Horizontal Intracortical Organization in the Cerebral Control of Limb Movement. ∗

Abstract

It has been widely assumed in theories of brain function that horizontal spread of excitations through the cortex is an important factor in cerebral integration. Not only the irradiation of discrete neural impulses through the fiber feltwork of the cortex, but also the mass conduction of intercellular electrical currents and potentials and the establishment of patterns of “field forces” spreading across the cortex have been presumed to play integrative roles of utmost importance in cerebral organization. The following experiments, however, undertaken to test the influence of such horizontal intracortical organization in the control of limb coordination have failed to demonstrate the existence of any major organizing influence of the sort. Lesions in the cortical arm areas of the monkey (Macaca mulatta) designed to disrupt any patterns of horizontal intracortical conduction either of discrete excitations or of mass electrical currents were found to cause only a slight, almost negligible, interference with motor coordination.

The lesions consisted of intersecting transverse and longitudinal cuts at intervals of about 2.4 mm made subpially with a thin knife and extending roughly through the depth of the cortex to the underlying medulla. Because the cuts filled immediately with blood, the effect of the operation was to partition the cortex by numerous vertical walls of clotted blood of about 0.08 mm thickness. The cuts interrupted the horizontal transmission of excitations through the cortex itself, but left intact the axon interconnections looping downward through the white matter. These incisions were placed throughout the exposed surface of the cortical arm region including areas 6, 4s, 4, 1, 2, 5, and 7 as represented on architectonic charts with some overlap into the neighboring trunk, leg, and face areas. As a control of the effects of these incisions the corresponding cortical area was destroyed completely by excision in other animals.