Neuroanatomy of Postural Stability: Links to Parkinson's Disease

Abstract

Postural stability is a complex task that requires the integration of many sensory inputs to produce an appropriate response for every environmental situation. The balance systems employ both reactive and anticipatory strategies to maintain the body's center of mass. The body's ability to maintain stability is limited by biomechanical constraints, such as the bodies' internal representation of position in space. The balance system has multiple internal representations of verticality including those in the vestibular and somatosensory cortexes that serve to orient the body and help to maintain balance. Moreover, the balance system uses cognitive resources to integrate sensory inputs. These cognitive resources are used to produce the appropriate motor responses in situations when the balance system is malfunctioning. Parkinson's disease (PD) is characterized by many motor symptoms, such as resting tremors, bradykinesia, and rigidity. PD is generally characterized by two subcategories of symptoms: the tremor type and the postural instability gait difficulties type (PIGD). Previous studies showed that the PIGD type is less responsive to current treatments, which include L-dopa. Thus, a better understanding of the balance system and how it affects the production of postural deficits is needed to better treat individuals suffering from the PIGD type of PD. Here, we review the candidate neural mechanism involved in balance, and inferences are made on how these balance networks may be affected by PD.