POLARIZATION OF THE HUMAN MOTOR CORTEX THROUGH THE SCALP

DIRECT currents (DC) applied directly to central nervous system struct ures produce substantial and longlasting effects in animal experiments . We tested the functional effects of very weak scalp DC (< 0.5 mA, 7 s) on the human motor cortex by assessing the changes in motor potenti als evoked by transcranial magnetic brain stimulation. We performed fo ur different experiments in 15 healthy volunteers. Our findings led to the conclusion that such weak (< 0.5 mA) anodal scalp DC, alternated with a cathodal DC, significantly depresses the excitability of the hu man motor cortex, providing evidence that a small electric field cross es the skull and influences the brain. A possible mechanism of action of scalp DC is the hyperpolarization of the superficial excitatory int erneurones in the human motor cortex. Neuro Report 9: 2257-2260 (C) 19 98 Rapid Science Ltd.