<p>Neurobiology is not my field of expertise, but this paper seems relevant:</p>

<p>Kent C. Berridge, Chao-Yi Ho, Jocelyn M. Richard, Alexandra G. DiFeliceantonio (2010) <a href="http://www.lsa.umich.edu/psych/research&amp;labs/berridge/publications/Berridge,%20Ho,%20Richard,%20&amp;%20DiFeliceantonio%202010%20Tempted%20brain%20eats%20Brain%20Res.pdf">The tempted brain eats: Pleasure and desire circuits in obesity and eating disorders.</a> <em>Brain Research</em>, 1350, 43-64.</p>

<blockquote>
  <p>What we eat, when and how much, all are influenced by brain reward mechanisms that
  generate “liking” and “wanting” for foods. As a corollary, dysfunction in reward circuits
  might contribute to the recent rise of obesity and eating disorders. Here we assess brain
  mechanisms known to generate “liking” and “wanting” for foods and evaluate their
  interaction with regulatory mechanisms of hunger and satiety, relevant to clinical issues.
  “Liking” mechanisms include hedonic circuits that connect together cubic-millimeter
  hotspots in forebrain limbic structures such as nucleus accumbens and ventral pallidum
  (where opioid/endocannabinoid/orexin signals can amplify sensory pleasure). “Wanting”
  mechanisms include larger opioid networks in nucleus accumbens, striatum, and amygdala
  that extend beyond the hedonic hotspots, as well as mesolimbic dopamine systems, and
  corticolimbic glutamate signals that interact with those systems. We focus on ways in
  which these brain reward circuits might participate in obesity or in eating disorders.</p>
</blockquote>

<p>You may also be interested in these two book chapters:</p>

<p>Smith, Kyle, Stephen V. Mahler, Susana Pecina, and Kent C. Berridge. “<a href="http://www.lsa.umich.edu/psych/research&amp;labs/berridge/publications/preprints/Smith%20Mahler%20Pecina%20&amp;%20Berridge%20-%20Pleasure%20chapter%20proofs.doc.pdf">Hedonic Hotspots:
Generating Sensory Pleasure in the Brain.</a>” In <em>Pleasures of the Brain</em>, edited by Morten
L. Kringelbach and Kent C. Berridge, 27–49. New York: Oxford University Press, 2009.</p>

<blockquote>
  <p>A vital question concerning sensory pleasure
  is how brain mechanisms cause stimuli
  to become pleasurable and liked. Pleasure
  is not an intrinsic feature of any stimulus,
  but instead refl ects an affective evaluation
  added to the stimulus by the brain. That is,
  as Frijda expresses it (Frijda, this volume;
  Frijda, 2006), a pleasure gloss or hedonic
  value must be actively ‘painted’ on sweet
  or other sensations to make them pleasant.
  Brain mechanisms of pleasure, whatever
  they are, must take a mere sensory signal
  and transform it into a hedonic and ‘liked’
  reward.</p>
  
  <p>Finding the brain mechanisms responsible
  for painting a pleasure gloss is a major
  challenge for affective neuroscience (Barrett
  and Wager, 2006; Berridge, 2003b; Damasio,
  1999; Davidson, this volume; Davidson and
  Irwin, 1999; Kringelbach, 2005; Kringelbach,
  this volume; LeDoux, 1996; Panksepp,
  1991; Peciña et al., 2006). Fortunately,
  progress on fi nding hedonic generators in
  the brain is being made. In this chapter we
  focus specifi cally on the neuroanatomical
  hedonic hotspots in the brain where neurochemical
  signals actually contribute causally
  to the generation of pleasure.</p>
</blockquote>

<p>Aldridge, J. Wayne, and Kent C. Berridge. “<a href="http://www.lsa.umich.edu/psych/research&amp;labs/berridge/publications/Aldridge%20&amp;%20Berridge%202010%20Neural%20coding%20of%20pleasure%20chapt%203%20in%20Pleasures%20of%20Brain.pdf">Neural Coding of Pleasure: ‘Rose-tinted Glasses’
of the Ventral Pallidum.</a>” In <em>Pleasures of the Brain</em>, edited by Morten L. Kringelbach
and Kent C. Berridge, 62–72. New York: Oxford University Press, 2009. </p>

<blockquote>
  <p>Pleasure is not a sensation. What is it then? Nico Frijda's answer in the "pleasure questions" section of this book (which he suggested a number of years ago) epitomizes an emerging consensus among many psychologists and neuroscientists (Frijda, Chapter 6, this book). He notes that pleasure "is a 'pleasantness gloss' added to whatever is pleasant". [...]</p>
  
  <p>Here we ask: how is a "pleasure gloss" encoded in brain activity? Where in the brain is this glossing operation performed and how does it work? Is it possible for neuroscientists to recognize the signature patterns of neural activity that represent a pleasure gloss? These are difficult questions that are only beginning to be addressed. The "pleasure gloss" metaphor, applied to the transformation of neural signals for a stimulus, is like a varnish that is applied on top of a dull object to transform it into a shiny one. Adding hedonic tone to the signal passed on to downstream structures, the neural gloss effectively gives the entire brain a "rose-tinted" hedonic perception of the stimulus as pleasant.</p>
  
  <p>In the context of neural firing signals, our idea is that a particular pattern of neuronal spikes or action potentials in crucial neurons may apply a glaze of pleasure on what might otherwise be an ordinary sensation or action signal.</p>
</blockquote>

