Thesis defense Urszula Gorska (Donders series 408)

30 September 2019

Listening in on consciousness. Discriminating states of consciousness with responses to periodic auditory and texture stimulation

In many cases severe brain injuries give rise to prolonged disorders of consciousness (PDOC). Assessing the exact level of consciousness in this clinical group is a challenging task as patients are typically not able to communicate.
In this work we implemented two methods based on auditory stimulation: 1) complex spectrotemporal sounds of natural auditory textures and 2) low- and medium rate auditory steady-state responses (ASSR) comprised of simple sounds within 4 - 40 Hz amplitude modulation range. We assessed EEG responses of multiple healthy subject groups, ranging from unconscious to conscious (deep sleep, passive, responding) as well as the PDOC patients, who were divided into unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS) groups.
The change detection signal in natural auditory textures was identified as parieto-occipital potential at the scalp. However not this potential, but the signal complexity measure differentiated in a better way between conscious and unconscious subject groups. Moreover, Relative Power and Phase Coherence of ASSR discriminated awake from sleeping controls and UWS from MCS patients. Both methods were positively correlated with the clinical behavioural assessment of PDOC patients. 
Summing up, the stimulation in auditory domain in combination with specific measures of brain activity can provide objective criterion for differentiating states of consciousness and thus may be a candidate for a cost-effective tool to estimate the level of neural dysfunction in PDOC patients.