Focal Brain Stimulation to Improve Motor Function Poststroke
By David Chiu, MD
Medical Director, Houston Methodist Eddy Scurlock Stroke Center

The treatment of residual motor disability continues to challenge clinicians and researchers who manage patients with acute ischemic stroke.1,2 Stroke-related disability will escalate over the coming decades; in the United States, by the year 2030, the prevalence of stroke will have increased by 25 percent.3 We now know that poststroke motor recovery requires neural plasticity, which is significantly compromised in the injured brain.4

Transcranial rotating permanent magnet stimulation (TRPMS)

At the Houston Methodist Neurological Institute, a team of researchers has initiated a pilot study of a revolutionary new tool, known as transcranial rotating permanent magnet stimulation (TRPMS), that delivers stimulation to specific preset localized areas of the brain. Developed by Santosh Helekar, MD, PhD, at Houston Methodist Hospital and Henning Voss, PhD, at Weill Cornell Medicine, the device is a portable, wearable cap.

Traditional rehabilitative methods have been insufficient at enhancing function through neural plasticity. Common strategies for recovery of limb movement include task-specific or repetitive task practice, which invokes motor learning and initiates dendritic sprouting, the formation of new synapses and alteration of existing ones.5 Other strategies for recovery of limb movement include constraint-induced movement therapy, body weight-supported treadmill training, and robot training.3 Several trials have also studied the use of noninvasive cortical stimulation through repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS) and robot-assisted gait training (RAGT), with varying levels of success.6

By contrast, the TRPMS device works through the rapid rotation of high-field-strength permanent magnets delivered in repeated pulses, which induce currents in the brain. Depending on the frequency at which the pulses are delivered, they can activate neurons or suppress them. For maximal functional benefit, it appears necessary to simultaneously excite the neurons in the affected hemisphere and depress the over-compensated inhibitory neuronal activity of the unaffected hemisphere.

Weakness of the limbs contralateral to the area of injury is the most common disability associated with ischemic stroke. The unique, single-center, Houston Methodist trial will recruit 30 poststroke patients in a randomized, double-blind, sham stimulation-controlled protocol that will evaluate the ability of TRPMS to effect recovery of upper limb function. TRMPS will be delivered for 40 minutes per session, five days a week for a four-week period.

One of our goals is to demonstrate that brain activity can be improved in the motor cortex areas as measured by functional MRI. In this pilot study, physicians at Houston Methodist were excited to see dormant motor, premotor and supplementary areas of the brain become significantly more active. The therapeutic focus in the upcoming trial will target specific measurements of motor function in the upper limb determined by scales such as the Fugl-Meyer test and Action Research Arm Test (ARAT) score.

Research has shown that repetitive neuronal stimulation strengthens functional connectivity in areas surrounding the damaged motor cortex, presumably leading to functional cortical reorganization. Consequently, the team will also apply stimulation to neurons in the adjacent premotor and supplementary motor cortices.

In the long arc of history, no treatment has been proven to foster recovery after a completed stroke. From this perspective, investigators are trying to tackle nothing less than the holy grail of neurology to bring about recovery in patients with chronic stroke.

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REFERENCES

1 Furlan L, Conforto AB, Cohen LG, Sterr A. Upper limb immobilization: a neural plasticity model with relevance to poststroke motor rehabilitation. Neural Plast. 2016; 2016:8176217.

2 Tang C, Zhao Z, Chen C, Zheng X, Sun F, et al. Decreased functional connectivity of homotopic brain regions in chronic stroke patients: a resting state fMRI study. PLoS One. 2016; 11(4):e0152875.

3Heidenreich PA, Trogdon JG, Khavjou OA, Butler I, Dracup K, et al. Forecasting the future of cardiovascular disease in the Unites States: a policy statement from the American Heart Association. Circulation. 2011;123:933-944.

4 Takeuchi N, Isumi S. Rehabilitation with poststroke motor recovery: a review with a focus on neural plasticity. Stroke Res Treat; 2013; 2013:128641.

5 Arya K, Pandian S, Verma R, Garg RK. Movement therapy induced neural reorganization and motor recovery in stroke: a review. J Bodyw Mov Ther. 2011;15(4): 528-537.

6 Brewer L, Horgan F, Hickey A Williams D. Stroke rehabilitation: recent advances and future therapies. Q J Med. 2013;106: 11-25.

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