ON THE PAROXYSMAL CEREBROCORTICAL DISCHARGES EVOKED BY REPETITIVE ELECTRICAL STIMULATION ON THE LATERAL GENICULATE BODY

Abstract

SummaryThe following are the results of an investigation on the brain potential changes simultaneously led from various cortical areas and the stimulated portion of the rabbits under light Dial‐urethane anesthesia, to whose lateral geniculate body a repetitive electrical stimulation was given.1. When a repetitive electrical stimulation is given to the dorsal nucleus of lateral geniculate body, either diphasic or tri‐phasic evoked potentials appear exclusively in the ipilateral visual area. If the stimulation is continued, either marked decline of the evoked potentials or the irregularity of the wave form is observed as the result. The cessation of the stimulation in this period causes the appearance of marked paroxysmal abnormal discharges with long duration following the stimulation.2. These discharges are the succession of α rhythm spikes of 8–13 cycles indifferent to the rhythm of the stimulation. The spikes are mostly of positive phase, and the potential gradually increases until it shows 0.5–2 mV. Then the discharges are usually followed by a low potential period, and the discharges in this period are limited to the ipsilateral visual cortex under optimal stimulation.3. The appearance of the discharges being strongly influenced by anesthetic as well as conditions of stimulation, deep anesthesia falls to show the discharges. The best condition for the discharge appearance with Dial‐urethane anesthesia is 10–30 V potential, 10–15 cycle frequency and 0.5 msec pulse duration.4. The portion to be stimulated best fitted for evoking the discharges are the dorsal nucleus of lateral geniculate body and the fibers involved in its cortical projection. No discharge of this type can be obtained from the ventral nucleus or preganglionic fibers.5. The parosyamal discharges are. classified under two types as to the mode of appearance and three types as to the mode of termination.6. A detailed estimination about the cortical portion with discharge appearance dixloses the possibility of an area slightly wider than regio striata, which is considered to be the visual cortex, including, ipsilaterally, the lateral part of regio retrosplenialis granuJiris, 3 and 4 of regio parietalis, and the junction between these and regio striata and, contralaterslly, the anterior lateral part of regio striata. In the latter instance, there appear some paroxysmal discharges of low potential with irregular spikes and mostly negative in phase, in‐as‐much different from that of the ipsilateral discharges.7. When either the stimulation is strong enough or the cortical excitation is accentuated, the discharge appearance is not limited to these areas, but they spread to the occipital, parietal and then to the frontal areas through the ipisilatteral cortex. Occasionally the march further extends to the contralateral areas. advancing in the same order as in the ipsihteral side. Such paroxysmal wave spread is usually preceded by the decline of the spontaneous braves.8. Although the proxysmal abnormal discharges appear not only in the ipsilateral visual areas but also in the dorsal nucleus of the lateral geniculnte body, itself respesenting stimulated portion, those of the lateral geniculate body trike place not always synchronous with those of the cortex.9. As to the process of the cortical response to the repetitive electrical stimulation there appear some diphasic belated discharges independent of the evoked potentials as the forerunner of the parosysmal discharges.10. We obtained some experimental data sufficiently secure in bringing up the conviction that the said pairoxysmal discharges are a phenomenon due to the electric resonance played in the reverberating circuit.