Supraspinal Control of Unilateral Locomotor Performance: An FMRI Study Using a Custom Pedaling Device
This study aimed to develop a novel unilateral pedaling device, validate its function, and use it in an fMRI study of bilateral vs. unilateral locomotor control. The new device is MRI compatible and allows for conventional coupled bilateral pedaling, along with decoupled unilateral pedaling. It was designed with an assistance mechanism to simulate the presence of the non-contributing leg while pedaling unilaterally. During coupled bilateral pedaling, the two legs work in unison: while one leg is extending in the downstroke, it provides support to lift the other leg back up as it is flexing in the upstroke. The device uses an eccentric pulley to stretch elastic bands during the downstroke, storing energy that is released back during the upstroke to assist the leg as the bands relax. A phantom scan in the MRI machine was performed, which confirmed that the device did not interfere with signal detection. Experiments were performed to test the function of the device, showing that the assistance mechanism was able to adequately simulate the presence of the non-contributing leg during unilateral pedaling. The velocity and EMG profiles matched between unilateral and bilateral pedaling, with consistent results across days. An fMRI study was performed to compare brain activation associated with coupled bilateral, right unilateral, and left unilateral pedaling in able-bodied individuals with a healthy nervous system. Task related brain activity was seen in the primary sensorimotor cortex (M1S1), Brodmann’s area 6 (BA6), and the cerebellum (Cb). The laterality of activation was shifted to the contralateral M1S1 and ipsilateral Cb during unilateral pedaling, but some bilateral activation remained. BA6 showed no lateralization in activity. Additionally, there was no difference in the magnitudes of the laterality shift in right and left pedaling, and bilateral pedaling was not shifted to either hemisphere. Volume during unilateral pedaling showed no significant change in any brain area across conditions. These observations of laterality and volume suggest the existence of common regions of brain activation for bilateral and unilateral pedaling. Mean intensity in the common area of activation was lower in M1S1, BA6, and Cb for right and left unilateral compared to bilateral pedaling.