Role of Inferior Frontoparietal Structures in Motor Control and Freezing of Gait in Parkinson’s Disease

Freezing of gait (FOG) is a disabling symptom of Parkinson’s disease (PD) in which patients are unable to step forward when desired. Abnormal brain circuits responsible for FOG in PD patients are unclear and experimental paradigms are needed to address this disabling symptom. We hypothesized that motor interruptions of lower limb movements while seated may be related to FOG and may indicate abnormal brain activities. In Study 1, we tested 19 PD patients and 20 healthy controls and showed that motor interruption or cessation of bilateral stepping while sitting correlated with the presence and severity of FOG and this effect persisted in the “on” dopaminergic medication state. In Study 2, we tested how these “lower limb motor blocks” or LLMB are related to changes in 4-30 Hz cortical activities recorded from 64-channel scalp electroencephalography. In 17 PD patients, we found that sporadic LLMB differed from typical steps in the right angular gyrus (RAG, F=154.6, P=0.0185, before and during LLMB>typical steps). LLMB also differed from cued stops in the right inferior frontal gyrus (F=32.0, P=0.0005, before LLMB>cued stops; F=42.0, P=0.0005, during LLMBPh.D