A recent study reveals why bipolar patients are prone to severe mood swings. According to a press release from the Salk Institute, researchers have determined that the brain cells of patients suffering from bipolar disorder are extremely sensitive to stimuli compared to other peoples’ brains.

The study’s findings were published today in the journal Nature, and are among the first that reveal what is happening at the molecular level inside the brain of a bipolar patient. It also suggests that lithium may not be a catchall treatment, working better for some patients than for others.

According to Rusty Gage, a professor at the Salk Institute’s Laboratory of Genetics and lead author of the recent study, “Researchers hadn’t all agreed that there was a cellular cause to bipolar disorder. So our study is important validation that the cells of these patients really are different.”

Over 5 million Americans suffer from bipolar disorder, and a widespread effective treatment strategy remains elusive. If lithium fails to keep the disorder at bay, psychiatrists have a patchwork of various antipsychotics, antidepressants, and mood stabilizers that attempt to address some of the symptoms, but they can only really treat depression or mania, and not both at once.

Cells collected from patients who responded well to lithium treatment revealed how the drug changes them. They placed a sample of neurons in a liquid solution containing lithium, and then measured their sensitivity.

The cells that had grown in lithium were less excitable than cells from a patient who hadn’t received any lithium treatment. The study did not reveal why lithium only works for some patients, but researchers have a jumping point to examine the differences in brain cells between more patients with bipolar disorder in hopes of finding out.