t _ ~ ,-., • ELSEVIER Electroencephalography and clinical Neurophysiology 95 (1995) 53-62 o Alterations of intrahippocampal cognitive potentials in temporal lobe epilepsy T. Grunwald a,*, C.E. Elger a, K. Lehnertz a, D. Van Roost b, H.J. Heinze c a University Clinic ofEpileptology, Sigmund-Freud-Str. 25, 53105 Bonn, Germany b University Clinic ofNeurosurgery, Sigmund-Freud-Str. 25, 53105 Bonn, Germany c University Clinic of Neurology, Magdeburg, Germany Accepted for publication: 16 January 1995 Abstract During presurgical evaluation event-related potentials were recorded with depth electrodes located longitudinally within the hippocampus in 25 patients suffering from unilateral temporal lobe epilepsy. Rare stimuli in a visual oddball paradigm elicited a pronounced negativity ("N o'') in the hippocampal body. Amplitudes were significantly reduced on the side of the primary epileptogenic area. Visual presentations of words in a recognition paradigm evoked an earlier negativity ("ENw") in anterior and a later negativity ("LNw") in posterior hippocampal structures. Both were sensitive for recognition effects and showed reduced amplitudes on the side of the primary epileptogenic area. Relating the differences of left and right hippocampal "No" and "ENw" amplitudes proved to be a sensitive method for topological diagnosis and allowed a correct lateralization of the primary epileptogenic area in all patientS. Amplitudes of the hippocampal ENw, evoked in the dominant hemisphere by first presentations, strongly correlated with the recognition rate, when the primary epileptogenic area was situated in the contralateral temporal lobe. This correlation was reduced by the presence of ipsilateral epileptogenic foci. Keywords: Event-related potentials; Intracerebral recording; Temporal lobe epilepsy; Hippocampus 1. Introduction Cognitive or endogenous event-related potentials (ERPs) can be elicited by a variety of motor, sensory and cognitive tasks. Their components, as derived from surface elec- trodes, are thought to reflect electrophysiological correlates of special subroutines of information processing. Cognitive potentials recorded with intrahippocampal depth electrodes have been described in several studies (e.g. Halgren et al. 1980; Altafullah et al. 1986; Smith et al. 1986; Velasco et al. 1986; Puce and Bladin 1987; Stapleton and Halgren 1987). In patients with temporal lobe epilepsies (TLEs) such intrahippocampal recordings can show marked ampli- tude differences of potentials evoked in classical oddball * Corresponding author. Tel.: 0049-228-287-5864; Fax: 0049-228-287- 6294. paradigms, in which the occurrences of rare stimuli are known to elicit a P300 component in surface recordings (Squires et al. 1981; McCarthy et al. 1987). Only few studies correlated the unilateral absence of limbic "P3-1ike activity" with the side of the primary epileptogenic area (Meador et al. 1987; Puce et al. 1989b). Though their results provide strong evidence for the usefulness of alter- ations of intrahippocampal potentials for the lateralization of epileptogenic loci, the sensitivity of the unilateral ab- sence of hippocampal oddball potentials seems to depend on the selection of patients (cf., Puce et al. t989a,b, 1991). Problems arise especially in view of patients in whom no ipsilateral absence of "P3-1ike potentials" was found, or in cases in which these components were absent on the side contralateral to the epileptogenic temporal lobe. Watanabe et al. (1988) even stated that limbic "P3-1ike potentials" had higher amplitudes ipsilateral to the epilep- togenic focus in all of the 13 patients who participated in 0013-4694/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0013-4694(95)00015-1 EEG 94630