Brain Advance Access originally published online on May 4, 2009
Brain 2009 132(8):2091-2101; doi:10.1093/brain/awp086
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Impaired consciousness during temporal lobe seizures is related to increased long-distance cortical–subcortical synchronization
1 INSERM, U751, Laboratoire de Neurophysiologie et Neuropsychologie, Marseille, F-13005, France 2 CHU Timone, Service de Neurophysiologie Clinique, Assistance Publique des Hôpitaux de Marseille, Marseille, F-13005, France 3 Faculté de Médecine, Université de la Méditerranée, Faculté de Médecine, Marseille, F-13005, France 4 INSERM, U642, Rennes, F-35000, France 5 Université de Rennes 1, LTSI, Rennes, F-35000, France 6 Service de neurophysiologie Clinique, Hôpital de la Pitié Salpétrière, Paris
Correspondence to: Fabrice Bartolomei, INSERM, U751, Laboratoire de Neurophysiologie et Neuropsychologie, Marseille, F-13005, France E-mail: fabrice.bartolomei{at}univmed.fr
Loss of consciousness (LOC) is a dramatic clinical manifestation of temporal lobe seizures. Its underlying mechanism could involve altered coordinated neuronal activity between the brain regions that support conscious information processing. The consciousness access hypothesis assumes the existence of a global workspace in which information becomes available via synchronized activity within neuronal modules, often widely distributed throughout the brain. Re-entry loops and, in particular, thalamo-cortical communication would be crucial to functionally bind different modules together. In the present investigation, we used intracranial recordings of cortical and subcortical structures in 12 patients, with intractable temporal lobe epilepsy (TLE), as part of their presurgical evaluation to investigate the relationship between states of consciousness and neuronal activity within the brain. The synchronization of electroencephalography signals between distant regions was estimated as a function of time by using non-linear regression analysis. We report that LOC occurring during temporal lobe seizures is characterized by increased long-distance synchronization between structures that are critical in processing awareness, including thalamus (Th) and parietal cortices. The degree of LOC was found to correlate with the amount of synchronization in thalamo-cortical systems. We suggest that excessive synchronization overloads the structures involved in consciousness processing, preventing them from treating incoming information, thus resulting in LOC.
Key Words: Temporal lobe epilepsy; consciousness; synchrony; EEG; global workspace
Abbreviations: BKG, background period; CG, posterior cingulate gyrus; EC, entorhinal cortex; ETSI, extra-temporal lobe synchronization index; h2, non-linear correlation coefficient; LOC, loss of conscious us; MS, middle part of the seizure period; MTG, middle temporal gyrus; P, lateral parietal cortex; SO, seizure onset period; TETSI, temporal–extra-temporal synchronization index; Th, thalamus; TSI, temporal lobe synchronization index
Received October 4, 2008. Revised February 25, 2009. Accepted February 27, 2009.
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