Asymmetric Activation of the Primary Motor Cortex during Observation of a Mirror Reflection of a Hand

Mirror therapy is an effective technique for pain relief and motor function recovery. It has been demonstrated that magnetic 20-Hz activity is induced in the primary motor cortex (M1) after median nerve stimulation and that the amount of the stimulus-induced 20-Hz activity is decreased when the M1 is activated. In the present study, we investigated how the image or the mirror reflection of a hand holding a pencil modulates the stimulus-induced 20-Hz activity in the M1. Neuromagnetic brain activity was recorded from 13 healthy right-handed subjects while they were either viewing directly their hand holding a pencil or viewing a mirror reflection of their hand holding a pencil. The 20-Hz activity in the left or the right M1 was examined after the right or the left median nerve stimulation, respectively, and the suppression of the stimulus-induced 20-Hz in the M1 by viewing directly one hand holding a pencil or by viewing the mirror image of the hand holding a pencil was assumed to indicate the activation of the M1. The results indicated that the M1 innervating the dominant hand was suppressed either by viewing directly the dominant hand holding a pencil or by viewing the mirror image of the non-dominant hand holding a pencil. On the other hand, the M1 innervating the non-dominant hand was activated by viewing the mirror image of the dominant hand holding a pencil, but was not activated by viewing directly the non-dominant hand holding a pencil. The M1 innervating either the dominant or the non-dominant hand, however, was not activated by viewing the hand on the side ipsilateral to the M1 examined or the mirror image of the hand on the side contralateral to the M1 exaimined. Such activation of the M1 might induce some therapeutic effects of mirror therapy

The mirror illusion induces high gamma oscillations in the absence of movement

We tested whether mirror visual feedback (MVF) from a moving hand induced high gamma oscillation (HGO) response in the hemisphere contralateral to the mirror and ipsilateral to the self-paced movement. MEG was recorded in 14 subjects under three conditions: bilateral synchronous movements of both index fingers (BILATERAL), movements of the right hand index finger while observing the immobile left index finger (NOMIRROR), and movements of the right hand index finger while observing its mirror reflection (MIRROR). The right hemispheric spatiospectral regions of interests (ROIs) in the sensor space, sensitive to bilateral movements, were found by statistical comparison of the BILATERAL spectral responses to baseline. For these ROIs, the post-movement HGO responses were compared between the MIRROR and NOMIRROR conditions. We found that MVF from the moving hand, similarly to the real movements of the opposite hand, induced HGO (55–85 Hz) in the sensorimotor cortex. This MVF effect was frequency-specific and did not spread to oscillations in other frequency bands. This is the first study demonstrating movement-related HGO induced by MVF from the moving hand in the absence of proprioceptive feedback signaling. Our findings support the hypothesis that MVF can trigger the feedback-based control processes specifically associated with perception of one's own movements

Cortical Functional Domains Show Distinctive Oscillatory Dynamic in Bimanual and Mirror Visual Feedback Tasks

It is believed that Mirror Visual Feedback (MVF) increases the interlimb transfer but the exact mechanism is still a matter of debate. The aim of this study was to compare between a bimanual task (BM) and a MVF task, within functionally rather than geometrically defined cortical domains. Measure Projection Analysis (MPA) approach was applied to compare the dynamic oscillatory activity (event-related synchronization/desynchronization ERS/ERD) between and within domains. EEG was recorded in 14 healthy participants performing a BM and an MVF task with the right hand. The MPA was applied on fitted equivalent current dipoles based on independent components to define domains containing functionally similar areas. The measure of intradomain similarity was a “signed mutual information,” a parameter based on the coherence. Domain analysis was performed for joint tasks (BM and MVF) and for each task separately. MVF created 9 functional domains while MB task had only 4 functionally distinctive domains, two over the left hemispheres and two bilateraly. For all domains identified for BM task alone, similar domains could be identified in MVF and joint tasks analysis. In addition MVF had domains related to motor planning on the right hemisphere and to self-recognition of action. For joint tasks analysis, seven domains were identified, with similar functions for the left and the right hand with exception of a domain covering BA32 (self-recognition of action) of the left hand only. In joint task domain analysis, the ERD/ERS showed a larger difference between domains than between tasks. All domains which involved the sensory cortex had a visible beta ERS at the onset of movement, and post movement beta ERS. The frequency of ERD varied between domains. Largest difference between tasks existed in domains responsible for the awareness of action. In conclusion, functionally distinctive domains have different ERD/ERS patterns, similar for both tasks. MVF activates contralateral hemisphere in similar manner to BM movements, while at the same time also activating the ipsilateral hemisphere. Significance: Following stroke cortical activation and interhemispheric inhibition from the contralesional side is reduced. MVF creates stronger ipsilateral activity than BM, which is highly relevant of neurorehabilitation of movements

