Ancient Chinese gamblers knew the secret. When a male cricket balked at fighting after a loss, its trainer would shake the insect in his hands and toss it into the air. That would restore the cricket's aggressiveness. Sounds simple, but Hans Hofmann, a postdoctoral neurobiologist in the department of psychology, says that trick could have implications for humans with depression.
Intrigued by the idea that agitating the crickets somehow gave them the will to fight again, Hofmann tested it scientifically. "When I described this to my colleagues," he recalls, "they told me, 'You're crazy; it isn't going to work.' But it did." Laboratory results, described in a February issue of the journal Nature, showed that 57 percent of the losing crickets regained their aggressiveness after being shaken and tossed.
It turned out that flying -- even briefly -- triggered the return of the crickets' fight. The next next step was to figure out how. Insect aggression is controlled by the brain, but the impulse to fly comes from an electrical signal generated in the thorax or chest area. When researchers severed the nerves connecting the thorax to the brain of a defeated cricket, the animal was still able to fly, but flight did not restore its willingness to fight. From that they deduced that the act of flying causes a neurotransmitter or some other chemical signal from the thorax to direct the brain to "reset" the cricket's aggressiveness.
According to Hofmann, this may be the first known example in nature in which a specific motor activity -- in this case, flight -- has an immediate effect on an unrelated behavior, such as aggression. The discovery might allow scientists to look for new treatments for conditions such as depression in humans. "Maybe we'll find a motor pattern that people can perform that will decrease their depression," Hofmann says. Sounds worth a gamble.