CC BY-SA 3.0
2012-02-27T18:17:55.947Z
Interesting.  I have to say the way they describe this "pleasure gloss" seems so subjective, since it never seems tied back to anything concrete, like a tendency to repeat the behavior in the future.
rob
CC BY-SA 3.0
2012-02-27T09:10:30.167Z
2012-02-27T09:10:30.167Z
Kaj_Sotala
<p>To add to yamad's answer (which is pretty good), for about a decade, the way pain was thought to lower the effect of rewards is by <a href="https://en.wikipedia.org/wiki/Tonic_(physiology)" rel="nofollow noreferrer">tonic</a> release of dopamine; in contrast, pleasure/reward triggers <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556904/" rel="nofollow noreferrer">phasic</a> release of dopamine. If you want an (imperfect) electrical analogy, the tonic release is the "DC" level and phasic are transients or spikes on top of that. <a href="https://doi.org/10.1038/nrn2333" rel="nofollow noreferrer">More correctly</a>:</p>

<blockquote>
  <p>Tonic dopamine activity refers to the level of
  extrasynaptic dopamine that is present at a
  steady-state concentration in the extracellular
  space. [...]</p>
  
  <p>Importantly, tonic
  dopamine levels regulate the responsiveness of
  the phasic dopamine system to salient
  environmental cues: high tonic dopamine
  attenuates phasic dopamine release whereas
  low tonic dopamine facilitates phasic dopamine
  firing. The level of tonic dopamine in the limbic
  striatum is in turn modulated by corticostriatal
  and hippocampal afferents and homeostasis</p>
  
  <p>Increased tonic dopamine is known to result from prolonged stress or pain, a
  mechanism that might have evolved to ensure rest and low activity levels during injury.</p>
</blockquote>

<p>And among the refs cited in support of that is a (pretty highly cited) experiment of <a href="https://www.ncbi.nlm.nih.gov/pubmed/12897785" rel="nofollow noreferrer">Floresco et al. (2003)</a>:</p>

<blockquote>
  <p>we report dissociable regulation of dopamine neuron discharge by
  two separate afferent systems in rats; inhibition of pallidal afferents selectively increased the population activity of dopamine
  neurons, whereas activation of pedunculopontine inputs increased burst firing. Only the increase in population activity increased
  ventral striatal dopamine efflux. After blockade of dopamine reuptake, however, enhanced bursting increased dopamine efflux
  three times more than did enhanced population activity. These results provide insight into multiple regulatory systems that
  modulate dopamine system function: burst firing induces massive synaptic dopamine release, which is rapidly removed by
  reuptake before escaping the synaptic cleft, whereas increased population activity modulates tonic extrasynaptic dopamine
  levels that are less influenced by reuptake.</p>
</blockquote>

<hr>

<p>That was the view circa 2008. A <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4866581/" rel="nofollow noreferrer">2016 review</a> paints a fairly different picture (citing only post-2009 primary studies for this update):</p>

<blockquote>
  <p>Recent studies suggest that dopamine neurons in the VTA [ventral tegmental area] and SN [substantia nigra] form a heterogeneous population tuned to either (or both) aversive or rewarding stimuli.</p>
  
  <p>The heterogeneity of dopamine neurons in response to aversive and rewarding stimuli suggests that they serve unique functional roles. Cells activated by reward and inhibited by punishment are well suited to code motivational valence, whereas neurons activated by both rewarding and punishing stimuli are likely to code motivational salience [stimulus awareness]. Neurons coding motivational valence [whether the stimulus is positive or negative in value] would provide a signal for reward seeking, evaluation, and value learning, in line with current theories on the role of dopamine in reward processing. In contrast, neurons coding motivational salience would provide a signal for detection and prediction of highly important events independent of valence, pursuant to dopamine's role in salience processing. These distinct aspects of dopamine neurotransmission might be neuroanatomically separate: dopaminergic neurons coding motivational valence have been found more commonly in the ventromedial SN and lateral VTA with projections to nucleus accumbens [NAc] shell, whereas neurons coding motivational salience are more often reported in the dorsolateral SN with projections to the nucleus accumbens core.</p>
  
  <p><a href="https://i.sstatic.net/5LfI6.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/5LfI6.png" alt="enter image description here"></a></p>
</blockquote>

<p>It's anybody's guess if this is the correct/complete picture. Time will tell.</p>

<p>The primary evidence for this updated view seems mostly based (in order of the number of citations) on 3 papers:</p>

<ul>
<li>Matsumoto and Hikosaka, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2739096/" rel="nofollow noreferrer">"Two types of dopamine neuron distinctly convey positive and negative motivational signals"</a>, Nature 2009; </li>
<li>Brischoux et al., <a href="https://doi.org/10.1073/pnas.0811507106" rel="nofollow noreferrer">"Phasic excitation of dopamine neurons in ventral VTA by noxious stimuli"</a>, PNAS 2009</li>
<li>Lammel et al., <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3112473/" rel="nofollow noreferrer">"Projection-specific modulation of dopamine neuron synapses by aversive and rewarding stimuli"</a>, Neuron 2011</li>
</ul>

<p>One open problem remains though: how are pain and pleasure balanced by the brain? For example, we expect that an organism could tolerate mild pain in order to reap a reward. Where is this balancing decision made? A tentative answer comes from the authors of the aforementioned review, who in a <a href="https://doi.org/10.1093/scan/nsw173" rel="nofollow noreferrer">newer (2017) empirical study</a> found that the decision area in this case is the medial orbitofrontal cortex:</p>

<blockquote>
  <p><a href="https://i.sstatic.net/jKafo.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/jKafo.png" alt="enter image description here"></a></p>
</blockquote>

<p>Alas this latter study used monetary rewards, so it's not terribly clear how well its result applies to lower species.</p>

