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Howe et al (2013) found that a dopamine signal becomes stronger as a goal is approached. The experiment involved rats running in a maze. If the rats were close to solving the maze, the dopamine signal became strong. The intensity of this signal did not depend on how fast the rats completed the maze.

Goal distance was defined in terms of space and distance (i.e. how far a rat was from the end of the maze). Would this dopamine signal also become stronger if the goal distance was defined using time instead? More specifically, if the rats were under some type of time pressure, would their dopamine signals become stronger?

Source

Mark W. Howe, Patrick L. Tierney, Stefan G. Sandberg, Paul E. M. Phillips, Ann M. Graybiel. Prolonged dopamine signalling in striatum signals proximity and value of distant rewards. Nature, 2013

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given that this finding is so new, it may not have been extended to other types of goals yet. very interesting question, though! –  Krysta Aug 22 '13 at 14:26
    
I thought that this finding was new too initially, but....they've been doing studies like these for 20 years. I'll cite some good ones. –  user3433 Aug 26 '13 at 3:15
    
And, that ^ wasn't as easy as I thought. –  user3433 Aug 27 '13 at 9:27
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1 Answer

EDIT: Note: This is an answer in progress, as trying to answer your specific question has led me to finding the answer to many other questions around it, but not that specific one.


Well, when one is in the process of completing a task where they pass by, say, measurable goals, then that's just pure reinforcement and you can literally feel the dopamine pumping through your brain towards the finish line each step you take...especially as you get closer and closer towards the finish line. Everyone has experienced that.

Which actually leads me to another interesting hypothesis, I bet the graph for the dopamine signal of these rats was exponential, wasn't it? I'll go look at the graphs now and check....I seriously havn't looked at them before this. And here they are:

enter image description here

Yup, exponential curves. Interesting the DA [nM] had quite a bit slower rate of acceleration of sloping up than its partner, the shorter timed one.

Whoa, you know what's weird....(and I"m sure they mentioned this in the study too) it looks like the brains of these rats actually know where they are at in the maze after a certain common point - which looks like around 2 seconds) and then the brain increases the signal to just the right spot so that it makes that curve which is like a predefined function in their heads (you could totally regress that) so it will eventually hit a specific point at just the right spot, Nearly the same spot as the rat that had the shorter test. It's a little higher, but not that much. I wonder why there's a big peak and then a drop very end though For that lower orange one.

You know, maybe the implications for that big tip at the end right before the finish line for the orange bottom rat with the long term test could represent our (humans) misrepresentation of how we will actually feel once we accomplish a long term goal and maybe realize that it wasn't as great as we thought it would be...like getting a new car maybe. Traveling. Etc. Maybe the rat just did not perceive the work he had to put in for the longer course to be a fair trade for whatever reward, if there was any reward at the end o the test.

He saw his small plate of cheese and disappointment filled his psyched as he approached it.... :(

Great great study. I bookmarked it, then went to pubmed and realized there are HUNDREDS of studies similar to this, some even in humans, many in monkeys.

Unfortunately I couldn't find what you wanted specifically (although I did find several potential derivatives) and I gotta go to sleep - super tired. I focused more on the studies done in monkeys, which there are a ton of, even though you asked about rats due to the fact that I believe you would like a citation with a mammal closer to humans if possible.

So here's where I left off at: just keep going through the citations on the side. If anyone wants to build upon my unfinished answer with their own answer by using the research I did, feel free to. This is the way academia works most of the time anyways.

http://www.ncbi.nlm.nih.gov/pubmed/2329364

Neuron. 2005 Jul 7;47(1):129-41. Midbrain dopamine neurons encode a quantitative reward prediction error signal. Bayer HM, Glimcher PW. http://www.ncbi.nlm.nih.gov/pubmed/15996553

Proc Natl Acad Sci U S A. 2011 Sep 13;108(37):15462-7. doi: 10.1073/pnas.1014457108. Epub 2011 Sep 6. Dopamine neurons learn to encode the long-term value of multiple future rewards. Enomoto K, Matsumoto N, Nakai S, Satoh T, Sato TK, Ueda Y, Inokawa H, Haruno M, Kimura M. Source Department of Physiology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan. http://www.ncbi.nlm.nih.gov/pubmed/21896766

