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A new study published in the Journal of Nature aimed to understand the neural code of stress to control anhedonia.

“The goal of the study was to understand what drives reduced reward-seeking in individuals who are susceptible to traumatic stress,” study author Mazen A. Kheirbek told us. “We were hoping to identify patterns of activity in the brains of mice that may be related to this process of anhedonia, and patterns that are associated with resiliency to developing anhedonia.”

The researchers believed these patterns may be present in the amygdala, a part of the brain known to be sensitive to stress and involved in reward-seeking behaviors. 

Anhedonia is a very common and debilitating feature of depression. People with anhedonia can experience a lack of motivation and enjoyment in activities that once brought joy. 

Nearly three quarters of individuals who suffer from depression have symptoms of anhedonia. Anhedonia can also exist within other mental health disorders but it’s most prevalent in association with depression. Interestingly, anhedonia has been found to be experienced by some people dealing with epilepsy, about 35 per cent.

“We used mouse models of stress, and electrophysiology to identify patterns of activity that differ between stress susceptible and resilient mice,” Kheirbek told us. “We found that there exists a pattern of activity in mice susceptible to stress that is related to indecision.” 

This pattern of activity interferes with normal reward processing and may be leading the mice to make fewer high-value reward choices. Stimulation of an input into the amygdala from the hippocampus could reverse this process and rescue the anhedonic behavior.

“The brain stimulation results were surprising and exciting,” Kheirbek told us.  “Showing that you could enhance brain dynamics related to resiliency (while also wiping out dynamics related to susceptibility) was very cool. We can hopefully begin to look for these kinds of dynamics in the human brain.”