More and more, doctors and patients dealing with severe depression, obsessive compulsive disorder, or even Parkinson’s disease turn to techniques such as deep brain stimulation and transcranial magnetic stimulation. While those treatments have proven effective in some cases, it has been unclear why the hodgepodge of stimulation sites and techniques all seem to work. A new study suggests one possibility: the different methods each activate parts of the brain common to one of its resting state networks.
For a few decades now, neuroscientists who specialize in functional magnetic resonance imaging, or fMRI, have focused on what our brains do when we do math problems, play games, choose between politicians, and much more. But as early as the mid-1990s, researchers realized they’d been missing something: What happens when we’re not doing anything at all? With that question, they began to explore what’s called the default mode network and other resting state networks (RSNs), collections of brain regions that are active and working together specifically as we let our minds and senses wander. But no one is quite sure what exactly these networks do.
As early as the mid-1990s, researchers realized they’d been missing something: What happens when we’re not doing anything at all?
Around the same time as some were exploring RSNs, others were pioneering the next generation of brain stimulation techniques, methods somewhat less crude than early forms of electroconvulsive therapy. Some new methods are invasive—deep brain stimulation, for example, requires an electrical implant in the brain—and some aren’t. Transcranial magnetic stimulation involves a targeted magnetic pulse originating outside the brain. They have one thing in common, though: Different techniques applied in different parts of the brain often achieve the same goals.
It works that way, Michael Fox and five others argue, because of resting state networks. To figure that out, the team reviewed clinical studies that had used deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), and a third method, transcranial direct current stimulation, or tDCS, to treat 14 disorders, including anorexia, depression, and Tourette syndrome. Across all 14 diseases except for one, epilepsy, they found correlations between resting-state activity in sites where DBS was effective and in others where TMS and tDCS were effective, indicating that such sites were all part of the same resting-state network. Backing that conclusion up was the observation that there seemed to be little, if any, connection between DBS regions that worked and regions where other kinds of stimulation had failed.
“Sites effective for the same disease tend to fall within the same brain network [and] ineffective sites fall outside this network,” the authors write in Proceedings of the National Academy of Science. Researchers who study psychiatric disorders had already started thinking in network terms, and now they have an even better reason to.