerebellar contributions to non-motor behaviour. This review will examine the methodology and findings of studies that have used transcranial current stimulation and transcranial magnetic stimulation of the cerebellum and discuss the contribution that brain stimulation techniques may make to cerebellar research.
Cerebellar stimulation has been used in recent years in an attempt to corroborate evidence gained from imaging and clinical work as to cerebellar involvement in non-motor behaviour, to infer the nature of this role and to localise function within the cerebellum. A wide range of tasks, targets and techniques has been used in this research and it is therefore appropriate to review the approaches taken in order to determine which approaches have proved most successful, to summarise the information that has been gained and to highlight the difficulties encountered so that methodological improvements may be suggested.
A further motivation for this review is that the nature of any cerebellar contribution to non-motor behaviours remains somewhat controversial and therefore examination of the findings of relevant studies may be of use within this context.
This review will first discuss the parameters used and the methodological decisions taken across all studies and then examine groups of studies categorised according to the behavioural function targeted.
Section snippets
Methods
A PubMed search was performed using the following search terms without restriction of date or database field: ((cerebellum) OR (cerebellar)) AND ((stimulation) OR (transcranial) OR (theta burst)). This search returned 7585 papers, which were assessed according to the following inclusion criteria:
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Living, neurologically normal, human subjects
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Cerebellar stimulation target
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Magnetic or electrical stimulation
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Transcranial, rather than deep brain or cortical stimulation
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Non-motor
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Not purely physiological,
Discussion
The results of our review showed that several transcranial magnetic stimulation (TMS) paradigms have been employed for cerebellar non-motor research. The paradigms used can be divided into single pulse and repetitive TMS (see Walsh and Rushworth, 1999 for a discussion of their differences). Single pulse TMS is generally delivered at an intensity sufficient to generate action potentials in targeted brain regions: this externally triggered discharge of neurons introduces temporary disorder into
Conclusion
Emerging from this review is a clear picture of the challenges involved in cerebellar stimulation, both in terms of methods and the interpretation of results. The diversity of targets selected for the stimulation of similar cerebellar regions highlights the benefits of using neuronavigation where available. Skull landmarks can be unreliable indicators of the presence of larger, cerebral regions, such as the dorsolateral prefrontal cortex (e.g. Herwig et al., 2001); these issues may be even more
Acknowledgement
We acknowledge the financial support of the Future and Emerging Technologies (FET) programme within the Seventh Framework Programme for Research of the European Commission, under FET-Open grant number: 222079 (HIVE) to RMB.
References (67)
- et al.
Modelling magnetic coil excitation of human cerebral cortex with a peripheral nerve immersed in a brain-shaped volume conductor: the significance of fiber bending in excitation
Electroencephalography and Clinical Neurophysiology
(1992) - et al.
The cerebellum and its role in word generation: a cTBS study
Cortex: a Journal Devoted to the Study of the Nervous System and Behavior
(2012) - et al.
Establishing safety limits for transcranial direct current stimulation
Clinical Neurophysiology
(2009) - et al.
Individualized model predicts brain current flow during transcranial direct-current stimulation treatment in responsive stroke patient
Brain Stimulation
(2011) - et al.
Role of the cerebellum in time perception: a TMS study in normal subjects
Journal of the Nerological Sciences
(2007) - et al.
A comprehensive review of the effects of rTMS on motor cortical excitability and inhibition
Clinical Neurophysiology: Official Journal of the International Federation of Clinical Neurophysiology
(2006) - et al.
Transcranial DC stimulation (tDCS): a tool for double-blind sham-controlled clinical studies in brain stimulation
Clinical Neurophysiology
(2006) - et al.
Change detection in children with autism: an auditory event-related fMRI study
NeuroImage
(2006) Transcranial magnetic stimulation: a primer
Neuron
(2007)- et al.
Transcranial magnetic stimulation in therapy studies: examination of the reliability of standard coil positioning by neuronavigation
Biological Psychiatry
(2001)