<hr>

<p>And on a really interesting [for me] research side, in some species dopmamine signaling not only alters behavior but induces morphological changes in response to the environment; examples include both <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992878/" rel="nofollow noreferrer">predator (e.g. Echinoid larvae)</a> and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4614769/" rel="nofollow noreferrer">prey (e.g. Daphnia)</a> changing their morphology in reaction to prey/predators via dompamine-mediated pathways. Although not obviously related to predator/prey behavior, but to the wider environment; dopamine <a href="https://doi.org/10.1016/j.preteyeres.2017.06.003" rel="nofollow noreferrer">mediates myopia (eye growth) in humans and other species</a>.</p>

<p>Finally, I only focused on the highlighted question at the end of the questotion-body. Your title question is actually substantially broader.</p>

<p>Just with respect to the rewarding side: liking and wanting are thought to have substantially different neurobiological circuitry, cf. the [highly cited] review of <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756052/" rel="nofollow noreferrer">Berridge et al. (2009)</a> (whose closely related work Kaj's answer indicated).</p>

<p>A similarly extensive line of work exists with respect to pain (i.e., the aversive side), e.g. see Baliki and Apkarian (2015) <a href="https://doi.org/10.1016/j.neuron.2015.06.005" rel="nofollow noreferrer">"Nociception, Pain, Negative Moods, and Behavior Selection"</a>.</p>

CC BY-SA 4.0
2018-08-25T13:05:00.697Z
2018-08-26T06:54:24.913Z
2018-08-26T06:54:24.913Z
got trolled too much this week
<p>I think part of the answer to your question is going to include the dopamine "reward" pathway in the basal ganglia. In particular, a leading theory of dopaminergic function is the <strong>predictive reward error</strong> or <strong>reinforcement learning</strong> hypothesis. In this theory, dopamine neurons signal expectations about the outcome of particular stimuli.</p>

<p>Some key experiments are outlined in <a href="http://www.ncbi.nlm.nih.gov/pubmed/9658025" rel="noreferrer">Schultz, 1998</a> (<a href="http://www.cs.ou.edu/~fagg/umass/classes/691c/papers/Schultz_98.pdf" rel="noreferrer">PDF</a>). First, an unexpected reward elicits a short activity increase in dopamine neurons. Second, if a conditioned stimulus (CS) precedes the reward, the dopamine neuron fires in response to the CS but not the reward. That is, the dopamine signal is now a predictive reward signal. Third, if the CS is presented and then the reward does not occur, the response to the CS occurs but the dopamine neuron depresses activity immediately after the reward <em>should have happened</em>.</p>

<p>So the theory goes that dopamine neurons are not simply saying whether a reward has occurred, but rather as a learning signal that adjusts predictions about rewards. If an unpredicted reward occurs, the neuron signals a positive error ("Oops, that was a reward I should know about!"). If a predicted reward occurs, the neuron signals no error at the time of the reward ("shrug, I knew that was going to happen"). If a predicted reward does not occur, the neuron signals a negative error ("Aw shucks, guess that bell doesn't mean food after all.").</p>

<p>A somewhat updated revision of the theory is outlined in a review by <a href="http://dx.doi.org/10.1038/nrn2022" rel="noreferrer">Redgrave and Gurney, 2006</a> (<a href="http://www.people.vcu.edu/~mreimers/SysNeuro/Redgrave%20-%20Dopamine%20and%20context.pdf" rel="noreferrer">PDF</a>). Importantly, they note that dopamine neurons suppress their activity in response to noxious stimuli (the <strong>pain</strong> aspect of your question). They also raise some tough questions about how exactly this dopamine signal interacts with other parts of the brain to mediate the learning suggested in the theory.</p>

<p>As with basically all neurobiology theory, a full understanding of how this signal that we detect in individual neurons translates into a coherent behavioral response program is a long ways away. But the basal ganglia, in general, are sometimes thought of as an action selection system (or "decision path" selection to use your words), so the ability of dopamine neurons to signal expectations is relevant.</p>

CC BY-SA 3.0
2012-02-28T01:33:27.757Z
Where you say "they note that dopamine neurons suppress their activity in response to noxious stimuli"...this is getting at what I am looking for.  Obviously it would be nice to see the other side, that 'dopamine neurons increase their activity in response to pleasurable stimuli', although I suppose this might be implied.
rob
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2012-02-28T01:36:21.047Z
And I don't really know what you mean by "dopamine neurons"...are these just things that are saying "this feels good!" or are they actually things that can contain logic for future behavior, which is the link that I am looking for?  Unfortunately I can't get at the article without paying so all I have to go on is your paraphrase...
rob
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2012-02-28T03:18:45.267Z
@rob try http://meta.cogsci.stackexchange.com/a/205/55
Jeff
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2012-02-28T03:23:27.877Z
@rob they actually contain 'logic', as you say. if they simply responded to hedonic stimuli, they would not respond to a CS. And indeed, this logic codes for 'future behavior': studies show that firing dopamine neurons do not simply reflect the current value of the stimulus, but the *discounted sum of all future values*. Wikipedia TD-learning for more info.
Jeff
CC BY-SA 3.0
2012-02-28T19:08:54.817Z
fyi, this is a pretty good answer, I'm going to dig through those articles.  I'm come back and accept this answer soon, unless of course someone else posts one that gets even closer to what I'm trying to understand. :)
rob
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2012-02-27T17:32:20.470Z
2012-11-02T15:21:04.640Z
2012-11-02T15:21:04.640Z
yamad
<p>If we are to view pleasure and pain as being essentially synonymous with the more mechanistic concept of reward and punishment (i.e. as a part of learning and motivation system) then do we understand how this actually occurs at a neurobiological level?  At least in "lower" animals, pain seems to simply cause an aversion response. Pain motivates the animal to stop whatever it was doing (possibly stopping the pain), and to avoid in the future repeating similar responses to those that preceded (and therefore were possibly causal toward) the incident that caused pain.</p>

