Dopamine is a neurotransmitter released by a set of neurons in the hypothalamus and the midbrain, which is the top portion of the brainstem. Midbrain dopamine neurons fire in response to rewarding stimuli. They also send signals to two major stations in the brain – the striatum, and the frontal cortex. Together, neurons in these three regions of the brain form a reward pathway. In fact, electrically stimulating this pathway causes the experience of a rewarding stimulus.
Dopamine neurons use a unique code for communicating information about rewards. The neurons signal when your reward expectations are wrong. If you watch the electrical activity of a dopamine neuron, you’ll see that when you get an unexpected reward, the neuron fires… You didn’t expect the reward, so things are better than you predicted. Now, if you’re trained that you get a reward every time a light goes on beforehand, then the dopamine neuron responds to the light. Now the light actually becomes the reward, because the reward is totally expected. Now if the light goes on, but you don’t get a reward, the dopamine neuron fires less…you got less reward than you expected.
The dopamine code propels us toward things that we expect will be rewarding, toward known rewards. But in space, short of mining asteroids for precious metals, most rewards are not within our sight. And yet we still explore the unknown.
Signals in the ventral striatum are increased when people see images of new places, compared with familiar ones. This brain region is part of the reward pathway that we saw before. It receives heavy input from midbrain dopamine neurons. People also tended to choose to explore images of new places, even when their reward value was unknown. This shows that our brain attributes more value to options that look new. It’s that “bonus” signal for new stimuli that reflects our inclination to explore.