Cerebellar cTBS Research Articles

Study of Cerebello-Thalamocortical Pathway by Transcranial Magnetic Stimulation in Parkinson's Disease

BackgroundAlthough functional changes in the activation of the cerebellum in Parkinson's disease (PD) patients have been consistently described, it is still debated whether such altered cerebellar activation is a natural consequence of PD pathophysiology or rather it involves compensatory mechanisms. Objective/HypothesisWe used different forms of cerebellar transcranial magnetic stimulation to evaluate the hypothesis that altered cerebello-cortical interactions can be observed in PD patients and to evaluate the role of dopaminergic treatment. MethodsWe studied the effects of a single cerebellar magnetic pulse over the excitability of the contralateral primary motor cortex tested with motor-evoked potentials (MEPs) (cerebellar-brain inhibition—CBI) in a group of 16 PD patients with (ON) and without dopaminergic treatment (OFF), and in 16 age-matched healthy controls. Moreover, we also tested the effects of cerebellar continuous theta-burst stimulation (cTBS) on MEP amplitude, short intracortical inhibition (SICI) and short intracortical facilitation (SICF) tested in the contralateral M1 in 13 PD patients in ON and OFF and in 16 age-matched healthy controls. ResultsCBI was evident in controls but not in PD patients, even when tested in both ON and OFF conditions. Similarly, cerebellar cTBS reduced MEP amplitude and SICI in controls but not in PD patients under any condition. Conclusion(s)These results demonstrate that PD patients have deficient short-latency and long-lasting cerebellar-thalamocortical inhibitory interactions that cannot be promptly restored by standard dopaminergic medication.

Cerebellar theta burst stimulation modulates short latency afferent inhibition in Alzheimer's disease patients

The dysfunction of cholinergic neurons is a typical hallmark in Alzheimer's disease (AD). Previous findings demonstrated that high density of cholinergic receptors is found in the thalamus and the cerebellum compared with the cerebral cortex and the hippocampus. We aimed at investigating whether activation of the cerebello-thalamo-cortical pathway by means of cerebellar theta burst stimulation (TBS) could modulate central cholinergic functions evaluated in vivo by using the neurophysiological determination of Short-Latency Afferent Inhibition (SLAI). We tested the SLAI circuit before and after administration of cerebellar continuous TBS (cTBS) in 12 AD patients and in 12 healthy age-matched control subjects (HS). We also investigated potential changes of intracortical circuits of the contralateral primary motor cortex (M1) by assessing short intracortical inhibition (SICI) and intracortical facilitation (ICF). SLAI was decreased in AD patients compared to HS. Cerebellar cTBS partially restored SLAI in AD patients at later inter-stimulus intervals (ISIs), but did not modify SLAI in HS. SICI and ICF did not differ in the two groups and were not modulated by cerebellar cTBS. These results demonstrate that cerebellar magnetic stimulation is likely to affect mechanisms of cortical cholinergic activity, suggesting that the cerebellum may have a direct influence on the cholinergic dysfunction in AD.

Cerebellar theta burst stimulation impairs eyeblink classical conditioning

Theta burst stimulation (TBS) protocols of repetitive transcranial magnetic stimulation (rTMS) have after-effects on excitability of motor areas thought to be due to LTP- and LTD-like processes at cortical synapses. The present experiments ask whether, despite the low intensities of stimulation used and the anatomy of the posterior fossa, TBS can also influence the cerebellum. Acquisition and retention of eyeblink classical conditioning (EBCC) was examined in 30 healthy volunteers after continuous theta burst stimulation (cTBS) over the right cerebellar hemisphere. In subjects who received cerebellar cTBS, conditioned responses were fewer and their onsets were earlier (in the last half of the acquisition blocks) than those from control subjects. There was, however, no effect of cerebellar cTBS on the re-acquisition of EBCC in another session of EBCC 7–10 days later. There was also no effect of cerebellar cTBS on the re-acquisition of EBCC in subjects not naïve to EBCC when the stimulation was delivered immediately before a re-acquisition session. Control experiments verified that suppressive effects of cTBS on EBCC were not due to changes in motor cortical excitability or sensory disturbance caused by cTBS. Based on previous EBCC studies in various cerebellar pathologies, our data are compatible with the hypothesis that cerebellar cTBS has a focal cerebellar cortical effect, and are broadly in line with data from studies of EBCC in various animal models. These results confirm that cerebellar TBS has measurable effects on the function of the cerebellum, and indicate it is a useful non-invasive technique with which to explore cerebellar physiology and function in humans.

Metabolic changes induced by theta burst stimulation of the cerebellum in dyskinetic Parkinson’s disease patients

Background Cerebellar repetitive transcranial magnetic stimulation may be effective in reducing peak-dose levodopa induced dyskinesia in Parkinson’s disease patients. It was proposed that the antidyskinetic effect could be due to modulation of cerebello-thalamo-cortical pathways. However the neural basis for these clinical effects have not yet been demonstrated. Methods We investigated the effects of repeated sessions of cerebellar continuous theta burst stimulation in Parkinson’s disease patients with levodopa induced dyskinesia on brain metabolism by means of positron emission tomography scan with fluorodeoxyglucose ( 18F-FDG) to characterize the specific cerebral network activated by cerebellar stimulation in these patients. Results We found that five days of bilateral cerebellar continuous theta burst stimulation (cTBS) were effective in reducing levodopa induced dyskinesia. Clinical changes were paralleled by a reduction of 18F-FDG metabolism in the cerebellum as revealed by positron emission tomography imaging. We found a global decrease in the metabolism of the bilateral cerebellar hemispheres, and a significant decrease in 18F-FDG uptake in correspondence of bilateral dentate nucleus. Conclusions Our study demonstrates the antidyskinetic effect of cerebellar cTBS in Parkinson’s disease patients with levodopa induced dyskinesia, is paralleled by modulation of the activity of the pathways connecting the cerebellar cortex with the deep cerebellar nuclei, confirming the hypothesis that the motor cerebellar circuit is involved in the generations of levodopa induced dyskinesia.