Science. 2008 Sep 19;321(5896):1690-2. doi: 10.1126/science.1160873. Reward-predictive cues enhance excitatory synaptic strength onto midbrain dopamine neurons. Stuber GD, Klanker M, de Ridder B, Bowers MS, Joosten RN, Feenstra MG, Bonci A. Source Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA 94608, USA. http://www.ncbi.nlm.nih.gov/pubmed/18802002

Nature. 2008 Jun 26;453(7199):1253-7. doi: 10.1038/nature06963. Epub 2008 May 11. Rapid strengthening of thalamo-amygdala synapses mediates cue-reward learning. Tye KM, Stuber GD, de Ridder B, Bonci A, Janak PH. Source Ernest Gallo Clinic and Research Center, University of California, San Francisco, Emeryville, California 94608, USA. http://www.ncbi.nlm.nih.gov/pubmed/18469802

J Neurosci. 1993 Mar;13(3):900-13. Responses of monkey dopamine neurons to reward and conditioned stimuli during successive steps of learning a delayed response task. Schultz W, Apicella P, Ljungberg T. Source Institut de Physiologie, Université de Fribourg, Switzerland. http://www.ncbi.nlm.nih.gov/pubmed/8441015

Neuroscience. 2001;103(1):65-85. Modeling functions of striatal dopamine modulation in learning and planning. Suri RE, Bargas J, Arbib MA. Source USC Brain Project, Los Angeles, CA 90089-2520, USA. suri@salk.edu http://www.ncbi.nlm.nih.gov/pubmed/11311788

J Neurophysiol. 1990 Mar;63(3):607-24. Dopamine neurons of the monkey midbrain: contingencies of responses to stimuli eliciting immediate behavioral reactions. Schultz W, Romo R. Source Institut de Physiologie, Université de Fribourg, Switzerland. http://www.ncbi.nlm.nih.gov/pubmed/2329364

PLoS Comput Biol. 2011 May;7(5):e1001133. doi: 10.1371/journal.pcbi.1001133. Epub 2011 May 12. An imperfect dopaminergic error signal can drive temporal-difference learning. Potjans W, Diesmann M, Morrison A. Source Institute of Neuroscience and Medicine (INM-6), Computational and Systems Neuroscience, Research Center Jülich, Jülich, Germany. w.potjans@fz-juelich.de http://www.ncbi.nlm.nih.gov/pubmed/21589888

Eur J Neurosci. 2000 May;12(5):1801-16. Influence of the predicted time of stimuli eliciting movements on responses of tonically active neurons in the monkey striatum. Sardo P, Ravel S, Legallet E, Apicella P. Source Laboratoire de Neurobiologie Cellulaire et Fonctionnelle, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille cedex 20, France. http://www.ncbi.nlm.nih.gov/pubmed/10792457


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I don't see how this answers the question. (-1) –  H.Muster Aug 26 '13 at 8:23
    
@h.muster It doesn't it's research getting towards answering the question, but does not answer it. It's a hard question to answer. I essentially was trying to get to the answer but midway through had to go to sleep. –  user3433 Aug 26 '13 at 21:41
    
So if you consider your answer incomplete, why do you post it here at all? –  H.Muster Aug 27 '13 at 7:22
    
@H.Muster I spent a long time on it and was hoping someone else could use what I found to answer it, in fact I'm not even sure a study exists that tests what the original question seeks. So if I consider my answer incomplete, but I state that upfront and invite others to jump off of it, why not post it here at all? Does it discourage others? Although a rare strategy, I'm not sure what downsides there are. Can you list some please? –  user3433 Aug 27 '13 at 9:16
    
Please pardon me, but what is the downside of providing an answer that does attempt to tackle the question? Exactly this! I thought that this is a Q&A site, not a brain storming site or a place to drop lots of references that only marginally touch the topic. –  H.Muster Aug 27 '13 at 9:45
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