An fMRI-compatible force measurement system for the evaluation of the neural correlates of step initiation.

Knowledge of brain correlates of postural control is limited by the technical difficulties in performing controlled experiments with currently available neuroimaging methods. Here we present a system that allows the measurement of anticipatory postural adjustment of human legs to be synchronized with the acquisition of functional magnetic resonance imaging data. The device is composed of Magnetic Resonance Imaging (MRI) compatible force sensors able to measure the level of force applied by both feet. We tested the device in a group of healthy young subjects and a group of elderly subjects with Parkinson's disease using an event-related functional MRI (fMRI) experiment design. In both groups the postural behavior inside the magnetic resonance was correlated to the behavior during gait initiation outside the scanner. The system did not produce noticeable imaging artifacts in the data. Healthy young people showed brain activation patterns coherent with movement planning. Parkinson's disease patients demonstrated an altered pattern of activation within the motor circuitry. We concluded that this force measurement system is able to index both normal and abnormal preparation for gait initiation within an fMRI experiment.

Validation of GDI, GPS and GVS for use in Parkinson's disease through evaluation of effects of subthalamic deep brain stimulation and levodopa.

The Gait Deviation Index (GDI), Gait Profile Score (GPS) and Gait Variable Scores (GVSs) have been proposed as measures of gait quality and validated for use with children with cerebral palsy. The aim of this study was to extend this validation to people with Parkinson's disease by evaluating the effects of subthalamic deep brain stimulation and levodopa on gait. 16 participants had their gait evaluated with stimulation, medication or a combination of both. The Unified Parkinson's Disease Rating Scale (UPDRS) showed statistically significant differences in agreement with previous studies. The GPS and GDI showed similar treatment effects as did GVS for hip and knee flexion/extension, as assessed with Cohen's d where medium or large. Overall the results suggest that these gait indices are sensitive to treatment in this group of patients and that their use in groups other than children with cerebral palsy is valid.