Geometry and orientation of thalamocortical arborizations in the cat somatosensory cortex as revealed by computer reconstruction.

The geometry of the intracortical arborization of single neurons from the ventroposterolateral thalamic nucleus in cat was studied with computer reconstruction after intraaxonal injections of horseradish peroxidase in fibers whose receptive field had been identified. The terminal arbors of slowly (SA) and rapidly (RA) adapting thalamocortical neurons were often (60%) composed of two separated bushes of 300-600 microns in diameter separated by a region of about the same size containing much less terminal ramifications. The bushes were aligned mainly along the mediolateral axis of the brain. It is proposed that this structural feature underlies the RA-SA banding already described in the somatosensory areas by physiological experiments.