Summary: Researchers report EEG systems could be useful tools in assessing the levels of awareness in patients in a vegetative state.
Source: University of Birmingham.
New research suggests that an electroencephalogram (EEG) could be a strong indicator of the level of awareness of patients in a vegetative state after a severe brain injury.
Functional magnetic resonance imaging (fMRI) has repeatedly shown that a significant minority of patients diagnosed as in the vegetative state are actually aware, but unable to show it reliably with their behaviour.
The new research findings, published in Annals of Neurology, suggest a correspondence between a patient’s ability to generate an EEG marker of attention to tactile stimulation, and their ability to produce the critical clinical marker of awareness by following verbal commands.
Crucially, this relationship existed for patients who could only follow commands with the more expensive methods of fMRI.
The mental demands of the EEG task are lower than the demands of the fMRI tasks. Furthermore, EEG is entirely portable, inexpensive, and available in the majority of hospitals.
The researchers state that this more simple EEG assessment may be capable of diagnosing a patient’s level of awareness without the need for expensive and challenging fMRI scans, thereby increasing the number of patients who may benefit from a more accurate diagnosis.
14 patients were selected for the study, across levels of awareness and behavioural ability; seven in a vegetative state, four in a minimally conscious state, two emerging from a minimally conscious state, and one with locked in syndrome.
Each patient’s surrogate decision maker provided informed, written consent for the patient’s participation in the study. As a scientific control, a sample of fifteen healthy volunteers also participated in the tasks.
The patients completed two sets of brain imaging tasks:
Vibrating stimulators affixed to each wrist and the upper back administered non-painful pulses five times per second while the patients’ EEGs were recorded. 80% of these vibrations occurred on the upper back. The relatively more infrequent vibrations on the wrists (20% of the time) produce changes in a healthy individual’s EEG that reflect attention being drawn toward the new location of stimulation.
During separate fMRI scans, patients were asked to engage in three established measures of a covert ability to follow commands – imagining playing tennis, imagining walking around the house, and counting target words in a stream of distractors.
All patients whose EEGs showed evidence of attention being directed toward the infrequent tactile stimuli were also able to display evidence of following commands in the fMRI tasks.
Similarly, most patients (five of six) who did not generate a response to the EEG task did not generate evidence of command following.
Dr Damian Cruse, from the University of Birmingham, explained, “A bedside EEG may work as a cost-efficient and portable way of improving the accuracy of diagnosis in disorders of consciousness. While current clinical diagnoses are accurate for many patients, recent reports estimate that as many as 15% of patients considered to be in a vegetative state could retain awareness that cannot be detected reliably from their behaviour alone.”
“The ultimate aim is to provide more accurate diagnoses for all patients, thus directing appropriate rehabilitation and therapy to those most likely to benefit.”
About this genetics research article
The research is a collaboration between researchers at the University of Birmingham, UK, The Brain and Mind Institute, University of Western Ontario, Canada, the University of Kent, UK and Department of Clinical Neurosciences at the University of Cambridge, UK.
Disorders of consciousness (DoC) are states that a person may enter when they emerge from coma following a severe brain injury. Patients in a vegetative state do not demonstrate purposeful behaviour and are considered to lack awareness. In contrast, patients in a minimally conscious state are considered to have fluctuating awareness and demonstrate variable, but reproducible, purposeful behaviour. Patients who demonstrate accurate communication and/or functional object use are considered emergent from a MCS. However, the accurate identification of a patient’s diagnostic group comprises a considerable clinical challenge.
Six of the patients in the trial had sustained traumatic brain injuries from motor vehicle accidents. The remaining eight patients had sustained non-traumatic brain injuries from different aetiologies including cardiac arrest (3 cases) and near-drowning.
Source:University of Birmingham Image Source: This NeuroscienceNews.com image is in the public domain. Original Research:Abstract for “Somatosensory attention identifies both overt and covert awareness in disorders of consciousness” by Raechelle M. Gibson, Srivas Chennu PhD, Davinia Fernández-Espejo PhD, Lorina Naci PhD, Adrian M. Owen PhD and Damian Cruse PhD in Annal of Neurology. Published online July 27 2016 doi:10.1002/ana.24726
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]University of Birmingham. “EEG Could Help Indicate Level of Awareness in Those With Consciousness Disorders .” NeuroscienceNews. NeuroscienceNews, 27 July 2016. <https://neurosciencenews.com/eeg-consciousness-awareness-4743/>.[/cbtab][cbtab title=”APA”]University of Birmingham. (2016, July 27). EEG Could Help Indicate Level of Awareness in Those With Consciousness Disorders . NeuroscienceNews. Retrieved July 27, 2016 from https://neurosciencenews.com/eeg-consciousness-awareness-4743/[/cbtab][cbtab title=”Chicago”]University of Birmingham. “EEG Could Help Indicate Level of Awareness in Those With Consciousness Disorders .” https://neurosciencenews.com/eeg-consciousness-awareness-4743/ (accessed July 27, 2016).[/cbtab][/cbtabs]
Somatosensory attention identifies both overt and covert awareness in disorders of consciousness
Objective: Some patients diagnosed with disorders of consciousness retain sensory and cognitive abilities beyond those apparent from their overt behaviour. Characterising these covert abilities is crucial for diagnosis, prognosis, and medical ethics. This multimodal study investigates the relationship between electroencephalographic evidence for perceptual/cognitive preservation and both overt and covert markers of awareness.
Methods: Fourteen patients with severe brain injuries were evaluated with an electroencephalographic vibrotactile attention task designed to identify a hierarchy of residual somatosensory and cognitive abilities: 1) somatosensory steady-state evoked responses, 2) bottom-up attention orienting (P3a event-related potential), and 3) top-down attention (P3b event-related potential). Each patient was also assessed with a clinical behavioural scale and two functional magnetic resonance imaging assessments of covert command following.
Results: Six patients produced only sensory responses, with no evidence of cognitive event-related potentials. A further eight patients demonstrated reliable bottom-up attention orienting responses (P3a). No patient showed evidence of top-down attention (P3b). Only those patients who followed commands, whether overtly with behaviour or covertly with functional neuroimaging, also demonstrated event-related potential evidence of attentional orienting.
Interpretation: Somatosensory attentional orienting event-related potentials differentiated patients who could follow commands from those who could not. Crucially, this differentiation was irrespective of whether command following was evident through overt external behaviour, or through covert functional neuroimaging methods. Bedside electroencephalographic methods may corroborate more expensive and challenging methods such as functional neuroimaging, and thereby assist in the accurate diagnosis of awareness.
“Somatosensory attention identifies both overt and covert awareness in disorders of consciousness” by Raechelle M. Gibson, Srivas Chennu PhD, Davinia Fernández-Espejo PhD, Lorina Naci PhD, Adrian M. Owen PhD and Damian Cruse PhD in Annal of Neurology. Published online July 27 2016 doi:10.1002/ana.24726