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 contralateral cortical hemisphere. Recently, many wearable robots assisting the movement of the hand have been developed, and several studies have proposed robotic mirror therapy (RMT) that provides mirrored movements of the unaffected hand on the affected hand with the robot controlled by electromyography or posture of the unaffected hand. 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 contralateral motor cortex 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 ipsilateral side for both subject groups, while the contralateral side showed significantly greater activation for healthy 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.

Laterality Index Calculations in a Control Study of Functional Near Infrared Spectroscopy

“…The Block Averaging analysis utilizes the HbO (used in this study) and HbR (not used in this study) while the GLM analysis ts HbO and HbR data to a model of an expected response (i.e., canonical or gamma function), which produces data in the form of a change in HbO and a change in HbR from the expected response. HbO and changes in HbO were reported in the current manuscript as HbO is more sensitive than HbR to changes in hemodynamic response and has been done in previous laterality index analyses (Huppert, Hoge et al 2006, Kim, Lee et al 2022.…”

“…Nishiyori, Bisconti et al 2016). The three formulas under the criterion of Ipsilateral vs. Contralateral did account for handedness and thus the formulas will change based on the hand performing the task(Kim, Lee et al 2022). The LI normalizes cortical activation differences between channels, thereby revealing which hemisphere experience a larger change during the task.…”

Review of Multimodal Data Acquisition Approaches for Brain-Computer Interfaces

“…The portability of fNIRS amplifies its utility, extending its reach from clinical domains to field studies, fostering flexibility in research endeavors. This modality is used in locomotory and ambulatory studies including yoga, [31] meditation, [32] robotic [33] and emotional [34] therapies. fNIRS is a virtuoso in unveiling the intricacies of deep brain structures that often evade other neuroimaging methodologies.…”