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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