Multiple tasks and neuroimaging modalities increase the likelihood of detecting covert awareness in patients with disorders of consciousness

Abstract

Minimal or inconsistent behavioral responses to command make it challenging to accurately diagnose the level of awareness of a patient with a Disorder of consciousness (DOC). By identifying markers of mental imagery being covertly performed to command, functional neuroimaging (fMRI), electroencephalography (EEG) has shown that some of these patients are aware despite their lack of behavioral responsiveness. We report the findings of behavioral, fMRI, and EEG approaches to detecting command-following in a group of patients with DOC. From an initial sample of 14 patients, complete data across all tasks was obtained in six cases. Behavioral evaluations were performed with the Coma Recovery Scale-Revised. Both fMRI and EEG evaluations involved the completion of previously validated mental imagery tasks-i.e., motor imagery (EEG and fMRI) and spatial navigation imagery (fMRI). One patient exhibited statistically significant evidence of motor imagery in both the fMRI and EEG tasks, despite being unable to follow commands behaviorally. Two behaviorally non-responsive patients produced appropriate activation during the spatial navigation fMRI task. However, neither of these patients successfully completed the motor imagery tasks, likely due to specific motor area damage in at least one of these cases. A further patient demonstrated command following only in the EEG motor imagery task, and two patients did not demonstrate command following in any of the behavioral, EEG, or fMRI assessments. Due to the heterogeneity of etiology and pathology in this group, DOC patients vary in terms of their suitability for some forms of neuroimaging, the preservation of specific neural structures, and the cognitive resources that may be available to them. Assessments of a range of cognitive abilities supported by spatially-distinct brain regions and indexed by multiple neural signatures are therefore required in order to accurately characterize a patient's level of residual cognition and awareness.

Assessing the feasibility of time-resolved fNIRS to detect brain activity during motor imagery

“…The results of that study showed that a patient who was clinically diagnosed as being in a vegetative state was able to follow commands by regulating her brain activity. This finding, along with other studies, highlight the ability of neuroimaging techniques to be used as tools to assess volition in brain injured patients [6][7][8] .…”

Substitute or complement? Defining the relative place of EEG and fMRI in the detection of voluntary brain reactions

“…Currently, fMRI is mostly used to corroborate the presence of awareness detected in EEG in patients with DOCs or to give additional information to the EEG results . Only one recent study has compared the activations obtained with both EEG and fMRI mental imagery tasks on a group of patients with DOCs (Gibson et al, 2014). Large divergences of responses were found between both methods in these patients, confirming the importance of employing multiple modalities.…”

“…Planning a finger movement is thus known to block or desynchronize the mu (8-12 Hz) and/or the beta (13-30 Hz) rhythm over the motor cortex whereas imagining a foot movement can enhance them (Pfurtscheller and Lopes da Silva, 1999;Pfurtscheller et al, 2006). In that respect, if a few recent EEG studies compared EEG and fMRI command-following in some patients with DOCs, Cruse et al, 2013;Gibson et al, 2014), a problematic issue is how to interpret similarities and discrepancies in the results. In the absence of a full understanding of the neural correlates of awareness, it is extremely complex to disentangle purely methodological differences, a reduced sensitivity of one neuroimaging method for example, from differences specifically related to the pathology.…”

“…For example, in the sample of 14 patients recruited by Gibson et al (2014), some of them were ineligible for the fMRI and/or the EEG evaluation and only six could complete both procedures. Promising results have recently been found in EEG as well as in fMRI (Schnakers et al, 2009;Goldfine et al, 2011;Cruse et al, 2012b;Gibson et al, 2013;Holler et al, 2013;Naci and Owen, 2013).…”

Komunikacja w grupie pacjentów z zaburzeniami świadomości – wnioskiz projektu InteRDoCTor

“…Initial behavioral assessment is usually made using CRS-r. Some evidences supporting such approach has been recently showed by Gibsoen et al [49].…”