Increasing motor cortex activation during grasping via novel robotic mirror hand therapy: a pilot fNIRS study

Abstract

Background Mirror therapy (MT) has been used for functional recovery of the affected hand by providing the mirrored image of the unaffected hand movement, which induces neural activation of the cortical hemisphere contralateral to the affected hand. Recently, many wearable robots assisting the movement of the hand have been developed, and several studies have proposed robotic mirror therapy (RMT) that uses a robot to provide mirrored movements of the unaffected hand to the affected hand with the robot controlled by measuring electromyography or posture of the unaffected hand. In some cases of RMT a mirror is placed to allow the person to observe only the unaffected hand but in others users simply observe the robotically assisted hand performing the mirrored movements, as was the case in this study. There have been limited evaluations of the cortical activity during RMT compared to MT and robotic therapy (RT) providing passive movements despite the difference in the modality of sensory feedback and the involvement of motor intention, respectively. Methods This paper analyzes bilateral motor cortex activation in nine healthy subjects and five chronic stroke survivors during a pinching task performed in MT, RT, and RMT conditions using functional near infrared spectroscopy (fNIRS). In the MT condition, the person moved the unaffected hand and observed it in a mirror while the affected hand remained still. In RT condition passive movements were provided to the affected hand with a cable-driven soft robotic glove, while, in RMT condition, the posture of the unaffected hand was measured by a sensing glove and the soft robotic glove mirrored its movement on the affected hand. Results For both groups, the RMT condition showed the greatest mean cortical activation on the motor cortex contralateral to the affected (non-dominant for the healthy group) hand compared to other conditions. Individual results indicate that RMT induces similar or greater neural activation on the motor cortex compared to MT and RT conditions. The interhemispheric activations of both groups were balanced in RMT condition. In MT condition, significantly greater activation was shown on the hemisphere ipsilateral to the affected (dominant for the healthy group) hand for both subject groups, while the contralateral side showed significantly greater activation for the healthy group in RT condition. Conclusion The experimental results indicate that combining visual feedback, somatosensory feedback, and motor intention are important for greater stimulation on the contralateral motor cortex of the affected hand. RMT that includes these factors is hypothesized to achieve a more effective functional rehabilitation due to greater and more balanced cortical activation.

Robot-Assisted Bimanual Training Improves Hand Function in Patients With Subacute Stroke: A Randomized Controlled Pilot Study

“…However, most of these devices are designed for shoulder, elbow, or wrist movements ( 25 , 28 ), there are few rehabilitation robots for the hand, such as the fingers. For robot-assisted BMT (RBMT) in the hand, Chen et al and Dong et al developed a task-oriented training protocol that uses an exoskeleton hand to perform RBMT ( 29 , 30 ). A functional brain imaging study on RBMT reported that, compared with unilateral hand movement, robot-assisted bilateral hand movement induced greater excitatory responses in the motor cortex ( 30 ), suggesting the clinical effectiveness of RBMT.…”

The effect of mirror therapy can be improved by simultaneous robotic assistance

“…But even shorter robotic proprioceptive training can modulate plasticity in stroke patients (Vahdat et al, 2019). Kim et al (2022) also demonstrated greater neural stimulation on the contralateral side of the motor cortex through bilateral robot-assisted training. Overall, both methods, mirror illusion and sensory input, show positive characteristics that are successfully combined in RMT.…”

“…They have the potential to improve the quality and intensity of rehabilitation treatments (Morone et al, 2020). Only few studies have investigated RMT so far (Beom et al, 2016;Kim et al, 2022). However, they have included mainly healthy people or patients with moderate upper limb impairment.…”

Increased both cortical activation and functional connectivity after transcranial direct current stimulation in patients with post-stroke: A functional near-infrared spectroscopy study

“…fNIRS has also been used to study cortical activation in patients with stroke. For example, Kim used fNIRS to study the oxy-Hb changes in patients with stroke in robotic mirror therapy to observe the efficacy of the therapy (39). Mihara also used fNIRS to study cortical activation differences between patients with stroke and healthy peers during ataxia gait (40).…”