<p>This sort of thing is not that hard to replicate in computational models, so it is clearly nothing magical.  Obviously, the subjective "experience" of pleasure and pain gets more into philosophy of mind and that's not what I am asking about. I am only concerned about the mechanism which can explain outwardly observable behavior -- especially in simpler animals -- such as the basic stimulus-response-reward/punishment learning that a mouse or bird can do.</p>

<p><strong>Do we understand the mechanism by which a pain signal causes the brain to suppress recently followed decision paths, and a pleasure signal causes the brain to reinforce them?</strong>  Or is this still completely mysterious at this time?</p>

CC BY-SA 3.0
2012-02-24T12:32:10.343Z
What's the point of calling it “pleasure” if you are not really interested in pleasure itself (i.e. the subjective experience)? What leads you to believe that conscious experience has no impact on outwardly observable behavior or that mice don't have any? It seems to me that there can be no reasonable answer with such conceptual confusion.
Gala
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2012-02-24T17:32:33.450Z
Call it "reward / punishment mechanism" if that makes more sense to you.  I'm from the "brain is a biological computer" camp, so I don't see consciousness or qualia as relevant, since they aren't definable in objective terms anyway (in my opinion).  Regardless, if it helps, forget I used the terms "pleasure" and just look at it as "do we understand the mechanism by which detection of goal satisfaction by the nerves causes the brain to cause recently used stimulus-response connections to be reinforced such that they are more likely to be reused in the future?"
rob
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2012-02-25T02:51:20.307Z
Mildly related [question](http://cogsci.stackexchange.com/q/442/29) I am also going to tag this question as behaviorism to avoid future qualia confusion.
Artem Kaznatcheev
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2012-02-25T09:59:28.633Z
Doesn't Pavlovian response cover this, and dopamine release from toward/away goals? Or are you thinking of something else?
Chris S
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2012-02-25T18:33:10.167Z
@ChrisS , I guess I'm looking for the neurobiological explanation of Pavlovian response.  Specifically, how the thing that we interpret as "pleasure" causes reinforcement, and the thing we interpret as "pain" causes suppression, of previously taken stimulus -> response decision paths.  The best I can find is stuff like this http://www.annualreviews.org/doi/pdf/10.1146/annurev.neuro.24.1.897 , which of course doesn't explain anything unless you shell out money.
rob
CC BY-SA 3.0
2012-02-25T20:37:21.617Z
Actually I should probably not say "Pavlovian" as much as Operant conditioning, since I'm talking about responses we might see as voluntary.  For instance, if I say 'sit', and the dog sits, and then I give the dog a treat....the pleasure from the treat somehow causes the decision path from stimulus (hear the word 'sit') to the response (sit) to be reinforced so that the dog will do the same thing in the future.  A naive implementation might be as simple as "pleasure bathes the brain in a chemical that causes all the 'warm' neurons to grow stronger"
rob
CC BY-SA 3.0
2012-02-26T09:07:51.477Z
@rob I think that you have to pick a frame of reference for your question before someone is going to be able to answer it effectively.  I think its a great question, but I think you are trying to frame it in both a "top down" (which is what I saw in it over in biology, and thought it would be great here) and bottom up (looking at it from the perspective of the individual circuits).  Both analysis methods are equally valid, but trying to reconcile one with the other has plagued researchers.  Much of what you might call pain is
Chuck Sherrington
CC BY-SA 3.0
2012-02-26T09:14:56.960Z
modulated in the spinal cord, and gated at the brainstem, so from a biological perspective, it's hard to quantify in terms of decision paths or framing it as a behaviorist input/output type model.  However, looking at it from the top down, you can gain a lot of powerful insight into what is going on without having to pick apart the minute details.  So, it's just a question of which aspect you want to tackle first to make it more manageable.
Chuck Sherrington
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2012-02-26T21:57:26.380Z
While I don't argue that there are all kinds of complexities, especially in higher mammals....I suspect that at the core, there is something fairly straightforward going on. Say it is "dopamine causes axon growth on neurons that are in their refractory period" -- that simple mechanism would explain simple learning by reward, from heroin addiction in humans to the kind of learning observed in nematode worms (C elegans).  But I've never seen any literature that actually makes a such a connection (heh). About as close as I can get is http://wireheading.com/article/addiction.html
rob
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2012-02-28T08:11:13.503Z
I don't know what “the brain is a biological computer” implies for you but if you mean that behavior is produced by the brain and ultimately explainable by chemical interactions in the brain then you ought to be interested in a (biological) account of feelings and be open to the idea that the relevant structures/processes have a causal role in behavior. Anything else amounts to a wicked kind of dualism, in which feelings happen totally outside of the brain machinery. Conflating pleasure with reward prevents you from even thinking about this problem.
Gala
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2012-02-28T19:03:14.030Z
@GaëlLaurans :  "reward" is not particularly accurate because it can be interpreted as being external...for instance, the treat given to the dog is the reward, but whatever happens in the dogs brain that causes it to be "positively reinforced" due to receiving the treat is the _____.  (I used the word "pleasure" for lack of a better term)
rob
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2012-02-28T19:05:39.207Z
... The way I use "pleasure" as a shortcut is identical to how I might use the word 'perceive redness' as a shortcut for saying 'whatever happens in the eye and brain typically caused by light in the wavelength range of roughly 630–740nm striking the retina but occasionally being caused in other ways'.  Note that I am not concerned about the qualia of redness, as I think that is a concept that is outside of hard science.
rob
CC BY-SA 3.0
2012-02-28T21:25:48.847Z
Whatever happens in the eye is not perception. Whatever happens in the brain does include things like consciousness and science can't simply define it away, no matter how hard it is. Note that studying the subjective experience of redness does not necessarily mean getting lost in philosophical discussion on qualia. There is in fact a lot of very interesting research on color categories and the like.
Gala
CC BY-SA 3.0
2012-02-28T21:55:18.400Z
@GaëlLaurans I don't want to debate philosophy with you. Not here anyway.  I don't think that "consciousness" is anything other than an illusion, but this is not what this question is about.  It is about a particular biological mechanism and what we understand of it.  I used words you didn't think were appropriate, so I reframed the question for you, not using those words. I think others understood what I was getting at, so I'll leave it at that.
rob
CC BY-SA 3.0
2012-02-29T01:10:18.597Z
@GaëlLaurans I'm curious what you have to say about the aspects rob considers irrelevant to his question -- namely, consciousness and pleasure. Could you write up a new question and at least one answer to get the ball rolling?
John Pick
CC BY-SA 3.0
2012-02-29T16:20:58.967Z
Thank you everyone who participated in this.  If anyone is interested, I have been developing a little program (it runs in javascript on a web page) that implements the mechanism I described.  In other words it implements operant conditioning, and graphically demonstrates the "weighting of recently followed decision paths in response to a reward or punishment".
rob
CC BY-SA 3.0
2012-02-29T16:21:23.460Z
My position is that it implements pleasure and pain in a machine, but most people would of course say I am an idiot for making such a claim. :)  If you'd like to see and discuss this offline so that I can get feedback prior to seeking a wider audience, email me: rjbrown at gmail.
rob
<neuroscience><behaviorism><sensation>
Do we understand the non-subjective mechanisms behind pleasure and pain?
rob
# Do we understand the non-subjective mechanisms behind pleasure and pain?

