Visual feedback modulates functional connectivity between anterior intraparietal sulcus and ipsilateral motor cortex


Mirror visual feedback (MVF) is used to improve functions of an impaired limb.  Transcranial magnetic stimulation (TMS) studies suggest that the motor cortex (M1) ipsilateral to the moving hand is activated with MVF. The mechanisms underlying this feedback are not well understood.  The purpose of this study is to determine if the anterior intraparietal sulcus (aIPS) mediates the activity of ipsilateral M1 during movement preparation with MVF.   Five subjects participated in the study and were tested in 4 conditions: 1) rest; 2) mirror; 3) no-mirror; and 4) action observation (AO). In the mirror and no-mirror conditions, subjects gripped a force transducer with their right index finger and thumb after an auditory cue. TMS pulses were delivered through two coils placed on the right hemisphere separated by 2, 4, 6, 8 or 10 ms; the first pulse over the aIPS (90% resting motor threshold) and the second pulse over the M1 (1 mV).  Responses to the TMS were recorded from the resting left first dorsal interosseous muscle.     aIPS-M1 ratios were facilitated in the mirror and AO conditions compared to rest at 2, 4 and 6 ms.  Specifically, the motor-evoked potential ratios (<1 means inhibition, >1 means facilitation) for rest, mirror, no-mirror and AO conditions at 2 ms were: 0.78 ± 0.28, 1.07 ± 0.33, 0.97 ± 0.29 and 1.09 ± 0.17, respectively.  The ratios at 4 ms were 1.20 ± 0.33, 0.81 ± 0.24, 0.91 ± 0.15 and 1.19 ± 0.41 in the mirror, rest, no-mirror and AO conditions.  At 6 ms, the ratios were 1.17 ± 0.19, 0.88 ± 0.22, 1.19 ± 0.24, 1.29 ± 0.23 in the mirror, rest, no-mirror and AO conditions.   These preliminary findings suggest that vision plays an important role in modulating aIPS-M1 interactions during movement preparation. 

Acknowledgments: This research project is funded by the Canadian Institutes of Health Research and Ontario Graduate Scholarship in Science and Technology (Institute of Medical Science, University of Toronto).