Mechanical Oscillation in Post-stroke Rehabilitation: Neuroplasticity and Brain-derived Neurotrophic Factor

Neuromuscular impairment following stroke can severely impact functional independence and quality of life. Postural instability and impaired balance after stroke increases the risk of fall and fall-related injuries, including fracture and traumatic brain injury. Although intensive rehabilitation aids in motor recovery, the outcome is often limited. Research has shown that one of the most effective modulators of cortical structure and function is repeated sensory input^1,2 and that the direct manipulation of sensory input can modulate brain plasticity and enhance the effects of motor training in individuals with stroke.^3,4,5

Whole-body vibration (WBV), a form of mechanical oscillation in which persons stand on a vibration platform for a period of time, has been shown to alter sensory inputs and stimulate both agonist and antagonist muscles in the lower limbs simultaneously. Similar to muscle tendon vibration, WBV uses an external drive to stimulate muscles to elicit reflexive activity and increase activity, especially during muscle contraction.^6,7

To date, no studies have reported on the mechanisms underlying WBV-induced improvement in balance and function. In this study, we investigate two hypotheses: that participants who receive WBV will demonstrate increased spinal motoneuronal pool excitability as measured by the H-reflex of the soleus and corticospinal excitability as measured by the motor-evoked potentials in the lower extremity muscle after training, and that participants who receive WBV will demonstrate increased brain-derived neurotrophic factor (BDNF), an important molecular modulator of neuroplasticity and subsequent motor function improvement. In this pilot project, we will investigate the results of 12 weeks of WBV training in relation to both of these hypotheses.

Twenty individuals with a history of a single cerebrovascular accident, either ischemic or hemorrhagic, age 21 to 70 years, will be recruited. Eligible participants must have undergone no form of rehabilitation or exercise in the previous three months. Study participants will undergo 40 minutes of WBV, three times a week for 12 weeks. Because participants will stand during WBV training, muscles of the lower extremity such as soleus and tibialis anterior muscles will receive most of the mechanical oscillation. We expect that corticospinal excitability corresponding to these muscles will be modulated after training.

Overall, we expect our findings to support that WBV will demonstrate effects for modulation of neuroplasticity that could lead to improved neuromotor function in humans. The results of the study will provide a better understanding of the molecular process contributing to neuroplasticity, which will help therapists develop an optimal therapeutic strategy for facilitating post-stroke motor recovery. We hope that the study will serve as the first step toward developing new therapies to promote neuroplasticity and cortical reorganization and subsequent recovery of neuromotor function following stroke.

Theoretical model. WBV training, combined with or without motor training, may increase neurotrophic factor production, promoting neuroplasticity that leads to neuromotor function in individuals with stroke. It has been shown that neuroplasticity plays a critical role in motor training, motor recovery and neuromotor function, and that neuroplasticity is mediated by brain-derived neurotrophic growth factor (BDNF). The first aim of the study is to determine the long-term effects of 12-week WBV training on spinal and cortical neuroplasticity in stroke. The second aim is to investigate whether 12 weeks of WBV training can promote molecular processes such as BDNF production that support neuroplasticity.

¹Nudo RJ, Postinfarct cortical plasticity and behavioral recovery. Stroke. 2007;38(2Suppl):840-5.

²Ward NS, Cohen LG. Mechanisms underlying recovery of motor function after stroke. Arch Neurol. 2004;61(12):1844-8.

³Celnik P et al. Somatosensory stimulation enhances the effects of functional hand tasks in patients with chronic stroke. Arch Phys Med Rehabil. 2007:88(11):1369-76.

⁴Conforto AB et al. Effects of somatosensory stimulation on motor function after subacute stroke, Neurorehabil Neural Repair. 2010; 24(3):263-72.

⁵Marconi B et al. Long-term effects on cortical excitability and motor recovery induced by repeated muscle vibration in chronic stroke patients. Neurorehabil Neural Repair. 2011;25(1):48-60.

⁶Pollock RD et al. Muscle activity and acceleration during whole body vibration: Effect of frequency and amplitude. Clinical Biomechanics. 2010;25(8):840-6.

⁷Ritzmann R et al. EMG activity during whole body vibration: Motion artifacts or stretch reflexes? European Journal of Applied Physiology. 2010;110(1):143-51.

Dr. James Chang, a research scientist in the department of Physical Medicine and Rehabilitation at McGovern Medical School at UTHealth, is the winner of the 2013 TIRR Memorial Hermann Innovations Grant Program Pilot Project Award. The $50,000 award is given annually to support the research mission of TIRR Memorial Hermann by facilitating innovative research that will improve the lives of patients worldwide and lead to applications for federally funded grants to be housed at the rehabilitation hospital. Victor H. Chang, MD, clinical director of the Brain Injury and Stroke Program at TIRR Memorial Hermann and an associate professor at McGovern Medical School, is co-investigator of the study.