The effect of neural pre-stimulus oscillations on post-stimulus somatosensory event-related potentials in disorders of consciousness

Abstract

Brain activity of people in a disorder of consciousness (DoC) is diffuse and different from healthy people. In order to get a better understanding of their cognitive processes and functions, electroencephalographic activity has often been examined in patients with DoC, including detection of event-related potentials (ERPs) and spectral power analysis. However, the relationship between pre-stimulus oscillations and post-stimulus ERPs has rarely been explored in DoC, although it is known from healthy participants that pre-stimulus oscillations predispose subsequent stimulus detection. Here, we examine to what extent pre-stimulus electroencephalography band power in DoC relates to post-stimulus ERPs in a similar way as previously documented in healthy people. 14 DoC patients in an unresponsive wakefulness syndrome (UWS, N = 2) or a minimally conscious state (MCS, N = 12) participated in this study. In an active oddball paradigm patients received vibrotactile stimuli. Significant post-stimulus differences between brain responses to deviant and standard stimulation could be found in six MCS patients (42.86%). Regarding relative pre-stimulus frequency bands, delta oscillations predominated in most patients, followed by theta and alpha, although two patients showed a relatively normal power spectrum. The statistical analysis of the relationship between pre-stimulus power and post-stimulus event-related brain response showed multiple significant correlations in five out of the six patients. Individual results sometimes showed similar correlation patterns as in healthy subjects primarily between the relative pre-stimulus alpha power and post-stimulus variables in later time-intervals. However, opposite effects were also found, indicating high inter-individual variability in DoC patients´ functional brain activity. Future studies should determine on an individual level to what extent the relationship between pre- and post-stimulus brain activity could relate to the course of the disorder.

Pupil-linked arousal reflects intracranial aperiodic neural activity in the human auditory cortex

“…The neural signals of interest (from the electrode-bytime matrix) were obtained by extracting values for each trial (between 1,000 ms before and 2,000 ms after sound onset). Trial power values were normalized to a baseline period (-250 ms to 0 ms; preceding stimulus onset) by calculating % signal change from baseline for the early intra-stimulus (0 ms to 350 ms) and late (250 ms to 750 ms) 57 post-stimulus time windows. While the stimulus playback only occurred between 0-250 ms, the early intra-stimulus time window was expanded to 0-350 ms to capture high gamma salience-related activity, which has been reported to cluster between 200-300 ms in the human auditory cortex 58 .…”