Modulatory effects of 1 Hz rTMS over the cerebellum on motor cortex excitability

Abstract

Clinical observations and data from animal experiments point to a physiological facilitatory influence of the deep cerebellar structures on the motor system through the cerebello-thalamo-cortical pathways. The aim of the present study was to explore the long-term effects of low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) over the cerebellum on short intracortical inhibition (SICI) and facilitation (ICF) of the motor cortex in normal subjects. Eight healthy subjects (mean age 26.9 +/- 3.1) underwent 1 Hz frequency rTMS delivered on the right cerebellar hemisphere. Before and after cerebellar rTMS, SICI and ICF were assessed in the motor cortex contralateral to the stimulated cerebellar hemisphere by means of a paired pulse paradigm with a conditioning subthreshold stimulus set to 80% of the motor threshold (MT) followed by a testing stimulus at 120% of MT intensity. Five different interstimulus intervals (ISIs) were used to assess SICI (2 and 4 ms) and ICF (7, 10 and 15 ms). Amplitude of the responses was expressed as the percentage of motor evoked potential (MEP) to test stimulus alone. Results showed a significant decrease of ICF at 10 ms ISI that persisted up to 20 min after cerebellar rTMS. This was the only significant modulatory effect of cerebellar stimulation on intracortical motor excitability A suppressive effect of the low-frequency TMS on Purkinje cells could be supposed, even if, the lack of effects on other facilitatory ISIs, stands for more complex modulatory effects of rTMS over cerebellum. The study is a further demonstration that rTMS over the cerebellum induces a long-lasting modulatory effect on the excitability of the interconnected motor area.

Cerebellar transcranial static magnetic field stimulation transiently reduces cerebellar brain inhibition

“…tSMS over the cerebellum, during which the stimulus intensity may have been 0.1-0.2 Tesla, did not affect the excitability of the contralateral motor cortex, and the duration of the aftereffect was very short in this study. On the other hand, delivering 1-Hz rTMS with an intensity of approximately 1 Tesla to the contralateral cerebellum can inhibit the excitability of the contralateral motor cortex and the effect can reportedly continue for over 20 min (Fierro et al, 2007). On the basis of these findings, we speculate that the ability of the stimulation to affect the excitability of the contralateral motor cortex, as well as the duration of the effect, may be related to the type of magnetic field, for instance, a static or varying magnetic field, or the strength of the magnetic field.…”

“…Thus, we tested this hypothesis by examining the CBI before and after applying tSMS over the cerebellum. Previous studies have shown that rTMS over the cerebellum modulates CBI (Celnik, 2015) and the excitability of the contralateral M1 (Oliveri et al, 2005;Fierro et al, 2007;Popa et al, 2010). Thus, if the excitability of the cerebellum is changed by tSMS, the excitability of the contralateral M1 may be modulated by applying tSMS over the cerebellum.…”

Physical Therapy for Cerebellar Ataxia

“…Furthermore, the NIBS to the cerebellum modulates cerebellar excitability [98,[129][130][131], motor function [132,133], and motor learning [32,[134][135][136][137][138] in healthy population. In patients with cerebellar ataxia, some previous studies reported about the effect of tDCS to the cerebellum on motor function [131,[139][140][141].…”

Transcranial Magnetic Stimulation of the Cerebellum

“…The effect lasted for up to 30 min afterwards. Fierro et al 43 (8 healthy subjects) explored the long-term effects of low frequency rTMS over the right cerebellum with 900 pulses at 1 Hz. Before and after cerebellar rTMS, SICI and ICF were assessed in the left motor cortex by a paired pulse paradigm (ISI 2-15 ms).…”