Unique brain signal found linked to depression may help treat ‘lack of interest’ symptom

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Scientists have identified a unique brain signal that plays a key role in shaping the influence of rewards on human behaviour, an advance that may lead to new treatments for depression.

Researchers from the Texas Children’s Hospital say the findings may particularly help develop therapies to treat the symptom of anhedonia, or lack of interest, associated with depression.

Humans derive pleasure from a range of mental and physical activities, sensory experiences, and social interactions that tend to affect how the brain is wired.

In both humans and animals, rewards in the form of food treats, gifts, or words of appreciation play a significant role in shaping the brain and behaviours in both humans and animals by serving as positive reinforcement.

However, the exact brain processes behind this phenomenon and how it affects future behaviours largely remains unknown, scientists say.

In the new study, published in the journal Nature Communications, researchers identified unique activity patterns in the brain’s frontal lobe that could be a signature in underlying processes associated with recognizing rewards.

This brain activity may play a role in how humans determine subsequent choices after a reward and shape future behaviours, they said.

The special brain activity was also found to be altered in patients with depression.

“Our study has addressed a longstanding fundamental question in neuroscience – which specific brain region and signal regulates the classic reward bias response, a famous example of which is the Pavlovian conditioning where dogs learned to associate the sound of a ringing bell to food,” study co-author Benjamin Hayden said.

People struggling with depression often experience despair for prolonged periods due to anhedonia – a medical term for the inability to feel joy in activities which were once pleasurable.

The latest findings point to a potential innovative avenue for treating this key symptom of depression when standard treatments fail.

In the study, scientists assessed the brain activity of 15 patients with medication-resistant epilepsy who were being monitored to localize the zone from where their seizures originated.

The participants performed a behavioural task when they were being monitored which objectively measured their anhedonia by observing subtle changes in behaviour related to reward.

Researchers found that a specific signal in the anterior cingulate cortex (ACC) of the brain’s frontal lobe likely plays a key role in evaluating reward stimuli and their outcomes.

“We found that the unequal assignment of reward between two correct responses in this task produced a response bias toward the more frequently rewarded stimulus,” study co-author Jiayang Xiao said.

“We found that based on feedback, most individuals modified their subsequent responses to make choices that were likely to get rewarded, irrespective of the accuracy of their answers,” Dr Xiao said.

Scientists hope the findings may improve the diagnosis and monitoring of patients with severe depression.

“Our findings present an exciting possibility that modulation of the ACC beta activity might be effective treatment anhedonia, a hypothesis we plan to test in future clinical trials,” they added.