Experimental design.

<p>We imaged the VSD signals from the somatosensory cortex of one hemisphere of the rat in response to electrical stimulation of the paws. To image the VSD signals, the light was band-pass filtered at 632 nm by an excitation filter (ExF) and reflected toward the cortex by a 650 nm dichroic mirror (DM). The emitted fluorescence was transmitted through the dichroic mirror, subsequently long-pass filtered at 665 nm by an emission filter (EmF), and finally imaged using a MICAM ULTIMA-L system composed by a high-speed camera and a corresponding processor unit (BrainVision Inc.). A 5-mm×5-mm cortical area was imaged, as schematically represented at the bottom. The black lines delimit the forepaw and hindpaw regions in the somatotopic map of the rat primary somatosensory cortex.