Simple actions that seem to be entirely voluntary -- flexing a muscle, for example -- are actually initiated by unconscious parts of the brain, a California behavioral scientist has found. Conscious awareness of the intention arises about three- to four-tenths of a second later and can either permit or cancel the intention.

The researcher's conclusion, which contradicts the usual assumption that voluntary actions are initiated exclusively by the conscious mind, is based on electrical monitoring of simple tasks. Attached electrodes monitored different kinds of brain activity when people were asked to flex a finger or a wrist at some unspecified time in the near future.

The monitors revealed that about half a second before the muscle flexed, an unconscious region of the brain began sending signals, apparently preparing the brain to carry out the action. About three- to four-tenths of a second later the people reported their first conscious awareness of the intention to flex the muscle. The muscle moved about one- to two-tenths of a second later.

"The conscious mind doesn't initiate voluntary actions," said Benjamin Libet, a specialist in sensory awareness who did the experiments at the University of California, San Francisco. He published his findings in The Brain and Behavioral Sciences, a scientific journal.

Libet says the fraction of a second between conscious awareness of the impending action and its actual occurrence gives the person time to veto the intent if desired. This brief interval, Libet said, is all that is needed for free will to maintain its reign over actions.