Preserved Covert Cognition in Noncommunicative Patients With Severe Brain Injury?

Abstract

Background. Despite recent evidence suggesting that some severely brain-injured patients retain some capacity for topdown processing (covert cognition), the degree of sparing is unknown. Objective. Top-down attentional processing was assessed in patients in minimally conscious (MCS) and vegetative states (VS) using an active event-related potential (ERP) paradigm. Methods. A total of 26 patients were included (38 ± 12 years old, 9 traumatic, 21 patients >1 year postonset): 8 MCS+, 8 MCS−, and 10 VS patients. There were 14 healthy controls (30 ± 8 years old). The ERP paradigm included (1) a passive condition and (2) an active condition, wherein the participant was instructed to voluntarily focus attention on his/her own name. In each condition, the participant's own name was presented 100 times (ie, 4 blocks of 25 stimuli). Results. In 5 MCS+ patients as well as in 3 MCS− patients and 1 VS patient, an enhanced P3 amplitude was observed in the active versus passive condition. Relative to controls, patients showed a response that was (1) widely distributed over frontoparietal areas and (2) not present in all blocks (3 of 4). In patients with covert cognition, the amplitude of the response was lower in frontocentral electrodes compared with controls but did not differ from that in the MCS+ group. Conclusion. The results indicate that volitional top-down attention is impaired in patients with covert cognition. Further investigation is crucially needed to better understand top-down cognitive functioning in this population because this may help refine brain-computer interface-based communication strategies.

Across the consciousness continuum—from unresponsive wakefulness to sleep

“…This suggests that the P300 in paradigms including passive and active conditions may support the detection of voluntary information processing in DOC. A more recent study, however, advises a cautious interpretation of these findings as volitional top-down attention can be impaired in patients with covert cognition (Schnakers et al, 2014). This questions the specificity of the task as it could lead to false negative results.…”

Conventional Structural Magnetic Resonance Imaging in Differentiating Chronic Disorders of Consciousness

“…However, it has been observed that in a certain population of patients, the capacity for consciousness remains undetectable, even by flawlessly performed behavioural testing, and covert cognition, i.e., signs of wilful brain activity may be revealed in a small percentage of patients that respond mentally to active neuroimaging or electrophysiological paradigms, despite the lack of any behavioral response [13,14,15]. Therefore, multiple studies have been aimed at optimising chronic DOC differential diagnosis and outcome prediction using several neuroimaging techniques, for example, cerebral 18 F-FDG PET, which was shown to complement bedside examinations and predict long-term recovery of patients with UWS [16].…”

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

“…Advances in neuroscientific methodology has led to optimism regarding potential clinical utility in diagnostic and prognostic considerations in patients with DoC, [22][23][24] in part due to several studies indicating that cognitive processing can be detected with imaging techniques in the absence of behavioral signs of consciousness. 5,[25][26][27][28][29] These studies applied tasks that require subjects to exert mental responses to command, 30,31 in contrast to merely passive paradigms eliciting only "automatic" responses. Hence, in order to infer consciousness, it is necessary to include tasks involving active cognitive processing in combination with 6 functional neuroimaging-and electrophysiological methods.…”