A physiological marker for assessing anxiety level in humans: frontal midline theta activity

The distinct theta rhythm in the frontal midline area during performance of mental tasks has been designated as Fm theta. Sixteen male university students who failed to show any appearance of Fm theta in 3 consecutive days were given diazepam 5 mg, amobarbital 80 mg, methylphenidate 15 mg and placebo, in a double-blind, crossover design. Scores were made on the state anxiety scale of STAI; EEGs were recorded before and during performance of an arithmetic addition. The test was repeated twice: before and one hr after drug administration. Fm theta appeared following the drug administration even in those who had never shown the appearance of Fm theta, and the appearance time of Fm theta increased in the following order: diazepam greater than amobarbital greater than placebo greater than methylphenidate. The scores of STAI decreased in the same order. The speed of performed tasks was increased by methylphenidate and placebo, but decreased by amobarbital and diazepam. These results suggest that relief from anxiety might be reflected in the appearance of Fm theta and that Fm theta might be a useful tool to measure the anxiety level in humans.