Symmetrical Epileptogenic Foci in Monkey Cerebral Cortex

Abstract

WE HAVE previously reported the results of a series of experiments in the cat concerning the interaction of acute relatively large bilateral epileptogenic foci in homologous areas of cerebral cortex1,2 (predominantly posterior sigmoid and suprasylvian gyri). In the intact animal, this interaction often resulted in the rapid production of persistent synchronous and symmetrical patterns of bilateral discharge including 21/2 to 31/2 cycles per second (cps) spike-slow wave complexes. Relevant behavioral concomitants of these bilateral discharges resembled some of the clinical phenomena observed in patients with idiopathic petit mal or grand mal seizures during similar bilater-$ al discharges: bilateral facial muscle and forelimb myoclonus, transient suspension or imperfect continuation of a repetitive act, and occasional generalized convulsive seizures.Investigations of the underlying anatomical pathways involved in this interaction of bilateral cortical foci indicated the significant role of the corpus callosum. Synchrony of bilateral discharge failed to occur after total section of corpus callosum. On the other hand, depth recordings indicated little involvement of medial thalamic structures.Moreover, the production of bilateral foci in preparations in whom all diencephalic, ros¬ tral mesencephalic, and most of dorsal hippocampal structures had been ablated did result in these synchronous patterns of bilat¬ eral discharge. A similar interaction occurred in preparations in which large bilateral blocks of cerebral cortex had been isolated from subcortical structures but remained connected by the corpus callosum.From a clinical standpoint, it is evident that the bilateral discharges of the patient with petit mal seizures are not equally dis¬ tributed throughout all recording areas over¬ lying cerebral cortex. Thus the "larval" bi¬ lateral discharges of spike and slow waves occur most prominently in frontal central areas.3 From an anatomical standpoint, it is evident that any conclusions based on the cat brain may not be entirely applicable to all areas of human cerebral cortex in view of (1) the marked evolution of neocortical areas.3 From an anatomical standpoint, it is evident that any conclusions based on the cat brain may not be entirely applicable to all areas of human cerebral cortex in view of (1) the marked evolution of neocortical areas, particularly frontal lobes in the pri¬ mates, (2) phylogenetic differences in callosal, cortical, and subcortical projections pathways of various neocortical areas,46 and (3) the regional differences in density of callosal pathways which occur in primates.5

Effect of Anterior Callosotomy on Bilaterally Synchronous Spike and Wave and Other EEG Discharges

“…Results observed were similar to those of experimental animal studies (Marcus and Watson, 1967;Marcus et al, 1968;Mutani et al, 1973;Musgrave and Gloor, 1980): partial disruption of synchrony as well as decrease in amount of generalized bilaterally synchronous spike and wave or sharp and slow wave discharges (GSW). Our results support these findings.…”

“…Experimental studies show that synchronization of generalized bilateral spike and wave discharges is mediated through the corpus callosum (Erickson, 1940;Marcus et al, 1968;Marcus and Watson, 1967;Mutani et al, 1973;Musgrave and Gloor, 1980). Callosotomy was developed to disrupt bilateral synchronization of epileptic discharges and thus reduce the severity of epileptic manifestations (Van Wagenen and Herren, 1940).…”

An Experimental Model of Some Varieties of Petit Mai Epilepsy Electrical‐Behavioral Correlations of Acute Bilateral Epileptogenic Foci in Cerebral Cortex

“…In our earlier experiments in the cat, topical strychnine, topical pentylenetetrazol (Metrazol), topical conjugated estrogens (Premarin) or bilateral freezing foci were employed (20)(21)(22). In all of our recent experiments in the monkey, we have employed epileptogenic lesions produced by the application of 1 conjugated estrogen to 10 x 6 mm rectangles of filter paper (23,24).…”

“…In the monkey, significant regional variations in the capacity for bilateral synchronous discharge were apparent (23,24). These variations were related to regional cortical differences in callosal projection and in capacity for local and propagated after discharge.…”

Focal Rhythmic EEG Slowing with Temporal Lobe Tumors

“…It has been shown in animals [12,13] that the cerebral cortex, surgi cally isolated from all deep structures except callosal connection with the opposite side, is capable of producing spikes, slow waves and spike-wave complexes. Presumably, some of the slowing and sharp activity near brain tumors has a similar origin.…”