Bernard T. Engel
Department of Psychiatry and Behavioral Sciences, Duke University Medical Center
This chapter includes three sections. The first part is an overview of the historical discoveries and evolution of concepts about the autonomic nervous system. The second part is a selective review of the experimental findings on operant conditioning of visceral function. The third part is a theoretical consideration of the significance of the findings that visceral responses can be brought under stimulus control. The chapter leans heavily on the writings of Sheehan (1936) for the review of the history of findings and concepts about the autonomic nervous system. It also examines the overviews by Kuntz (1953) and Pick (1970); however, it became clear that they also used Sheehan as a primary source. Thus, whereas specific citations to Sheehan are not included in the first part, his work is followed in detail and anyone who wishes to get closer to the original sources should read the original. The second part includes a review of a number of issues relevant to the topic of visceral learning. Therefore, the chapter considers not only studies of operant conditioning of autonomic responses, but also studies on visceral perception. Although it trys to address the salient issues, no effort is made to provide a complete survey of the literature. However, it does try to provide interested readers with enough guidelines to enable them to find that literature. The third part tries to give some conceptual meaning to the findings reported in the previous part, and attempts are made to fit those concepts into the concepts introduced in the history section.
Throughout most of recorded history little or no differentiation was made between the physiological nature of the autonomic nervous system and the functional significance of its actions. Furthermore, much of the speculation about function was part of the broader question of the way the nervous system worked, in general. Galen's hypothesis that “animal spirits” were generated by the brain and conveyed to the endorgans dominated thinking for more than one millennium. He proposed that the brain was the organ primarily responsible for regulating performance by communicating sympathy” or “consent” among the different parts of the body. He also identified seven pairs of cranial nerves, among which the sixth had three main branches: the superior, recurrent laryngeal and costal. Thus, Galen included the vagus nerve and the sympathetic trunk as part of an anatomical and physiological unit. It is noteworthy that he felt that it was through these nerves that the viscera received “an 'exquisite' sensitivity from the brain, and a motor power from the spinal cord” (Sheehan, 1936, p. 1083). The “'exquisite' sensitivity” of the brain in the control of visceral function lies at the heart of the nature of visceral conditioning as that concept is understood today. It was not until the 17th century that Galen's model of the autonomic nervous system-a designation that did not pear until the late 19th century-began to be refined and eventually modified. Willis made several important anatomi cal and physiological observations and psychological speculations. He was the first to describe the spinal accessory nerve and the vagus nerve (which was referred to by him and others as the eighth nerve). He also was the first to note that stimulation of the vagal branch arisi rig from the aortic arch (which is now called the depressor nerve) caused the heart to slow. He erred in perpetuating the view that the “intercostal” nerve originated in the brain. Willis was also among the first to introduce the concepts of voluntary and involuntary movement. According to Willis, the involuntary animal spirits flowed from the cerebellum to the body through the vagus and intercostal nerves: The voluntary spirits emanated from the brain