Table 1.

Survey of the different neurophysiological techniques of stimulation to investigate brain function in UWS and MCS.

Technique	Availability	Ease of Application	Analysis Complexity	Information on Brain Connectivity	Diagnostic Utility
resting state EEG	high	high	moderate-high	significant	allows differentiating UWS/MCS but not identifying fLIS unless using advanced analyses (dWPLI, graph theoretic network lagged-phase synchronization, network parameters)
short-latency EPs	high	high	low	low	do not allow clear UWS/MCS differentiation but can be useful concerning prognosis
long-latency EPs (ERPs)	high	high	moderate-high	moderate	allows differentiating UWS/MCS but not identifying fLIS unless using advanced analyses (lagged-phase synchronization and network parameters following NIBS) or dedicated stimulation approaches (e.g., VMI and AMI)
TMS-EEG	low	low	high	significant	allows differentiating UWS/MCS and identifying fLIS by using advanced analyses
sleep assessment	moderate	moderate	moderate	moderate	is more useful concerning prognosis than differential diagnosis, as sleep patterns are significantly related to outcome
pain assessment	low-moderate	moderate	moderate	moderate	allows differentiating UWS/MCS and identifying fLIS unless assessing the cognitive components of the evoked responses and using advanced analyses (e.g., LEPs single features, GBO, response to TMS)

Legend: AMI, audio-motor integration; dWPLI, directed Weighted Phase Lag Index; EEG, electroencephalogram; EPs, evoked potentials; ERPs, event-related potentials; fLIS, functional Locked-In Syndrome; GBO, gamma-band oscillations; LEPs, laser-evoked potentials; MCS, minimally conscious state; NIBS, non-invasive brain stimulation; TMS, transcranial magnetic stimulation; UWS, unresponsive wakefulness syndrome; VMI, visuo-motor integration.