How Dopamine Works

As we previously explained, dopamine is one of more than 100 chemicals known as neurotransmitters, which enable neurons in the brain to communicate with one another and manage everything that happens in our body [source: Purves et al.].

Like all neurotransmitters, dopamine goes through a cycle, which begins with it being synthesized by a neuron (called the presynaptic cell). That cell releases the dopamine and it floats out into the synapse, the gap between neurons, and then makes contact and binds with structures called receptors on the other neuron, which then transmit the signal to the second neuron. After the dopamine accomplishes its mission, it's rapidly removed and degrades. The effects of dopamine on your brain depend a lot on which neurons are involved and which receptors are binding the dopamine [sources: Brookshire, Purves et al.].

As molecules go, dopamine is fairly compact, consisting of just 22 atoms. Only a tiny portion of the brain's 100 billion or so neurons — as few as 20,000 — generate dopamine, most of them in midbrain structures such as the substantia nigra, which helps control movement, and the prefrontal cortex [sources: Angier, Deans].

Those specialized neurons make dopamine by taking an amino aside called tyrosine and combining it with an enzyme, tyrosine hydroxylase. Add another step to the chemical reaction and you would get a different neurotransmitter, norepinephrine [source: Deans].

In terms of evolutionary history, dopamine has been around for a long time, and it's found in animals from lizards to humans. But people have a lot of dopamine and over time, we seem to have evolved to produce more and more of it, possibly because it helps enable us to be aggressive and competitive. As evolutionary psychiatrist Emily Deans wrote in 2011, "dopamine is what made humans so successful." Researchers have found that humans have about three times as many dopamine-producing neurons as other primates [source: Parkin].

Dopamine's function at the most basic level is to enable signals to pass through synapses from one neuron to another. But that's the high-level view. Up closer, the networks that use dopamine are composed of vast numbers of neurons, and the effects of releasing dopamine can vary, depending upon what types of neurons are involved and which of the five different types of receptors are using the dopamine to connect the neurons. The particular role the neurons are playing can also be a factor [source: Brookshire].

Dopamine's effects depend upon which of the four pathways is used in the brain and body where it's working to facilitate communication. The first is the nigrostriatal tract, which has to do with motor control in the body. When neurons in that system stop working, it can lead to disorders such as Parkinson's.

Another is the mesocortical pathway, which runs from the ventral tegmental area to the dorsolateral frontal cortex in the brain. It's the pathway associated with planning, prioritizing, responsibility and other executive function activities.

There's also the tuberinfundibular pathway, which connects the hypothalamus and the pituitary gland, and blocks the secretion of milk in the female breast. Blocking this pathway of dopamine enables breastfeeding.

Finally, there's the mesolimbic pathway, which is connected to the brain's limbic system, which controls reward and emotion, and includes the hippocampus and the medial frontal cortex. That's the pathway that gets the most attention, since it's connected with problems such as addiction[source: Deans].

Dopamine plays a role in kidney and heart function, nausea and even psychosis. Many treatments for schizophrenia target dopamine [source: Brookshire].

Until recently, not much was known about the precise mechanisms by which neurons use dopamine. It was thought that it mostly took place through something called volume transmission, in which dopamine spread slowly and nonspecifically across large areas of the brain, and in the process happened to make the right contacts with the certain neurons. But in 2018, Harvard University medical researchers published a paper revealing that specialized sites on those cells release dopamine in an extremely fast —think milliseconds — and precise manner to target sites [source: Jiang].

But all that probably seems ho-hum to you, so in the next section, let's get back to the role of dopamine in the brain's reward system and in pleasure.

The earliest experiments involving dopamine function were performed back in the 1950s and 1960s by a researcher named James Olds, who discovered that when rats' brains received a jolt of electrical stimulation in a certain area, they'd keep performing an action such a yanking a lever over and over [source: Chen].

Because dopamine played a role in transmitting the signals, scientists initially suspected that it had something to do with pleasure. People with clinical depression tend to have low levels of dopamine in their brains, which led researchers to hypothesize that low levels of dopamine caused a person to experience less pleasure.

That idea keeps bouncing around in the popular media, because it seems to make good sense. But by the late 1980s, it had been disproven by research. In experiments, animals whose dopamine cells were killed off by drugs still seemed to enjoy the taste of sugar when it was squirted into their mouths, as evidenced by their facial expressions. But they wouldn't seek out additional tastes of the sugar [source: Chen].

