Attentional demands of state transitions in posture and balance

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Quiet standing in an upright posture comprises a continuously controlled balance state. This dynamical state can be considered as 'steady' in the sense that the position of Centre of Mass (CoM) is kept within the limits of stability (LoS) against the pull of gravity and that following a perturbation to body balance resulting, for example, in slight forward sway, the balance control system will try to recover by returning to the initial balance state. However, in normal circumstances people frequently change their posture either voluntarily (eg reaching to pick up an object) or in response to external factors in the environment (eg an unexpected push). These events, which cause transitions between different postural states with changes in patterns of sensory stimulation and altered coordination of body segments, seem effortless but nevertheless need to be properly planned and executed in order to maintain balance. The dynamics of transitions between steady behavioural states have been extensively investigated in voluntary bilateral limb movements but there has been little research examining transitions between steady states in the sensorimotor control of posture and balance. We will examine the role of predictive and reactive control processes, the integration of multimodal sensory information and the demands on attention during transitions between states and stabilization in the new balance state. We will use behavioural and functional brain imaging to shed light on the dynamics of postural control and the underlying brain mechanisms and the changes that occur associated with elderly impairments in adaptation to external changes affecting body posture.