rTMS over the cerebellum modulates temperature detection and pain thresholds through peripheral mechanisms

Repetitive transcranial magnetic stimulation (rTMS) of motor and prefrontal cortex has been shown to modulate pain perception. Even though evidence suggests an involvement of cerebellar structures in pain processing, the effect of rTMS over the cerebellum on pain perception has not yet been investigated.

This study aimed to test the effects of rTMS over the cerebellum on sensory perception, particularly controlling for peripheral stimulation effects.

Sensory perception was determined as temperature detection and temperature pain thresholds. Experiment one explored the effects of four different rTMS protocols (flat figure-of-eight coil; 120% motor resting threshold; 1000 stimuli; 1 Hz and 10 Hz; medial and right lateral cerebellum) on sensory thresholds in 10 healthy volunteers using pairwise comparisons. The most efficient protocol of experiment one was compared in a second experiment with two control conditions (rTMS with a sham coil over the cerebellum [sham] and repetitive magnetic stimulation [rMS] of the neck) by using robust statistics (MANOVA).

The first experiment demonstrated pronounced effects on sensory perception for 1Hz rTMS over the lateral cerebellum. The second experiment confirmed this result in comparison to sham. However, rMS over the neck had a similar effect like rTMS over the cerebellum.

Our findings suggest that changes in sensory perception after rTMS over the cerebellum are largely due to stimulation effects on peripheral structures and support recent reports of analgesic effects of neck rMS. They advocate the critical review of the proposed analgesic effects of rTMS and encourage the future use of proper control conditions in rTMS research.