How would you fancy a holiday to Greece or Thailand? Would you like to buy an iPhone or a new pair of shoes? Would you be keen to accept that enticing job offer? Our lives are riddled with choices that force us to imagine our future state of mind. The decisions we make hinge upon this act of time travel and a new study suggests that our mental simulations of our future happiness are strongly affected by the chemical dopamine.
Dopamine is a neurotransmitter, a chemical that carries signals within the brain. Among its many duties is a crucial role in signalling the feelings of enjoyment we get out of life's pleasures. We need it to learn which experiences are rewarding and to actively seek them out. And it seems that we also depend on it when we imagine the future.
Tali Sharot from University College London found that if volunteers had more dopamine in their brains as they thought about events in their future, they would imagine those events to be more gratifying. It's the first direct evidence that dopamine influences how happy we expect ourselves to be.
When we learn about new experiences, neurons that secrete dopamine seem to record the difference between the rewards we expect and the ones we actually receive. In encoding the gap between hope and experience, these neurons help us to repeat rewarding actions.
This was clearly demonstrated in 2006, when Mathias Passiglione showed that people's ability to learn about rewards could be improved by giving them a drug called L-DOPA. It's a precursor to dopamine, a sort of parent molecule that can increase the concentrations of its offspring. Passiglione asked volunteers to learn links between different symbols and different financial rewards. He found that under the influence of L-DOPA, they were better at picking the symbols that earned them the most cash.
Passiglione's study was important, but his volunteers were forced to make a fairly artificial choice between two virtual symbols in a constrained lab setting. What happens in real life, when choices are complex and our decisions hinge on our ability to think about the future?
To answer that, Sharot recruited 61 volunteers and asked them to say how happy they'd feel if they visited one of 80 holiday destinations, from Greece to Thailand. All of the recruits were given a vitamin C supplement as a placebo and 40 minutes later, they had to imagine themselves on holiday at half of the possible locations. After this bout of fanciful daydreaming, they had to take another pill but this time, half of them were given L-DOPA instead of the placebo. Again, they had to imagine themselves in various holiday spots.
The next day, Sharot brought the volunteers back. By this time, they would have broken down all the L-DOPA in their system. She asked them to choose which of two destinations they'd like to go to, from the set that they had thought about the day before. Finally, they rated each destination again.
By the end of the experiments, they perceived their imaginary holidays to be more enjoyable if they had previously thought about the locations under the influence of L-DOPA (while vitamin C, as predicted, had no effect). The implication is clear: think about the future with more dopamine in the noggin and you'll imagine that you have a better time.
Critically, this wasn't because they were feeling happier in the actual moment. All the recruits filled in questionnaires about their emotional state every time they took a pill and these revealed that the dopamine boost didn't actually affect the present state of mind. All it did was change their predictions of their future state of mind. These happier predictions affected their choices too - more often than not, they chose to travel to destinations that they had envisioned through dopamine-tinted goggles.
How dopamine has its way is unclear. Sharot suggests that it could boost how much we want something when we imagine it. Its effects could also tie into its role in learning. When we imagine the future, this chemical strengthens the link between what we think about and any feelings of enjoyment we might gain from it. This model fits with the fact that some neurons in the striatum become more active the more pleasure we expect from an experience.
Either way, it's clear that our knowledge of dopamine's myriad roles is just beginning. Broadening that knowledge is important for understanding our own behaviour, which, as Sharot says, "is largely driven by estimations of future pleasure and pain".
Reference: Current Biology 10.1016/j.cub.2009.10.025
More on Sharot's work and dopamine:
9/11 memories reveal how flashbulb memories are made in the brain
The neuroscience of optimism - how the brain creates a rosy outlook
Why information is its own reward - same neurons signal thirst for water, knowledge