Virtual reality visual feedback and its effect on brain excitability

This dissertation examines manipulation of visual feedback in virtual reality (VR) to increase excitability of distinct neural networks in the sensorimotor cortex. The objective is to explore neural responses to visual feedback of motor activities performed in complex virtual environments during functional magnetic resonance imaging (fMRI), and to identify sensory manipulations that could further optimize VR rehabilitation of persons with hemiparesis. In addition, the effects of VR therapy on brain reorganization are investigated. An MRI-compatible VR system is used to provide subjects with online visual feedback of their hand movement. First, the author develops a protocol to analyze variability in movement kinematics between experimental sessions and conditions and its possible effect on modulating neural activity. Second, brain reorganization after 2 weeks of robot-assisted VR therapy is examined in 10 chronic stroke subjects in terms of change in extent of activation, interhemispheric dominance, connectivity network of ipsilesional primary motor cortex (iM1) and the interhemispheric interaction between iM 1 and contralesional M1 (cM 1). After training, brain activity during a simple paretic hand movement is re-localized in terms of bilateral change in activity or a shift of interhemispheric dominance (re-lateralization) toward the ipsilesional hemisphere that is positively correlated with improvement in clinical scores. Dynamic causal modeling (DCM) shows that interhemispheric coupling between the bilateral motor cortices tends to decrease after training and to negatively correlate with improvement in scores for clinical scales, and with the amount of re-lateralization. Third, the dissertation studies if visual discordance in VR of finger movement would facilitate activity in select brain networks. In a study of 12 healthy subjects, the amplitude of finger movement is manipulated (hypometric feedback) resulting in higher activation of contralateral M1. In a group of 11 stroke subjects, bidirectional, hypometric and hypermetric,VR visual discordance is used. Both feedback conditions cause small increase in activity of the iM1 contralateral to movement and stronger recruitment of both posterior parietal cortices and the ipsilesional fusiform gyrus (iFBA). Fourth, the effect of mirrored-visual feedback on the activity of the ipsilesional sensorimotor cortex of stroke subjects is examined. While subjects move the non-paretic hand during the fMRI experiment, they receive either veridical feedback of the movement or a mirrored feedback. The results show recruitment of iM1 and both posterior parietal cortices during the mirrored feedback. Effective connectivity analysis show increase correlation of iM1 and contralesional SPL (cSPL) with iFBA suggesting a role of the latter in the evaluation of feedback and in visuomotor processing. DCM analysis shows increased modulation of iM1 by cSPL area during the mirrored feedback, an observation that proves the influence of visual feedback on modulating primary motor cortex activation. This dissertation provides evidence that it is possible to enhance brain excitability through manipulation of virtual reality feedback and that brain reorganization can result from just two weeks of VR training. These findings should be exploited in the design of neuroscience-based rehabilitation protocols that could enhance brain reorganization and motor recovery

The rehabilitation of motor and cognitive disorders after stroke

Following a stroke there can be a large range of different deficits, with poor motor function and cognition being particularly important for outcome. Rehabilitation of these deficits is thus an important priority for clinicians. In this thesis, I present 5 experimental chapters aiming to generate cognitive and motor benefits for the stroke survivor. In Chapter 2, prolonged Mirror Therapy was applied to chronic stroke survivors. In Chapter 3, Mirror Therapy was applied in a home based for chronic stroke survivors. In both these Chapters 2 and 3 benefits in unimanual performance of the affected limb and functional improvements of daily activities are being reported. Chapter 4 considered the application of Mirror Therapy to early subacute stroke participants and tested the neural correlates behind any effect. Changes in brain activation within both the ipsi- and contralesional hemispheres were noted. Functional Electrical Stimulation was applied to chronic stroke patients in Chapter 5. Improvements in motor performance were noted, along with the amelioration of visuomotor neglect. Linked changes in activity in the ipsi- and contralesional hemispheres were again noted. Finally, in Chapter 6, Computer Progressive Attention Training was applied in early subacute stroke patients, comparing performance with patients who received no extra intervention. Importantly, the training not only improved the tested functions but also other cognitive processes not targeted in training (e.g., long-term memory). Taken together, the experimental work provides evidence of strategies that can be followed by clinicians to improve functional ability after stroke. In the final chapter the above findings are being discussed together with clinical implications of motor and cognitive rehabilitation approaches