You know the feeling.
That smug, down-to-the-bone sense of satisfaction you get when you've done something great.
Whether it's hitting a new PR at the gym, getting into a flow state that lets you get through a mountain of work, or finally achieving a goal you've been working towards, that feeling can be deeply motivating to keep up the good work.
That feeling is dopamine cascading through your body.
Dopamine is a neurotransmitter produced by the brain, which acts as a chemical messenger between brain cells. Although it is produced by just a handful of cells, dopamine has a powerful effect on many physical and cognitive functions, including movement, motivation and memory.
It’s also responsible for the feelings of reward and pleasure, which is why it’s also called “the pleasure neurotransmitter”.
On the down side, dopamine is also responsible for addictive behaviors, like addiction to drugs, food, shopping, sex, gambling, and various other addictions.
(The reason that drugs like cocaine, amphetamines and heroin are so addictive is that they increase the release of dopamine and then act as dopamine re-uptake inhibitors - meaning that dopamine is active in the brain for extended periods.)
Now, you’re probably not a drug addict. So what does all this have to do with you?
Well, what if you started thinking about achieving your goals with the same satisfaction an addict thinks about the next fix?
You would be one of the most driven and productive people you know.
The good news is that your brain is already wired for that, because dopamine is also released by positive experiences. It happens every time you achieve a goal, when you exercise, or have a good social interaction.
Dopamine improves many aspects of cognitive performance, including motivation, memory and focus. Studies in lab animals have shown that dopamine is crucial for the formation of memories, and it appears to be particularly important for motivation-based learning  and goal-directed behavior .
Or, put simply, dopamine is what allows us to form lasting memories , and makes us want to “get after it” and get the job done.
Now, although the ability to memorize things is important, improving memory alone is not enough to set us apart as star achievers.
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Your success in life is more dependent on your ability to learn from your experiences, and to be able to distinguish good decisions from bad.
In a study published in the journal Nature , volunteers were treated with drugs that either increased or decreased dopamine levels, and were then asked to perform a reward-based learning task. Each volunteer was shown pairs of symbols on a computer. Each symbol had a certain amount of money assigned to it, with some symbols representing loss, and others gain. Researchers then assessed the participants’ ability to maximize their gain.
As it turned out, the volunteers who had the highest levels of dopamine ended up with the most money at the end.
Every time the participants were rewarded for choosing the correct symbol, their dopamine committed that positive experience to their memory and helped them remember how to replicate the experience later.
Another study  has shown that participants with low levels of dopamine in the brain were more impulsive compared to those with higher dopamine levels.
All of this evidence indicates that dopamine plays an important role in mental performance and tapping into this system has the potential to improve memory, learning, decision-making and planning.
It is important to note, however, that the relationship between dopamine levels and performance follows an inverted U-shaped curve . That is, both excess and deficiency can impair mental performance. For that reason, the trick to optimal performance is not to increase dopamine as much as you can, but to find a balance in the middle of that U-shaped curve.
Everything in moderation, even when it comes to dopamine.
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Dopamine can also have a profound impact on your physical and athletic performance.
To a certain extent, all the functions mentioned above - improved learning, motivation and focus - have huge benefits on our physical performance, but dopamine does even more than that.
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Studies on lab rats  have shown that running increases the activity of brain cells that produce dopamine. What is even more interesting is that this effect is more pronounced in trained rats  who have been running for 8 weeks than in untrained rats (8 weeks in rat years being roughly equivalent to a couple of human years).
When the researchers examined rats that were genetically bred specifically for high-capacity running (taking the term rat-race to a whole new level), they observed that these rats were more sensitive to dopamine than their regular-running counterparts. These rats also had a higher dopamine turnover, meaning that dopamine-producing neurons were more active.
These studies show that genetic differences in dopamine expression may account for the better performance in some rats, and that efficiency of dopamine signalling might predict physical abilities. So, if you are a lab rat (especially one who likes to run), dopamine can really enhance your performance.
But what about humans?
Unfortunately, the story in humans is not as clear, although it does appear that dopamine can improve physical performance in some situations.
There are several possible reasons for discrepancies in studies on humans, and most stem from the fact that scientists do not have as much control over our environment like they do with rats. Although some studies did not find that dopamine affects physical performance, other studies do confirm the same findings as in lab animals.
Just like in rats, genetic differences in the dopamine receptor gene may explain different exercise capacity in different people. One study  has shown that although prolonging dopamine activity does not affect athletic performance of cyclists in mild weather, it did improve their time-trial scores in hot weather. This result indicates that dopamine may be important in increasing exercise capacity under stressful conditions (such as heat) and ties back to the idea that dopamine delays the central nervous system fatigue during intense exercise.
These studies imply that in regular folks, exercise briefly increases dopamine levels in the brain, making us feel energized and focused, but as dopamine becomes depleted, fatigue sets in.
In elite athletes, dopamine does not get depleted as quickly, leaving them in the state of heightened performance for a longer period of time. So, if we can raise our levels of dopamine and make it hang around the brain a little longer, we could mimic the endurance and maybe even performance of elite athletes.
Further evidence of the impact of dopamine on mental and physical performance comes from patients with Parkinson’s disease.
Parkinson’s disease is characterized by the loss of cells that make dopamine. The most obvious symptoms of the disease are related to movement, and include tremors, slow movement and rigid muscles. However, Parkinson’s patients often have cognitive symptoms as well, such as difficulties with planning and organization, focus and memory.
Fortunately, treatment with a dopamine precursor not only improves motor symptoms, but can also restore memory, focus and planning ability .
While Parkinson’s disease is the most severe form of dopamine deficiency, there are also milder symptoms of dopamine depletion.
Some signs of low dopamine levels are:
- Inability to handle stress
- Mood swings
- Inability to concentrate
- Failure to finish tasks
- Low sex drive
- Gastrointestinal disturbances
While none of these symptoms are caused exclusively by low dopamine, balancing your dopamine levels can improve both physical and cognitive symptoms. This is especially important considering that dopamine depletion can be caused by a wide variety of dietary and lifestyle factors, including overtraining, frequent alcohol use, excessive sugar, caffeine, stress, lack of sleep and drug use.
"Dopamine depletion can be caused by lifestyle factors, from overtraining to excess alcohol."
While we can easily stay away from some of these situations, others are probably part of your everyday life and are not easily avoided.
Some of us deal with low dopamine productively by exercising, meditating or paying extra attention to our nutrition. Others try to overcome sleep deprivation by drinking coffee all day, satisfy their hunger with junk food, “relax” with a drink or two every evening, or even exercise to the point of exhaustion.
People in the second group do things that raise dopamine levels briefly, but end up lowering them even further in the long term. In the meantime, their productivity and performance continue to suffer and only end up causing more stress.
Dopamine improves every aspect of human performance. So whether you're trying to get a great time on your next marathon, or need the mental edge to turn in a game-changing piece of work, it's dopamine that will help you get motivated to get it done.
It contains all the necessary precursors and cofactors to help your body balance its dopamine levels so you can be at your best every day.