Neural correlates of hypokinetic gait in Parkinson’s disease: An fMRI study

Objective: To investigate the neural correlates of hypokinetic gait in Parkinson’s disease (PD) using functional magnetic resonance imaging (fMRI).
Background: Although hypokinetic gait is frequent and has a negative impact on quality of life in PD, its underlying mechanisms remain poorly understood. Assuming that the brain regions recruited during real and imagined gait strongly overlap, mental imagery of brisk gait may be a successful approach to study hypokinetic gait in PD.
Methods: Fifteen ‘‘on-drugs’’ PD patients (8 males; mean age 5 65.1 6 9.4 years) and fifteen controls matched for age, gender and mental imagery skills were trained to perform video-taped trials of comfortable and brisk gait on a 25 meter-path. The study was organ- ized as a block-design fMRI experiment where subjects were instructed to rehearse themselves performing comfortable and brisk gait and to press a key to indicate when they completed each 25 meter-imagined gait trial. The imagined speed reserve (ISR) defined as the difference between imagined brisk and comfortable gait speeds was measured as a control of behavioral performance. Imaging data processing and analyses were performed using SPM8. The first-level individual contrast images representing the comparison between brisk and comfortable gait were entered as two separate groups (controls vs patients) in an ANOVA with the corresponding ISRs as correlation regressors.
Results: Compared with controls, patients showed hypokinetic gait during real gait training as their increase in speed during brisk relatively to comfortable gait was related to an increase in step ca- dence (r50.87; p<0.001) but not in step length (r50.11). ISRs meas- ured during fMRI and their real counterparts measured offline strongly correlated in patients (r50.88; p<0.001) and controls (r50.59; p50.02). Between-group comparison (p<0.001, uncorrected) of fMRI data showed that increasing imagined gait speed was strongly associated with increased activity of the left posterior parietal cortex in controls and with decreased activity of this region in patients.
Conclusions: Our findings suggest that hypokinetic gait in PD is related to the impaired functioning of the left posterior parietal cortex. This area may represent a target for therapeutic interventions aimed at alleviating gait disturbances in PD.