(Asked by: username_0 on 2012-02-23)

If we are to view pleasure and pain as being essentially synonymous with the more mechanistic concept of reward and punishment (i.e. as a part of learning and motivation system) then do we understand how this actually occurs at a neuusername_0iological level? At least in "lower" animals, pain seems to simply cause an aversion response. Pain motivates the animal to stop whatever it was doing (possibly stopping the pain), and to avoid in the future repeating similar responses to those that preceded (and therefore were possibly causal toward) the incident that caused pain.

This sort of thing is not that hard to replicate in computational models, so it is clearly nothing magical. Obviously, the subjective "experience" of pleasure and pain gets more into philosophy of mind and that's not what I am asking about. I am only concerned about the mechanism which can explain outwardly observable behavior -- especially in simpler animals -- such as the basic stimulus-response-reward/punishment learning that a mouse or bird can do.

**Do we understand the mechanism by which a pain signal causes the brain to suppress recently followed decision paths, and a pleasure signal causes the brain to reinforce them?** Or is this still completely mysterious at this time?

**Tags:** neuroscience, behaviorism, sensation

> **Comments:**
> **username_1**: What's the point of calling it “pleasure” if you are not really interested in pleasure itself (i.e. the subjective experience)? What leads you to believe that conscious experience has no impact on outwardly observable behavior or that mice don't have any? It seems to me that there can be no reasonable answer with such conceptual confusion.  
> **username_0**: Call it "reward / punishment mechanism" if that makes more sense to you.  I'm from the "brain is a biological computer" camp, so I don't see consciousness or qualia as relevant, since they aren't definable in objective terms anyway (in my opinion).  Regardless, if it helps, forget I used the terms "pleasure" and just look at it as "do we understand the mechanism by which detection of goal satisfaction by the nerves causes the brain to cause recently used stimulus-response connections to be reinforced such that they are more likely to be reused in the future?"  
> **username_2**: Mildly related [question](http://cogsci.stackexchange.com/q/442/29) I am also going to tag this question as behaviorism to avoid future qualia confusion.  
> **username_3**: Doesn't Pavlovian response cover this, and dopamine release from toward/away goals? Or are you thinking of something else?  
> **username_0**: @ChrisS , I guess I'm looking for the neuusername_0iological explanation of Pavlovian response.  Specifically, how the thing that we interpret as "pleasure" causes reinforcement, and the thing we interpret as "pain" causes suppression, of previously taken stimulus -> response decision paths.  The best I can find is stuff like this http://www.annualreviews.org/doi/pdf/10.1146/annurev.neuro.24.1.897 , which of course doesn't explain anything unless you shell out money.  
> **username_0**: Actually I should pusername_0ably not say "Pavlovian" as much as Operant conditioning, since I'm talking about responses we might see as voluntary.  For instance, if I say 'sit', and the dog sits, and then I give the dog a treat....the pleasure from the treat somehow causes the decision path from stimulus (hear the word 'sit') to the response (sit) to be reinforced so that the dog will do the same thing in the future.  A naive implementation might be as simple as "pleasure bathes the brain in a chemical that causes all the 'warm' neurons to grow stronger"  
> **username_4**: @username_0 I think that you have to pick a frame of reference for your question before someone is going to be able to answer it effectively.  I think its a great question, but I think you are trying to frame it in both a "top down" (which is what I saw in it over in biology, and thought it would be great here) and bottom up (looking at it from the perspective of the individual circuits).  Both analysis methods are equally valid, but trying to reconcile one with the other has plagued researchers.  Much of what you might call pain is  
> **username_4**: modulated in the spinal cord, and gated at the brainstem, so from a biological perspective, it's hard to quantify in terms of decision paths or framing it as a behaviorist input/output type model.  However, looking at it from the top down, you can gain a lot of powerful insight into what is going on without having to pick apart the minute details.  So, it's just a question of which aspect you want to tackle first to make it more manageable.  
> **username_0**: While I don't argue that there are all kinds of complexities, especially in higher mammals....I suspect that at the core, there is something fairly straightforward going on. Say it is "dopamine causes axon growth on neurons that are in their refractory period" -- that simple mechanism would explain simple learning by reward, from heroin addiction in humans to the kind of learning observed in nematode worms (C elegans).  But I've never seen any literature that actually makes a such a connection (heh). About as close as I can get is http://wireheading.com/article/addiction.html  
> **username_1**: I don't know what “the brain is a biological computer” implies for you but if you mean that behavior is produced by the brain and ultimately explainable by chemical interactions in the brain then you ought to be interested in a (biological) account of feelings and be open to the idea that the relevant structures/processes have a causal role in behavior. Anything else amounts to a wicked kind of dualism, in which feelings happen totally outside of the brain machinery. Conflating pleasure with reward prevents you from even thinking about this pusername_0lem.  
> **username_0**: @GaëlLaurans :  "reward" is not particularly accurate because it can be interpreted as being external...for instance, the treat given to the dog is the reward, but whatever happens in the dogs brain that causes it to be "positively reinforced" due to receiving the treat is the _____.  (I used the word "pleasure" for lack of a better term)  
> **username_0**: ... The way I use "pleasure" as a shortcut is identical to how I might use the word 'perceive redness' as a shortcut for saying 'whatever happens in the eye and brain typically caused by light in the wavelength range of roughly 630–740nm striking the retina but occasionally being caused in other ways'.  Note that I am not concerned about the qualia of redness, as I think that is a concept that is outside of hard science.  
> **username_1**: Whatever happens in the eye is not perception. Whatever happens in the brain does include things like consciousness and science can't simply define it away, no matter how hard it is. Note that studying the subjective experience of redness does not necessarily mean getting lost in philosophical discussion on qualia. There is in fact a lot of very interesting research on color categories and the like.  
> **username_0**: @GaëlLaurans I don't want to debate philosophy with you. Not here anyway.  I don't think that "consciousness" is anything other than an illusion, but this is not what this question is about.  It is about a particular biological mechanism and what we understand of it.  I used words you didn't think were appropriate, so I reframed the question for you, not using those words. I think others understood what I was getting at, so I'll leave it at that.  
> **username_5**: @GaëlLaurans I'm curious what you have to say about the aspects username_0 considers irrelevant to his question -- namely, consciousness and pleasure. Could you write up a new question and at least one answer to get the ball rolling?  
> **username_0**: Thank you everyone who participated in this.  If anyone is interested, I have been developing a little program (it runs in javascript on a web page) that implements the mechanism I described.  In other words it implements operant conditioning, and graphically demonstrates the "weighting of recently followed decision paths in response to a reward or punishment".  
> **username_0**: My position is that it implements pleasure and pain in a machine, but most people would of course say I am an idiot for making such a claim. :)  If you'd like to see and discuss this offline so that I can get feedback prior to seeking a wider audience, email me: rjbrown at gmail.  

