EEG synchronization upon reward in man

Objectives: It was tested whether reward in humans is associated with EEG synchronization similar to that seen in animals. Methods: In two experiments (I and II) the EEG was recorded from frontal, central, and parietal positions before, during, and after drinking or oral stimulation. In Experiment I, subjects (n=11) who had either been thirsty for 16 h or had quenched thirst before recordings, drank 400 ml of water. In Experiment II, thirsty subjects (n=11) either drank 400 ml of water or sucked on a soother. The recording epochs included a 3 min baseline, an interval of about 5 min during which subjects drank or sucked on the soother, and a 7 min post-drinking interval. Results: During the drinking epoch, beta band-power (12–30 Hz) was enhanced in both conditions of Experiment I and II, respectively. In Experiment I, after drinking, lower alpha power (8–10 Hz) was higher when subjects were thirsty than when they were not. Lower alpha was also enhanced in the post-drinking interval of both conditions of Experiment II, and after sucking, lower alpha synchronization was in addition accompanied by increased theta activity (4–8 Hz). Conclusions: Increased beta activity during drinking and sucking in thirsty subjects presumably reflects non-specific activation related to the motivational strength of sensorimotor regulation during consumatory behavior. The thirst dependent lower alpha synchronization after drinking, generated not only by water consumption but also by surrogate oral stimuli, can be considered a reflection of the drive reducing and rewarding qualities of oral stimulation and consumatory behavior.