Abstract
Alterations in consciousness are central to epileptic manifestations, and involve changes in both the level of awareness and subjective content of consciousness. Generalised seizures are characterised by minimal responsiveness and subjective experience whereas simple and complex partial seizures demonstrate more selective disturbances. Despite variations in ictal origin, behaviour and electrophysiology, the individual seizure types share common neuroanatomical foundations generating impaired consciousness. This article provides a description of the phenomenology of ictal consciousness and reviews the underlying shared neural network, dubbed the 'consciousness system', which overlaps with the 'default mode' network. In addition, clinical and experimental models for the study of the brain correlates of ictal alterations of consciousness are discussed. It is argued that further investigation into both human and animal models will permit greater understanding of brain mechanisms and associated behavioural consequences, possibly leading to the development of new targeted treatments.
Highlights
Alterations in consciousness are central to epileptic manifestations, and involve changes in both the level of awareness and subjective content of consciousness
Generalised seizures are characterised by complete loss of consciousness, whereas complex partial seizures often cause selective and limited disturbances that may culminate into motor/sensory aphasia or transient inattention [27,41]; end-points that are open to misinterpretation as loss of consciousness
The Ictal Consciousness Inventory (ICI) reveals the nature of impairment in consciousness, allowing differentiation between those seizure types principally generating a deficit in the level of awareness (generalised seizures, including absence or tonic-clonic) and those modifying the contents of consciousness
Summary
Examined, analysed and explored from a multitude of perspectives, the multi-faceted concept of consciousness is the modern day academic enigma. The principal dichotomy central to current International League Against Epilepsy classification is the distinction between ‘partial’ seizures (involving focal brain regions or confined to one hemisphere) and generalised seizures (involving diffuse regions throughout both hemispheres) [25]. Within this dichotomy resides the major definitional criterion: impairment of consciousness differentiates between ‘simple’ and ‘complex’ partial seizures [5]. A synopsis of current insights into the neural foundations underlying seizure sub-types (generalised tonic-clonic, absence and complex partial seizures) and specific clinical phenomenology of ictal consciousness concludes this review
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