Fronto-parietal connectivity is a non-static phenomenon with characteristic changes during unconsciousness.
BACKGROUND
It has been previously shown that loss of consciousness is associated with a breakdown of dominating fronto-parietal feedback connectivity as assessed by electroencephalogram (EEG) recordings. Structure and strength of network connectivity may change over time. Aim of the current study is to investigate cortico-cortical connectivity at different time intervals during consciousness and unconsciousness. For this purpose, EEG symbolic transfer entropy (STEn) was calculated to indicate cortico-cortical information transfer at different transfer times.


METHODS
The study was performed in 15 male volunteers. 29-channel EEG was recorded during consciousness and propofol-induced unconsciousness. EEG data were analyzed by STEn, which quantifies intensity and directionality of the mutual information flow between two EEG channels. STEn was computed over fronto-parietal channel pair combinations (10 s length, 0.5-45 Hz total bandwidth) to analyze changes of intercortical directional connectivity. Feedback (fronto → parietal) and feedforward (parieto → frontal) connectivity was calculated for transfer times from 25 ms to 250 ms in 5 ms steps. Transfer times leading to maximum directed interaction were identified to detect changes of cortical information transfer (directional connectivity) induced by unconsciousness (p<0.05).


RESULTS
The current analyses show that fronto-parietal connectivity is a non-static phenomenon. Maximum detected interaction occurs at decreased transfer times during propofol-induced unconsciousness (feedback interaction: 60 ms to 40 ms, p = 0.002; feedforward interaction: 65 ms to 45 ms, p = 0.001). Strength of maximum feedback interaction decreases during unconsciousness (p = 0.026), while no effect of propofol was observed on feedforward interaction. During both consciousness and unconsciousness, intensity of fronto-parietal interaction fluctuates with increasing transfer times.


CONCLUSIONS
Non-stationarity of directional connectivity may play a functional role for cortical network communication as it shows characteristic changes during propofol-induced unconsciousness.
Department of Anesthesiology, Helios Clinic Wuppertal, Witten/Herdecke University, Wuppertal, Germany ; Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
Gisela
G
Untergehrer
Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
Denis
D
Jordan
Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
Eberhard F
EF
Kochs
Department of Neurology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
Rüdiger
R
Ilg
Department of Anesthesiology, Helios Clinic Wuppertal, Witten/Herdecke University, Wuppertal, Germany ; Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
Gerhard
G
Schneider
D000328:Adult; D063132:Connectome / Q000379:methods*; D003243:Consciousness / Q000502:physiology*; D004569:Electroencephalography; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D008297:Male; D010296:Parietal Lobe / Q000502:physiology*; D013997:Time Factors; D014474:Unconsciousness / Q000503:physiopathology*