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Open Access Highly Accessed Research article

Pattern changes of EEG oscillations and BOLD signals associated with temporal lobe epilepsy as revealed by a working memory task

Helka FB Ozelo13, Andréa Alessio12, Maurício S Sercheli1, Elizabeth Bilevicius2, Tatiane Pedro2, Fabrício RS Pereira4, Jane M Rondina5, Benito P Damasceno2, Fernando Cendes2 and Roberto JM Covolan16*

Author Affiliations

1 Neurophysics Group, Gleb Wataghin Physics Institute, University of Campinas, Unicamp, Campinas, Brazil

2 Neuroimaging Laboratory, School of Medical Sciences, University of Campinas, Unicamp, Campinas, Brazil

3 Department of Natural Sciences, Mathematics and Education, Federal University of São Carlos, UFSCar, Araras, Brazil

4 Centre Hospitalier Régional Universitaire, Université Montpellier 1, Montpellier, França

5 Sobbel Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK

6 Universidade Estadual de Campinas, Instituto de Física "Gleb Wataghin". Rua Sérgio Buarque de Holanda, 777 - Cidade Universitária Zeferino Vaz, Campinas, SP CEP 13083-859, Brazil

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BMC Neuroscience 2014, 15:52  doi:10.1186/1471-2202-15-52

Published: 25 April 2014

Abstract

Background

It is known that the abnormal neural activity in epilepsy may be associated to the reorganization of neural circuits and brain plasticity in various ways. On that basis, we hypothesized that changes in neuronal circuitry due to epilepsy could lead to measurable variations in patterns of both EEG and BOLD signals in patients performing some cognitive task as compared to what would be obtained in normal condition. Thus, the aim of this study was to compare the cerebral areas involved in EEG oscillations versus fMRI signal patterns during a working memory (WM) task in normal controls and patients with refractory mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS). The study included six patients with left MTLE-HS (left-HS group) and seven normal controls (control group) matched to the patients by age and educational level, both groups undergoing a blocked design paradigm based on Sternberg test during separated EEG and fMRI sessions. This test consisted of encoding and maintenance of a variable number of consonant letters on WM.

Results

EEG analysis for the encoding period revealed the presence of theta and alpha oscillations in the frontal and parietal areas, respectively. Likewise, fMRI showed the co-occurrence of positive and negative BOLD signals in both brain regions. As for the maintenance period, whereas EEG analysis revealed disappearance of theta oscillation, fMRI showed decrease of positive BOLD in frontal area and increase of negative BOLD in the posterior part of the brain.

Conclusions

Generally speaking, these patterns of electrophysiological and hemodynamic signals were observed for both control and left-HS groups. However, the data also revealed remarkable differences between these groups that are consistent with the hypothesis of reorganization of brain circuitry associated with epilepsy.

Keywords:
EEG; fMRI; Alpha and theta rhythms; Working memory; Temporal lobe epilepsy