Attentional demands of state transitions in posture and balance

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.

The proposed project tests the hypothesis that transitions between dynamic postural states involve attention-demanding cognitive mechanisms governing sensory motor transformations for control of balance and that inefficient handling of the fluctuations in cognitive demand in the elderly contributes to impaired balance. We propose functional brain imaging when executing transitions in oscillatory ankle movements in a simulated balance task to identify underlying neural circuits. Eleven experiments will be carried out under three headings. The first heading concerns adaptation of postural stability to abrupt transitions between body sway entrainment states as a function of cross-modal interference. The second group of experiments focuses on age-related effects on transitions between postural states as a function of additional demands for attentional resources. The third set of studies involves brain imaging of periodic ankle torque control with entrainment by an oscillatory visual stimulus. The research brings together two senior researchers, Wing, with a world class reputation for research on sensory motor function and control of movement force and timing, and Kourtzi, who is an international leader in the study of using functional brain imaging to study adaptive visual processing. The work draws on recent BBSRC investment in a new 12-camera motion analysis lab for behavioural studies and fMR compatible movement tracking facilities for brain activation studies. The named postdoctoral fellow on the proposal, Johannsen, is a promising new researcher in the control of posture and balance