OPTICAL IMAGING OF RAT SOMATOSENSORY CORTEX REVEALS REPRESENTATIONAL OVERLAP AS TOPOGRAPHIC PRINCIPLE

WE measured reflectance changes by means of optical imaging of intrins ic signals to study the topography of the paw representations in rat s omatosensory cortex. Following circumscribed tactile stimulation of si ngle digits or pads, we found large and partially overlapping areas of reflectance changes (Delta R). The diameters of their focal zones def ined at 75% maximal Delta R were in the range of 150 mu m and preserve d all details of the underlying maps. Zones of overlap were in the ran ge 15-25% measured at half-maximal Delta R. In contrast, we found shar p boundaries with no overlap between the fore- and hindpaw representat ions. The data suggest that large and overlapping cortical maps consti tute a normal type of neural representation supporting the idea of a d istributed neural processing scheme.