While dopamine doesn't cause pleasure, it does influence how pleasure affects the brain. But there are different views of how it accomplishes that. One school of thought is that dopamine's biggest influence is reinforcing the pleasure, so that the brain develops an expectation of experiencing that outcome from the action [source: Chen]. Research on gamblers, for example, have shown that their brains experience as much dopamine activity when they come close to winning as when they actually win. It's almost as if the chemical is urging them on, telling them that they'll win the next time (even if they didn't last time) [source: Chase and Clark].

Another view is that dopamine simply helps the brain to feel more motivated to do something so that the body feels energetic enough to pull that lever again and again [sources: Chen, Salamone and Correa].

Dopamine doesn't force someone to stick a needle into his or her arm, smoke meth or take a hit from a crack pipe, nor does it create the pleasure that a drug user experiences from getting high. But dopamine does play a role in drug abuse and addiction, by reinforcing the effects of using those drugs.

When a person gets high, it causes a surge in production of dopamine in the neurons in the striatum, including the nucleus accumbens, structures that are part of the brain's reward network. That increase in the chemical enables neurons to make more connections, and plays an important role in programming the brain to connect drugs with pleasure, so that it develops an expectation of a reward and motivation to take them again [source: Volkow, Fowler and Wang, et al.].

"Large surges of dopamine teach the brain to seek drugs at the expense of other, healthier goals and activities," warns an article on the National Institute on Drug Abuse's website.

But while dopamine increases when someone uses certain drugs, not everybody who experiences that surge necessarily becomes an addict. Instead, scientists believe, dopamine acts in combination with a range of other genetic, developmental and/or environmental influences to program some people's brains to develop a compulsion to take those drugs. Imaging studies, for example, have found that people who turn into addicts may already have differences in their dopamine circuitry that make them more vulnerable to getting hooked [source: Volkow, Fowler and Wang, et al.].

The dopamine produced from using drugs is much more intense and long-lasting than the dopamine response from something like eating or another normal activity. Also unlike eating, the dopamine response from drugs doesn't stop when the act is over. The overflow of dopamine is what produces the high.

When an addict uses drugs repeatedly, his or her brain changes in response. It tries to compensate for the surge in dopamine production by shutting down some of its dopamine receptors. But that only exacerbates the situation. The brain is still programmed to want the pleasure that the drugs created, so an addict has to use more and more of the drug to replicate the effect. Additionally, shutting down dopamine receptors reduces the amount of pleasure that an addict gets from any activity, not just taking drugs — a condition called anhedonia. That also may drive a person to shoot up more heroin or smoke more and more meth, because nothing else feels good anymore.

Finally, having fewer dopamine receptors is associated with an increase in impulsivity, which may lead an addict to engage in increasingly reckless behavior in pursuit of a high [source: Butler Center].

Just as dopamine plays a role in drug addiction, it also can help wire a person's brain to engage in other sorts of risky behavior, such as gambling, dangerous sports and promiscuous sex. And some people appear to be naturally wired to take those sorts of chances.

The reason is that dopamine-producing neurons have structures called autoreceptors, which help to limit dopamine release when those cells are stimulated. In a study published in 2008, Vanderbilt University researcher David Zald and colleagues found that people who have a high tolerance for taking risks tend to have fewer of these autoreceptors, while people who shy away from anything that might seem dangerous tend to have more. That means that risk-takers tend to have larger amounts of dopamine released in their brains.

"The fewer available dopamine autoreceptors an individual has, the less they are able to regulate how much dopamine is released when these cells are engaged," Zald explained in a 2008 Vanderbilt press release. "Because of this, novelty and other potentially rewarding experiences that normally induce dopamine release will produce greater dopamine release in these individuals."

And having high levels of dopamine can stimulate risk-taking behavior. A study published by University College London researchers in 2015 found that subjects whose dopamine level was boosted with medication more often chose risky options that involved potential gains in experiments, though the same effect wasn't seen when the risky options involved potential losses. The researchers noted that their work identified an influence upon decision making and emotion that was distinct from dopamine's established role in training the reward system [source: Rutledge, Skandali, Dayan and Dolan].