Contralateral Activation and Enhanced Rigidity in Parkinson’s Disease: Neural and Non-neural Contributions

INTRODUCTION Parkinsonian rigidity is described as a uniform increase in resistance to passive motion throughout the entire range of motion. Evidence indicates that rigidity is influenced by both non-neural and neural factors. The non-neural component of rigidity is the result of alterations in the mechanical properties of the muscle and connective tissues [1]. The neural mechanisms underlying rigidity include aberrant reflex responses to passive stretch and shortening. Previous research has revealed that a contralateral contraction enhances parkinsonian rigidity [2]. However, the changing contributions of the neural and non-neural components of rigidity in response to the contralateral contraction have not been previously investigated. The purpose of the current study was to compare the changes in neural and non-neural contributions to parkinsonian rigidity in response to contralateral activation. It was hypothesized that the contralateral contraction would result in greater contributions of the neural component of rigidity.