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Consulting the vestibular system is simply a must if you want to optimize gaze shifts

Kathleen E. Cullen, Jessica X. Brooks
DOI: http://dx.doi.org/10.1093/brain/awu052 978-980 First published online: 19 March 2014

Even simple activities like reaching for our morning cup of coffee require precisely coordinated movements of multiple parts of the body. Successive attempts at these movements are characterized by ‘repetition without repetition’ (Bernstein, 1967). For this reason, it is thought that the brain does not enforce the details of a specific movement trajectory, but rather uses on-line feedback to optimize acquisition of the movement goal. However, a study in this issue of Brain demonstrates that when we make coordinated movements of the eyes and head to redirect our gaze, we use an optimal strategy that depends on vestibular sensory input: a strategy unavailable to patients with total vestibular loss. These results provide the first evidence that the vestibular system is critical for optimizing voluntary movements (Saglam et al., 2014).

When we make coordinated eye and head movements to redirect our axis of gaze relative to space (gaze = eye-in-head + head-in-space), movement accuracy is preserved even when the head’s trajectory is experimentally altered (Cullen, 2004). This happens because within milliseconds vestibular feedback rapidly alters the motor commands to the eye and head musculature to ensure gaze accuracy (Sylvestre and Cullen, 2006). For example, when a load is transiently applied to the head during a gaze shift, both the response duration and dynamics of neurons commanding the eye movement are updated—midflight—to preserve global movement accuracy. Thus, variability across movement trajectories is not problematic because the end goal of the movement is achieved as a result of on-line vestibular feedback. However, a remaining challenge has been to develop theoretical approaches to explicitly assess whether the gaze (as well as limb; Scott, …

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