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Sexual response is primarily a function of the nervous system. Muscles and blood vessels and other anatomic structures become involved only as a result of the stimulation of the nerves which control those organs. Factors which affect the level of an individual’s capacity to respond sexually must be factors which in some way determine the capacities of the nervous system, or some portion of it, to be affected by sexual stimuli.

There is usually considerable variation in an animal’s capacity to respond sexually at different periods in its life, and even on different occasions within a short span of time. The newly-born animal’s capacity to be sexually aroused may be less than the capacity of the somewhat older animal. Individuals who have reached old age are no longer as capable of responding as they were at an earlier age. The capacity of an animal to respond in a particular sexual situation may be considerably reduced or may totally disappear if the stimulation is continued without interruption for a protracted period of time. Individuals who are physically exhausted, starved, or in ill health are not easily aroused sexually; or if they are aroused, they may not be capable of effective action and may fail to reach orgasm. Such data suggest that anything that modifies the physiologic level at which an animal functions may, through its effect upon the nervous system, modify the general nature of its sexual behavior.

Neural Mechanisms of Sexual Response
The data which we have now accumulated on the gross physiology and psychology of sexual response and orgasm make it possible to recognize some of the internal mechanisms which may be involved.

Since there are no essential differences between the responses of females and males to tactile and other sensory stimulation, such responses must depend upon internal mechanisms which are essentially the same in the two sexes. On the other hand, since there are marked differences between females and males in their responses to psychologic stimuli, it seems apparent that those responses must depend upon some mechanism which functions differently in the two sexes.

It is the function of the exploring scientist to describe what he finds, whether or no the observed phenomena are explainable in terms of the known anatomy and known physiologic processes. We have described, as far as we have been able to obtain the data, what happens to the mammalian body when it responds sexually. While it now seems possible to identify some of the internal mechanisms which may account for that behavior, at points we shall find that there is nothing yet known in neurologic or physiologic science which explains what we have found. These are the areas in which, it may be hoped, the neurologist and physiologist may do further research.

It has been important to understand the gross behavior of the sexually responding animal, for too much of the physiologic and experimental work has, so far, been concentrated on explaining the nature of genital responses, and has ignored the fact that all parts of the body may be involved whenever there is sexual response and orgasm. There have been studies of the effects of the stimulation of end organs of touch in genital and perineal areas, studies of the nerves that connect those end organs with lower portions of the spinal cord, studies of the sexual function of that end of the cord, and studies of the nerves that transmit impulses from the cord to the genital and pelvic structures which are involved in a sexual response. In addition, there have been studies of the possible function of certain portions of the brain, particularly of the cerebrum, in connection with sexual response; but, once again, they have been studies of cerebral function in connection with genital response. The neurologic and experimental studies should now be extended in directions which may explain why the whole animal body is involved whenever there is any sort of sexual response.
For neurologic studies of the genital area see, for instance: Eberth 1904. Marshall 1922:264-272. Stone 1923b :88-90, 104. Semans and Langworthy 1938. Bard 1940:556 fiF. Kuntz 1945:304-323. Hooker in Howell (Fulton edit.) 1949:1202-1205. Kuntz 1951:101-106. For studies of the brain in relation to sexual response, see for example: Bard 1934, 1936, 1939, 1940, 1942. Brooks 1937. Rioch 1938. Stier 1938. Klüver and Bucy 1938, 1939. Davis 1939. Maes 1939. Dempsey and Rioch 1939. Beach 1940, 1942a, 1942b, 1943, 1944, 1947a, 1947b. Brookhart, Dey, and Ranson 1941. Brookhart and Dey 1941. Dey, Leininger, and Ranson 1942. Clark 1942. Langworthy 1944.

Evidence of Nervous Function
There is nothing which needs to be emphasized more than this fact that the entire body of the animal is involved whenever there is any sexual response. The tactile or other sensory stimulation of any part of the body, and not of the genitalia alone, may initiate these responses. Psychologic stimulation may, in many instances, bring responses that are quite identical with those effected by tactile stimulation. Sexual responses may involve changes in the function of the circulatory system, of the respiratory system, of the sensory capacities of the animal, of all of the glands of the body, and of the muscular activities in every part of the body. Orgasm is similarly a function of the whole animal body. The internal mechanisms which are responsible for such activity must be mechanisms which can affect all parts of the body. There are three such mechanisms which, conceivably, might accomplish that end.

