Commissural projections of the cortical hand motor area in monkeys

The topographical organization of the contralateral cortical projections of the motor hand area was studied with autoradiographic methods in 11 macaque monkeys. Two general observations were noted in the material studied. (1) The commissural cortico-cortical connections of the motor hand area were directed to the contralateral precentral gyrus. The projections were preferentially directed to both homotopic and non-homotopic areas. (2) Focally labeled areas of motor cortex (diameter 900 micrometers) gave rise to individual terminal columns of label (diameter 600-900 micrometers). Larger areas of labeled motor cortex, (3,000 micrometers in diameter) gave rise to contralateral terminal bands of label. These bands (600-1,000 micrometers in width) were oriented in an antero-posterior direction and appeared to be formed by a sequence of adjacent labeled columns.