[Interictal EEG coherence in patients with partial temporal lobe epilepsy]. / Coherencia cerebral interictal en pacientes con epilepsia parcial del lóbulo temporal.

AIMS: The purpose of this research was to study the spatio-temporal characteristics of the correlation that exists between two simultaneous EEG signals (coherence) in the interictal period in patients with partial epilepsy that is presumably symptomatic of the temporal lobe (ILAE). PATIENTS AND METHODS: A study of 13 patients, aged between 17-60 years, was conducted (53% females). A digital EEG was performed on each patient using the 10/20 system of electrode location. 24 artifact-free segments were selected from the recording made in a rest-waking state with the patient's eyes closed. Fourier's transformation was employed to obtain cross spectrum matrices, which were then used to calculate the intrahemispheric (Cohintra) and interhemispheric (Cohinter) coherences expressed by the Z transformation. These values were ordered by regions considering the known anatomical connections. RESULTS: In both the overall and the individual analyses, we found greater alterations of the Cohintra and the Cohinter in the temporal regions, and there was a predominance of the left hemisphere. The individual analysis of coherence, unlike the visual interpretation of the EEG recording, showed significant alterations in all the patients in the sample. CONCLUSIONS: Incorporating this type of tool would enable us to reach a more accurate topographic diagnosis in cases of epilepsy of unknown aetiology. At the same time the possible means of medical and surgical treatment available would be widened.

Coherencia cerebral interictal en pacientes con epilepsia parcial del lóbulo temporal / Interictal eeg coherence in patients with partial temporal lobe epilepsy

Aims. The purpose of this research was to study the spatio-temporal characteristics of the correlation that exists between two simultaneous EEG signals (coherence) in the interictal period in patients with partial epilepsy that is presumably symptomatic of the temporal lobe (ILAE). Patients and methods. A study of 13 patients, aged between 17-60 years, was conducted (53% females). A digital EEG was performed on each patient using the 10/20 system of electrode location. 24 artifact-free segments were selected from the recording made in a rest-waking state with the patient’s eyes closed. Fourier’s transformation was employed to obtain cross spectrum matrices, which were then used to calculate the intrahemispheric (Cohintra) and interhemispheric (Cohinter) coherences expressed by the Z transformation. These values were ordered by regions considering the known anatomical connections. Results. In both the overall and the individual analyses, we found greater alterations of the Cohintra and the Cohinter in the temporal regions, and there was a predominance of the left hemisphere. The individual analysis of coherence, unlike the visual interpretation of the EEG recording, showed significant alterations in all the patients in the sample. Conclusions. Incorporating this type of tool would enable us to reach a more accurate topographic diagnosis in cases of epilepsy of unknown aetiology. At the same time the possible means of medical and surgical treatment available would be widened (AU)

Objetivo. Estudiar las características espacio-temporales de la correlación que existe entre dos señales simultáneas del EEG (coherencia) en el período interictal en pacientes con epilepsia parcial presumiblemente sintomática del lóbulo temporal (ILAE). Pacientes y métodos. Se estudiaron 13 pacientes (53% del sexo femenino), con edades de 17-60 años. A cada paciente se le realizó un EEG digital, utilizando el sistema 10/20 de colocación de electrodos. Del trazado en vigilia con ojos cerrados, se seleccionaron 24 segmentos, libres de artefactos. Mediante la transformada de Fourier, se obtuvieron matrices de espectros cruzados, con las que se calcularon la coherencias intrahemisféricas (Cohintra) e interhemisféricas (Cohinter), expresadas mediante la transformación Z. Estos valores se ordenaron por regiones considerando las conexiones anatómicas conocidas. Resultados. Tanto en el análisis global como individual encontramos mayores alteraciones de la Cohintra y la Cohinter en las regiones temporales, y predominó el hemisferio izquierdo. El análisis individual de la coherencia, a diferencia de la interpretación visual del EEG, evidenció alteraciones significativas en todos los pacientes de la muestra. Conclusiones. La incorporación de este tipo de herramienta permitiría un diagnóstico topográfico más preciso en las epilepsias cuya etiología se desconoce, y ampliaría las posibilidades de tratamiento médico y quirúrgico (AU)

Dynamic event-related potentials and rapid source analysis reveals an intermittent short-lasting dysfrontality in schizophrenia.

