Deep brain stimulation enhances movement complexity during gait in individuals with Parkinson's disease.

Deep brain stimulation (DBS) is associated with substantial improvements in motor symptoms of PD. Emerging evidence has suggested that nonlinear measures of complexity may provide greater insight into the efficacy of anti-PD treatments. This study investigated sample entropy and complexity index values in individuals with PD when DBS was OFF compared to ON. Five individuals with PD using DBS performed a four-minute treadmill walking task while 3D kinematics were collected over two periods of 30 s. Participants were tested in the DBS-ON and DBS-OFF conditions. Sample entropy (SE) and complexity index (CI) values were calculated for ankle, knee and hip joint angles. Paired samples t-tests were used to compare mean SE and CI values between the DBS-OFF and DBS-ON conditions, respectively. No differences in SE or CI were observed between the DBS-ON and DBS-OFF conditions at the ankle. At the knee, the DBS-ON was associated with greater SE and CI values than the DBS-OFF condition. At the hip, DBS-ON was associated with greater SE and CI values than the DBS-OFF condition. DBS enhances complexity of movement at the hip and knee joints while complexity at the ankle joint is not significantly altered. Greater complexity of knee and hip joint motion may represent increased adaptability and a greater number of available strategies to complete the gait task.

Normalizing EMG to Background Muscle Activation Masks Medication-Induced Reductions in Reflex Amplitudes in Parkinsonian Rigidity.

OBJECTIVES: Exaggerated reflex responses to passive stretch and shortening contribute to parkinsonian rigidity. Studies have reported medication-induced reductions in rigidity in the absence of attenuated reflex magnitudes. The purpose of this study was to determine if normalization procedures mask medication-induced reductions in reflex responses in Parkinson's disease. METHODS: Twelve participants with PD performed passive wrist flexion and extension movements after a 12-hour withdrawal from dopaminergic medication and 60 minutes after medication was administered. EMG was recorded from wrist flexors and extensors. Raw EMG signals were conditioned and normalized to mean background EMG amplitudes collected 100 ms prior to the onset of passive movement by division and by subtraction. RESULTS: Raw EMG amplitudes were significantly reduced. No medication-related reductions were observed during passive flexion or extension when EMG amplitudes were normalized by division. When EMG amplitudes were normalized by subtraction, significant reductions were observed following administration of dopaminergic medication during flexion and extension. Dopaminergic medication was associated with significant reductions in rigidity work scores and significant increases in moment-angle slope plots. CONCLUSIONS: These findings demonstrate that EMG normalization techniques may hinder data interpretation in studies of altered reflex responses in individuals with Parkinson's disease following the administration of dopaminergic medication.