Dynamical model of the body sway of bipedally standing rat with olivo-cerebellar dysfunction

During quiet standing, human and animal body continuously move and this body motion, called body sway, is known to change characteristically depending on some neural ataxia. As a typical case, chaotic complexity of the body sway is reported to increase depending on the progression of spinocerebellar ataxia. In order to investigate the mechanism of such change of body sway, we measured the body sway of bipedally standing rat with and without neural ataxia, and Lyapunov component is calculated. The mechanism is also analyzed using dynamical control model. Our previous research discussed whether change in posture control gain may explain the change in chaotic complexity and we failed. Then we modified the system model by including a characteristic motion of the neural ataxia: tremor. As a result, the increasement of chaotic complexity was confirmed by rat with ataxia, and this change was explained by the model with the effect of tremor.