Mirror Illusion Modulates M1 Activities and Functional Connectivity Patterns of Perceptual-Attention Circuits During Bimanual Movements: A Magnetoencephalography Study

Video mirror feedback induces more extensive brain activation compared to the mirror box: an fNIRS study in healthy adults

BACKGROUND

Mirror therapy (MT) has been shown to be effective for motor recovery of the upper limb after a stroke. The cerebral mechanisms of mirror therapy involve the precuneus, premotor cortex and primary motor cortex. Activation of the precuneus could be a marker of this effectiveness. MT has some limitations and video therapy (VT) tools are being developed to optimise MT. While the clinical superiority of these new tools remains to be demonstrated, comparing the cerebral mechanisms of these different modalities will provide a better understanding of the related neuroplasticity mechanisms.

METHODS

Thirty-three right-handed healthy individuals were included in this study. Participants were equipped with a near-infrared spectroscopy headset covering the precuneus, the premotor cortex and the primary motor cortex of each hemisphere. Each participant performed 3 tasks: a MT task (right hand movement and left visual feedback), a VT task (left visual feedback only) and a control task (right hand movement only). Perception of illusion was rated for MT and VT by asking participants to rate the intensity using a visual analogue scale. The aim of this study was to compare brain activation during MT and VT. We also evaluated the correlation between the precuneus activation and the illusion quality of the visual mirrored feedback.

RESULTS

We found a greater activation of the precuneus contralateral to the visual feedback during VT than during MT. We also showed that activation of primary motor cortex and premotor cortex contralateral to visual feedback was more extensive in VT than in MT. Illusion perception was not correlated with precuneus activation.

CONCLUSION

VT led to greater activation of a parieto-frontal network than MT. This could result from a greater focus on visual feedback and a reduction in interhemispheric inhibition in VT because of the absence of an associated motor task. These results suggest that VT could promote neuroplasticity mechanisms in people with brain lesions more efficiently than MT.

CLINICAL TRIAL REGISTRATION

NCT04738851.

Reversed Mirror Therapy (REMIT) after Stroke-A Proof-of-Concept Study

In mirror training (MIT), stroke patients strive to move their hands while looking at the reflected image of the unaffected one. The recruitment of the mirror neurons and visual-proprioceptive conflict are expected to facilitate the paretic voluntary movement. Here, a reversed MIT (REMIT) is presented, which requires moving hands while looking at the reflected image of the paretic one, giving the illusion of being unable to move the unimpaired hand. This study compares MIT and REMIT on post-stroke upper-limb recovery to gain clues on the mechanism of action of mirror therapies. Eight chronic stroke patients underwent two weeks of MIT and REMIT (five sessions each) in a crossover design. Upper-limb Fugl-Meyer, Box and Block and handgrip strength tests were administered at baseline and treatments end. The strength of the mirror illusion was evaluated after each session. MIT induced a larger illusory effect. The Fugl-Meyer score improved to the same extent after both treatments. No changes occurred in the Box and Block and the handgrip tests. REMIT and MIT were equally effective on upper-limb dexterity, challenging the exclusive role of mirror neurons. Contrasting learned nonuse through an intersensory conflict might provide the rationale for both forms of mirror-based rehabilitation after stroke.

Associated Mirror Therapy Enhances Motor Recovery of the Upper Extremity and Daily Function after Stroke: A Randomized Control Study

Bimanual cooperation plays a vital role in functions of the upper extremity and daily activities. Based on the principle of bilateral movement, mirror therapy could provide bimanual cooperation training. However, conventional mirror therapy could not achieve the isolation of the mirror. A novel paradigm mirror therapy called associated mirror therapy (AMT) was proposed to achieve bimanual cooperation task-based mirror visual feedback isolating from the mirror. The study was aimed at exploring the feasibility and effectiveness of AMT on stroke patients. We conducted a single-blind, randomized controlled trial. Thirty-six eligible patients were equally assigned into the experimental group (EG) receiving AMT and the control group (CG) receiving bimanual training without mirroring for five days/week, lasting four weeks. The Fugl-Meyer Assessment Upper Limb subscale (FMA-UL) for upper extremity motor impairment was used as the primary outcome. The secondary outcomes were the Box and Block Test (BBT) and Functional Independence Measure (FIM) for motor and daily function. All patients participated in trials throughout without adverse events or side effects. The scores of FMA-UL and FIM improved significantly in both groups following the intervention. Compared to CG, the scores of FMA-UL and FIM were improved more significantly in EG after the intervention. The BBT scores were improved significantly for EG following the intervention, but no differences were found in the BBT scores of CG after the intervention. However, no differences in BBT scores were observed between the two groups. In summary, our study suggested that AMT was a feasible and practical approach to enhance the motor recovery of paretic arms and daily function in stroke patients. Furthermore, AMT may improve manual dexterity for poststroke rehabilitation.

