Abstract
Numerous studies have highlighted the possibility of modulating the excitability of cerebro–cerebellar circuits bi-directionally using transcranial electrical brain stimulation, in a manner akin to that observed using magnetic stimulation protocols. It has been proposed that cerebellar stimulation activates Purkinje cells in the cerebellar cortex, leading to inhibition of the dentate nucleus, which exerts a tonic facilitatory drive onto motor and cognitive regions of cortex through a synaptic relay in the ventral–lateral thalamus. Some cerebellar deficits present with cognitive impairments if damage to non-motor regions of the cerebellum disrupts the coupling with cerebral cortical areas for thinking and reasoning. Indeed, white matter changes in the dentato–rubral tract correlate with cognitive assessments in patients with Friedreich ataxia, suggesting that this pathway is one component of the anatomical substrate supporting a cerebellar contribution to cognition. An understanding of the physiology of the cerebro–cerebellar pathway previously helped us to constrain our interpretation of results from two recent studies in which we showed cognitive enhancements in healthy participants during tests of arithmetic after electrical stimulation of the cerebellum, but only when task demands were high. Others studies have also shown how excitation of the prefrontal cortex can enhance performance in a variety of working memory tasks. Thus, future efforts might be guided toward neuro-enhancement in certain patient populations, using what is commonly termed “non-invasive brain stimulation” as a cognitive rehabilitation tool to modulate cerebro–cerebellar circuits, or for stimulation over the cerebral cortex to compensate for decreased cerebellar drive to this region. This article will address these possibilities with a review of the relevant literature covering ataxias and cerebellar cognitive affective disorders, which are characterized by thalamo–cortical disturbances.
Highlights
Clinicians have been directly exciting the cerebellar cortex with implanted electrodes in epileptic patients and in those with schizophrenia and depression since the 1970s with good therapeutic results [1], demonstrating the use of constant electrical stimulation for the treatment of behavioral disorders and epilepsy
Many studies involving healthy participants and certain patient populations demonstrate the value of non-invasive brain stimulation (NIBS) as the technique of choice for producing plastic changes in the brain, and as a research tool for testing hypotheses about how motor and cognitive functions are performed and how cerebro–cerebellar circuits subserve these operations
(2) NIBS could be used as an adjunct to other types of therapy (e.g., cognitive rehabilitation therapy (CRT) or cognitive behavioral therapy (CBT)), improving their therapeutic efficacy when treating the decline of cerebellar cognitive functions
Summary
Clinicians have been directly exciting the cerebellar cortex with implanted electrodes in epileptic patients and in those with schizophrenia and depression since the 1970s with good therapeutic results [1], demonstrating the use of constant electrical stimulation for the treatment of behavioral disorders and epilepsy. Transcranial brain stimulation techniques [often referred to as non-invasive brain stimulation (NIBS)], such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), are realized to have the capacity to systematically modify behavior by inducing lasting changes in underlying brain functions, and are useful approaches to studying brain–behavior relationships in healthy participants. They have been used to study mechanisms of cortical plasticity, and both techniques have been implicated as therapeutic tools for the treatment of motor and cognitive deficits in patients after stroke, and in cerebellar disease [2, 3]. Cathodal stimulation has an opposite effect, i.e., dis-inhibition of the cerebral cortex by www.frontiersin.org
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