Professor Grobstein told me last week about a recent article reporting a finding that merely thinking about a motor behavior improves one's coordination in the performance of that behavior at a later time. He cited this finding as support for the existence of an I-fnc. While I am still not completely convinced of the existence of an I-fnc per se, it is my interest here to further explore this notion of the I-fnc as it relates to CPGs and CDs, which we have outlined as being the communication between the CPGs and between the I-fnc and the CPGs. The first question is obvious, what exactly is this I-fnc? How does it interact with internal "noises" to influence patterns of outputs from and the processing of inputs to the NS? Per usual, this raises the question of whether it is feasible to observe this I-fnc at work or even within ourselves? A concrete example:

One interesting behavior -- which while not as straightforward an example as that of the Pleurobrachia pileus' not withdrawing its proboscis when you hit it while it is eating -- involves the physiological response to exercise stress and the modification in behavior which occurs with repeated exercise. One interesting observation has been that the behavior of habitual exercise -- while eliciting the physiological stress response -- actually increases a person's ability to cope with psychological stressors. A number of immediate neuroendocrinological changes lead to long-term changes: alterations in resting peripheral catecholamine levels, in central monoamine levels, increased central opioid activity, cardiovascular changes, etc. -- the list goes on and on. And in fact, one of the strongest pieces of evidence for a biological basis for this phenomenon is that there might be long-term changes in the HPA axis in highly trained athletes which actually results in an elevated threshold of the degree of physical or psychological stress required to elicit the physiological stress response (Wittert etal., 1996).

One common observation is of the "runner's high" which is well known to be associated with an overall elevation in affective state. At the basis of this elevation in affective state is believed to be an elevated level of endogenous opioid activity -- commonly known as the endorphins and enkephalins -- which has been observed in highly trained athletes and fitness fanatics. In an article in Medicine and Science in Sports and Exercise, Thoren etal (1990) propose a physiological basis for the activation of the opioid systems with exercise. They hypothesize that sustained rhythmic motion of the skeletal muscles activates mechanoreceptors (ergoreceptors) in the skeletal muscles with contraction and flexion. These afferent fibers synapse on the raphe nucleus, the brain's broadcast center for seratonin, as well as on the periaqueductal gray which has a concentration of opioid receptors.

In light of these observations, then it is even more intriguing to learn that not all people have the same affective response to exercise stress, and in fact, personality behavior pattern appears to influence the affective and physiological effects of exercise stress. When Hardy etal (1989) exposed Subjects who display extreme type A or type B behavior patterns to exercise stress, they found that at the lower exercise intensity levels, type As rated themselves as higher in affect than Bs. On the other hand, during and after high intensity affect, type As actually showed a greater degree of epinephrine responsivity to exercise stress and a lower self-reported affective state. Other similar questions regarding the role of individual differences in how training affects the mind > and body have been raised by the observation that some highly trained athletes suffer from bouts of overtraining syndrome and others do not.

These elegant examples of how the motor outputs provide inputs to the nervous system which alter the nature of how a person processes inputs from her environment and in turn how a persons personality affects the nature of the mental impact of these changes. The release of endogenous opioids in response to exercise stress can be concluded as being rewarding (for reasons not addressed herein -- refer to ICSA and motivated behavior experiments for more information), reinforcing the behavior of exercise and increasing the likelihood of that behavior. But exactly how that habitual behavior affects the body appears to depend upon something greater than personality -- possible an I-fnc.

Hardy, Charles J., Robert G. McMurray, & Sue Roberts. (1989) A/B types and psychological responses to exercise stress. Journal of Sport & Exercise Psychology, 11, 141-151.

Thoren, Peter, etal. (1990) Endorphins and exercise: physiological mechanisms and clinical implications. Medicine and Science in Sports & > Exercise, 22(4), 417-428.

Wittert, Gary A. etal (1996) Adaptation of the hypothalamopituitary adrenal axis to chronic exercise stress in humans. Medicine & Science in Sports & Exercise, 28(8), 1015-19.

Very interesting set of issues, and a nice example of output causing input which in turn causes changes in the nervous system itself. Important. Less clear where CD fits into the whole thing. And, very intriguing in relation to your opening questions: "thinking about doing something" would seem to involve/require "I-function", whereas it isn't obvious (to me, at least) that the exercise effects you talk about do. Maybe that helps us to further specify what is meant by an "I-function". Yes, of course, we'll talk more about that. PG