Effect of optic flow on gait control in healthy subjects and patients with Parkinson*s Disease.

Visual stimuli influence gait in Parkinson*s disease (PD). In the present study
we aim to asses whether wide-field visual presentation of a radially expanding
dot flow, which induces the illusion of forward self-motion, supports gait. In
addition, the transition from this wide- to a narrow flow field will be
examined. When subjects (both PD patients and healthy controls) walk on a
treadmill no optic flow is generated because there is no spatial change
relative to the surrounding. In this condition, the visual illusion of forward
locomotion can be given by allowing subjects to watch optic flow projected on a
wide screen while walking on the treadmill. Our hypothesis is that due to
insufficient basal ganglia output to particularly the medial frontal cortex, PD
patients will show excessive gait obstruction during narrowing of the flow
field because their own initiation to maintain walking is reduced when external
stimulus support fails.

We want to gain more fundament insight in disturbed sensorimotor integration in
PD, particularly with regard to the impact of visual stimuli on the cerebral
organization underlying gait control. Such knowledge provides arguments for
targeted patient selection for specific treatment- and care strategies.

PD patients will be selected from the database of the Movement Disorder Clinic
from the Dept. of Neurology UMCG. Both patients with a recent diagnosis and
patients with mild disease progression will be selected, based on the Unified
Parkinson Disease Rating Scale (UPDRS III), score <30. In addition, control
subjects matched for age and gender will be included. Next to standard clinical
PD assessment, Mini Mental State Examination (MMSE) will take place.

During treadmill walking, subjects (PD patients, healthy controls) will look at
the presentation of radially expanding optic flow. Effects on gait due to (i)
narrowing of the flow-field and (ii) stopping the visual motion will be
assessed. The most appropriate parameters will be chosen by pilot studies.
E.g.: speed of the treadmill if the subject determines it by the speed of his
walking. Alternatively, the treadmill is locked to the walking speed at which
the subject feels comfortable, which implies backwards displacement due to
slower walking or motor blocks. Step frequency might possibly provide a measure
too. For this study, a simple robust parameter will be used. Subject*s
movements on the treadmill are recorded by sensors that detect the locations of
foot pressure.

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As to avoid fall accidents, subjects (patients included) will ware a safety
harness attached to the ceiling. In this way, a disturbance of balance will not
result in falling as subjects will hang at the same level. In this situation
they can easily regain balance by positioning their feet on the floor. In case
of loss of balance, an observer will stop the treadmill and provides support.

If refraining from taking parkinson medication for 12 hours is considered to be
a burden, the experiment will be done before taking new medication ('end of
dose' assessment).