Identical event-related potentials to target and frequent stimuli of visual oddball task recorded by intracerebral electrodes M. Kukleta a, * , M. Bra ´zdil b , R. Roman a , P. Jura ´k c a Department of Physiology, Medical Faculty, Masaryk University, Brno, Czech Republic b First Department of Neurology, Medical Faculty, Masaryk University, Brno, Czech Republic c Laboratory of NMR Electronics, Academy of Sciences, Brno, Czech Republic Accepted 31 March 2003 Abstract Objective: The shape of visually elicited event-related potentials (ERP) of epileptic patients during their presurgical evaluation with intracerebral electrodes was investigated in the study. Methods: Twenty intractable epileptic patients with depth electrodes at several intracranial locations in the frontal, temporal, parietal lobes, and in the amygdalo-hippocampal complex participated in the study. To evoke the ERP, a standard visual oddball task was used with target stimuli, and frequent non-habituated and habituated stimuli. The averaged responses of the 3 groups were superimposed and visually analyzed whether the shape appeared identical or non-identical. Results: The EEG response to target and frequent stimuli was recorded in 660 intra-cerebral sites. In 88 sites (14 different patients) localized in the amygdala, parahippocampal gyrus, superior, middle, and inferior temporal gyri, fusiform and lingual gyri, sensorimotor cortex, prefrontal cortex, hippocampus, and cingulated gyrus, the identical ERPs to target and both groups of frequent stimuli were observed. In 442 sites located in the above listed structures, and in the basal ganglia and parietal cortex, the shape of the ERP differed from 0.3 to 0.47 s on after the stimulus. The remaining 130 sites did not yield the task-specific potential change. Conclusions: The existence of identical ERPs to target and frequent stimuli in the oddball task suggests that a part of mental operations underlying the brain engagement in this task is not dependent on the way of responding. q 2003 International Federation of Clinical Neurophysiology. Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords: Event-related potential; Intra-cerebral EEG recording in humans; Oddball task 1. Introduction In the cognitive brain research, the registration of event- related potentials (ERP) continues to be a basic and ever- productive method. Especially the P3 component, firstly described by Sutton et al. (1965) and Desmedt et al. (1965), has been attracting the attention of researchers for decades. This wave appears in averaged records after rare (target) external stimuli presented, in a random order, with frequent ones. It is peaking about 300 ms after an acoustic signal, and some 100–150 ms later after a visual signal. In the scalp recordings, its amplitude is largest over the centroparietal regions for acoustic as well as visual stimulation. The P3 evoked by a visual signal has been analyzed thoroughly since the 1960s, and available evidence demonstrates its large dependence on experimental conditions of psycho- logical character (Donchin et al., 1978; Hillyard and Picton, 1987). This long-latency positive waveform is generally viewed as reflecting decision or cognitive closure of the recognition processing, or as the updating of memory for future actions (Smith et al., 1970; Hillyard et al., 1971; Hillyard and Picton, 1987; Iragui et al., 1993). Actually, the P3 is mostly considered as an electrophysiological con- comitant of mental processes linked with the cognitive elaboration of target signals. Frequent signals are believed to be unable to produce comparable electrophysiological changes. Many studies using scalp electroencephalography (EEG), intracerebral EEG, and myoelectroencephalography (MEG) have attempted to localize structures where the P3 is generated (Basile et al., 1997; ; Baudena et al., 1995; Bra ´zdil, et al., 1999; Goto et al., 1996; Halgren et al., 1995a,b, 1998; Kropotov and Ponomarev, 1991; McCarthy et al., Clinical Neurophysiology 114 (2003) 1292–1297 www.elsevier.com/locate/clinph 1388-2457/03/$30.00 q 2003 International Federation of Clinical Neurophysiology. Published by Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S1388-2457(03)00108-1 * Corresponding author. Tel.: þ 420-5-42126656; fax: þ 420-5-126561. E-mail address: mkukleta@med.muni.cz (M. Kukleta).