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New Approach Allows Magnetic Brain Stimulation to Target Deep Brain Structures

Transcranial magnetic stimulation (TMS) is a highly precise and noninvasive brain stimulation tool approved by the U.S. Food and Drug Administration for the treatment of major depression and other conditions. TMS can only directly stimulate the outermost layer of the brain, but a recent study by researchers at the National Institute of Mental Health (NIMH) suggests that mapping a person’s brain architecture may make it possible to guide TMS to deep brain targets. Based on previous findings, researchers Bruce Luber, Ph.D., Zhi-De Deng, Ph.D., and Sarah H. Lisanby, M.D., in the NIMH Intramural Research Program and colleagues at Duke University School of Medicine hypothesized that it might be possible to activate deep brain structures by stimulating the surface-level structures they are connected to in the brain network. To test this hypothesis, they targeted the subgenual cingulate, a structure located deep behind the eyes, which is thought to be a key node in brain circuits involved in depression. The sample included 10 healthy participants, who ranged in age from 19 to 33. In the first session, the researchers mapped functional and anatomical connections in each participant’s brain using two types of brain imaging, functional MRI (fMRI) and diffusion tensor imaging. Using these data, they identified the right frontal pole, located just behind the forehead, as the nearest TMS-accessible brain area connected to the subgenual cingulate target. They then mapped the precise location in the right frontal pole for each participant to determine the exact stimulation site. In a follow-up session, participants received TMS. The researchers positioned the TMS coil above the participant’s previously mapped right frontal pole and delivered a series of TMS pulses that varied in intensity. The researchers used fMRI to measure participants’ brain activity during the TMS session. The data showed that TMS pulses to the right frontal pole led to increased activation in the subgenual cingulate in a dose-dependent way: as the intensity of the TMS pulses increased, so did activation of the deep brain target. According to the researchers, incorporating this kind of brain mapping into standard TMS procedures could significantly advance research and clinical science. By mapping links between deep brain regions and more surface-level areas, researchers and clinicians may be able to target key brain structures that are typically only accessible through invasive approaches such as deep brain stimulation. Further studies that replicate the findings with larger, more diverse samples and that test additional sites and deep targets can help researchers and clinicians validate the approach and better understand when, how, and for whom this technology is most effective. According to the researchers, this new approach to TMS offers a promising tool for precise, noninvasive stimulation of deep brain targets and could yield insights into neurocircuitry that advance both research and treatment.