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## 3 answers

### Answer by username_8 on 2012-02-27. Score: 16 | Accepted answer

I think part of the answer to your question is going to include the dopamine "reward" pathway in the basal ganglia. In particular, a leading theory of dopaminergic function is the **predictive reward error** or **reinforcement learning** hypothesis. In this theory, dopamine neurons signal expectations about the outcome of particular stimuli.

Some key experiments are outlined in [Schultz, 1998](http://www.ncbi.nlm.nih.gov/pubmed/9658025) ([PDF](http://www.cs.ou.edu/~fagg/umass/classes/691c/papers/Schultz_98.pdf)). First, an unexpected reward elicits a short activity increase in dopamine neurons. Second, if a conditioned stimulus (CS) precedes the reward, the dopamine neuron fires in response to the CS but not the reward. That is, the dopamine signal is now a predictive reward signal. Third, if the CS is presented and then the reward does not occur, the response to the CS occurs but the dopamine neuron depresses activity immediately after the reward *should have happened*.

So the theory goes that dopamine neurons are not simply saying whether a reward has occurred, but rather as a learning signal that adjusts predictions about rewards. If an unpredicted reward occurs, the neuron signals a positive error ("Oops, that was a reward I should know about!"). If a predicted reward occurs, the neuron signals no error at the time of the reward ("shrug, I knew that was going to happen"). If a predicted reward does not occur, the neuron signals a negative error ("Aw shucks, guess that bell doesn't mean food after all.").

A somewhat updated revision of the theory is outlined in a review by [Redgrave and Gurney, 2006](http://dx.doi.org/10.1038/nrn2022) ([PDF](http://www.people.vcu.edu/~mreimers/SysNeuro/Redgrave%20-%20Dopamine%20and%20context.pdf)). Importantly, they note that dopamine neurons suppress their activity in response to noxious stimuli (the **pain** aspect of your question). They also raise some tough questions about how exactly this dopamine signal interacts with other parts of the brain to mediate the learning suggested in the theory.

As with basically all neuusername_0iology theory, a full understanding of how this signal that we detect in individual neurons translates into a coherent behavioral response program is a long ways away. But the basal ganglia, in general, are sometimes thought of as an action selection system (or "decision path" selection to use your words), so the ability of dopamine neurons to signal expectations is relevant.

