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Shawn Reese1, Claire Smith1, Alex Olmos1, Jocarol Shields1, Caleb Voskuil2, Xin Ye3, Matt Stock4, Joshua Carr2 and Jason DeFreitas1

1Oklahoma State University, Stillwater, OK

2Texas Christian University, Fort Worth, TX

3University of Hartford, West Hartford, CT

4University of Central Florida, Orlando, FL

Mirror illusions are utilized in the rehabilitation of impaired limbs due to injury and stroke to stimulate the affected limb’s associated motor cortex and peripheral neural pathways during movements with the healthy limb without actual movement of the affected limb. However, how mirror illusions affect communication between the two hemispheres, and whether the type of contraction in the healthy limb plays a role are still unknown. PURPOSE: To determine the effects of mirror illusion during different contraction types on interhemispheric inhibition. METHODS: Ten healthy individuals have completed this study so far. A figure-eight transcranial magnetic stimulation coil was used to stimulate the hand area of the right primary motor cortex during dynamic and isometric contractions of the right hand. Ipsilateral silent period (iSP) was used as a measure of interhemispheric inhibition. Participants were instructed to fix their gaze in the same location for 2 visual conditions: No mirror, and Bilateral mirror illusion. The effect of the mirror illusion was defined as the change in iSP from the no mirror to the bilateral condition. Since the data is currently too underpowered for standard null-hypothesis testing, we utilized Cohen’s d as an estimate of the preliminary effect sizes. RESULTS: Mirror illusions during dynamic contractions show a rise in interhemispheric inhibition, with mean iSP increasing from 35.4ms to 36.7ms (3.5% change; d = 0.15). However, mirror illusions during isometric contractions show a reduction in inhibition, with mean iSP decreasing from 39.6ms to 37.5ms (-5.4% change; d = -0.27). CONCLUSION: The effects of mirror illusions on interhemispheric inhibition seems to be dependent on the type of contraction (dynamic vs. isometric). If these results hold firm with further sampling, then contraction type may be an important consideration for how hemispheric communication is modulated in mirror illusion therapy and upper extremity rehabilitation.

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