The data show that light stimulation generate an outward current associate with an increase of membrane resistance. It should be noted a reduction of spontaneous EPSC by light stimulation. To determine whether light action on MC are exclusively due to a reduction of excitatory synaptic transmission impinging on the recorded MC the experiment were reproduced in the presence of glutamatergic antagonists (NBQX 10 µM et APV 50 µM). Such condition did not prevent the effect produced by light stimulation.