The cortical response to direct stimulation of the corpus callosum in the cat

The cortical response to direct stimulation of the corpus callosum consists of a brief surface-positive spike which originates deep in the cortex, followed by a slower positive-negative wave sequence which derives from structures extending to varying depths of cortex. The spike is assigned to dromic and antidromic axonal and possibly cell body discharge. The wave sequence is assumed to represent predominantly a response propagated upward along apical dendrites. The excitability cycle, strychnine spike driving, and post-tetanic potentiation phenomena are described, and the direct callosal response is compared with that elicited by homatotopic cortical stimulation. The antidromic callosal response is described in preparations in which dromic fibers had previously been allowed to degenerate. The response is remarkably similar to the normal mixed dromic and antidromic response, and it is inferred that the latter may be mediated synaptically via retrograde axonal collaterals. The interpretation of potential reversal in the cortical volume conductor is considered in relation to the probable anatomical substrate of the callosal response.