Abstract
Motor recovery after stroke is an unsolved challenge despite intensive rehabilitation training programs. Brain stimulation techniques have been explored in addition to traditional rehabilitation training to increase the excitability of the stimulated motor cortex. This modulation of cortical excitability augments the response to afferent input during motor exercises, thereby enhancing skilled motor learning by long-term potentiation-like plasticity. Recent approaches examined brain stimulation applied concurrently with voluntary movements to induce more specific use-dependent neural plasticity during motor training for neurorehabilitation. Unfortunately, such approaches are not applicable for the many severely affected stroke patients lacking residual hand function. These patients require novel activity-dependent stimulation paradigms based on intrinsic brain activity. Here, we report on such brain state-dependent stimulation (BSDS) combined with haptic feedback provided by a robotic hand orthosis. Transcranial magnetic stimulation (TMS) of the motor cortex and haptic feedback to the hand were controlled by sensorimotor desynchronization during motor-imagery and applied within a brain-machine interface (BMI) environment in one healthy subject and one patient with severe hand paresis in the chronic phase after stroke. BSDS significantly increased the excitability of the stimulated motor cortex in both healthy and post-stroke conditions, an effect not observed in non-BSDS protocols. This feasibility study suggests that closing the loop between intrinsic brain state, cortical stimulation and haptic feedback provides a novel neurorehabilitation strategy for stroke patients lacking residual hand function, a proposal that warrants further investigation in a larger cohort of stroke patients.
Highlights
Despite intensive rehabilitation training according to evidencebased guidelines, functional restoration in patients with severe and persistent motor deficits following stroke is very limited (Kwakkel et al, 2003)
Post-hoc tests revealed a significant increase of MEP amplitude only in the brain state-dependent stimulation (BSDS) + haptic feedback (HF) condition; all other conditions showed a significant decrease compared to baseline
The specific timing of cortical stimulation has been identified as a critical factor that requires further investigation, with regard to both intrinsic brain activity and the respective rehabilitation exercise, for improving the consistency of brain stimulation effects during neurorehabilitation (Plow et al, 2009)
Summary
Despite intensive rehabilitation training according to evidencebased guidelines, functional restoration in patients with severe and persistent motor deficits following stroke is very limited (Kwakkel et al, 2003). Continuous stimulation with frequencies between 3 and 20 Hz (Khedr et al, 2005; Malcolm et al, 2007; Chang et al, 2010) and intermittent theta-burst protocols with 2 s-trains of short 50 Hz bursts (Talelli et al, 2012; Hsu et al, 2013) have both been applied to increase ipsilesional M1 excitability prior to neurorehabilitative training. In a complementary experiment, Koganemaru et al (2010) applied 8 s trains of repetitive 5 Hz TMS alternating with 50 s periods of neurorehabilitative training. All these approaches used pre-defined stimulation parameters independent of the actual behavioral state of the patient
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