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Have you ever felt the rush of racing down a back-country road at 90 miles per hour, the tingling feeling of slowly creeping up the track of a roller coaster, each tick pinging your stomach with a wild sensation of excitement and fear combined?

For individuals living with anhedonia -- a condition in which the patient is no longer able to feel pleasure -- these mind-blowing experiences feel flat, emotionless, and unenjoyable.  

In a recent study published in Science, researchers stimulated the brains of rats to induce the feelings of anhedonia, in hopes of finding a way to better explain how the phenomenon arises in the brain.

Anhedonia

"Anhedonia," Greek for "without pleasure," is a symptom of various psychiatric illnesses including schizophrenia and depression.

When we experience pleasure, dopamine flows through our brain's "reward center" -- the striatum.

According to Joshua Garfield, pleasure can be broken down into two categories: anticipatory and consummatory.  

"So you've been invited to dinner with a friend, and they tell you they're cooking one of your favorite foods," he told ScienceAlert. "You experience anticipatory pleasure upon hearing this news, and -- assuming they actually cook it well -- consummatory pleasure during and immediately after eating it."

Both anticipatory and consummatory pleasure play a key role in our ability to learn.

"If you feel a great deal of anticipatory pleasure, but then the thing you were anticipating turns out to be underwhelming, this may register as a 'prediction error' that helps you reassess the value of the goal," Garfield said.

The Study

In the experiment, Stanford neuroscientist Emily Ferenczi used brain imaging and stimulation techniques to induce anhedonia in rats. Her findings showed that anhedonia affects the mPFC (medial prefrontal cortex), which controls the release of dopamine into the striatum.

"We have integrated a diverse set of chronic and acute optogenetic tools with functional magnetic resonance imaging (fMRI) to provide a bridge between the causal, cellular specificity of rodent optogenetics and the brainwide observations that characterize human neuroimaging, with the goal of locally manipulating and globally visualizing neural activity to understand the regulation of reward-seeking behavior," Ferenczi wrote.

Treatment

Anhedonia is typically treated according to the disorder it's associated with rather than as a disease itself. If depression is considered the cause, for example, a doctor might recommend medication or personal therapy.