Effect of Optic Flow Modulation on Circuits for Motor Organisation,
an activationstudy with fMRI.

By visual presentation of dots moving that move from the center of a monitor
screen, with increasing speed, to the peripheral screenside (optic flow) the
illusion of forward self-motion is induced. It mimicks basic features of gait
sensation. In Parkinson's Disease (PD), freezing of gait may occur when the
patient approaches a small corridor. On the other hand visual stimuli may also
support motor patterns in PD. In the present fMRI study, we want to find out
what the effect of optic flow is on cerebral circuitry involved in the
organisation of movement.

In the present fMRI experiment, the sensation of forward motion in depth will
be induced by optic flow. By periodically interupting this sensation, we try to
evoke responses in motor-related circuitry in oreder to gain insight in the
pathophysiology underlying 'freezing of gait' in PD.

fMRI measurement will be obtained during the presentation of the following
visual stimulus patterns:

In condition 1 (*flow forward) dots will appear from the center of a virtual
horizon, in radially moving with increasing speed into the lower part of the
screen. In condition 2 ('flow reversed'), the dots move in opposite direction
which induces the illusion of departure. In condition 3, radnom dot movements
serves as control. In al 3 conditions black curtains will repeatedly move from
the lateral outsides thus narrowing the flow pattern.
Analysis of stimulus-related differences in cerebral activation is done on
voxel-level by Statistical Parametric Mapping.

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