Limbic P300s in temporal lobe epilepsy with and without Ammon's horn sclerosis

Limbic P300 potentials can be recorded within the mesial temporal robes of patients with temporal lobe epilepsy (TLE). To delineate possible mechanism s of their generation and pathological alteration, we analysed limbic P300s in 55 TLE patients with and 29 without Ammon's horn sclerosis (AHS) and co rrelated their amplitudes with neuronal cell counts in 30 histopathological specimens. Limbic P300 amplitudes were reduced on the side of the epilepto genic focus only in patients with AHS. Moreover, in AHS patients, limbic P3 00 latencies were prolonged bilaterally; and in patients with left-sided AH S, amplitudes were reduced bilaterally. Both findings suggest bilateral fun ctional deficits in TLE with unilateral AHS. Limbic P300 areas correlated s ignificantly with neuronal densities of dentate gyrus granule cells but not hippocampal pyramidal cells in the CA1-4 (cornu ammonia) subfields. This f inding points to a potential mechanism for the bilateral effects of unilate ral AHS as both dentate gyri exhibit strong reciprocal contralateral connec tivity.