1. Chain Reactions
The action of any part of an animal’s body may be directly responsible for a chain of activities—a series of successive steps in which each act initiates the succeeding act in the chain. Such a chain of responses may be involved, for instance, when the driver of an automobile steers his course along a particular path, and is able to pass other cars without consciously planning the movements of his steering gear. His sensory perception of the objects which lie ahead, his adjustments for the distances which are involved, for the speed of his own car, for the speed of the approaching car, and for the movements of his hands or arms which may steer him safely past the approaching car, may represent such a chain of responses. The initial action is responsible for the next action and that in turn determines the following act, until the ultimate end is achieved.

Sexual activities similarly represent chains of responses. The stimulation of end organs, and the consequent stimulation of the nerves which connect those end organs with the lower end of the spinal cord, and of the nerves which go from the cord to the muscle fibers in the walls of the circulatory system, may directly account for the rises in pulse rate and blood pressure and for the increased peripheral circulation which is responsible for the tumescence of various body structures during sexual response. These circulatory disturbances are then responsible for the changes which are to be observed in the breathing rate, and that these physiologic disturbances are responsible for the spectacular muscular activities which characterize sexual response. But the present data do not show that these phenomena appear in sequence, one after the other. On the contrary, there is an instantaneous and simultaneous appearance of all of these physiologic changes as soon as the animal is stimulated and begins to respond.
Beach 1947b :241 also points out the inadequacy of a chain reaction hypothesis in sexual response.

It is not impossible that there are some aspects of the later developments in sexual response—like the ultimate build-up of neuromuscular tensions, the increasing loss of sensory perception, and the ultimate disturbance of the breathing rate as an individual approaches orgasm —which may be products of physiologic developments which appear earlier in the course of the sexual activity. But this cannot be true of most of the phenomena which appear during sexual response and orgasm. A rise in pulse rate, a rise in blood pressure, a rise in breathing rate, a diminution of the capacity for sensory perception, glandular secretions, and a development of neuromuscular tensions over the whole body, appear to develop simultaneously, sometimes within a fraction of a second, as soon as the animal is stimulated and begins to respond.

2. Blood-Distributed Agents
The coordination of the functions of separated parts of the body is sometimes effected through blood-circulated agents, such as hormones. For instance, many of the physiologic aspects of certain emotional reactions, such as anger, may be duplicated by the injection of adrenaline into the blood stream, and it is generally understood that the appearance of raised pulse rates, raised blood pressures, and still other aspects of an angry animal may be a direct product of the secretion of adrenaline from the adrenal glands into the blood stream. But the speed with which sexual responses may occur is far greater than that which could be effected by any blood-circulated substance such as adrenaline. While it may not take more than a few seconds for adrenaline to be carried by the blood over short distances in the animal’s body, it takes a longer time for it to circulate to all parts of the body. Sexual responses, however, may be initiated, carried through their complex course, and completed within a matter of seconds.

It is possible that there is adrenaline secretion during the more advanced stages of any protracted sexual activity, and this in the late stages of sexual response may reinforce some of the physiologic changes which the nervous system has initiated; but adrenaline cannot be responsible for most of the changes which appear as soon as there is sexual stimulation.

3. Nervous Mechanisms
Our best reasons for believing that sexual responses must depend primarily upon nervous mechanisms are the speed with which all parts of an animal’s body may become involved, the steady and convulsive build-up of neuromuscular tensions as the action develops, the abrupt build-up of tensions at the approach of orgasm, the remarkable rigidity which may develop just before orgasm, the explosive discharge of neuromuscular tensions at orgasm, and the abrupt cessation of tension after orgasm. There are no other means of intercommunication which act as quickly as nervous mechanisms, and no other mechanism that can bring so nearly simultaneous reactions from all parts of the body. The gradual and steady accumulation of neuromuscular tensions during sexual arousal is a known characteristic of some other nervously controlled responses. The explosive discharge which characterizes orgasm is the sort of phenomenon that cannot be ascribed to anything except a neural mechanism.

