Cognitive deficit related to seizure pattern in centrencephalic epilepsy

Theidentifying characteristics oftheelectroencephalogram incentrencephalic epilepsy havebeen outlined byPenfield andJasper (1954) asincluding a bilaterally synchronous onset ofabnormality which consists ofwave-and-spike activity atorneara frequency of3persecond. Thisisincontrast tothe E.E.G. abnormality seenincasesoffocal cortical epilepsy inwhichsharp wavespredominate, begin in arestricted area, andspread either slowly ornotat alltoother parts ofthebrain. Theseizures inthese twotypes ofepilepsy alsodiffer, thecentrencephalic seizures including 'absence' attacks, myoclonic jerks, akinetic attacks, andmajorseizures, while the attacks infocal cortical epilepsy varywiththelocation ofthefocus. Inthecaseoffocal discharge, theE.E.G. abnormality isofcourse assumed tooriginate fromthis focus. Inthecentrencephalic typeofepilepsy, however, thebilaterally synchronous onsetofE.E.G. abnormality ledJasper andKershman(1941) to believe that theorigin herewasinsomesubcortical region whichhadwidespread connexions withcortical areas sothatitcould actaspacemaker forthe entire cortex. Thisinterpretation wasgiven strong support byanexperimental study inthecat, inwhich stimulation ofasmall areainthemedial thalamus evokedwidespread bilaterally synchronous 3 per second spike-and-wave activity inthecortex (Jasper andFortuyn, 1947). Williams (1953), recording from children withpetit malattacks, confirmed theimportant roleofthethalamus intheproduction of pathological spike-and-wave activity. Sincetheabnormalities infocal andnon-focal epilepsy apparently derive fromdifferent anatomical loci, itisreasonable tosuppose that they maygive rise todifferent functional disturbances. Penfield and Jasper (1954) havesuggested thattheareainvolved incentrencephalic seizures plays animportant role inthemaintenance ofa state ofconsciousness. Mirsky, Primac, Ajmone-Marsan, Rosvold, and Stevens (1960) havemadeadirect comparison ofthe performance offocal andnon-focal groups onatest 'NowatSt.Joseph's Hospital, Hamrlton, Canada. demanding sustained attention (continuous performance test). Theyfoundthatthepatients with centrencephalic epilepsy wereimpaired whereas thosewithfocal cortical epilepsy werenot.On memorytests, however, thecentrencephalic group performed better thana groupofpatients with bitemporal epilepsy, indicating somespecificity of dysfunction. Thepresent study provides further support forsuch afunctional differentiation, andatthesametime suggests a further differentiation basedupona division ofthecentrencephalic groupinto twosubgroups. METHOD