Abstract
1. The cortical response to electrical stimulation applied to the cortical surface was investigated in the rabbit with particular attention to its regional difference. Three types of response corresponding to cortical areas were distinguished.
2. The first type of response consisted of a surface-positive potential of 5-10 msec. duration followed by a surface-negative one. On the positive potential were superimposed two positive spikes and a sequence of three inflections. The distribution of the response was limited to area striata of Rose.
3. The second type consisted of a surface-positive potential of 3-5 msec. duration followed by a surface-negative one. The surface-positive potential was preceded by one or two positive spikes. The distribution of the response extended over regio postcentralis and regio parietalis of Rose.
4. The third type consisted of a simple surface-negative potential of 5-10 mesc. duration. It was distributed over regio praecentralis and area retrosplenialis granularis dorsalis of Rose.
5. The potentials of these three types changed in amplitude as well as in form according to intensities of stimulation, but could be distinguished from one another above a certain level of intensity.
6. A pick-up needle electrode was inserted into various layers of the cortex to record responses at different depths. Positive and negative deflections and positive spikes of the first and the second types of response reversed in sign at a certain depth characteristic of each. The sign reversal of the positive spikes took place in deeper layers than that of the positive deflection, and the layer in which the negative deflection reversed was found deepest. Before the sign reversal of the positive deflection took place, a marked phase shift was observed in the first type, but not in the second type. With the third type any conventional sign reversal could not be observed in most cases.
