Mental imagery paradigms for the assessment of awareness in patients with disorders of consciousness: a systematic literature review

Introduction

Behavioural assessments are the current gold standard tool for determining the level of awareness in disorders of consciousness (DoC), but cannot be applied in all patients. Neuroimaging and/or neurophysiological responses to mental imagery tasks are emerging as a potentially more sensitive tool for assessing awareness, especially in patients with injuries to the motor systems that often accompany impairments in consciousness. This review summarises and critically appraises the current evidence to determine if functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) based mental imagery paradigms are viable tools for assessing awareness in patients with DoC.

Methods

We conducted a systematic literature review according to the PRISMA guidelines. PubMed, Embase, and PsycInfo databases were searched for studies investigating fMRI or EEG based mental imagery paradigms for detecting awareness in patients with DoC.

Results

A total of 17 studies were identified for inclusion in this review (eleven investigating fMRI paradigms and six EEG protocols). Across all fMRI studies and five out of the six EEG studies, mental imagery paradigms were able to detect awareness in patients with DoC, with different degrees of accuracy. In one fMRI and one EEG study, mental imagery paradigms were a useful tool for communication with patients.

Discussion

There is promising evidence that both fMRI and EEG based mental imagery paradigms could become viable tools for assessing awareness in patients with DoC. Further research is needed to validate preliminary findings in larger samples of patients with different aetiologies and including longitudinal assessments.