> **Comments:**
> **username_0**: Where you say "they note that dopamine neurons suppress their activity in response to noxious stimuli"...this is getting at what I am looking for.  Obviously it would be nice to see the other side, that 'dopamine neurons increase their activity in response to pleasurable stimuli', although I suppose this might be implied.  
> **username_0**: And I don't really know what you mean by "dopamine neurons"...are these just things that are saying "this feels good!" or are they actually things that can contain logic for future behavior, which is the link that I am looking for?  Unfortunately I can't get at the article without paying so all I have to go on is your paraphrase...  
> **username_9**: @username_0 try http://meta.cogsci.stackexchange.com/a/205/55  
> **username_9**: @username_0 they actually contain 'logic', as you say. if they simply responded to hedonic stimuli, they would not respond to a CS. And indeed, this logic codes for 'future behavior': studies show that firing dopamine neurons do not simply reflect the current value of the stimulus, but the *discounted sum of all future values*. Wikipedia TD-learning for more info.  
> **username_0**: fyi, this is a pretty good answer, I'm going to dig through those articles.  I'm come back and accept this answer soon, unless of course someone else posts one that gets even closer to what I'm trying to understand. :)  

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### Answer by username_6 on 2012-02-27. Score: 6

Neuusername_0iology is not my field of expertise, but this paper seems relevant:

Kent C. Berridge, Chao-Yi Ho, Jocelyn M. Richard, Alexandra G. DiFeliceantonio (2010) [The tempted brain eats: Pleasure and desire circuits in obesity and eating disorders.](http://www.lsa.umich.edu/psych/research&labs/berridge/publications/Berridge,%20Ho,%20Richard,%20&%20DiFeliceantonio%202010%20Tempted%20brain%20eats%20Brain%20Res.pdf) *Brain Research*, 1350, 43-64.

> What we eat, when and how much, all are influenced by brain reward mechanisms that
> generate “liking” and “wanting” for foods. As a corollary, dysfunction in reward circuits
> might contribute to the recent rise of obesity and eating disorders. Here we assess brain
> mechanisms known to generate “liking” and “wanting” for foods and evaluate their
> interaction with regulatory mechanisms of hunger and satiety, relevant to clinical issues.
> “Liking” mechanisms include hedonic circuits that connect together cubic-millimeter
> hotspots in forebrain limbic structures such as nucleus accumbens and ventral pallidum
> (where opioid/endocannabinoid/orexin signals can amplify sensory pleasure). “Wanting”
> mechanisms include larger opioid networks in nucleus accumbens, striatum, and amygdala
> that extend beyond the hedonic hotspots, as well as mesolimbic dopamine systems, and
> corticolimbic glutamate signals that interact with those systems. We focus on ways in
> which these brain reward circuits might participate in obesity or in eating disorders.

You may also be interested in these two book chapters:

Smith, Kyle, Stephen V. Mahler, Susana Pecina, and Kent C. Berridge. “[Hedonic Hotspots:
Generating Sensory Pleasure in the Brain.](http://www.lsa.umich.edu/psych/research&labs/berridge/publications/preprints/Smith%20Mahler%20Pecina%20&%20Berridge%20-%20Pleasure%20chapter%20proofs.doc.pdf)” In *Pleasures of the Brain*, edited by Morten
L. Kringelbach and Kent C. Berridge, 27–49. New York: Oxford University Press, 2009.

> A vital question concerning sensory pleasure
> is how brain mechanisms cause stimuli
> to become pleasurable and liked. Pleasure
> is not an intrinsic feature of any stimulus,
> but instead refl ects an affective evaluation
> added to the stimulus by the brain. That is,
> as Frijda expresses it (Frijda, this volume;
> Frijda, 2006), a pleasure gloss or hedonic
> value must be actively ‘painted’ on sweet
> or other sensations to make them pleasant.
> Brain mechanisms of pleasure, whatever
> they are, must take a mere sensory signal
> and transform it into a hedonic and ‘liked’
> reward.
>
> Finding the brain mechanisms responsible
> for painting a pleasure gloss is a major
> challenge for affective neuroscience (Barrett
> and Wager, 2006; Berridge, 2003b; Damasio,
> 1999; Davidson, this volume; Davidson and
> Irwin, 1999; Kringelbach, 2005; Kringelbach,
> this volume; LeDoux, 1996; Panksepp,
> 1991; Peciña et al., 2006). Fortunately,
> progress on fi nding hedonic generators in
> the brain is being made. In this chapter we
> focus specifi cally on the neuroanatomical
> hedonic hotspots in the brain where neurochemical
> signals actually contribute causally
> to the generation of pleasure.

Aldridge, J. Wayne, and Kent C. Berridge. “[Neural Coding of Pleasure: ‘Rose-tinted Glasses’
of the Ventral Pallidum.](http://www.lsa.umich.edu/psych/research&labs/berridge/publications/Aldridge%20&%20Berridge%202010%20Neural%20coding%20of%20pleasure%20chapt%203%20in%20Pleasures%20of%20Brain.pdf)” In *Pleasures of the Brain*, edited by Morten L. Kringelbach
and Kent C. Berridge, 62–72. New York: Oxford University Press, 2009.

> Pleasure is not a sensation. What is it then? Nico Frijda's answer in the "pleasure questions" section of this book (which he suggested a number of years ago) epitomizes an emerging consensus among many psychologists and neuroscientists (Frijda, Chapter 6, this book). He notes that pleasure "is a 'pleasantness gloss' added to whatever is pleasant". [...]
>
> Here we ask: how is a "pleasure gloss" encoded in brain activity? Where in the brain is this glossing operation performed and how does it work? Is it possible for neuroscientists to recognize the signature patterns of neural activity that represent a pleasure gloss? These are difficult questions that are only beginning to be addressed. The "pleasure gloss" metaphor, applied to the transformation of neural signals for a stimulus, is like a varnish that is applied on top of a dull object to transform it into a shiny one. Adding hedonic tone to the signal passed on to downstream structures, the neural gloss effectively gives the entire brain a "rose-tinted" hedonic perception of the stimulus as pleasant.
>
> In the context of neural firing signals, our idea is that a particular pattern of neuronal spikes or action potentials in crucial neurons may apply a glaze of pleasure on what might otherwise be an ordinary sensation or action signal.

> **Comments:**
> **username_0**: Interesting.  I have to say the way they describe this "pleasure gloss" seems so subjective, since it never seems tied back to anything concrete, like a tendency to repeat the behavior in the future.  