Neuroimaging studies have identified regional brain dysfunctions in schizophrenia, but their dynamic consequences remain unclear. This study reports electrophysiological evaluation of medicated schizophrenic patients during performance of the Wisconsin Card Sorting Test. Using event-related potentials (ERPs), averaged after passing through several band pass filters, and source analysis with variable-resolution brain electrical tomography, cerebral sources were visualized at every latency point of the evoked potential. ERPs which differed from the control group were elicited principally in frontal, central, and parietal regions, within the delta and theta frequency ranges. Significant differences emerged at three different latencies (S1, S2, S3) in frontal/midline areas and at the anterior temporal electrode site T3 for slow potentials. The left occipitoparietal region showed significant differences within the alpha and beta 2 ranges, respectively. Medial fronto-orbital area and anterior cingulate cortex contributed to the development of the frontal ERPs and the lateral inferior frontal area to the temporal (T(3)) evoked-potential, while the precuneus/medial region generated the posterior activity recorded on the scalp. The significant intervals S1 and S3 were synchronous between the medial frontal and lateral inferior frontal region, while in the S2 interval the medial frontal areas were parallel with the precuneus/medial occipitotemporal region. A simultaneous functional imbalance between frontal subregions and posterior areas was uncovered. Here, we show for the first time an intermittent functional deficiency of specific brain areas during task-directed mentation in schizophrenia, which by its brevity is not accessible by neuroimaging methods measuring hemodynamic activity.

Abnormal functional asymmetry in occipital areas may prevent frontotemporal regions from achieving functional laterality during the WCST performance in patients with schizophrenia.

There is much evidence of frontotemporal lateralized abnormalities in schizophrenia. However, the relationship has not yet been examined between performance on the Wisconsin Card Sorting Test, with supposed anterior left dominance and event-related potential (ERP) asymmetry. ERPs recorded at homologous bilateral sites were compared using statistical permutation methods. Patients had an unexpected abnormal lateralization over occipital regions, preceding slow anterior potentials. This indicates a defect in early stages of information processing, which may contribute to prevent further hemispheric lateralization during performance.

Induced oscillations and the distributed cortical sources during the Wisconsin card sorting test performance in schizophrenic patients: new clues to neural connectivity.

Prefrontal dysfunction has been associated with schizophrenia. Activation during Wisconsin card sorting test (WCST) is a common approach used in functional neuroimaging to address this failure. Equally, current knowledge states that oscillations are basic forms of cells-assembly communications during mental activity. Promising results were revealed in a previous study assessing healthy subjects, WCST and oscillations. However, those previous studies failed to meet the functional integration of the network during the WCST in schizophrenics, based on the induced oscillations and their distributed cortical sources. In this research, we utilized the brain electrical tomography (variable-resolution brain electromagnetic tomography) technique to accomplish this goal. Task specific delta, theta, alpha and beta-2 oscillations were induced and simultaneously synchronized over large extensions of cortex, encompassing prefrontal, temporal and posterior regions as in healthy subjects. Every frequency had a well-defined network involving a variable number of areas and sharing some of them. Oscillations at 11.5, 5.0 and 30 Hz seem to reflect an abnormal increase or decrease, being located at supplementary motor area (SMA), left occipitotemporal region (OT), and right frontotemporal subregions (RFT), respectively. Three cortical areas appeared to be critical, that may lead to difficulties either in coordinating/sequencing the input/output of the prefrontal networks-SMA, and retention of information in memory-RFT, both preceded or paralleled by a deficient visual information processing-OT.

Brain electrical field measurements unaffected by linked earlobes reference.

Recent theoretical analysis supports the possibility that using a linked earlobe reference in EEG studies might appreciatively distort the measured electrical field due to current flow over a low resistance path across the wire joining both ears. Such an effect would invalidate published quantitative EEG norms. Evidence for the balancing effect of this distortion was sought for in the EEG of 4 patients with well localized unilateral lesions, a situation in which this distortion would be most apparent. Statistical tests failed to reveal significant differences between EEGs recorded when ears were linked or unlinked. An analysis of the equivalent circuit reveals that a high skin/electrode impedance effectively makes the linked ear reference behave as an ordinary reference.