Do mirror glasses have the same effect on brain activity as a mirror box? Evidence from a functional magnetic resonance imaging study with healthy subjects.

Christopher Milde,Herta Flor,Pinar Kirsch,Martin Diers,Robin Bekrater-Bodmann,Mariela Rance,Jens Foell,Jörg Trojan,Xaver Fuchs,Maurice Ptito

doi:10.1371/journal.pone.0127694

Abstract

Since its original proposal, mirror therapy has been established as a successful neurorehabilitative intervention in several neurological disorders to recover motor function or to relieve pain. Mirror therapy seems to operate by reactivating the contralesional representation of the non-mirrored limb in primary motor- and somatosensory cortex. However, mirror boxes have some limitations which prompted the use of additional mirror visual feedback devices. The present study evaluated the utility of mirror glasses compared to a mirror box. We also tested the hypothesis that increased interhemispheric communication between the motor hand areas is the mechanism by which mirror visual feedback recruits the representation of the non-mirrored limb. Therefore, mirror illusion capacity and brain activations were measured in a within-subject design during both mirror visual feedback conditions in counterbalanced order with 20 healthy subjects inside a magnetic resonance imaging scanner. Furthermore, we analyzed task-dependent functional connectivity between motor hand representations using psychophysiological interaction analysis during both mirror tasks. Neither the subjective quality of mirror illusions nor the patterns of functional brain activation differed between the mirror tasks. The sensorimotor representation of the non-mirrored hand was recruited in both mirror tasks. However, a significant increase in interhemispheric connectivity between the hand areas was only observed in the mirror glasses condition, suggesting different mechanisms for the recruitment of the representation of the non-mirrored hand in the two mirror tasks. We conclude that the mirror glasses might be a promising alternative to the mirror box, as they induce similar patterns of brain activation. Moreover, the mirror glasses can be easy applied in therapy and research. We want to emphasize that the neuronal mechanisms for the recruitment of the affected limb representation might differ depending on conceptual differences between MVF devices. However, our findings need to be validated within specific patient groups.

Highlights

The idea of using altered visual feedback to relieve phantom limb pain by using a mirror box (MB) was originally proposed by Ramachandran et al [1]
Areas of significant functional MRI (fMRI)-response were determined using clusters identified by a z > 3.0 threshold and a corrected cluster threshold of p = 0.05 assuming a Gaussian random field for the z-statistics
Imaging data revealed significant fMRI activations in the left sensorimotor cortex corresponding to the moving right hand in both mirror visual feedback (MVF) conditions (MNI coordinates: MB x = -40, y = -22, z = 56, Z = 7.0; mirror glasses (MG) x = -38, y = -24, z = 60, Z = 7.26)

Summary

Introduction

The idea of using altered visual feedback to relieve phantom limb pain by using a mirror box (MB) was originally proposed by Ramachandran et al [1]. There is increasing evidence that a reactivation of the affected limb representation in the sensorimotor strip and accompanying neuroplasticity is an important neuronal correlate of the MVF related neurorehabilitation [13,15,16]. It remains unclear how the sensorimotor representation of the non-mirrored (affected) limb becomes functionally recruited because studies examining the functional connectivity between brain areas during MVF are still rare [13,17]

Methods

Results

Discussion

Conclusion