Ray of light in the right location boosts motivation

HOW do you keep a rat motivated? A burst of light in the brain might help.

In an attempt to locate and boost the brain cells responsible for motivation in rats, Melissa Warden at Stanford University in California and colleagues inserted electrodes into two brain regions thought to control the feeling. They then placed the animals in a tank of water from which there was no escape. The rats swam around seeking an exit. After a while, they gave up and floated motionless. Sometimes they tried again later.

Although activity in the rat medial prefrontal cortex correlated with the movement, some neurons in this area seemed to be linked to motivation. These neurons became inactive when the rats gave up swimming, but they stayed active in rats outside the tank that stopped moving.

To see if they could boost motivation, the team genetically engineered another group of rats to express a light-responsive protein in their neurons. They then implanted a fibre-optic cable into part of another region of the brain - the dorsal raphe nucleus - which usually receives input from the "motivational" region of the medial prefrontal cortex. When the light was switched on in short bursts, the brain region was activated and the rats swam around for longer, suggesting that they were more motivated to find an escape route (Nature, doi.org/jsd).

The team hopes that the finding will eventually help doctors treat the lack of motivation seen in people with depression.

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