Anhedonia, the inability to experience pleasure from any activities which would typically be found enjoyable. A sufferer cannot feel joy, happiness or any other positive emotions normally found through hobbies, physical exercise, social gatherings and sexual activity. Those with anhedonia have unchanging moods and will feel emotionally empty regardless of what is happening around them.
In a study published in the journal Science, scientists stimulated the brains of rats to induce feelings of anhedonia, seeking to explain how the phenomenon arises in the brain. Hopefully, this understanding could one day lead to better treatments for depression and other related mood disorders.
Anhedonia, which is Greek for ‘without pleasure’, is a symptom of several psychiatric illnesses, including depression and schizophrenia.
Normally when we experience pleasure, the neural signalling chemical dopamine floods a part of our brain’s reward centre called the striatum.
According to Business Insider, as Stanford neuroscientist Emily Ferenczi and her colleagues conducted a further investigation as they used brain imaging and stimulation techniques to induce anhedonia in rats.
First, they stimulated dopamine neurons in the animals’ midbrains (where dopamine exerts its effects) by shining light on light-sensitive nerve cells, a technique known as optogenetics. This caused a boost in activity in the reward area or striatum, which was measured by functional magnetic resonance imaging (fMRI), a technique that detects blood flow in the brain.
Next they stimulated neurons in the rats’ mPFC, and found that it decreased activity in the striatum. In one experiment, the stimulation made the animals lose their interest in drinking sugar water, which they normally prefer over plain water. In another experiment, stimulating the mPFC made rats less social when presented with another young rat.
Finally, stimulating the mPFC strengthened its connections to other areas of the brain, while weakening connections to some regions involved in depression and schizophrenia, the researchers report in the study.
The results suggest that anhedonia causes its effects via the mPFC, which controls the release of dopamine in wide-ranging parts of the brain. These findings are in line with those of several previous studies of anhedonia.
As an after thought, this research reveals how our brain circuitry can go awry and suck the enjoyment out of life – and point toward a possible way to counteract the problem.