Covariation of phasic cortical and cardiovascular responses: Effects of alertness

Effects of maintaining an alert state on event-related brain potentials (ERPs) and evoked cardiovascular responses were examined in an auditory detection task. Subjects were instructed to detect a possible difference in frequency between two successively presented tones in 5 s periods. Two types of trials were compared. In the first no tones were presented and subjects had to maintain an alert state for the full five seconds (uninterrupted trials). In the second type the alert state was interrupted by the presentation of visual stimuli which were presented in the second half of the 5 s period (interrupted trials). Both types of trial elicited ERPs with a negative shift consisting of a frontal and a parietal part. Uninterrupted trials elicited a stronger and longer lasting negative shift. This difference was maximal at parietal sites. The stronger negative shift was accompanied by a stronger deceleration in the heart rate response, which started at about the same time as the cortical effect but lasted somewhat longer. Furthermore, uninterrupted trials evoked a stronger decrease in the blood pressure response. This effect showed the expected delay when compared to the effect on heart rate (HR). The cardiovascular data confirmed the hypotheses concerning effects of maintaining an alert state, but the cortical data partly contradicted them. Altogether, the current findings do not contradict an active network involved in alertness, but they do not confirm the expected stronger involvement of the right hemisphere and involvement of prefrontal areas in this function.