July 2 (HealthDay News) -- New information about brain circuit activity may help explain why some people who take the sleep aid Ambien (zolpidem) walk, eat, talk on the phone and even drive while not fully awake -- and without remembering it the next morning.

The drug has also been shown to awaken minimally conscious patients into a conscious state.

In experiments with mice, researchers at Georgetown University Medical Center in Washington, D.C., found that zolpidem shuts down some powerful brain circuits but activates other circuits when they're deprived of activity.

"Brain cells or neurons are highly reactive to incoming activity throughout life," study corresponding author Molly M. Huntsman, an assistant professor in the department of pharmacology, said in a news release.

"When brain activity is silenced, many neurons automatically react to this change. We see this in our study, which suggests that inhibitory neurons responsible for stopping neural activity are themselves shut down by zolpidem. The excitatory neurons, responsible for transmitting activity, are then allowed to re-awaken and become active again, without monitoring, because the inhibitory neurons are 'asleep'," she explained.

While it appears that zolpidem shuts down active neural pathways and perhaps triggers activity in others, the actual mechanism isn't known.

"Nevertheless, the paradoxical activation of brain circuits by a powerful sedative definitely needs more attention in additional studies in both human and animal models," Huntsman said.

The study was published in this week's Proceedings of the National Academy of Sciences journal.

SOURCE: Georgetown University Medical Center, news release, June 29, 2009