Drinking related direct current positive potential shift in the human EEG depends on thirst

Scalp recorded direct current (DC)-potential shifts were examined in 11 human subjects who had either thirsted for 16 h or had quenched thirst before recordings. The recording epoch included a 3-min baseline, an interval of about 5 min during which subjects drank 400 ml of water, and a 7-min post-drinking interval. Consistent with previous data, when thirsty, subjects displayed a widespread negative DC-potential shift during drinking which was replaced by a positive DC shift at the transition to the post-drinking interval. The positivity after drinking lasted for about 2 min and averaged 146 microV at frontal recording sites. Quenching thirst before recordings reduced the positive DC-potential shift upon drinking, whereas changes in preceding drinking related DC negativity appeared to be secondary. The post-drinking positive DC-potential shift depending on the subject's motivational state can be considered an indicator of reward associated with quenching thirst, pointing to a lowered frontocortical excitability during reward.