Modulation of Functional Connectivity in Response to Mirror Visual Feedback in Stroke Survivors: An MEG Study

Background. Several brain regions are activated in response to mirror visual feedback (MVF). However, less is known about how these brain areas and their connectivity are modulated in stroke patients. This study aimed to explore the effects of MVF on brain functional connectivity in stroke patients. Materials and Methods. We enrolled 15 stroke patients who executed Bilateral-No mirror, Bilateral-Mirror, and Unilateral-Mirror conditions. The coherence values among five brain regions of interest in four different frequency bands were calculated from magnetoencephalographic signals. We examined the differences in functional connectivity of each two brain areas between the Bilateral-No mirror and Bilateral-Mirror conditions and between the Bilateral-Mirror and Unilateral-Mirror conditions. Results. The functional connectivity analyses revealed significantly stronger connectivity between the posterior cingulate cortex and primary motor cortex in the beta band (adjusted p = 0.04) and possibly stronger connectivity between the precuneus and primary visual cortex in the theta band (adjusted p = 0.08) in the Bilateral-Mirror condition than those in the Bilateral-No mirror condition. However, the comparisons between the Bilateral-Mirror and Unilateral-Mirror conditions revealed no significant differences in cortical coherence in all frequency bands. Conclusions. Providing MVF to stroke patients may modulate the lesioned primary motor cortex through visuospatial and attentional cortical networks.

Implementing technology enhanced real-time action observation therapy in persons with chronic stroke: A pilot study

This pilot study examined a novel technology-enhanced real-time action observation therapy (TERTAOT) of symmetrical bilateral movements in survivors of chronic stroke regardless of their ability to move their paretic limb(s). The TERTAOT used a Kinect XBox One to project mirror images of non-paretic limbs as participants performed symmetrical bilateral motor tasks involving whole-body movements in sitting or standing. The participants received eight weeks of treatment consisting of 30-minutes of conventional physical therapy (balance training, gait training, neuromuscular reeducation, and generalized strength training) and 30-minutes of the TERTAOT protocol per session (three sessions per week for a total of 24 sessions). Ten Meter Walk Test (10MWT), Five Times Sit-to-Stand (5TSTS), Timed Up and Go (TUG), Motor Activity Log - Quality of Movement (QOM) and Amount of Use (AOU) were administered at baseline (pretest), 4 weeks (posttest 1) and 8 weeks (posttest 2) post-TERTAOT, and 3 months after TERTAOT ended (retention). A General Linear Model Repeated Measures (parametric test) or the Friedman Test (non-parametric test) was used to compare outcomes across time points, depending on the normality of data distribution. Bonferroni post-hoc corrections were applied. Seventeen participants completed >80% of TERTAOT sessions without adverse events. The effect of time was significant for 10MWT (p = .001), 5TSTS (p = .001), TUG (p = .005), QOM (p = .001), and AOU (p = .017). TERTAOT may be feasible to be implemented in an outpatient setting. Improvements in functional outcomes including gait, balance, and use of upper limbs were observed after eight weeks of conventional therapy and TERTAOT protocol in survivors of chronic stroke.

Cortical neural activity evoked by bilateral and unilateral mirror therapy after stroke

OBJECTIVE

This study aimed to investigate the differential effects of bilateral and unilateral mirror therapy (MT) on motor cortical activations in stroke patients by magnetoencephalography (MEG).

METHODS

Sixteen stroke patients and 16 right-handed healthy volunteers were recruited. All participants were required to perform 4 conditions: resting, no mirror with bilateral hand movements (Bilateral-No mirror), mirror with bilateral hand movements (Bilateral-Mirror) and mirror with unilateral hand movements (Unilateral-Mirror). Beta oscillatory activities in the primary motor cortex (M1) were collected during each condition using MEG. The percentage change of beta oscillatory activity was calculated for each condition to correct the baseline differences.

RESULTS

In the stroke group, the percentage change of M1 beta oscillatory activity significantly decreased more in the Bilateral-Mirror condition than in the Bilateral-No mirror and Unilateral-Mirror conditions. In the healthy group, no significant differences in the percentage change of beta oscillatory activity were found among the 3 conditions. Further, a significant difference in the percentage change of beta oscillatory activity only in the Bilateral-Mirror condition was found between the 2 groups.

CONCLUSIONS

This study provides new information on the differential cortical activations modulated by bilateral and unilateral MT.

SIGNIFICANCE

Bilateral MT led to greater M1 neural activities than unilateral MT and bilateral movements without a mirror in stroke patients.