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SRI Magazine 2016

SRI Magazine 2016

Brain stimulation plus rehab equals better mobility after a stroke

Gentle electric current applied through the head helps patients regain some function

The practice of stimulating brain cells with a mild electrical current has been around for centuries, but recently transcranial direct current stimulation (tDCS) has been undergoing a bit of a renaissance. Google “tDCS” and you’ll find plenty of device manufacturers, DIY kits (a 9-volt battery and a couple of electrodes) and articles on the various benefits, from boosting math skills to treating tinnitus. Internet hype aside, the science is still catching up. Researchers are seeking to understand how or whether this kind of noninvasive stimulation can induce neuroplasticity—the brain’s ability to change and adapt in response to injury and experience.

Dr. Joyce Chen, a scientist in the Hurvitz Brain Sciences Research Program at Sunnybrook Research Institute, has been studying the use of tDCS among stroke patients undergoing rehab to recover mobility. Though physical exercise alone can help reinvigorate neural pathways, Chen wondered, “what if you can stimulate the brain with tDCS during rehab exercises? Would that be akin to giving a double dose of therapy?”

In this small pilot study, Chen recruited five patients who’d suffered a stroke at least six months earlier, after which the brain’s natural healing process would have tapered and any mobility improvements could be attributed to the tested therapies. The patients had moderate to severe mobility impairment, but to be eligible for the study they had to be able to muster a flicker of movement, says Chen. “We needed some neural cell activity to work with.”

Over the course of two weeks, patients underwent 10 tDCS sessions of 20 minutes while doing their usual physical and occupational therapy exercises. The tDCS device is portable and compact: patients wore a battery pack and two electrode pads that were wrapped against their scalp—in this case, a few inches above each ear, covering the brain’s motor-function regions. The electrical current, just 1.5 milliamps, causes a slight and fleeting tingling or itchy sensation. Brain cells can either be excited or inhibited, and Chen’s study did both. A positive electrode worked to enhance cell activity in the stroke-affected cortex, while a negative electrode worked to hamper the unaffected, overactive side. (One theory is that the healthy, overactive region may be inhibiting the affected side.)

Brain cells can either be excited or inhibited, and Chen’s study did both.

Improvement in mobility among the participants was dramatic, says Chen. Using statistical modelling, as well as subjective accounts, all patients showed significant improvements in their ability to engage with their arm or hand. Most notably, resting state functional magnetic resonance imaging (fMRI) showed increased connectivity between two important areas of the brain involved in motor control. “The fact that the motor and premotor cortices are talking to each other may be the reason these patients improved,” says Chen. “But at this point, we don’t really know the mechanism behind this.” Because the premotor cortex has been shown to play an important role in the recovery of movements after a stroke, Chen is encouraged by the fMRI results and what they could mean for future studies. “Maybe then this premotor region could be used as a target to refine the brain stimulation,” she says. “What if we excite that particular region more? Would we see even more benefits?”

Chen’s is the first stroke study to examine brain connectivity changes related to the combination of tDCS and another therapy. By understanding the brain’s response to tDCS, Chen hopes to begin to elucidate its mechanism of action. “A lot of research, including ours, is showing that if you simultaneously couple the therapy—in our case rehab—with brain stimulation, it has an additive effect,” she says.

Participants in the study reported feeling effects of the therapies (better mobility) for at least one week. Because tDCS devices are compact, portable and simple to operate, Chen can foresee brain stimulation becoming a practical home-based therapy that patients could self-administer. “You can envision sending this home with the patient for regular booster sessions,” she says. But these are early days, she adds. “There is debate in the field of brain stimulation. There’s enough evidence showing effects if you couple tDCS with therapy, but results from meta-analyses of all the studies is equivocal—it works for some people, but not for everyone.” Chen attributes this ambivalence to a lack of understanding for how parameters of brain stimulation (for example, duration, intensity, whether to enhance or inhibit cells) and individual differences affect overall response to this therapy. “Each study ends up doing something a little different, so there’s a big push to standardize the protocols so that we can compare apples with apples.”

In the meantime, Chen’s stroke research continues with a new study that will test a personalized, targeted approach to tDCS therapy, reflecting different theories about the neural underpinnings of mobility repair. “Up until now, researchers have been applying a one-size-fits-all approach. However, different people may require different methods: for some people, we may enhance only the unaffected side of the brain; for others, excite the affected side,” she says, clearly delighted by the myriad study prospects in the realm of stroke recovery alone. Beyond which, the very old and very low-tech practice of brain stimulation seems to offer unending fodder for research and potentially innovative therapies that could literally change the way we think.

Chen’s research is supported by the National Institutes of Health, the Mary Crown and William Ellis Foundation, and the Rosalyn and Richard Slifka Family Foundation.