Objective: To quantify and compare functional magnetic resonance imaging (fMRI) activity during ankle dorsiflexion in people with and without Parkinson’s disease (PD).

Background: PD is a neurodegenerative disorder that affects the way people move. Despite a greatly improved understanding of the brain changes underlying upper limb function, we still have limited knowledge on how PD affects the brain circuit that regulates lower limb movements. Previous imaging approaches often relied on motor imagery paradigms that are limited by the lack of overt movement or control of the mental process involved in imagining the execution of a movement.

Method: Here, we used a novel MRI-compatible setup to measure force production during dorsiflexion of the ankle. We collected fMRI data from 6 PD tested off antiparkinsonian medication (mean age: 61.7 ± 8.4, 2 m/4 f) and 6 controls (mean age: 59.5 ± 6.6, 4 m/2 f). Participants also underwent a 2-minute walking test outside the MRI scanner during which several gait parameters were calculated from 6 APDM sensors (APDM, Inc) that were attached to all four limbs, sternum and the lumbar region.

Results: Of note, the absolute head motion, quantified as the displacement of the combined medio-lateral, anterior-posterior and superior-inferior planes, was 0.118 mm (± 0.030) for the PD group and 0.119 mm (±0.039) for the control group. Pilot data suggest that compared with healthy individuals, PD have: 1) a slower rate of force development and force relaxation during ankle dorsiflexion that correlates with disease duration, and 2) reduced brain activity across both the basal ganglia–thalamo–cortico and cerebellar–thalamo–cortico motor circuits. Moreover, we found that: 3) force-related activity in the foot representation in the primary motor cortex (M1) was negatively correlated with disease duration and 4) the reduced activity in the foot representations in M1 and cerebellum was associated with increased lateral step variability of the tested/more affected foot.

Conclusion: Collectively, data suggest the feasibility of this fMRI paradigm in engaging the brain circuitry controlling lower limb movements in PD while keeping head motion minimal. It appears that in addition to dopaminergic deficiency, the abnormal activity of the cerebellum may underlie lower limb symptoms in PD. Therefore, a possible approach for treating parkinsonian symptoms is to attempt to normalize cerebellar function.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-network-deficits-during-lower-limb-movements-in-parkinsons-disease/