Monday, March 12, 2007

Dopamine and desire

Dopamine and desire

'What's my motivation?'

From the outside, it's hard to tell what most motivates an animal to seek a reward: the pleasure of the reward itself (roughly, liking), the satisfaction of getting it (wanting), or the acquired association between behavior and reward (learning).

"Wanting and liking are what some philosophers of mind have called 'folk psychological' terms about how the mind is organized," explains Jon Horvitz, PhD, a neuroscientist at Boston College. Although he doubts real brains have clearly demarked scripts for "wanting" or "liking," he says it helps to draw some rough distinctions to enable research into dopamine's behavioral pathway.

The Seattle researchers--graduate student Siobhan Robinson, undergraduate Suzanne Sandstrom, psychologist Victor Denenberg, PhD, and biochemist Richard Palmiter, PhD--chose a knockout approach to get a fair comparison between behavior with and without dopamine. Then, they threw caffeine into the mix to compensate for the motor lethargy but not the cognitive deficits caused by low dopamine.

Dopamine appears to be involved both in goal-directed and motor behavior. On the inside, dopamine-producing neurons extend into neighboring motivational and motor parts of the brain. And on the outside, when scientists block dopamine release, rewards such as food, sex and cocaine stop reinforcing behavior. But what does this mean: Do we stop liking them? Wanting them? Or learning that they're good? Once scientists know, they might be able to devise better therapeutic manipulations using dopamine or to design interventions that bypass the dopamine system.

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