The equivalent in animals is dopamine: there is no amount of dopamine beyond which an animal would prefer not to get more dopamine.
Dopamine is the brain’s universal signal that something an animal did was good for it.
My understanding is that dopamine signaling is more involved in anticipation of an outcome, to engage the process that coordinates action towards or away from that outcome, rather than in experiencing a reward of having reached a positive outcome. Notably, dopamine is involved in anticipation of negative outcomes as well as positive ones!
In popular culture and media, dopamine is often portrayed as the main chemical of pleasure, but the current opinion in pharmacology is that dopamine instead confers motivational salience; in other words, dopamine signals the perceived motivational prominence (i.e., the desirability or aversiveness) of an outcome, which in turn propels the organism’s behavior toward or away from achieving that outcome.
The wikipedia entry is a little unclear, but it is correct that dopamine is not a pleasure stimulus.
Dopamine is a prediction error signal.
Dopamine is released when animals receive a reward (such as food when hungry, or water when thirsty) that they are not expecting. This causes changes in the brain that increase the probability of the animal initiating whatever action they just did in similar sensory contexts/environments. The animals don’t necessarily “enjoy” the dopamine or want the dopamine, they enjoy and want the food or water.
When we say the food or water is “rewarding” we mean, operationally, that it reinforces (increases the frequency of) the preceding behavior. Mechanistically, we think this reinforcement is mediated by the dopamine signal.
In clicker-training, once the animal knows a clicker sound always predicts a real reward, dopamine is released when they hear the clicker, because this is the moment they get the news that a reward is coming. This brings the timing of dopamine closer in time to the behavior that caused it, improving temporal credit assignment for the neural weight updates. When the actual reward arrives, it is expected, so no additional dopamine is released.
Likewise, once the animal knows (or believes) their behavior in response to a given cue will be rewarded, dopamine is released when they initiate the action, because this is the moment they first get the update that a reward is coming; then no additional dopamine at clicker or reward time as those are expected.
Failure to get an expected reward causes a transient decrease in dopamine at the time the animal had expected the reward. This disappointment signal leads to changes in the brain to decrease the probability of the animal initiating whatever action they just did in similar contexts/environments.
So, this is the sense in which dopamine marks the anticipation or prediction of a reward.
(there is also evidence that dopamine plays a role in signaling unexpected punishments, and that serotonin is also involved in signaling unexpected rewards and/or punishments; but I don’t know the literature on those claims as well).
My understanding is that dopamine signaling is more involved in anticipation of an outcome, to engage the process that coordinates action towards or away from that outcome, rather than in experiencing a reward of having reached a positive outcome. Notably, dopamine is involved in anticipation of negative outcomes as well as positive ones!
Wikipedia (emphasis added)—
The wikipedia entry is a little unclear, but it is correct that dopamine is not a pleasure stimulus.
Dopamine is a prediction error signal.
Dopamine is released when animals receive a reward (such as food when hungry, or water when thirsty) that they are not expecting. This causes changes in the brain that increase the probability of the animal initiating whatever action they just did in similar sensory contexts/environments. The animals don’t necessarily “enjoy” the dopamine or want the dopamine, they enjoy and want the food or water.
When we say the food or water is “rewarding” we mean, operationally, that it reinforces (increases the frequency of) the preceding behavior. Mechanistically, we think this reinforcement is mediated by the dopamine signal.
In clicker-training, once the animal knows a clicker sound always predicts a real reward, dopamine is released when they hear the clicker, because this is the moment they get the news that a reward is coming. This brings the timing of dopamine closer in time to the behavior that caused it, improving temporal credit assignment for the neural weight updates. When the actual reward arrives, it is expected, so no additional dopamine is released.
Likewise, once the animal knows (or believes) their behavior in response to a given cue will be rewarded, dopamine is released when they initiate the action, because this is the moment they first get the update that a reward is coming; then no additional dopamine at clicker or reward time as those are expected.
Failure to get an expected reward causes a transient decrease in dopamine at the time the animal had expected the reward. This disappointment signal leads to changes in the brain to decrease the probability of the animal initiating whatever action they just did in similar contexts/environments.
So, this is the sense in which dopamine marks the anticipation or prediction of a reward.
(there is also evidence that dopamine plays a role in signaling unexpected punishments, and that serotonin is also involved in signaling unexpected rewards and/or punishments; but I don’t know the literature on those claims as well).