Dear Judith,

You were the only one who responded to my question: DOES CLOSING YOUR EYES
HAVE ANY EFFECT ON YOUR DYSKINESIA?  Your answer "WOW! - It stops..."  does
not surprise me.
So now back to  the original question;  "What is dyskinesia?"

I believe that vision pathology -  either vision perception (in the eye) 
or vision processing (in the brain) is a major component of motor pathology
in PD. In fact I would go so far as to say that the same pathology which
causes akinesia when off or undermedicated will cause dyskinesia in the
presence of dopamine.  Our sensory perceptions monitor our performance of
motor activities by monitoring how these motor activities impact on the
environment.  For example when we take  a step one should feel the impact
of the ground under the foot as it lands on the ground.  Similarly, when we
move in the environment,  for example walking through it or even moving in
a chair,  there is visual feedback of the apparent motion of the
environment as it appears to move in response to our eyes moving to a
different vantage point.  This motion is monitored peripherally in  our
field of  vision below conscious awareness.  However, if this motion is
percieved to be  in conflict with what experience (conditioning) has taught
us is the expected response in relation to the given motor activity, then
the motor activity stops (i.e. we freeze).  For example freezing in a
doorway occurs, I believe, is not due to the  doorway but rather to the
opaque walls which frame the doorway by blocking peripheral monitoring of
this apparent motion.  If the pathology lies in the processing of normally
perceived  information then motor activity continues but attempts to comply
with the aberrantly processed information.  And therein lies the real
answer to the question "What is dyskinesia?"  Dyskinesia is the body's
attempt to conform to pathologic processing of peripherally perceived
visual information.  There is an autonomic component to dyskinesia (for
example tension potentiates dyskinesia). Normally visual feedback is a
consequence of the motor activity.  In this case the motor activity is a
consequence of the feedback.   The actual pathology lies in the processing
of low velocity motion and small changes in velocity.  Objects "seen" in
the periphery appear to move at different speeds as a function of how far
they are from the eye.  Real data can be displayed on the periphery of the
eye in such a way as to fool the subject  into believing that this data is
apparent only  and is feedback of motor activity.  Such a display can
dramatically suppress dyskinesia.   Also, accelerating optical flow of
apparent motion will suppress dyskinesia because a small change in velocity
 of a rapidly moving object will be  relatively 
insignificant in relation to the overall velocity of the apparent motion
(compared to the same small change in velocity relative to a much slower
moving object).  This is why running will suppress dyskinesia and walking
more slowly will exacerbate it.  It is also why such activities as bike
riding or skiing will suppress dyskinesia.  Many physical therapists
encourage PD'ers to walk with exagerated arm swing as a means of rhytmic
reinforcement of the cadence of gait.  This, I believe is fundamentally
wrong as many PD'ers have discovered unconsciosly themselves.  How many
times do we see PD'ers walking with their hands anchored in their back (or
front) pockets, or clutching a handbag with both hands or carrying a  cane
without really using it?  All are socially acceptable ways of not having an
arm swing.   Apparent motion is defined by how the environment appears to
move relative to the motion of our bodies.  A swinging arm forces us to try
and process low speed changes in velocity as the arm slows, stops and
changes direction.

I know this was long ... my hope is that some of you may find this to be of
interest.  Critical feedback is encouraged.

Regards,

Tom Riess