Publications (2)13.42 Total impact
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Article: Impaired consciousness in temporal lobe seizures: role of cortical slow activity.
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ABSTRACT: Impaired consciousness requires altered cortical function. This can occur either directly from disorders that impair widespread bilateral regions of the cortex or indirectly through effects on subcortical arousal systems. It has therefore long been puzzling why focal temporal lobe seizures so often impair consciousness. Early work suggested that altered consciousness may occur with bilateral or dominant temporal lobe seizure involvement. However, other bilateral temporal lobe disorders do not impair consciousness. More recent work supports a 'network inhibition hypothesis' in which temporal lobe seizures disrupt brainstem-diencephalic arousal systems, leading indirectly to depressed cortical function and impaired consciousness. Indeed, prior studies show subcortical involvement in temporal lobe seizures and bilateral frontoparietal slow wave activity on intracranial electroencephalography. However, the relationships between frontoparietal slow waves and impaired consciousness and between cortical slowing and fast seizure activity have not been directly investigated. We analysed intracranial electroencephalography recordings during 63 partial seizures in 26 patients with surgically confirmed mesial temporal lobe epilepsy. Behavioural responsiveness was determined based on blinded review of video during seizures and classified as impaired (complex-partial seizures) or unimpaired (simple-partial seizures). We observed significantly increased delta-range 1-2 Hz slow wave activity in the bilateral frontal and parietal neocortices during complex-partial compared with simple-partial seizures. In addition, we confirmed prior work suggesting that propagation of unilateral mesial temporal fast seizure activity to the bilateral temporal lobes was significantly greater in complex-partial than in simple-partial seizures. Interestingly, we found that the signal power of frontoparietal slow wave activity was significantly correlated with the temporal lobe fast seizure activity in each hemisphere. Finally, we observed that complex-partial seizures were somewhat more common with onset in the language-dominant temporal lobe. These findings provide direct evidence for cortical dysfunction in the form of bilateral frontoparietal slow waves associated with impaired consciousness in temporal lobe seizures. We hypothesize that bilateral temporal lobe seizures may exert a powerful inhibitory effect on subcortical arousal systems. Further investigations will be needed to fully determine the role of cortical-subcortical networks in ictal neocortical dysfunction and may reveal treatments to prevent this important negative consequence of temporal lobe epilepsy.Brain 11/2010; 133(Pt 12):3764-77. · 9.46 Impact Factor -
Article: Localizing value of ictal-interictal SPECT analyzed by SPM (ISAS).
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ABSTRACT: The goal of neuroimaging in epilepsy is to localize the region of seizure onset. Single-photon emission computed tomography with tracer injection during seizures (ictal SPECT) is a promising tool for localizing seizures. However, much uncertainty exists about how to interpret late injections, or injections done after seizure end (postictal SPECT). A widely available and objective method is needed to interpret ambiguous ictal and postictal scans, with changes in multiple brain regions. Ictal or postictal SPECT scans were performed by using [99mTc]-labeled hexamethyl-propylene-amine-oxime (HMPAO), and images were analyzed by comparison with interictal scans for each patient. Forty-seven cases of localized epilepsy were studied. We used methods that can be implemented anywhere, based on freely downloadable software and normal SPECT databases (http://spect.yale.edu). Statistical parametric mapping (SPM) was used to localize a single region of seizure onset based on ictal (or postictal) versus interictal difference images for each patient. We refer to this method as ictal-interictal SPECT analyzed by SPM (ISAS). With this approach, ictal SPECT identified a single unambiguous region of seizure onset in 71% of mesial temporal and 83% of neocortical epilepsy cases, even with late injections, and the localization was correct in all (100%) cases. Postictal SPECT, conversely, with injections performed soon after seizures, was very poor at localizing a single region based on either perfusion increases or decreases, often because changes were similar in multiple brain regions. However, measuring which hemisphere overall had more decreased perfusion with postictal SPECT, lateralized seizure onset to the correct side in approximately 80% of cases. ISAS provides a validated and readily available method for epilepsy SPECT analysis and interpretation. The results also emphasize the need to obtain SPECT injections during seizures to achieve unambiguous localization.Epilepsia 10/2005; 46(9):1450-64. · 3.96 Impact Factor