Finally, the electroencephalograms which are now available (Figure 140f) show that there are remarkable changes in brain potentials in the course of sexual response, and that it is the development of these and their sudden release at orgasm which provide the most characteristic aspects of sexual response and orgasm. For these several reasons, the search for the mechanisms of sexual response may be concentrated primarily upon the structure and function of the vertebrate nervous system.

Figures 141f-142f. Diagrams of neural mechanisms in mammalian
sexual response to tactile and psychologic stimulation


Tactile Stimulation and Reflex Arcs
It is obvious from the record which we have already given, as well as from everyday experience, that physical contacts, touch, and pressure may bring sexual responses only because there are sensory structures in the external surface of the animal’s body which respond to such stimulation. These sensory structures are the end organs of touch, and it is on these that many sexual responses depend.

We have already pointed out that end organs which are sensitive to such other physical stimuli as light, heat, and sound may also be involved, but we have emphasized that there are no experimental data which show exactly how these other end organs function in connection with sexual response.

The stimulus received by any such organ is transmitted by afferent (in-going) nerves to the spinal cord. The cord in turn may transmit the impulses by efferent (out-going) nerves to those muscles with which they are directly connected (Figure 141). This may lead to a spontaneous and quite involuntary action of muscles which can be and are ordinarily voluntarily controlled. The prominent muscular action of the pelvis and lower limbs may be accounted for as the direct product of such a simple reflex arc. Because the stimulation of any part of the cord may be extended to all parts of the cord, the reflex arcs may involve not only the particular part of the body which was originally stimulated, but other parts of the body as well. Genital stimulation, for instance, brings not only pelvic responses but responses of the muscles in every other part of the body.
Impulses originating in tactile stimulation of the pelvic area are transmitted to the sacral area of the cord chiefly by way of the internal pudendal nerve. The efferent irnpulses include spinal impulses which travel via the internal pudendal nerve to the muscles about the genitalia, causing them to tense. Parasympathetic impulses travel via the erigens nerves to the blood vessels of the genital area, causing tumescence. The striped muscles of the pelvic area and lower limbs are thrown into spasm by spinal impulses from the sacral area; the smooth muscle is thrown into spasm by sympathetic impulses originating in the lumbar area, traveling to the genitalia mainly via the hypogastric nerves. See, for instance: Stone 1923b:89-90, 94, 104. Semans and Langworthy 1938. Kuntz 1945:308-312. Munro et al. 1948:903-910. Hooker in Howell (Fulton edit.) 1949:1203-1204. Whitelaw and Smithwick 1951: 121-130.

A major portion of the experimental work that has been done on the physiology of sexual response has been concerned with these relatively simple aspects of the problem, and the location of those areas of the spinal cord which are concerned with a major portion of the pelvic and lower limb responses is specifically known.

Function of the Sacro-Lumbar Area
The experimental work has shown that lower portions of the cord, namely, the sacral and lumbar areas (Figure 141), are the mediating centers upon which genital reflexes and pelvic responses depend. As long as the end organs and the afferent nerves are intact, and as long as the sacro-lumbar areas of the cord and the efferent nerves are intact, it is possible to secure pelvic responses and responses of the lower limbs even though other portions of the cord and considerable portions of the brain of the animal may be damaged. This is demonstrated when the cord is actually cut above the sacro-lumbar area in laboratory experiments with animals. It is also demonstrated by human paraplegics. These are individuals who have had the spinal cord injured or cut at some point above the sacro-lumbar area as the result of an accident, some surgical operation, or some other damage.
That a sacral center mediates tumescence and a lumbar center mediates ejaculation and corresponding muscular contractions in the female is generally accepted in the literature. See: Kuntz 1945:309, 322-323. Talbot 1949:266. However, sacral nerves may play a part in ejaculation according to Munro et al. 1948:910, and lumbar nerves may also be involved in tumescence according to: Kuntz 1945:308-309. Root and Bard 1947:87-89.

