• The Future of Deep Brain Stimulation

    Ed Boyden is a professor at the Massachusett’s Institute of Technology who leads the Synthetic Neurobiology group. He’s credited with important contributions towards the revolutionary field of optogenetics. Essentially, it involves a bunch of molecular tools that make specific groups of neurons switch-on-and-offable simply by shining a light on them. This incredible innovation has given neuroscientists unprecedented level of precision in controlling the activity of different types of neuron in experiments trying to unpick the brain’s mind-bogglingly complex circuitry.

    It seems that he and his research team may well have done it again. They have developed another potentially incredibly powerful innovation that could fundamentally change how we approach Deep Brain Stimulation (DBS). This new approach is called Temporal Interference Stimulation (TIS) and the breakthrough it offers is enabling deep brain structures to stimulated without having to cut through the skull and actually insert electrodes into the brain.

    The DBS approaches currently used in humans involve passing electrodes through holes in the skull all the way down to deep brain areas in order to deliver pulses of electrical stimulation at the desired location. This has become a relatively routine medical intervention that fundamentally improves quality of life for thousands of people suffering from a range of brain illnesses all over the world. It has proven effective in a variety of chronically-debilitating diseases including Parkinson’s Disease, Major Depression and Obsessive Compulsive Disorder helping to circumvent common problems whereby patients either don’t get any improvement from their medications, or do at first but then the drugs stop working after a period of time.

    DBS therapy is most striking in people with Parkinson’s patients. Gradual death of the dopamine neurons that play an important role in initiating voluntary movements is the root cause of Parkinson’s disease. Dopamine-boosting agents often help with their movement difficulties but the benefits do not usually last forever. The invention of NICE-approved DBS therapy has been a lifesaver for many thousands of people. By applying an electrical current to either the thalamus, globus pallidus or subthalamic nuclei, limb movements can be controlled as normal. Their distinctive seemingly hesitant, shuffling walking style can be replaced with a normal, confident striding gait at the flick of a switch.

    The surgically-implanted electrodes often yield remarkable improvements in their symptoms, but having to cut holes in people’s skulls and physically implant wires in their brains is fraught with risks and potential complications. TIS, at some point in the future, could offer the same benefits but without the need to put any man-made objects inside the brain.

    We’ve had technologies that are capable of influencing brain activity from the skull surface for many years. Both Transcranial Direct Current Stimulation (tcDCS), which sends electrical currents across the skull, and Transcranial Magnetic Stimulation (TMS), which produces transient magnetic fields that extend across the skull, are both able to influence brain activity without the need for invasive surgery. But tcDCS and TMS are unable to influence areas deep inside the brain with any precision, they can only modulate brain activity at the surface. With TIS, all that it set to change as the technology progresses from experiments with mice, through larger and larger mammals, until it is eventually (hopefully) proven to be safe and effective in humans.

    As with all brilliant scientific solutions, TIS is elegant in its simplicity. A high frequency electrical current has no effect on brain tissue. At lower frequencies electrical currents can disrupt the usual flow of information in whatever brain tissue it is passed through. Here’s the clever bit. By applying two different sources of high frequency electrical current, at carefully separated positions on the scalp surface, where the two currents overlap sufficiently to cause interference in a way that reduces the frequency of the combined electrical signal it’s possible to alter how the brain tissue functions. Every other region that the electric currents pass through on the way down to the target location is unaffected – only where the beams cross.

    The team’s recent paper, published in the journal Cell (free to download!), describes how this technique was used to selectively stimulate the mouse hippocampus, deep inside the temporal lobes, from the top of the skull. While reaching down to the human basal ganglia from the skull surface is a much greater challenge – penetrating to a much greater depth, across a much thicker skull – this proof of principle makes the dream of deep brain stimulation without surgery seem a realistic prospect in the not too distant future.

    In addition to these monthly blogs, you can follow me on Twitter (@drjacklewis) where I post articles on breakthroughs in brain science and related topics. I also do a fortnightly science podcast with the lovely Lliana Bird. I also present a TV series called Secrets of the Brain on Insight TV. You can watch series 1 on Sky channel 564 (It’s on most nights!), or you can stream it here. Series 2 is out in Autumn 2017…

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