N170 asymmetry as an index of inferior occipital dysfunction in patients with symptomatic occipital lobe epilepsy

Abstract

a b s t r a c tObjective: Localizing epileptic foci in posterior brain epilepsy remains a difficult exercise in surgery for epilepsy evaluation. Neither clinical manifestations, neurological, EEG nor neuropsychological evaluations provide strong information about the area of onset, and fast spread of paroxysms often produces mixed features of occipital, temporal and parietal symptoms. We investigated the usefulness of the N170 event-related potential to map epileptic activity in these patients. Methods: A group of seven patients with symptomatic posterior cortex epilepsy were submitted to a high-resolution EEG (78 electrodes), with recordings of interictal spikes and face-evoked N170. Generators of spikes and N170 were localized by source analysis. Range of normal N170 asymmetry was determined in 30 healthy volunteers. Results: In 3 out of 7 patients the N170 inter-hemispheric asymmetry was outside control values. Those were the patients whose spike sources were nearest (within 3 cm) to the fusiform gyrus, while foci further away did not affect the N170 ratio. Conclusions: N170 event-related potential provides useful information about focal cortical dysfunction produced by epileptic foci located in the close neighborhood of the fusiform gyrus, but are unaffected by foci further away. Significance: The N170 evoked by faces can improve the epileptic foci localization in posterior brain epilepsy.

Neuropsychological abnormalities in children with the Panayiotopoulos syndrome point to parietal lobe dysfunction

“…The normal results of the N170 visual-evoked potentials support normal lower occipital lobe function in the neighborhood of the fusiform gyrus [12], a result consistent with the normal function of the ventral visual pathway. This is in line with previous studies which have demonstrated a normal level of performance of these patients in a wide range of neuropsychological tests, namely, those evaluating occipital lobe function [9,20].…”

“…The N170 right to left hemisphere ratio was within the normal range defined in Lopes et al [12] in all cases except in patient 1 where it was increased (1.82). The average N170 ratios for the patients with left hemisphere spikes (1.00), right spikes (0.96), or independent bilateral spikes (0.98) were also within the normal range and overlapping.…”

“…During the wake EEG, visual-evoked potentials with the presentation of faces was performed, as well as the N170 potential quantified for both hemispheres, as described in Lopes et al [12]. Briefly, black and white photos of Portuguese faces taken from the Coimbra's Neuropsychological Assessment Battery [13] were randomly presented for 200 ms in a LCD screen at a distance of 1 m, with an intertrial period of 750 ms.…”

“…Briefly, black and white photos of Portuguese faces taken from the Coimbra's Neuropsychological Assessment Battery [13] were randomly presented for 200 ms in a LCD screen at a distance of 1 m, with an intertrial period of 750 ms. The 35-channel EEG recording was converted to the activity of two fixed regional sources placed in the fusiform gyrus position of a predefined standard BEM model [14] in such a way that each source expressed the contribution of a hemisphere to the N170 potential associated with faces [12]. The ratios between the left and right hemispheres were calculated for each patient (Table 3).…”

A role for the precuneus in thought–action fusion: Evidence from participants with significant obsessive–compulsive symptoms

“…However, it has been linked to both clinical and non-clinical anxieties, which support a role in TAF: Alterations in the upper beta frequencies have been found in comparisons between non-clinical controls and OCD patients (Maihöfner et al, 2007; Velikova et al, 2010) and schizophrenic patients (Yeragani et al, 2006). Furthermore, synchronized activity in the upper beta band has been found during modulations of a sense of agency (Kang et al, 2011). …”