This essay will address the question: How does one think differently about the nervous system and behavior given the concepts of motor symphony and central pattern generators.

These two concepts have clarified a lot for me regarding movement. Central pattern generators explain how one can perform a movement at a fast pace without the benefit of sensory feedback (for example, my typing on the computer or riding a bike); but also how movement can be modified by the constant flow of sensory feedback. It seem that the constant proprioceptive flow that we get to the cerebellum will impact on the motor output but that this is a continuous, subcortical feedback that serves to modify the motor symphony. For example, when riding a bicycle, the motor symphony is the pattern that has been written regarding the movement of the legs to keep the pedals going. There is a constant proprioceptive flow from all the muscle receptors in the legs telling the cerebellum about the length, tension and position of the muscle. If one hits a pothole in the road, for example, the sensory feedback quickly changes and the motor symphony hopefully quickly adjusts so that the pedaler can keep the bike upright. So although sensory feedback is not necessary to generate the movement, it is a necessary component of a smooth and coordinated movement. Although the score for this motor symphony has been written, it can easily and readily be modified by sensory input.

This idea of central pattern generators also helps to clarify pathological motor behavior such as what we might see in an individual who sustains a head injury and has resultant spasticity; and also raises some interesting questions. Is the spasticity explained by the possibility that the individual no longer has the ability to modify the motor scores? Are the central program generators running out of control without inhibition/modification of higher centers? If this is the case, then it would suggest that the higher centers serve to provide modification and inhibition, not facilitation. However, how then do we account for the activity that is generated in the cortex which results in direct alpha motoneuron activity? Also , is the stretch reflex, which is proposed to be hyperactive in individuals with spasticity, really the thing that is running out of control or is it a more complex central pattern generator of activity? These issues are important when considering intervention for individuals with motor disorders. Should the intervention focus on modifying the central program generator activity, and if so, how might this be accomplished? Are central program generators modifiable or is it the score that is modifiable? And how would one have an impact on either of these?

A final thought that has been generated based on our discussions of CPG and motor symphonies, is related to the concepts of genetic versus influenced by experience. I agree that certain motor symphonies are genetically wired, such as walking, coughing, talking, etc; and that others are created by need or desire (such as driving a car, playing the piano or riding a bicycle). Is there a difference between the innate CPG and the created ones? How is it that innate motor patterns can be modified based on culture or experience (for example the gait patterns and stance may differ depending on culture). And finally, what constitutes writing a score for a new CPG such as learning to ski or ride a bike? If new scores can be written, is it easier to write them when the nervous system is young and plastic? What makes a motor score more easily composed? Is it sensory feedback or motor repetition, or something else? These will have important implications for working with individuals with motor dysfunction. For example, the individual who has sustained a stroke and now has a non-functional arm. What kinds of intervention will best help this individual re-learn how to move that arm? Will increased tactile and proprioceptive input that helps them "feel" the arm assist them with regaining movement? Will passive assisted movement of the arm help them? Will attempts to get them to consciously and volitionally move their arm help them to modify the CPG to the just right degree for movement? Since none of these scenarios work well in all (or even many) individuals I wonder if there is something else that we are missing.

Sophisticated/interesting thoughts/questions. Yes, motor scores modifiable by sensory input. But there is an interesting question about how fast. Sensory input averaged over time can modify output, but whether output correctable when hitting a pothole depends on how quickly one wants a correction. Yes, spasticity tends to imply loss of inhibition rather than facilitation, but both operate. Directly, as well as by gating sensory input. Yes, certainly encourages thinking about therapeutics. Not sure there is a general answer though. Suspect one has to explore variety of possibilities raised for each syndrome separately, and, potentially, for each individual separately. PG