Three years ago the New England Journal of Medicine published a remarkable case study : “Cycling for Freezing Gait”. The report from doctors in the Netherlands describes a man with severe Parkinson’s disease who was virtually unable to walk, but, when put on a bike, rode beautifully, including the ability to turn, raise off the seat for power, and comfortably dismount.
Parkinson’s disease is largely due to loss of dopaminergic neurons, most of which are found in the substantia nigra. Deficits are attributed to problems in the basal ganglia circuitry depicted on the figure to the right. The basal ganglia are involved in motor systems, particularly in learned, patterned motor movements. The basal ganglia form a “loop” that feeds back to motor cortex (basal ganglia loops not illustrated). Recent ideas emphasize the role of the basal ganglia in motor learning and suggest that the basal ganglia function by linking motor actions to internally generated rhythms.
View the video below to see the remarkable dissociation of abilities in the patient.
Walking and bike riding seem remarkably similar: both are complex, learned motor routines, that have become automatic, are rhythmic and involve a high degree of balance. Why the remarkable difference in function and dysfunction? The research team suggests that the rhythmic feedback from the pedals may be an important difference.
Taking this one-step further, one may speculate that Parkinson’s disease is, in part, a deficit in supplying internally generated rhythms, and the pedals, or other external rhythms, may be an external aid. This may be similar to the therapeutic effects of dance or music (as in ipod therapy). I am not an expert on Parkinson’s disease or the motor systems. I’m curious about what others think. I especially invite comments suggesting mechanisms.