An animal that has the cord damaged above the sacro-lumbar area may respond to tactile stimulation of its genitalia, perineum, or other pelvic areas, and may still become tumescent in those areas, develop a genital erection, and reach orgasm. Unfortunately, because the full extent of the physiologic changes which occur in sexual response has not hitherto been comprehended, there are no good data on the responses which probably occur in the lower limbs of such an experimental animal.
Erection and ejaculation in an animal with a severed spinal cord is noted, for example, in: Marshall 1922:264-265. Bard 1940:556. Beach 1942a:213, 215. Munro et al. 1948. Fulton 1949:140. Talbot 1949:266-267 (a concise discussion of the effects of cord damage to sexual function).

When the human paraplegic receives genital or pelvic stimulation, he does not feel the stimulation or the consequent physiologic changes in those areas, although he may observe them; and he is not conscious of sexual satisfaction when he has coitus or engages in other sexual activities, even though he may come to erection and reach orgasm. This indicates that a brain, and a cord which is intact between the level of stimulation and the brain, are necessary for the attainment of that change of physiologic state which the human animal recognizes as sexual satisfaction. A paraplegic may, however, be conscious of tactile stimulation of portions of the body innervated by nerves which connect with those parts of the cord that are located above the point of damage, and may receive erotic satisfaction from the stimulation of an upper portion of his or her body, even when the pelvis and lower limbs are unresponsive.
The inability of the true paraplegic to perceive orgasm is noted in Munro et al. 1948:905, 909-910, implied in Talbot 1949:269, and recorded by Dr. L. W. Freeman (verbal communic.). Hyndman and Wolkin 1943:144 add “For . . . orgasm to be sensually appreciated, the spinal connections with the brain must, of course, be intact.”

Psychologic stimulation, depending primarily on the function of the cerebrum, may also effect pelvic and lower-limb responses. This also depends, to a considerable degree, on the sacro-lumbar areas of the cord (Figure 142). If those portions of the cord are completely removed in an experimental animal, or seriously damaged in a human subject, or if those areas are separated from the brain by a complete cutting (transection) of the cord above the sacro-lumbar areas, then psychologic stimulation no longer brings pelvic or genital or lower-limb responses.
The inability of psychologic stimulation to effect genital response after damage to the cord above the lumbar area is discussed in: Hyndman and Wolkin 1943:143-144. Kuntz 1945:309. Root and Bard 1947:87-88. Talbot 1949: 266-267. Hooker in Howell (Fulton edit.) 1949:1203. Even compression of the cord may produce erectile impotence in humans. Cf. Eisberg 1925:66, 132, 308.

The cat is one of the experimental animals in which the sacral area of the cord and all of the lumbar area except the uppermost (the first lumbar) segment may be removed without eliminating the animal’s responses to the tactile stimulation of genital or other pelvic areas, or its responses to psychologic stimulation. But in the case of this animal it has been demonstrated that such responses are largely eliminated if the first lumbar segment is also removed. This upper end of the lumbar area is connected with the genital area by the hypogastric nerve which is one of the branches of the so-called autonomic system, and this appears to be at least one of the paths by which nervous impulses which are the product of psychologic stimulation are transmitted to the genital area (Figure 142).
By-passing of a transection of the cord via the hypogastric nerve is described for the cat by Root and Bard 1947:86-89.

On the other hand, in man and in some of the other mammals in which there are other connections (additional to the hypogastric nerve) between portions of the spinal cord which are anterior to the sacro-lumbar areas, and other parts of the autonomic nervous system, it is not improbable that there may be some residue of pelvic response when the entire sacro-lumbar area is removed. There is need for a more exact examination of this matter in further work with experimental animals and with clinical cases in the human animal. However, since the human paraplegics who have had the connection between the brain and the sacro-lumbar area completely severed, report failures to achieve erection through psychologic stimulation, it is probable that the major portion of the responses of the pelvic areas and of the lower limbs even in the human species depend upon the integrity of at least the upper segments of the lumbar area, and upon the existence of intact connections between the brain and that portion of the cord.

