Mice overcome fear, depression with natural Prozac

Mice forced to swim endlessly until they surrendered and just floated, waiting to drown, could be conditioned to regain their will to live when a tone they associated with safety was played.

To make a mouse depressed, they used a method favored by drug companies called learned helplessness.

"You put an animal into a pool of water and it can't get out. It gives up and it stops swimming and it just floats," Kandel said.

"When you give the animal an antidepressant, it starts swimming again. When we played the tone, it started to swim again just as it did with the antidepressant."

It affected dopamine, while antidepressants work on serotonin.

Mice conditioned by the "safety" tone also had more newborn brain cells in the dentate gyrus, a part of the brain linked with learning and depression.

"Learning involves alterations in the brain and gene expression," Kandel said. "Psychotherapy is only a form of learning."