Effects of somatosensory stimulation on corticomotor excitability in patients with unilateral cerebellar infarcts and healthy subjects - preliminary results.
BACKGROUND
In healthy humans, somatosensory stimulation in the form of 2 h-repetitive peripheral afferent nerve stimulation (SS) increases excitability of the contralateral motor cortex. In this preliminary study, we explored effects of SS on excitability to transcranial magnetic stimulation (TMS) in patients with unilateral cerebellar infarcts and age-matched controls.


METHODS
Ten patients with infarcts in one cerebellar hemisphere and six age-matched controls participated in the study. Each subject participated in one session of active, and one session of sham SS delivered to the median nerve ipsilateral to the cerebellar infarct in patients, and to the homologous nerve in controls. Before and after each session, the following TMS measures were performed: resting motor threshold (rMT), motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and short-interval intracortical facilitation (SICF). Amplitudes of motor evoked potentials were normalized to amplitudes of supramaximal M responses (MEP/M ratios).


RESULTS
In the control group, there was a significant increase in rMT, and a significant increase in MEP/M ratios after active, but not after sham SS. There were no significant differences in rMT or MEP/M ratios in the group of patients after active or sham SS. There were no significant differences in SICI or SICF after active or sham SS in either group.


CONCLUSIONS
Consistent with results reported in rodents, these preliminary findings suggest for the first time in humans, that normal cerebellar activity is required so that SS can modulate excitability of the sensorimotor cortex.
Hospital das Clínicas/São Paulo University, São Paulo, Brazil ; Hospital São Rafael, Salvador, Brazil ; Rua Waldemar Falcão n 1547 ap 1201 Horto Florestal 40.295-010, Salvador, Bahia Brazil.
Suzete Nascimento
SN
Farias da Guarda
Hospital das Clínicas/São Paulo University, São Paulo, Brazil ; Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil.
Adriana Bastos
AB
Conforto
Somatosensory stimulation; Stroke; Transcranial magnetic stimulation