Deep-brain stimulation – Now noninvasively
Deep brain stimulation is a neurosurgical approach that requires implanting of electrodes in the brain, as a means to treat neurological conditions. The implanted battery-operated neurostimulator will block electrical signals from certain target areas in the brain, which most commonly include the subthalamic nucleus and the globus pallidus interna. Even though deep brain stimulation is used to treat neurological conditions, the procedure poses some surgical risk to the patient. Holes need to be drilled in the skull for the implantation of the stimulating electrodes, plus the control device needs to be inserted under the skin in the upper chest.
Complications of this surgery may include brain bleeds, stroke, seizure, headache, nausea and infection, albeit rare. In addition, the stimulation itself can also cause side effects such as problems with speech, balance and mood (mania and depression), as well as numbness or tingling sensations, and muscle tightness. From this, deep brain stimulation risks and side effects seem to outway the positive outcomes of treatment, but not anymore.
Grossman and colleagues recently published their article “Noninvasive deep brain stimulation via temporally interfering electric fields”. From their research, they proved that a noninvasive approach for electrically stimulating neurons in deep brain tissue of living mice, is not only possible, but decidedly safe.
Deep brain stimulation in the hippocampus of mice by means of temporal interference.
The bright green area indicates the stimulated deep brain target.
Grossman et al., 2017
Their noninvasive approach is nested in the concept of temporal interference. This can be explained as the application of two high-frequency oscillating electric fields on the scalp, with slightly different frequencies of which the difference corresponds to a low frequency that the brain will be able to follow directly. When stimulating the brain tissue with the two applied fields, neurons are able to demodulate and follow the envelope modulation that results from the overlapping temporal interference between the fields.
A great benefit is that no harmful effects in the brain have been noted with noninvasive deep brain stimulation. The superficial neurons are spared with temporal interference stimulation, which would otherwise result in strongly stimulated surface regions and modulation of multiple brain networks. The temporal interference strategy further makes it possible to precisely stimulate target brain tissues by alteration of either the number of electrodes implanted, or their location. The location of the applied electric field can further be controlled by changes in the currents, rather than moving the electrodes to another area. Nevertheless, the invasive approach of neural stimulation is still stated by some as the better option as one can more easily and intuitively exert control. The noninvasive stimulation strategy, therefore, still needs some scrutiny to ascertain its efficiency.
This novel approach paves the way for more accessible treatment for a variety of conditions, such as Parkinson’s disease, dystonia, epilepsy, Tourette syndrome, obsessive compulsive disorder, depression and perhaps autism, with lower cost and less risk than was previously possible. In fact, noninvasive brain machine interfaces are already being used in a variety of research and treatment paradigms. The temporal interference strategy can, therefore, prove vital to the search for specific target areas for treatment, especially deeper targets, which also brings us back to the importance of the Worldwide Brain Mapping Project.
Nir Grossman, David Bono, Nina Dedic, Suhasa B. Kodandaramaiah, Andrii Rudenko, Ho-Jun Suk, Antonino M. Cassara, Esra Neufeld, Niels Kuster, Li-Huei Tsai, Alvaro Pascual-Leone, Edward S. Boyden (2017) Noninvasive Deep Brain Stimulation via Temporally Interfering Electric Fields Cell 169(6):p1029–1041.
Waldert S (2016) Invasive vs. Non-Invasive Neuronal Signals for Brain-Machine Interfaces: Will One Prevail? Front. Neurosci. 10:295. doi: 10.3389/fnins.2016.00295