Late EEG after-effects in humans following hyperventilation. I. A comparison between intero- and exteroceptive influences.

Using a modification of the computer period analysis of the EEG (Aladjov and Daskalova 1987) we studied the late after-effects (until the 30th min) in human EEG (monopolar leads at F1, C3, P3 and 01) following two kinds of influences: a) short interoceptive one: 3 min hyperventilation (HV) and b) a series of 5 trains of visual light flashes (VS), presented in 5-7 min intervals. The changes in the ongoing EEG in the 2nd min after each VS and in intervals of 5 min after HV were compared with the values before the stimulation. VS did not elicit long-lasting EEG after-effects, which characterized the single interoceptive influence (HV) and consisted mainly of beta-2 (24-36 Hz) EEG activity increase in all studied cortical regions (Nikolov and Kisselkova 1988). Moreover, the exteroceptive stimulation (VS) had no essential influence on the late EEG after-effects after HV, when both kinds of stimulation were applied in the same experiment.