Detecting number processing and mental calculation in patients with disorders of consciousness using a hybrid brain-computer interface system

Abstract

BackgroundFor patients with disorders of consciousness such as coma, a vegetative state or a minimally conscious state, one challenge is to detect and assess the residual cognitive functions in their brains. Number processing and mental calculation are important brain functions but are difficult to detect in patients with disorders of consciousness using motor response-based clinical assessment scales such as the Coma Recovery Scale-Revised due to the patients’ motor impairments and inability to provide sufficient motor responses for number- and calculation-based communication.MethodsIn this study, we presented a hybrid brain-computer interface that combines P300 and steady state visual evoked potentials to detect number processing and mental calculation in Han Chinese patients with disorders of consciousness. Eleven patients with disorders of consciousness who were in a vegetative state (n = 6) or in a minimally conscious state (n = 3) or who emerged from a minimally conscious state (n = 2) participated in the brain-computer interface-based experiment. During the experiment, the patients with disorders of consciousness were instructed to perform three tasks, i.e., number recognition, number comparison, and mental calculation, including addition and subtraction. In each experimental trial, an arithmetic problem was first presented. Next, two number buttons, only one of which was the correct answer to the problem, flickered at different frequencies to evoke steady state visual evoked potentials, while the frames of the two buttons flashed in a random order to evoke P300 potentials. The patients needed to focus on the target number button (the correct answer). Finally, the brain-computer interface system detected P300 and steady state visual evoked potentials to determine the button to which the patients attended, further presenting the results as feedback.ResultsTwo of the six patients who were in a vegetative state, one of the three patients who were in a minimally conscious state, and the two patients that emerged from a minimally conscious state achieved accuracies significantly greater than the chance level. Furthermore, P300 potentials and steady state visual evoked potentials were observed in the electroencephalography signals from the five patients.ConclusionsNumber processing and arithmetic abilities as well as command following were demonstrated in the five patients. Furthermore, our results suggested that through brain-computer interface systems, many cognitive experiments may be conducted in patients with disorders of consciousness, although they cannot provide sufficient behavioral responses.

Multifactor consciousness level assessment of participants with acquired brain injuries employing human–computer interfaces

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The Clinical Diagnostic Utility of Electrophysiological Techniques in Assessment of Patients With Disorders of Consciousness Following Acquired Brain Injury: A Systematic Review

“…A high false negative rate up to 29% showed that the electrophysiological test failed to detect active mental effort in a considerable number of healthy subjects, while other studies identified all control subjects as responders. 27,74,75,83,84 There was also a wide variety in sensitivity rates in the patient group, ranging from 0% to 100%. Here, a sensitivity rate of 0% showed that none of the included patients with discernible behavioral evidence of command-following (MCS+) were classified as responders in the active task.…”

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“…Table 2 illustrates calculated rates of sensitivity and specificity per study in healthy subjects and patients with DoC, except from five studies, due to results only confined to the group level, 73,77 lack of reports on individual patient behavioral responses, 81,82 or because comparison between EEG-responses and behaviorally based diagnosis was not possible. 75 Sensitivity and specificity rates in patients with DoC were calculated with the behavioral assessment as the reference standard, although a true gold standard to confirm consciousness level is nonexistent. In healthy controls, the studies displayed a relatively wide variability with regard to sensitivity rates, ranging from 71% to 100%.…”

Enhancing clinical communication assessments using an audiovisual BCI for patients with disorders of consciousness

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