CENTRAL AUTONOMIC MECHANISMS 



975 



of spinal autonomic activities. The focal points of a 

 number of these patterns of control seem to be highly 

 localized in the medulla oblongata. Here we can spot 

 them chiefly by picking up the points of efferent 

 flow. It has already been argued that the ordinary 

 concept of neural 'center" is hardly adequate for the 

 consideration of these neural patterns, which may be 

 extensive. These brain-stem autonomic circuits must 

 also have the capacity for feeding to the diencephalon 

 and cortex and of bringing into play at these higher 

 levels still further patterns of integration, which in 

 turn may feed back into the brain stem and cord. 



Interactions between the somatic and autonomic 

 mechanisms must not be overlooked. It has been 

 clearly shown that these interactions are not only 

 present but exceedingly important. Changes in the 

 environment which affect initially the soma can be 

 brought into close relationship with autonomic re- 

 sponses as well. These somatovisceral and viscero- 

 somatic circuits are also modulated by influences 

 from higher regions. This modulation may be tonic or 

 it may be brought into play by ascending impulses 

 arising in these circuits. 



The midbrain contains relatively few of the more 

 spectacular autonomic mechanisms, but through this 

 region a flood of ascending and descending impulses 

 pass, including those picked up by the reticular 

 formation from the great afferent pathways and passed 

 on in some fashion to activate and otherwise modify 

 the activities of the cerebral cortex. Here also we have 

 a set-up for chemical modulation; just as in the me- 

 dulla we find the activities of the respiratory and other 

 centers modified by changes in the blood, in the mid- 

 brain also we may find important effects by certain 

 hormones, such as epinephrine, through which the 

 complicated neural discharges characteristic of emo- 

 tional responses may be reinforced and prolonged. 



In the diencephalon, autonomic functions are cen- 

 tered largely in the hypothalamus which is intimately 

 related to the reticular formation of the brain stem. 

 Here again we have focal areas, as in the medulla, 

 which can be artificially aroused to activity by direct 

 stimulation under laboratory conditions or which can 

 be destroyed and thus modify the total picture of auto- 

 nomic activity. This small region seems to be a cross- 

 roads for complicated circuits subserving patterns of 

 behavior, many of which appear to be primitive; but 

 also we have an organization capable of inhibiting 

 primitive reaction patterns, for example savageness 

 and rage. While the hypothalamus is necessary for the 

 maximum expression of rage, it also normally contains 



some sort of arrangement which makes it possible for 

 the domestic animal to react more favorably to his 

 fellow animals. This is evidently true for man as well 

 as for the carnivore or ungulate. 



The thalamus participates in this type of activity, 

 chiefly because it provides means of communication 

 between cerebral structures and the hypothalamus 

 and lower brain stem. The interactions of the cerebral 

 cortex and the thalamus in the integration of sensa- 

 tion have received much consideration from clini- 

 cians and physiologists, and newer findings on the 

 rhinencephalic or limbic portions of the hemisphere 

 and their participation in autonomic activities offer 

 great promise for advances, not only in the partial 

 elucidation of problems of einotional behavior but of 

 the regulation of the internal milieu of the organism. 

 It is evident that the farther we go and the more we 

 study, the more interactions are uncovered, for every- 

 thing which has been said in this chapter argues 

 against the concept that any portion of the brain 

 serves as an isolated structural or functional entity. 



Specific participation of the sympathetic and para- 

 sympathetic divisions of the autonomic or vegetative 

 division of the nervous system in these processes has 

 received little emphasis in the foregoing paragraphs. 

 They nevertheless emphasize the fact that all levels 

 of the nervous system have a similar basic organiza- 

 tion. The concept of levels is valid only because it 

 expresses increasing potentialities for interaction and 

 integration. As one passes from the spinal cord 

 through the brain, the addition of increasing numbers 

 of neurons brings increasing possibilities for, and 

 probabilities of, interaction. Physiologically and 

 anatomically, we are beginning to have glimmerings 

 of the basic types of fundamental neural circuits. 

 However, who knows but what the concepts of 'cir- 

 cuits,' of 'feed-back' and of 'reverberation' may one 

 day seem to contemporary scientists as ridiculous as 

 the humoral theory of disease does to us. The latter 

 theory, however, marked a great advance in medical 

 and biological science, sufficient unto its day. One can 

 perhaps look forward to the time when the inter- 

 actions of peripheral ganglia, spinal cord, medulla, 

 pons, midbrain, diencephalon, cerebellum and telen- 

 cephalon will present to the scientist a unified and not 

 altogether incomprehensible picture, not constituted 

 of segmental moieties or theories of emotion or of the 

 laws of learning, but a system in which the vegetative, 

 the somatic and the psychic may be blended in their 

 true proportions. It will not be a simple picture. 



