A PERMANENT CHANGE IN BRAIN FUNCTION RESULTING FROM DAILY ELECTRICAL STIMULATION

Brief bursts of nonpolarizing electrical brain stimulation were presented once each day at constant intensity. At first the stimulation had little effect on behavior and did not cause electrographic afterdischarge. With repetition the response to stimulation progressively changed to include localized seizure discharge, behavioral automatisms and, eventually, bilateral clonic convulsions. Thereafter, the animal responded to each daily burst of stimulation with a complete convulsion. The effect was obtained from bipolar stimulation of loci associated with the limbic system, but not from stimulation of many other regions of the brain. Parametric studies and control observations revealed that the effect was due to electrical activation and not to tissue damage, poison, edema, or gliosis. The changes in brain function were shown to be both permanent and trans-synaptic in nature. Massed-trial stimulation, with short inter-burst intervals, rarely led to convulsions. The number of stimulation trials necessary to elicit the first convulsion decreased as the interval between trials approached 24 hours. Further increase in the inter-trial interval had little effect on the number of trials to first convulsion. High-intensity stimulation studies revealed that the development of convulsions was not based simply on threshold reduction, but involved complex reorganization of function. Experiments with two electrodes in separate parts of the limbic system revealed that previously established convulsions could facilitate the establishment of a second convulsive focus, but that the establishment of this second convulsive focus partially suppressed the otherwise permanent convulsive properties of the original focus. © 1969.