The discovery of the biomarker could lead to advances in less invasive treatments that modulate brain activity
“Like a symphony where you have some high-pitched instruments and some low-pitched instruments, we can take these brain signals and decompose them into frequencies in different ranges." Christopher Rozell, neuroengineer, Georgia Institute of Technology and study co-author
Scientists have found a new biomarker in the brain that represents the first known signal for the presence or absence of depression.
The biomarker was discovered during a trial involving 10 people in which deep brain stimulation (DBS) was used to ease symptoms in people with severe depression. The intervention involves using implanted electrodes to stimulate the brain with pulses of electricity.
The implanted device not only delivered electricity to the brain, it sensed neural activity. Analysing that activity, and correlating it with clinical ratings, led researchers to a biomarker that indicated when a person was better. This appears to be the first known signal of the presence or absence of depression in the brain.
Helen Mayberg, a neurologist at the Icahn School of Medicine at Mount Sinai, and co-senior author of the study, told Scientific American: “This is to me, studying depression for more than 30 years, the closest clue to know, fundamentally, ‘What is depression, and how do we think about how the brain can be repaired?’”
The new biomarker lets doctors know when a person’s symptoms call for an adjustment in the stimulation and when they don’t. If tested further, it might even serve as a predictor of depression relapse. This would enable a larger number of doctors to care effectively for people who have undergone DBS.
“This biomarker suggests that brain signals can be used to help understand a patient’s response to DBS treatment and adjust the treatment accordingly,” said Joshua A. Gordon, director of NIH’s National Institute of Mental Health. “The findings mark a major advance in translating a therapy into practice.”
During the six months of the trial, the device collected brain data that displayed the combined activity of thousands of neurons. “Like a symphony where you have some high-pitched instruments and some low-pitched instruments, we can take these brain signals and decompose them into frequencies in different ranges,” said Christopher Rozell, a neuroengineer at Georgia Institute of Technology, co-senior author on the study.
The study participants also had a weekly clinical assessment. Within a couple of months, most participants felt somewhat better. After six months, symptoms had diminished by at least half in nine of the 10 individuals, and seven achieved remission. Only six of them, however, had usable brain data, and five of the six showed the typical pattern of improvement.
Using data from those five people, Rozell and his team built artificial intelligence software to compare participants’ brain wave patterns at the start of the study, when they were sick, with those patterns at the end, when they were better. The researchers found a coordinated change in a few frequency bands that could distinguish a sick brain from a brain that was well to 90% accuracy. “It’s the very first time that we’ve really been able to get a brain readout of recovery,” said Rozell.
The finding might also lead to advances in less invasive treatments that modulate brain activity, such as TMS, which involves placing a coil on the scalp to create a magnetic field, according to Gordon Baltuch, a neurosurgeon at Columbia University Irving Medical Center. “Neuromodulation could potentially help a cohort of people who have a disease which is not only disabling but is fatal,” to tens of thousands of people in the USA every year, he said.
There is also a possibility that other biomarkers for depression could be discovered – if, for example, changes in a person’s face or voice, or in brain waves detected at the surface of the brain, were found to correlate with the internal signal. The researchers in the DBS study found a pattern of facial expressions that changed in tandem with the brain’s state, which is a promising sign.
“There are probably many ways we will be able to read out from the brain, invasively and non-invasively,” said Rozell. “It opens the floodgates for people to be able to look for these sorts of signals.”
There has long been a debate about whether the causes of depression are biological or social in origin – or, as some believe, a combination of the two. This new research has, for the first time, discovered a biomarker in the brain that correlates to with the presence of depression. This correlation does not demonstrate causation, of course, but the most significant part of the discovery is that clinicians will now be able to use the presence or absence of the biomarker to track whether patients are getting better or not. Some people have severe depression that is resistant to most conventional treatments, and there is now hope that direct brain stimulation can be used in a more targeted way to treat that group of patients.