---

### Answer by username_7 on 2018-08-25. Score: 0

To add to username_8's answer (which is pretty good), for about a decade, the way pain was thought to lower the effect of rewards is by [tonic](https://en.wikipedia.org/wiki/Tonic_(physiology)) release of dopamine; in contrast, pleasure/reward triggers [phasic](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556904/) release of dopamine. If you want an (imperfect) electrical analogy, the tonic release is the "DC" level and phasic are transients or spikes on top of that. [More correctly](https://doi.org/10.1038/nrn2333):

> Tonic dopamine activity refers to the level of
> extrasynaptic dopamine that is present at a
> steady-state concentration in the extracellular
> space. [...]
>
> Importantly, tonic
> dopamine levels regulate the responsiveness of
> the phasic dopamine system to salient
> environmental cues: high tonic dopamine
> attenuates phasic dopamine release whereas
> low tonic dopamine facilitates phasic dopamine
> firing. The level of tonic dopamine in the limbic
> striatum is in turn modulated by corticostriatal
> and hippocampal afferents and homeostasis
>
> Increased tonic dopamine is known to result from prolonged stress or pain, a
> mechanism that might have evolved to ensure rest and low activity levels during injury.

And among the refs cited in support of that is a (pretty highly cited) experiment of [Floresco et al. (2003)](https://www.ncbi.nlm.nih.gov/pubmed/12897785):

> we report dissociable regulation of dopamine neuron discharge by
> two separate afferent systems in rats; inhibition of pallidal afferents selectively increased the population activity of dopamine
> neurons, whereas activation of pedunculopontine inputs increased burst firing. Only the increase in population activity increased
> ventral striatal dopamine efflux. After blockade of dopamine reuptake, however, enhanced bursting increased dopamine efflux
> three times more than did enhanced population activity. These results provide insight into multiple regulatory systems that
> modulate dopamine system function: burst firing induces massive synaptic dopamine release, which is rapidly removed by
> reuptake before escaping the synaptic cleft, whereas increased population activity modulates tonic extrasynaptic dopamine
> levels that are less influenced by reuptake.

---

That was the view circa 2008. A [2016 review](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4866581/) paints a fairly different picture (citing only post-2009 primary studies for this update):

> Recent studies suggest that dopamine neurons in the VTA [ventral tegmental area] and SN [substantia nigra] form a heterogeneous population tuned to either (or both) aversive or rewarding stimuli.
>
> The heterogeneity of dopamine neurons in response to aversive and rewarding stimuli suggests that they serve unique functional roles. Cells activated by reward and inhibited by punishment are well suited to code motivational valence, whereas neurons activated by both rewarding and punishing stimuli are likely to code motivational salience [stimulus awareness]. Neurons coding motivational valence [whether the stimulus is positive or negative in value] would provide a signal for reward seeking, evaluation, and value learning, in line with current theories on the role of dopamine in reward processing. In contrast, neurons coding motivational salience would provide a signal for detection and prediction of highly important events independent of valence, pursuant to dopamine's role in salience processing. These distinct aspects of dopamine neurotransmission might be neuroanatomically separate: dopaminergic neurons coding motivational valence have been found more commonly in the ventromedial SN and lateral VTA with projections to nucleus accumbens [NAc] shell, whereas neurons coding motivational salience are more often reported in the dorsolateral SN with projections to the nucleus accumbens core.
>
> [![enter image description here](https://i.sstatic.net/5LfI6.png)](https://i.sstatic.net/5LfI6.png)

It's anybody's guess if this is the correct/complete picture. Time will tell.

The primary evidence for this updated view seems mostly based (in order of the number of citations) on 3 papers:

* Matsumoto and Hikosaka, ["Two types of dopamine neuron distinctly convey positive and negative motivational signals"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2739096/), Nature 2009;
* Brischoux et al., ["Phasic excitation of dopamine neurons in ventral VTA by noxious stimuli"](https://doi.org/10.1073/pnas.0811507106), PNAS 2009
* Lammel et al., ["Projection-specific modulation of dopamine neuron synapses by aversive and rewarding stimuli"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3112473/), Neuron 2011

One open pusername_0lem remains though: how are pain and pleasure balanced by the brain? For example, we expect that an organism could tolerate mild pain in order to reap a reward. Where is this balancing decision made? A tentative answer comes from the authors of the aforementioned review, who in a [newer (2017) empirical study](https://doi.org/10.1093/scan/nsw173) found that the decision area in this case is the medial orbitofrontal cortex:

> [![enter image description here](https://i.sstatic.net/jKafo.png)](https://i.sstatic.net/jKafo.png)

Alas this latter study used monetary rewards, so it's not terribly clear how well its result applies to lower species.

---

And on a really interesting [for me] research side, in some species dopmamine signaling not only alters behavior but induces morphological changes in response to the environment; examples include both [predator (e.g. Echinoid larvae)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992878/) and [prey (e.g. Daphnia)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4614769/) changing their morphology in reaction to prey/predators via dompamine-mediated pathways. Although not obviously related to predator/prey behavior, but to the wider environment; dopamine [mediates myopia (eye growth) in humans and other species](https://doi.org/10.1016/j.preteyeres.2017.06.003).

Finally, I only focused on the highlighted question at the end of the questotion-body. Your title question is actually substantially broader.

Just with respect to the rewarding side: liking and wanting are thought to have substantially different neuusername_0iological circuitry, cf. the [highly cited] review of [Berridge et al. (2009)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756052/) (whose closely related work Kaj's answer indicated).

A similarly extensive line of work exists with respect to pain (i.e., the aversive side), e.g. see Baliki and Apkarian (2015) ["Nociception, Pain, Negative Moods, and Behavior Selection"](https://doi.org/10.1016/j.neuron.2015.06.005).


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