Why information is its own reward - same neurons signal thirst for water, knowledge

Blogging on Peer-Reviewed ResearchTo me, and I suspect many readers, the quest for information can be an intensely rewarding experience. Discovering a previously elusive fact or soaking up a finely crafted argument can be as pleasurable as eating a fine meal when hungry or dousing a thirst with drink. This isn't just a fanciful analogy - a new study suggests that the same neurons that process the primitive physical rewards of food and water also signal the more abstract mental rewards of information.

i-42e8802e05c5a6453db57d4089c876de-SPOILERS.jpgHumans generally don't like being held in suspense when a big prize is on the horizon. If we get wind of a raise or a new job, we like to get advance information about what's in store. It turns out that monkeys feel the same way and like us, they find that information about a reward is rewarding in itself.

Ethan Bromberg-Martin and Okihide Hikosaka trained two thirsty rhesus monkeys to choose between two targets on a screen with a flick of their eyes; in return, they randomly received either a large drink or a small one after a few seconds. Their choice of target didn't affect which drink they received, but it did affect whether they got prior information about the size of their reward. One target brought up another symbol that told them how much water they would get, while the other brought up a random symbol.

After a few days of training, the monkeys almost always looked at the target that would give them advance intel, even though it never actually affected how much water they were given. They wanted knowledge for its own sake. What's more, even though the gap between picking a target and sipping some water was very small, the monkeys still wanted to know what was in store for them mere seconds later. To them, ignorance is far from bliss.


Bromberg-Martin and Hikosaka demonstrated that even more clearly with a second, slightly different task. This time, the monkeys always received information about their watery rewards and the initial choice of symbol simply determined how quickly this information was provided. After a few goes, the monkeys clearly wanted their info immediately. If the researchers swapped the target that provided the most instant information, the monkeys swapped the direction of their gaze.

This preference for knowledge about the future was intimately linked to the monkeys' desire for water. The same neurons in the middle of their brains signalled their expectations of both rewards - the watery prizes and knowledge about them.

All the neurons in question release the signalling chemical dopamine. While the monkeys were making their choices, Bromberg-Martin and Hikosaka recorded the activity of 47 dopamine neurons in their midbrains. These neurons became very excited when the monkeys saw a symbol that predicted a large amount of water, while the symbol that cued a smaller drink inhibited the neurons. The same dopamine neurons were excited during trials where the monkey only saw the symbol that heralded forthcoming information, and they were inhibited if they monkey only saw the other non-informative symbol.

So the same population of midbrain neurons signal changes in both the thirst for water and for knowledge. The more active they are, the stronger that thirst is. One monkey had a stronger preference for early information than the other and indeed, its dopamine neurons were more active when it saw the informative symbol. Even for each individual monkey, the neurons were more active on specific trials where they showed a preference for advanced knowledge.

Dopamine neurons are thought to be involved in learning about rewards - by adjusting the connections between other neurons, they "teach" the brain to seek basic rewards like food and water. Bromberg-Martin and Hikosaka think that these neurons also teach the brain to seek out information so that their activity becomes a sort of "common currency" that governs both basic needs and a quest for knowledge.

Reference: Neuron 10.1016/j.neuron.2009.06.009

More neuroscience:

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So there is actual objective evidence that curiosity can be as important a desire as food and water! I feel more normal now!!! Thank you!

By oscarzoalaster (not verified) on 15 Jul 2009 #permalink

Nice to know that I'm more normal too! :)

By the way, does this also explain why I get terribly voracious after long hours of tedious, noncreative tasks, but can survive with little or no food as long as I'm engaging something new, fun and educative?

By 5acos(phi/2) (not verified) on 15 Jul 2009 #permalink

There is a description in Neal Stephson's latest book, "Anathem," in which he describes a wine as tasting like drinking your favorite book. I thought that pretty accurately described how I felt about getting info and learning. This study now explains why that is...thanks for posting this.

By Mike Olson (not verified) on 16 Jul 2009 #permalink

I grok this

By Henk Langeveld (not verified) on 16 Jul 2009 #permalink

This is phenomenal. I definitely need to check in here more often.
This helps explain--I think--why hours fly by, with no hunger for food on my part, when I'm writing poetry, or acting!

I collect concepts. I don't really enjoy doing puzzles like crosswords because, while they are amusing, they don't seem to teach me anything of lasting value.

Figuring things out, from the frivolous to the practical, has always been really rewarding for me. Every wrong idea is immediately discarded with relief. After collecting so many concepts, everything in science just keeps getting more exciting because everything is meaningful.

Young children will not watch programs that do not make sense. Grand masters cannot remember pieces on a chessboard better than an ordinary person if the pieces are placed in a random, meaningless way.

I still remember gasping when I first saw the Scientific American article about gravitational lensing. Now, when I read about gravitational microlensing being used to detect planets 20,000 light years away, I derive great pleasure tracing the thread over the last 25 years, and I laugh at the professors who asked me why I was wasting my time reading about that. They will never experience the joy in that aspect of the Universe.

So the more concepts you collect, the more things make sense, and the easier it is to learn more. The pleasure this gives can be nearly as intense as Love, and a kind of love it is. You need not live in a world in which things happen for no reason, and Hell is the impossibility of reason.

You need to get to a critical threshold for the whole process to become self-reinforcing. Unfortunately, most people never get there, so they think it is weird. They are at the mercy of events that could be foreseen, but they just couldn't be bothered, and so live frightened in Denial (see current worldwide depression for examples).

Joseph Campbell said to follow your bliss. It does seem that in life you get what you love... and in the end, that is all you get.

We have no right to use sentient beings for experiments.

By Christopher (not verified) on 20 Jul 2009 #permalink

I find the popular interest in this type of research to be more interesting than the research.

Most of us are aware of what types of activities give us pleasure, pain, anxiety, etc... So why do many people feel like they have learned something when some monkeys or rats or a brain image shows what they already know?

If the monkeys in the above research showed no preference for information in advance, would that change the way you think about how your own brain works?

@Chuck - yes it would change the way I think.
Before I used to think that my thirst for knowledge was unusual and illogical
Now i know that it makes sense.

But wouldn't they get the same results from cows or iguanas or fruit flies?