Demonstration of discrete place‐defined columns—segregates—in the cat SI

The SI forelimb area of cats was examined with receptive field (RF) mapping techniques. Arrays of closely spaced, near‐radial microelectrode penetrations were inserted into the crown of postsigmoid gyrus of ketamine anesthetized subjects and minimal RFs were obtained at several depths. The minimal RF was defined as the skin site providing the strongest input to each recorded cluster of neurons. Data analysis showed that all studied cortical territories contained groups of discrete cortical columns, 300–400 μm in diameter. The columns were regarded as topographic entities because no change in minimal RF location could be observed within their boundaries. The boundaries of columns were sharp and could be unequivocally distinguished because the minimal RFs sampled on opposite sides of a boundary occupied displaced, nonoverlapping positions.