Impaired consciousness in epilepsy.

Departments of Neurology, Neurobiology, and Neurosurgery, Yale University School of Medicine, New Haven, CT 06520, USA.
The Lancet Neurology (Impact Factor: 21.82). 09/2012; 11(9):814-26. DOI: 10.1016/S1474-4422(12)70188-6
Source: PubMed

ABSTRACT Consciousness is essential to normal human life. In epileptic seizures consciousness is often transiently lost, which makes it impossible for the individual to experience or respond. These effects have huge consequences for safety, productivity, emotional health, and quality of life. To prevent impaired consciousness in epilepsy, it is necessary to understand the mechanisms that lead to brain dysfunction during seizures. Normally the consciousness system-a specialised set of cortical-subcortical structures-maintains alertness, attention, and awareness. Advances in neuroimaging, electrophysiology, and prospective behavioural testing have shed light on how epileptic seizures disrupt the consciousness system. Diverse seizure types, including absence, generalised tonic-clonic, and complex partial seizures, converge on the same set of anatomical structures through different mechanisms to disrupt consciousness. Understanding of these mechanisms could lead to improved treatment strategies to prevent impairment of consciousness and improve the quality of life of people with epilepsy.

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    ABSTRACT: Intrinsic connectivity network (ICN) technique provides a feasible way for evaluating cognitive impairments in epilepsy. This EEG-fMRI study aims to comprehensively assess the alterations of ICNs affected by generalized spike-and-wave discharge (GSWD) during absence seizure (AS). Twelve fMRI sessions with GSWD, and individually paired non-GSWD sessions were acquired from 16 patients with AS. Ten ICNs corresponding to seizure origination and cognitive processes were extracted using independent component analysis. Intra- and inter-network connectivity alterations of the ICNs were observed through comparisons between GSWD and non-GSWD sessions. Sequential correlation analysis between GSWD and the ICN time courses addressed the immediate effects of GSWD on ICNs during AS. GSWD-related increase of intra-network connectivity was found only in the thalamus, and extensive decreases were found in the ICNs corresponding to higher-order cognitive processes including the default-mode network, dorsal attention network, central executive network and salience network. The perceptive networks and motor network were less affected by GSWD. Sequential correlation analysis further demonstrated different responses of the ICNs to GSWD. In addition to GSWD-related functional excitation in the thalamus and functional suspension in the default-mode network, this study revealed extensive inhibitions in the other ICNs corresponding to higher-order cognitive processes, and spared perceptive and motor processes in AS. GSWD elevated synchronization of brain network activity and sequentially affected the ICNs.
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    ABSTRACT: The link between epilepsy and sleep is well established on many levels. The focus of the current review is on re-cent neuroimaging investigations into the alterations of consciousness that are observed during absence seizures and the descent into sleep. Functional neuroimaging provides simultaneous cortical and subcortical recording of activity throughout the brain, allowing a detailed definition and characterization of large-scale brain networks and the interactions between them. This has led to the identification of a set of regions which collectively form the consciousness system, which includes contributions from the default mode network (DMN), ascending arousal systems, and the thalamus. Electrophysiological and neuroimaging investigations have also clearly dem-onstrated the importance of thalamocortical and corticothalamic networks in the evolution of sleep and absence epilepsy, two phenomena in which the subject experiences an alteration to the conscious state and a disconnec-tion from external input. However, the precise relationship between the consciousness system, thalamocortical networks, and consciousness itself remains to be clarified. One of the fundamental challenges is to understand how distributed brain networks coordinate their activity in order to maintain and implement complex behaviors such as consciousness and how modifications to this network activity lead to alterations in consciousness. By tak-ing into account not only the level of activation of individual brain regions but also their connectivity within spe-cific networks and the activity and connectivity of other relevant networks, a more specific quantification of brain states can be achieved. This, in turn, may provide a more fundamental understanding of the alterations to con-sciousness experienced in sleep and epilepsy.