Balance Dysfunction in Parkinson's Disease.

Stability and mobility in functional motor activities depend on a precise regulation of phasic and tonic muscular activity that is carried out automatically, without conscious awareness. The sensorimotor control of posture involves a complex integration of multisensory inputs that results in a final motor adjustment process. All or some of the components of this system may be dysfunctional in Parkinsonian patients, rendering postural instability one of the most disabling features of Parkinson's disease (PD). Balance control is critical for moving safely in and adapting to the environment. PD induces a multilevel impairment of this function, therefore worsening the patients' physical and psychosocial disability. In this review, we describe the complex ways in which PD impairs posture and balance, collecting and reviewing the available experimental evidence.