A new physiological tool for assessing anxiolytic effects in humans: frontal midline theta activity.

The theta activity which appears in the frontal midline area during performance of mental tasks has been designated as "Fm theta". In the present study, the possible use of zopiclone as an anxiolytic agent was investigated using Fm theta, in a comparison with diazepam. Sixteen male university students were given placebo, diazepam 5 mg, zopiclone 5 mg and 10 mg, in a double-blind, cross-over design. EEGs were recorded before and during performance of an arithmetic addition test. This test was repeated twice, prior to and 1 h following drug administration. Diazepam markedly increased Fm theta; however, both zopiclone 10 mg and placebo only slightly affected Fm theta, while zopiclone 5 mg failed to affect Fm theta. Scores of state anxiety were reduced markedly by diazepam and only slightly by zopiclone 10 mg, but were not affected by either zopiclone 5 mg or by placebo. Task performance was reduced markedly and in a dose-dependent manner by zopiclone, and very slightly by diazepam. These results suggest that zopiclone possesses a rather potent hypnotic effect, rather than an anxiolytic effect, and that Fm theta might be a useful tool in predicting the clinical efficacy of anxiolytic drugs in normal humans.