Somatosensory inputs modulate the excitability of cerebellar-cortical interaction.

OBJECTIVE

Transcranial magnetic stimulation (TMS) delivered over the cerebellum 5-7 ms prior to a stimulus over the contralateral primary motor cortex (M1) reduces the excitability of M1 output, a phenomenon termed cerebellar brain inhibition (CBI). The cerebellum receives sensory information for adaptive motor coordination and motor planning. Here, we explored through TMS whether a peripheral electrical stimulus modulates CBI.

METHODS

We studied the effect of right median nerve electrical stimulation (ES) on CBI from right cerebellum (conditioning stimulus, CS) to left M1 (test stimulus, TS) in 12 healthy subjects. The following ES-CS inter-stimulus intervals (ISIs) were tested: 25, 30 and 35 ms. CS-TS ISI was set at 5 ms.

RESULTS

We found significantly weaker CBI when the ES was delivered 25 ms (p < 0.001) and 35 ms (p < 0.001) earlier the CS over the ipsilateral cerebellum and a trend for 30 ms ES-CS ISI (p = 0.07).

CONCLUSIONS

We hypothesize that the activation of cerebellar interneurons together with intrinsic properties of Purkinje cells may be responsible of the decreased CBI when the peripheral stimulation preceded the cerebellar stimulation of 25 and 35 ms.

SIGNIFICANCE

To test the interaction between somatosensory inputs and cerebello-cortical pathway may be important in a variety of motor tasks and neuropsychiatric disorders.