Cognitive Deficit Related to Seizure Pattern in Centrencephalic Epilepsy.

The identifying characteristics of the electroencephalogram in centrencephalic epilepsy have been outlined by Penfield and Jasper (1954) as including a bilaterally synchronous onset of abnormality which consists of wave-and-spike activity at or near a frequency of 3 per second. This is in contrast to the E.E.G. abnormality seen in cases of focal cortical epilepsy in which sharp waves predominate, begin in a restricted area, and spread either slowly or not at all to other parts of the brain. The seizures in these two types of epilepsy also differ, the centrencephalic seizures including 'absence' attacks, myoclonic jerks, akinetic attacks, and major seizures, while the attacks in focal cortical epilepsy vary with the location of the focus. In the case of focal discharge, the E.E.G. abnormality is of course assumed to originate from this focus. In the centrencephalic type of epilepsy, however, the bilaterally synchronous onset of E.E.G. abnormality led Jasper and Kershman (1941) to believe that the origin here was in some subcortical region which had widespread connexions with cortical areas so that it could act as pacemaker for the entire cortex. This interpretation was given strong support by an experimental study in the cat, in which stimulation of a small area in the medial thalamus evoked widespread bilaterally synchronous 3 per second spike-and-wave activity in the cortex (Jasper and Fortuyn, 1947). Williams (1953), recording from children with petit mal attacks, confirmed the important role of the thalamus in the production of pathological spike-and-wave activity. Since the abnormalities in focal and non-focal epilepsy apparently derive from different anatomical loci, it is reasonable to suppose that they may give rise to different functional disturbances. Penfield and Jasper (1954) have suggested that the area involved in centrencephalic seizures plays an important role in the maintenance of a state of consciousness. Mirsky, Primac, Ajmone-Marsan, Rosvold, and Stevens (1960) have made a direct comparison of the performance of focal and non-focal groups on a test