Penfield formulated the concept of the “central-encephalic system” and “central-encephalic epilepsy”: the central-encephalic system is localized in the oral regions of the brain stem, includes the ascending reticular formation of this area and is a system responsible for the highest level of neuronal integration.
According to the hypothesis put forward by Penfield & Jasper, in case of primary-generalized epilepsy, the epileptogenic focus is localized in the central-encephalic system. The discharge, appearing here, is instantly generalized, spreading bilaterally and synchronously to both hemispheres. According to the authors, the beginning of the discharge from the central-encephalic system explains many clinical phenomena of primary-generalized epilepsy and, in particular, simultaneous instantaneous deactivation of consciousness and bilateral convulsive phenomena.
With the discovery of the neurotransmitter system, it was shown that stimulation of the midbrain reticular formation leads to the activation or inhibition of a number of neurotransmitters involved in epileptogenesis. In this regard, it is possible that the central-encephalic system influences the occurrence of seizures and the level of consciousness indirectly through the system of mr-amines, primarily GABA.
Doose, Avoli, Gloor developed the concept of cortico-reticular, and then talamo-cortical epilepsy. Experimental studies have discovered the existence of a special conductive thalamo-cortical system in the intralaminar region of the thalamus, which they called the “recruiting system”. The irritation of this system in experimental animals led to a very wide spread of excitation in both hemispheres of the brain.
Using the penicillin model of generalized epilepsy, Avoli and Gloor (1994) recorded the electrical activity of the brain under conditions of sequential switching off of the thalamus and forebrain. When the thalamus was irritated in decorticated animals, no peak-wave activity was obtained. Also, epi-activity was not observed during stimulation of the forebrain under conditions of thalamus inactivation by injection of KC1.
Only in intact animals, while preserving the structure and function of both the forebrain and the thalamus, was it possible to reproduce the typical generalized peak-wave activity of 3 Hz during penicillin application. Thus, it was convincingly proved that an integrative system consisting of the cerebral cortex and the thalamus is involved in the occurrence of generalized 3 Hz activity. The question of what is primary in the process of generating this activity remains open to the present.
According to the cortico-thalamic concept, the discharge that occurs primarily in the cortex extends to the intralaminar nucleus of the thalamus through the “recruiting system” with subsequent instantaneous involvement both bilateral and synchronous of both hemispheres. Experimental and clinical (during neurosurgical operations) studies by a number of authors also showed an important role in the generalization of the epileptic discharge of such structures of the central nervous system as the cingulate gyrus, orbitofrontal cortex, amygdalo-hippocampal complex, black substation.
As noted above, the peak-wave complex reflects two processes: a peak is an epileptic excitation, a slow wave is an inhibitory anti-epileptic mechanism. V.A. Karlov, V.V. Gnezditsky (2003), when mapping the EEG and studying the brain activity caused by the method of multi-step dipole localization, showed a separate localization of the peak and a slow wave, and the absolute prevalence of peak localization during absance epilepsy in the mediobasal regions of the frontal and temporal regions was proved.
Thus, the concept of focal origin at least in part of generalized epilepsy is currently being confirmed. In generalized epilepsy, the discharge is a consequence of the instantaneous synchronization of the paroxysmal depolarization shift of epileptic neurons.