Why do Seizures Cause Loss of Consciousness?

Blumenfeld, Hal; Taylor, Jacob M.

doi:10.1177/1073858403255624

Cited by 148 publications

(104 citation statements)

References 96 publications

(57 reference statements)

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“…3) [8,13,57]. For temporal lobe epilepsy, it seems that loss of consciousness occurs by seizure activity arising from the temporal lobe and propagating to subcortical structures; this may inhibit the arousal functions of the thalamus, basal forebrain and upper brainstem, to widely deactivate frontal and parietal association cortex [24,71].…”

Section: Default Mode Network Involvement In Complex Partial Seizuresmentioning

confidence: 99%

The Default Mode Network and Altered Consciousness in Epilepsy

Danielson

Guo

Blumenfeld

2011

Behavioural Neurology

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139

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Abstract. The default mode network has been hypothesized based on the observation that specific regions of the brain are consistently activated during the resting state and deactivated during engagement with task. The primary nodes of this network, which typically include the precuneus/posterior cingulate, the medial frontal and lateral parietal cortices, are thought to be involved in introspective and social cognitive functions. Interestingly, this same network has been shown to be selectively impaired during epileptic seizures associated with loss of consciousness. Using a wide range of neuroimaging and electrophysiological modalities, decreased activity in the default mode network has been confirmed during complex partial, generalized tonic-clonic, and absence seizures. In this review we will discuss these three seizure types and will focus on possible mechanisms by which decreased default mode network activity occurs. Although the specific mechanisms of onset and propagation differ considerably across these seizure types, we propose that the resulting loss of consciousness in all three types of seizures is due to active inhibition of subcortical arousal systems that normally maintain default mode network activity in the awake state. Further, we suggest that these findings support a general "network inhibition hypothesis," by which active inhibition of arousal systems by seizures in certain cortical regions leads to cortical deactivation in other cortical areas. This may represent a push-pull mechanism similar to that seen operating between cortical networks under normal conditions.

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Section: Default Mode Network Involvement In Complex Partial Seizuresmentioning

confidence: 99%

The Default Mode Network and Altered Consciousness in Epilepsy

Danielson

Guo

Blumenfeld

2011

Behavioural Neurology

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139

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“…The arrow in panel A indicates the intravenous injection of 0.2 mg bicuculline. mation flow in the brain via different mechanisms, with some seizures producing greater and others less neuronal activity, either of which may disrupt normal processing (Blumenfeld and Taylor, 2003).…”

Section: Figmentioning

confidence: 99%

Relative Changes in Cerebral Blood Flow and Neuronal Activity in Local Microdomains during Generalized Seizures

Nersesyan

Hermán

Erdogan³

et al. 2004

J Cereb Blood Flow Metab

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Summary:There is broad agreement that generalized tonicclonic seizures (GTCS) and normal somatosensory stimulation are associated with increases in regional CBF. However, the data regarding CBF changes during absence seizures are controversial. Electrophysiologic studies in WAG/Rij rats, an established animal model of absence seizures, have shown spikewave discharges (SWD) that are largest in the perioral somatosensory cortex while sparing the visual cortex. Recent functional magnetic resonance imaging (fMRI) studies in the same model have also shown localized increases in fMRI signals in the perioral somatosensory cortex during SWD. Because fMRI signals are only indirectly related to neuronal activity, the authors directly measured CBF and neuronal activity from specific microdomains of the WAG/Rij cortex using a specially designed probe combining laser-Doppler flowmetry and extracellular microelectrode recordings under fentanyl/haloperidol anesthesia. Using this approach, parallel increases in neuronal activity and CBF were observed during SWD in the whisker somatosensory (barrel) cortex, whereas the visual cortex showed no significant changes. For comparison, these measurements were repeated during somatosensory (whisker) stimulation, and bicuculline-induced GTCS in the same animals. Interestingly, whisker stimulation increased neuronal activity and CBF in the barrel cortex more than during SWD. During GTCS, much larger increases that included both the somatosensory and visual cortex were observed. Thus, SWD in this model produce parallel localized increases in neuronal activity and CBF with similar distribution to somatosensory stimulation, whereas GTCS produce larger and more widespread changes. The normal response to somatosensory stimulation appears to be poised between two abnormal responses produced by two physiologically different types of seizures.

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“…It has been shown that DMN is involved in loss of consciousness in epilepsy [25,26]. Thus, findings of decreased DMN connectivity in GE have been interpreted to be related to ictal unconsciousness [23,24].…”

Section: Introductionmentioning

confidence: 99%

Impaired language function in generalized epilepsy: Inadequate suppression of the default mode network

Gauffin¹,

Ettinger-Veenstra²,

Landtblom³

et al. 2013

Epilepsy & Behavior

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We aimed to study the effect of a potential default mode network (DMN) dysfunction on language performance in epilepsy. Language dysfunction in focal epilepsy has previously been connected to brain damage in language associated cortical areas. In this work, we studied generalized epilepsy (GE) without focal brain damage, to see if the language function was impaired.We used functional magnetic resonance imaging (fMRI) to investigate if the DMN was involved. Eleven persons with GE and 28 healthy controls were examined with fMRI during a sentence reading task. We could demonstrate impaired language function, reduced suppression of DMN, and, specifically, an inadequate suppression of activation in the left anterior temporal lobe and the posterior cingulate cortex, as well as an aberrant activation in the right hippocampal formation. Our results highlight the presence of language decline in people with epilepsy of not only focal, but also generalized origin.

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Why do Seizures Cause Loss of Consciousness?

Cited by 148 publications

References 96 publications

The Default Mode Network and Altered Consciousness in Epilepsy

The Default Mode Network and Altered Consciousness in Epilepsy

Relative Changes in Cerebral Blood Flow and Neuronal Activity in Local Microdomains during Generalized Seizures

Impaired language function in generalized epilepsy: Inadequate suppression of the default mode network

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