![]() responding to a question, blinking on command, etc.) or non-motor (e.g. In practice, however, the only means of assessing whether a person (other than oneself) is conscious is if the person can report so through a recognizably voluntary response-be it motor (e.g. a dissociation between the level of consciousness and cognition that can be demonstrated through motor versus exclusively non-motor behaviour 12-14). Conversely, a person can be said to be conscious if, at a given moment, there is something that it is like to be that person, 4, 10 regardless of whether this state might not be apparent to an external observer, as is the case with patients with complete locked-in syndrome 11 or disorder of consciousness patients with cognitive motor dissociation (i.e. ![]() 7 in the context of disorders of consciousness and Wesensten and Badia 8 and Brualla et al. work by Laureys et al., 5 Owen et al., 6 and Giacino et al. 3 In principle, it can be argued that someone is unconscious if, at a given moment, there is nothing that it is like to be that person, 4 regardless of whether there remains measurable residual neural processing as observed through reflexive behavioural or neuroimaging responses to stimulation ( cf. 2 Since the early days of EEG research, the delta rhythm has been closely associated with an absence of consciousness. Finally, we conclude that false inferences of unconscious states can be best avoided by examining measures of electrophysiological complexity in addition to spectral power.ĮEG, delta oscillations, consciousness, disorders of consciousness, Angelman syndrome Introductionĭelta oscillations, usually defined as 1–4 Hz rhythms, are among the most studied EEG oscillations, 1 having been first observed in the early 20th century. We also consider implications concerning theories of consciousness, such as integrated information theory and the entropic brain hypothesis. Having reviewed this literature, we discuss plausible mechanisms that would resolve the seeming contradiction between high amplitude delta oscillations and consciousness. At the same time, a largely parallel body of recent work has reported convincing evidence that the complexity or entropy of EEG and magnetoencephalographic signals strongly relates to an individual’s level of consciousness. The foregoing studies complement an older, yet largely unacknowledged, body of literature that has documented awake, conscious patients with high amplitude delta oscillations in clinical reports from Rett syndrome, Lennox-Gastaut syndrome, schizophrenia, mitochondrial diseases, hepatic encephalopathy, and non-convulsive status epilepticus. These studies include work in Angelman syndrome, epilepsy, behavioural responsiveness during propofol anaesthesia, postoperative delirium, and states of dissociation from the environment such as dreaming and powerful psychedelic states. ![]() Recently, however, many studies have reported the presence of prominent delta activity during conscious states, which casts doubt on the hypothesis that high amplitude delta oscillations are an indicator of unconsciousness. ![]() This strong correlation between loss of consciousness and high amplitude delta oscillations is thought to stem from the widespread cortical deactivation that occurs during the ‘down states’ or troughs of these slow oscillations. High amplitude delta oscillations are frequently observed in states of diminished consciousness, including slow wave sleep, anaesthesia, generalized epileptic seizures, and disorders of consciousness, such as coma and the vegetative state. A common observation in EEG research is that consciousness vanishes with the appearance of delta (1–4 Hz) waves, particularly when those waves are high amplitude.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |