The Thirst for Knowledge

19 July 2009
Posted by Chris Smith.

Imagine you've been told you've won a prize.  But you don't know how much.  It could be pennies or it could be millions.  Most of us would be itching to find out about the size of the prize.  Now researchers in the States have discovered that uncovering information about future rewards is actually rewarding in itself, and uses the same pathways in the brain as our response to very basic rewards such as food or drink.

Impact of a drop of water.This is research by Ethan Bromberg-Martin and Okihide Hikosaka, who report their results in this week's edition of the journal Neuron.  They were working with a pair of thirsty rhesus monkeys, who had been trained to choose between two different images on a computer screen using their eyes.

In return for picking a target, the monkey randomly got either a big drink or a small drink.  The key point is that looking at one image brought up a symbol showing information about the size of their upcoming reward drink, while picking the other image only brought up a random, unrelated symbol.

The researchers found that after just a few days of training, the monkeys pretty much always picked the image that told them about the size of the reward, even though it didn't affect the size of the drink they got - they just wanted to know what was coming.  The researchers also did a test where the monkeys could choose to look at a symbol telling them that information about their reward was coming up, or a random symbol, and again they showed a strong preference for the information.

The scientists then looked at what parts of the brain were responsible for this, and focused on dopamine-releasing neurons, which are known to be involved in reward pathways.  They recorded the activity of 47 of these nerve cells in the monkeys' midbrains, and found that they became very active when the monkeys were shown the symbol for an upcoming big drink, but the symbol for a small upcoming drink switched them off.

Interestingly, the scientists found that the same group of neurons were also activated in the tests where the monkeys only saw a symbol telling them information was on the way, but switched off if they saw the random, non-informative symbol.

This tells us that the same nerve pathways in the brain are responsible for processing actual physical rewards, as information about upcoming rewards.  Dopamine neurons are thought to work by adjusting the connections between other nerve cells, helping to teach the brain about basic rewards such as food or drink.  But these new results suggest that dopamine neurons also teach the brain to seek out information, as well as just basic physical needs.

Of course, this is research done in non-human primates, but our brains are very similar to those of monkeys, and it's likely that the same pathways may be at work in our brains.  Perhaps these dopamine neurons are very active in Naked Scientists listeners, as they thirst for knowledge.

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