Functional Boundaries in the Sensori-Motor Cortex of the Monkey. ∗

Abstract

The method of local strychninization of the cerebral cortex of the monkey has already established the existence of functional boundaries between the major subdivisions of the sensori-motor cortex, so far as sensation is concerned.

Further study of the problem by the same method, supplemented by recording the action potentials of the cortex, has confirmed the existence of functional boundaries on the “sensory” side and established the existence: of such boundaries on the “motor” side.

Strychnine applied locally to any region of the cortex induces in that region typical changes of the “spontaneous” action potentials, notably the appearance of “strychnine-spikes”. Though the structural dissimilarity of the various cortical regions precludes the attribution of these spikes to any one specific structural element in the cortex, the, distribution of the spikes over the cortex differs with difference in architectonic structure of the regions strychninized.

Local strychninization of any one or two square millimeters of area 4 of any subdivision of the sensori-motor cortex “fires” the whole of area 4 of this subdivision and also its postcentral portion. Outside this subdivision no spikes appear.

This is evidenced by the accompanying figure obtained before and after strychninization of one square millimeter of arm area 4.

Since the action potentials were taken from arm area 4 at a place as far removed as possible (12 mm.) from the locus of strychninization, the figure illustrates the occurrence of spikes throughout this area. Although the electrodes on the face area were only 2 mm. from those on the arm area, no spikes appear in the record from the face area; and although the electrodes on the leg area were only 2 mm. from the locus of strychninization in the arm area, no spikes appear in the record from the leg area.