The use of the EEG for assessment of vigilance changes caused by beta-blockers.

The aim of this study was to investigate the changes of vigilance caused by beta-blockers. A recently developed method to measure the vigilance fluctuations, based on the EEG spectra, was employed together with self-rating. Repeated vigilance measurements were made in 20 healthy volunteers before and after administration of placebo, propranolol and metoprolol in random sequence. Both EEG analysis and self-rating confirmed that the vigilance level was significantly decreased after administration of beta-blockers compared to placebo. No significant difference between propranolol and metoprolol could be found. The results suggest that the decrease in systolic blood pressure after beta-blockade may be responsible for the drug-induced drowsiness. However, some of the observations made in the study can be interpreted as indirect proof that central mechanisms are also involved, and that both propranolol and metoprolol have sedative properties comparable to those observed with conventional psychotropic drugs.