In the zeitgeist, dopamine is having a moment. In the news and viral social media posts on “dopamine hacking” or listened to podcasts that touch how this molecule in your brain should be harnessed to boost mood and productivity. However, a current neuroscience research suggests that prevalent strategies for controlling dopamine are based on a limited idea of its functioning.
Dopamine is one of the brain’s chemical messengers called neurotransmitters. It works with tracking your reaction to something rewarding like food, sex, money or getting an answer right. There are various kinds of dopamine neurons located in the uppermost part of the brainstem that synthesize dopamine and disseminate it all over the brain. Whether neuron type influences the function of its dopamine production has been open to debate.
The recently published research shows a correlation between neuron type and dopamine function whereby one type of DA neuron plays an unexpected role, making this neurotransmitter quite different from what most scientists, clinicians and members of lay public have thought about it till now.
Dopamine Neuron Firing
At least 50 years ago there was already an idea about how important dopamine is for reward processing. Dopamine neurons keep track of discrepancies between anticipated rewards for a certain act and obtained ones by naming such difference reward prediction errors.
Going out to dinner at a new restaurant which looks like nothing special just yet can illustrate reward prediction errors in action. If your meal is very good, then there will be a positive reward prediction error (RPE) thus you’re likely to come back as well as get same meal next time. With every return trip home RPE gets slightly smaller until eventually amounts to zero when you anticipate great dinner ahead. But if your first meal was terrible, then there will be negative RPE henceforth you probably won’t return back there again.
Reward prediction errors are conveyed by DA neurons through their firing rates as well as patterns of dopamine release used by the brain for learning. They do this in two ways.
Phasic firing is characterized by rapid bursts of dopamine that lead to a short and strong peak. For example, it happens when you receive an unexpected reward or more rewards than you expected; for instance, if your waiter gives you a free dessert or put on your check a nice note with smiley face. Phasic firing codes reward prediction errors.
On the other hand, tonic firing means background activity interspersed with phasic bursts which occurs slowly for these neurons between no surprises. Tonic firing is like valley floors whereas phasic firing is like mountain peaks.
Dopamine Functions
However, dopamine does more than just tracing information utilized in generating REWARD PREDICTION ERRORS. I have always been interested in all other roles played by dopamine from my own research that measures brain areas containing dopamine neurons among humans.
It is approximately fifteen years ago, since there were the first reports indicating that dopamine neurons do respond to aversive events like a puff of air on your eye, a mild electric shock or losing money, which was previously considered to be impossible for dopamine. According to these studies, some dopaminergic neurons only react to reward while others respond both rewards and negative experiences leading researchers to believe that there could be more than one dopamine system in the brain.
Thereafter came several other experiments which also showed that indeed there is more than one type of dopamine neuron. Recently research has determined seven different dopamine neurons by considering their genetic profiles.
The article published in August 2023 was the first study dissecting dopamine function with respect to neuron subtype. In this research by Northwestern University’s Dombeck Lab focused on three kinds of dopamine neurons namely, two monitored rewards and aversive events while one tracked movement such as when mice used in the trial started running faster.
Dopamine release
Present media discussions about managing effects of dopamine have been based only on spike-like bursts. During phasic burst firing of dopamine neurons, (for signaling reward prediction errors) release occurs throughout the brain. These peaks happen too fast as they can occur many times within seconds by these dopamine cells.
On another note, sometimes it increases slowly until you get a desired reward. In a part of the brain called striatum this ramp pattern has been found by researchers; ten years ago. The steepness of the ramp reflects how valuable a reward is and how difficult it is to obtain it i.e., motivation encoding.
This can also be explained using an example from restaurant setting where release occurs slowly over time (ramp). As you wait for your amazing meal that you just ordered your levels of Dopamine keeps increasing steadily reaching crescendo proportions when eventually the waiter puts food before you and you start eating.
However, the exact mechanisms underlying dopamine ramping are still unknown and this type of release might relate to goal pursuit and learning. Future research on dopamine ramping will affect how scientists understand motivation and will ultimately improve advice on how to optimally hack dopamine.
Dopamine(s) in disease and neurodiversity
Dopamine has been commonly associated with drug addiction, neurodegenerative diseases and neurodevelopmental disorders such as attention-deficit/hyperactivity disorder (ADHD); but recent studies indicate that this understanding may soon change. Function of only three out of seven known subtypes of dopamine neurons have been characterized by researchers so far.
In fact there is some evidence already that the understanding of disease is being updated with the discovery of dopamine diversity. The authors of a recent paper which related dopamine neuron type with function noted that in Parkinson’s disease those dopamine neurons whose work was focused on movement were one among the most affected while two other types did not show much damage. This could open up more specific treatment options for patients.
In the future, information about the variety of dopamine will keep changing and getting better; hence better understanding related to diseases and brain diversity.
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