At the end of Thursday's class, we discussed the possibility that the motor symphonies involved in cricket singing are genetically preprogrammed. When discussing the role of genetic factors in behavior, it is essential for one to distinguish between the implication that such behaviors are preprogrammed as in the concept of fixed action patterns and a conceptualization of the pattern for motor symphonies as an interaction between genetic factors, an input/output loop involving the organism and its environment, and information of such interactions in the past store somehow in the brain. That is, rather than approaching behavior as the turning on of a motor symphony, the click, and the playing out of a behavior, the whirr of a recorded message, a more appropriate model of human behavior would be more of an interactive satellite video conference with an archive of past behaviors built in. What is genetically programmed, rather, is the structure of the muscles which are utilized in these behaviors. The utilization of these muscles is what is being learned from day one. In fact, the oral motor activity displayed by neonates, which emerges prenatally, involves the constant conveyance of information between the environment and its behavior. By putting objects in their mouths and sucking on them, neonates' activity serves as a means by which they explore objects in their immediate environment as they conform their mouths to the shapes of the objects. This conceptualization of motor symphonies raises the question of whether or not these motor symphonies are also, like other behaviors, malleable/susceptible to reorganization from experience. Let us consider the case of Ralph, a worker in a soap factory. Ralph falls into a soap vat one day at work and looses his right leg. Will the motor symphonies for walking, running, etc. which are supposedly turned on by the CPG reorganize to accommodate the absence of this limb? Approaching the issue of amputation from the input side, the article on phantom limbs described amputees' perception of pain from the missing limb and of the movement of the imaginary limb in coordination with other movements as being the same as they were prior to the amputation. Furthermore, the authors' suggestion that the pain perceived at the location of the amputation is due to continual motor output from the motor cortex indicates that the motor symphony does not in fact reorganize after amputation of a limb. To the contrary, a recent article by Latash and Anson, "What Are Normal Movements in Atypical Populations?" suggests that motor symphonies are coordinated "priorities" and form the basis for patterns of motor outputs. They hypothesize that, "disorders of perception of the environment and decision-making, structural or biochemical changes within the central nervous system, and/or structural changes of the effectors, the central nervous system may reconsider its priorities. . . may lead to different patterns of voluntary movement." According to Latash and Anson, what amputation involves is a "major disruption of the biomechanical and neurophysiological relations developed during the lifetime." The subsequent loss of input from proprioreceptors regarding balance of weight, position, etc. would result in the person's not being able to walk even with a prosthetic limb if the central nervous system could not reorganize to take into account the loss of this information. This assertion implies that post-amputation, the person must learn to walk all over again relying on primarily visual information rather than input from proprioreceptors. In strong support of the notion of motor symphony reorganization and accommodation is that of the large number of amputees who continue to run and to participate in other physical activities with the aid of prosthetics. These arguments suggest that the click whirr notion of behavior as motor symphonies which are activated by CPGs does not sufficiently account for the plasticity of the human brain and its ability to organize and reorganize (to learn) through experience. For further discussion of other examples of CNS reorganization of motor patterns, I highly recommend reviewing this article posted at: this article.
Interesting and highly approriate concerns. The CPG notion was essential to (help) move beyond "reflex" based conceptualizations of behavior. But the "click whirr" idea associated with it is clearly proving incorrect in its own turn. We've actually been testing this very proposition in frogs in our lab, and coming up with observations quite similar to those you outline. PG