MSGID: 1:317/3 648007eb   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    How does dopamine regulate both learning and motivation?    
      
     Date:   
         June 6, 2023   
     Source:   
         Netherlands Institute for Neuroscience - KNAW   
     Summary:   
         A new study brings together two schools of thought on the function   
         of the neurotransmitter dopamine: one saying that dopamine provides   
         a learning signal, the other saying that dopamine drives motivation.   
      
      
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   A new study from the Netherlands Institute for Neuroscience brings   
   together two schools of thought on the function of the neurotransmitter   
   dopamine: one saying that dopamine provides a learning signal, the   
   other saying that dopamine drives motivation. 'But it is probably both',   
   says Ingo Willuhn.   
      
   It is well-known that the dopamine system is implicated in signaling   
   reward- related information as well as in actions that generate rewarding   
   outcomes.   
      
   This can be investigated using either Pavlovian and operant conditioning   
   experiments. Pavlovian conditioning describes how your brain makes an   
   association between two situations or stimuli that previously seemed   
   unrelated.   
      
   A famous example is Pavlov's experiment, where a dog heard a sound before   
   receiving food. After several such pairings of the sound with food   
   delivery, the sound alone began to cause the dog to salivate. Operant   
   conditioning, or instrumental learning, differs from this in that the   
   behavior of an individual is important to earn a food reward. Meaning   
   that the individual after hearing a sound, has to perform a so-called   
   operant action to receive the reward. In animal experiments, such a   
   operant response is often the pressing of a lever.   
      
   Dopamine measurements in nucleus accumbens In the final PhD paper of   
   Jessica Goedhoop in collaboration with Tara Arbab and Ingo Willuhn from   
   the Netherlands Institute for Neuroscience, they take a closer look   
   at the role of dopamine signaling in learning and motivation. The team   
   directly compared the two conditioning paradigms: male rats underwent   
   either Pavlovian or operant conditioning while dopamine release was   
   measured in the nucleus accumbens, a brain region central for processing   
   this information.   
      
   During the experiments a cue light was illuminated for a duration of   
   5 seconds.   
      
   For the Pavlovian group, a food pellet was delivered into the reward   
   magazine directly after the cue light turned off. For the operant   
   conditioning group, turning off the cue light was followed by extension   
   of the lever below the cue light into the operant box. The lever was   
   retracted after one lever press, which immediately resulted in the   
   delivery of one food pellet reward into the food magazine. If there was   
   no lever press within 5 seconds after lever extension, the lever was   
   retracted and no reward was delivered.   
      
   Sustained dopamine release in operant conditioning Rats in both   
   groups released the same quantity of dopamine at the onset of the   
   reward-predictive cue. However, only the operant-conditioning group showed   
   a subsequent, sustained plateau in dopamine concentration throughout   
   the entire 5-second cue presentation (throughout cue presentation and   
   before lever press).   
      
   This dopamine sustainment was observed reliably and consistently   
   throughout systematic manipulation of experimental parameters and   
   behavioral training.   
      
   Therefore, the researchers believe that sustained dopamine levels may   
   be an intermediate between learning and action, conceptually related to   
   the motivation to generate a reward-achieving action.   
      
   Ingo Willuhn: 'There have been a lot of studies on dopamine. We have a   
   decent idea of when dopamine is released in the brain, but there is still   
   lots of discussion on what the precise variables are that determine such   
   dopamine signaling. Essentially discussion on what dopamine "means." To   
   investigate this, scientists usually perform either Pavlovian or operant   
   conditioning experiments. But they test slightly different things. Both   
   have to do with learning an association between a neutral stimulus   
   and a reward. But operant conditioning requires the motivation to   
   perform an action in addition to that (to earn the reward). Therefore,   
   we compared the two types of conditioning in the same experiment.'   
   Adding a piece to the puzzle 'Our results bring together the two camps   
   of scientists that often battle with each other: one says that dopamine   
   is a so-called reward-prediction error signal, meaning that dopamine is   
   released when something better than expected happens, and is suppressed   
   when something worse than expected happens. It is a learning (or teaching)   
   signal. The other camp says that this is not true. They say that dopamine   
   has something to do with motivation. Increased dopamine release will   
   invigorate the subjects and they work harder to get the reward.   
      
   There have been a few attempts in the past to bring these two camps   
   together, but there is still need for more knowledge on the subject.'   
   'What we saw in our study is that only in the operant-learning task   
   dopamine levels stayed high. It seems that the motivation is encoded in   
   this plateau.   
      
   Reward prediction is the initial dopamine peak, but how much the   
   signal stays up, reflects motivation. Thus, our paper suggests that   
   there is a possibility that dopamine is involved in both, learning and   
   motivation. The next steps will be to get more details out of this. We   
   need to replicate the experiments and make them more sophisticated. The   
   more sophisticated you make it, the more precise our predictions   
   have to be. We are going to build on it and see whether it still   
   holds up.'  Implications 'Dopamine is not only involved in everyday   
   life but also in disorders such as addiction, Parkinson's disease, and   
   schizophrenia. Because of the two camps existing, there is disagreement   
   about what happens exactly. For example, some researchers say that when   
   addicts take drugs dopamine release increases and as a consequence all   
   the environmental cues become more meaningful. Addicts learn that these   
   cues are associated with the drug and they take more and more drug,   
   because they are constantly reminded of the drug everywhere. In this   
   view, addiction is misguided learning. Other researchers would say that   
   motivation to take the drug intensifies with more frequent drug intake,   
   because the drug elevates dopamine release. This study indicates that   
   it may be both. Depending on the precise timing, both systems could   
   be the driver, and both could be involved.'  'This is also relevant   
   for the clinic. Prescribed drugs can influence both learning and   
   motivation systems at the same time: and then it can get messy. If   
   you give schizophrenic patients classic antipsychotic medication,   
   they become slow and cannot act much because their motivation system is   
   down. Parkinson's patients take pro-dopamine drugs essentially because   
   they lost their dopamine, but some patients start to gamble because their   
   dopamine system is on overdrive suddenly. We cannot influence learning   
   and motivation components separately. As soon as you give a drug it is   
   going to hit all of it, so it is good to keep that in mind.'   
       * RELATED_TOPICS   
             o Mind_&_Brain   
                   # Parkinson's # Schizophrenia # Illegal_Drugs # Insomnia   
                   # Intelligence # Educational_Psychology # Neuroscience #   
                   Learning_Disorders   
       * RELATED_TERMS   
             o Dopamine o Dopamine_hypothesis_of_schizophrenia o   
             Neurotransmitter o Methamphetamine o Neuroscience o   
             Computational_neuroscience o Emotion o Learning_disability   
      
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   Story Source: Materials provided by   
   Netherlands_Institute_for_Neuroscience_-_KNAW. Note: Content may be   
   edited for style and length.   
      
      
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   Journal Reference:   
      1. Jessica Goedhoop, Tara Arbab, Ingo Willuhn. Anticipation of   
      Appetitive   
         Operant Action Induces Sustained Dopamine Release in the Nucleus   
         Accumbens. The Journal of Neuroscience, 2023; 43 (21): 3922 DOI:   
         10.1523/ JNEUROSCI.1527-22.2023   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230606111734.htm   
      
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