Using classical evoked-potential techniques and 100-micron deflections of one vibrissa, at least three loci of potentials were identified in cats' cortices. 2. The relationships of these loci to cortical landmarks and to each other varied sufficiently to prevent specification of homologies between animals. 3. Attempts to differentiate the loci on functional criteria were unsuccessful. The areal extent of each locus appeared similar and there was evidence of a specific somatotopic pattern within each locus; in each locus different vibrissae were represented at different cortical points. 4. Latencies differed slightly between the loci, being shortest at the most rostral site and longest at the caudal site. In all loci, off-center latencies were longer, but this difference was detected only after complete maps of all three loci were produced. 5. The focus of potentials for an individual vibrissa was radically different, depending on the parameter measured (negative peak, positive peak, and latency). The focus of potentials could also be shifted by changing the velocity or direction of the stimulus. 6. The effects of these stimulus parameters on the cortical map suggest that a cortical focus represents more than simply a point on the skin surface.
