Abstract
In recent years, mirror visual feedback (MVF) therapy combined with electrical stimulation (ES) have been proposed for patients with hemiparesis. However, the neurophysiological effect remains unknown. We investigated the effects of MVF by itself and along with electromyogram-triggered ES (ETES) on hemodynamic responses using functional near-infrared spectroscopy (NIRS). Eighteen healthy subjects participated in this study. We measured changes in brain oxygenation using 48 NIRS channels. We investigated the effects of three main factors of visual feedback (observation of a mark, right hand, and hand movements via mirror) with or without ES on bilateral precentral gyrus (PrG), postcentral gyrus (PoG), supplementary motor area (SMA), supramarginal gyrus area (SMG), and angular gyrus (AG) to determine the contribution of each factor. The results showed that the left PoG was significantly more activated when performing mirrored tasks (MT) than when performing circle or Right-hand Tasks (RTs). In addition, the right PoG and right SMA in MT were significantly more activated than in MT + ES cases. Our findings suggested that observation of movements through the mirror caused activation of the postcentral gyrus rather than the PrG, and MVF along with ETES decreased cortical activation.
Highlights
In mirror visual feedback (MVF) therapy, subjects perform movements of the unimpaired limb while watching a mirrored reflection of their movements superimposed over the unseen impaired limb; this technique was introduced by Ramachandran and Rogers-Ramachandran (1996)
A post hoc test showed that oxygenated hemoglobin (oxy-Hb) concentration in mirrored tasks (MT) was the location of the near-infrared spectroscopy (NIRS) channels marked with the 3D digitizer were superimposed on individual cortical surfaces
The individual NIRS channels were classified into bilateral precentral gyrus (PrG), postcentral gyrus (PoG), supplementary motor area (SMA), supramarginal gyrus area (SMG), and angular gyrus (AG)
Summary
In mirror visual feedback (MVF) therapy, subjects perform movements of the unimpaired limb while watching a mirrored reflection of their movements superimposed over the unseen impaired limb; this technique was introduced by Ramachandran and Rogers-Ramachandran (1996). The neurophysiological effects induced by MVF have been investigated using various methods including transcranial magnetic stimulation (TMS), electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI). TMS studies have shown that MVF increases human primary motor cortex (M1) activity of the stationary hand in healthy subjects (Garry et al, 2005; Fukumura et al, 2007; Kumru et al, 2016). FNIRS does not require immobilization of subjects in constrained postures, and measurements can be done during motor tasks This technique is advantageous for measuring neural responses when studying action execution (Balconi and Cortesi, 2016). The effects of MVF combined with ES on motor and daily function have been studied in patients with hemiparesis. The present study used fNIRS and focused on the effects of MVF alone and MVF along with ES to investigate hemodynamic changes in the brain
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