Most people know what it's like to feel sadness, but until recently, there wasn't much research on the science behind the emotion.
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A new study published Thursday in the journal Cell suggests the brain's amygdala and hippocampus play a role. The amygdala is a region of the brain typically associated with the experience of emotions, and more intensely, fear. The hippocampus, which is associated with memory, can also play a role in emotion.
"We really wanted to get at, you know, when you're feeling down or feeling happy, what exactly is happening in the brain at those moments," Vikaas Sohal, lead researcher at the University of California, San Francisco, told NPR.
Although previous researchers have used fMRI and positron emission tomography (PET) technologies and have “revealed fundamental insights into the neural networks of emotion,” scientists wrote, “these experiments cannot identify real-time neural correlates for slower changes in emotional state, such as changes in mood, that evolve over hours or days.”
Instead, their new findings are based on intracranial electroencephalography (iEEG) recordings from the human limbic system, collected over several days as participants periodically rated their mood.
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The recordings were performed in 21 patients with severe epilepsy, all of whom were awaiting brain surgery and then underwent the recordings procedure for the purpose of seizure localization and treatment.
“Because iEEG measures neural activity directly from the brain, these recordings offer the potential to detect fast oscillatory network interactions that correlate in real time with changes in mood,” according to the researchers.
Sohal said he hoped the recordings would help answer the question, “When patients are sitting there, or watching TV or talking with their family or waiting or being anxious, which regions of the brain are talking to each other?”
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He and his colleagues also asked participants to complete mood-state surveys with custom-designed questionnaires.
The team noticed that in most patients, there was “one network that over and over would tell us whether they were feeling happy or sad,” Sohal said. “Maybe you're feeling down and so you start remembering times in your life when bad things have happened, or you are starting to remember those experiences and that is what is making you feel down.”
But the study couldn’t confirm Sohal’s assumptions about the circuit, nor could it show whether that network communication was the result or cause of a mood change, NPR reported. Still, Sohal hopes the findings add a bit of comfort to those with depression.
“As a psychiatrist, it's incredibly powerful to just be able to say to patients, ‘Hey, I know there's something happening in your brain when you're feeling down,’” Sohal said.
The findings — and future research on the topic — may lead to better understanding of mood disorders and potential treatment options, researchers said.
Joshua Gordon, who directs the National Institute of Mental Health, told NPR that finding such circuits in the brain can help scientists think about developing treatment tools aimed specifically at circuits.
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