Willful Modulation of Brain Activity in Disorders of Consciousness

Abstract

BackgroundThe differential diagnosis of disorders of consciousness is challenging. The rate of misdiagnosis is approximately 40%, and new methods are required to complement bedside testing, particularly if the patient's capacity to show behavioral signs of awareness is diminished. MethodsAt two major referral centers in Cambridge, United Kingdom, and Liege, Belgium, we performed a study involving 54 patients with disorders of consciousness. We used functional magnetic resonance imaging (MRI) to assess each patient's ability to generate willful, neuroanatomically specific, blood-oxygenation-level-dependent responses during two established mental-imagery tasks. A technique was then developed to determine whether such tasks could be used to communicate yes-or-no answers to simple questions. ResultsOf the 54 patients enrolled in the study, 5 were able to willfully modulate their brain activity. In three of these patients, additional bedside testing revealed some sign of awareness, but in the other two patients, no voluntary behavior could be detected by means of clinical assessment. Moreover, one patient was able to use our technique to answer yes or no to questions during functional MRI. In contrast, it remained impossible to establish any form of communication at the bedside. ConclusionsThese results show that a small proportion of patients in a vegetative or minimally conscious state have brain activation reflecting some awareness and cognition. Careful clinical examination will result in reclassification of the state of consciousness in some of these patients. This technique may be useful in establishing basic communication with patients who are ostensibly unresponsive. 20.P, et al. Cortical processing of noxious somatosensory stimuli in the persistent vegetative state.

Stratification of unresponsive patients by an independently validated index of brain complexity

“…In VS patients, the absence of behavioral signs of consciousness per se cannot be considered a proof of the absence of consciousness 2, 33. For this reason, the alternative term unresponsive wakefulness syndrome, which is more descriptive and more neutral regarding the patient's capacity for consciousness, has recently been recommended 34.…”

“…Practically, by approximating an optimal tradeoff between sensitivity and specificity, the PCI test may represent an important step within a hierarchical diagnostic flow of DOCs. For example, one may apply PCI after a first screening with tests characterized by high sensitivity and low specificity, such as positron emission tomography assessment of cortical metabolic rates35; then, patients with PCI max  > PCI* could be selected to confirm the presence of covert consciousness through more demanding tests characterized by maximal specificity, such as functional MR imaging active paradigms 33…”

The auditory P300-based single-switch brain–computer interface: Paradigm transition from healthy subjects to minimally conscious patients

“…Omitted values (−) indicate that no measurements were conducted. Figure 6: Presence of a P300 in the complex paradigm for patient PA 10 at the channels Fz, Cz and Pz. The averaged data segments of the low standard tones (blue curve; marker type: •) versus the low deviant tones (green curve; marker type: +) can be seen with the LTS as target stream.…”

“…In addition, different neuroimaging and electrophysiological techniques have revealed signs of intact cortical processing and awareness in unresponsive patients diagnosed with vegetative state (VS) and minimally conscious state (MCS) [9,10]. MCS is a disorder of consciousness (DOC) that is clinically identi-fied on the basis of behavioral assessment that shows the presence of non-reflexive responses to visual and auditory stimulation [11,12].…”

“…MCS is a disorder of consciousness (DOC) that is clinically identi-fied on the basis of behavioral assessment that shows the presence of non-reflexive responses to visual and auditory stimulation [11,12]. Severe motor impairment might, however, prevent the disclosure of awareness even during a careful repeated examination, leading to a rate of misdiagnosis of approximately 40 % [10]. To overcome this problem, EEG-based BCI systems might offer a unique opportunity in supporting the bedside clinical assessment of unresponsive patients and eventually, in providing them with a means of communication.…”