Gait disorders in Parkinson's disease - Neuroanatomical and physiological organization of gait

Gait is a voluntary, automatic and reflex rhythmic activity: it is generate d by a central pattern generator identified from animal models. This spinal gait generator (SCC) is controlled by various parts of the central nervous system: the descending tracts and locomotor regions of the brainstem, the cerebellum, the basal ganglia, the motor and parietal cortex and the hippoc ampus. Kinesthetic inputs which project to the SCC and the cerebellum, play an important role in the production of postural reflex responses;vestibula r and visual inputs mainly control balance. Gait mainly depends on the relationship between posture. balance and moveme nt: As concerns posture each segment is under the control of both periphera l and central nervous systems and is used as a system of reference to organ ize movements of adjacent segments. Balance is maintained by sensory inputs which provide corrective mechanisms: anticipatory postural responses, refl ex postural responses and voluntary responses. Different descriptive parameters may be proposed: Analysis of kinematic (di splacement, speed and acceleration of segments) and kinetic parameters duri ng the four successive stages of gait (posture, initiation, rhythmic gait a nd return to the initial posture) provides an understanding of neurological gait disorders. In particular the relationship between the center of press ure and the center of gravity is used to analyze infraclinical gait abnorma lities. New and sophisticated investigations methods are available: The optoelectro nic system provides a tridimensional analysis of movement and can be combin ed with forceplate and electromyographic recordings. Theses methods constit ute an interesting contribution to the clinical analysis of gait. Classification: This is established according to clinical data and the posi tionment of the lesion among the structures of the nervous system. The phys iopathological approach is then specified taking into account the lesions o f the muscular, skeletal and nervous structures.