The importance of the sacro-lumbar area of the cord was one of the first things known about the neurology of sexual response. As early as 1863 it was known that the direct electrical stimulation of certain sacral areas would bring genital erection and other sexual responses from laboratory mammals, and this subsequently was demonstrated for human subjects.
In 1863 Eckhardt found that stimulation of the erigens nerves produced erection in the dog.

It has also been known for half a century that ejaculation may be effected by the direct stimulation of certain sacro-lumbar areas. 
For a detailed description of the production of erection and ejaculation through electrical stimulation of the sacral segments, see: Durfee, Lerner, and Kaplan 1940. As early as 1863 Eckhardt noted that tactile stimulation of the penis could not cause erection in a dog whose pudendal nerve was severed, and in 1879 Nikolsky reported contraction of penile blood vessels on cutting the erigens nerves. See Kuntz 1945:308.

Unfortunately, however, most of the neurologists and laboratory experimentalists have taken orgasm and ejaculation to be synonymous phenomena. Since we now understand that this is not so, it seems possible that the prostate and other glands which are necessary to effect ejaculation may be brought into action by the direct stimulation of sacral centers without the development of responses that are sexual in any strict sense. Consequently all of this work needs to be reviewed for evidence that a true orgasm may be effected as a result of the direct stimulation of these sacro-lumbar centers. It should be recalled that the mechanical stimulation of the prostate gland via the rectum, as in a prostatic massage, may bring an exudation of semen from the penis and sometimes a propulsive exudation which appears to be an ejaculation, even when there is no genital erection or other evidence of sexual response.

On the other hand, it is also to be noted that the stimulation of the interior of the rectum, of the sort that is involved in a prostatic massage, may also exert pressure upon the perineal nerve masses, and it is known that this may bring specifically sexual responses with orgasm. This is frequently realized by persons who have been the recipients in anal coitus, and apparently may sometimes be involved in the ejaculatory responses which occur during a prostatic massage.

Both the laboratory experimental work and the work with human subjects have further demonstrated that genital erection and responses to the point of orgasm usually depend upon the integrity of the pudendal and erigens nerves, which are efferent nerves connecting the sacral area of the cord with the muscles of the genital and pelvic areas. If these nerves are accidentally damaged or surgically cut, erection in the male is no longer effected. The effect of damage to the pudendal nerve of the female has not been clearly recorded in the experimental or medical literature.

In the course of mammalian evolution the forepart of the brain has been the portion of the central nervous system which has evolved most elaborately. There are fewer basic differences between the sacro-lumbar areas of the cord in the human animal and the sacro-lumbar areas in the lower mammals. The importance of the sacro-lumbar areas in sexual response explains why we find human sexual behavior much closer to the sexual behavior of the infra-human species, and even of the lower mammalian species, than most persons might have anticipated and than some persons would like to believe.

Role of Upper Portions of Cord
In regard to sexual response there is very little precise information concerning the role of those portions of the cord which lie above (anterior) to the sacro-lumbar area. As long as genital and pelvic responses were considered the major portion or even the whole of sexual response, and as long as the demonstrated function of the sacro-lumbar area seemed to account for all genital and pelvic responses, there was a tacit assumption that the thoracic and cervical areas of the cord had little or no direct connection with sexual behavior. The integrity of these upper portions of the cord was obviously necessary for the transmission of psychologic stimulation from the cerebrum to the genital and pelvic areas, but, apart from that, there has been little experimental work to show what role this upper end of the cord may have in sexual response.
Bilateral anterior chordotomy, the partial transection of the cord to relieve intractable pain, usually interferes with or prevents tumescence and orgasm in both sexes. The transection is usually done above the lumbar area. Hyndman and Wolkin 1943:143 conclude that the operation “. . . is almost certain to abolish erection and orgasm in the male and orgasm in the female . . . the desire for intercourse is not abolished.” Stookey 1943:430 adds, “In the male, ejaculation becomes impossible; erection is not interfered with but orgasm is lost. In the female also there may be a loss of orgasm.”

If, however, it is understood that tactile stimulation of other portions of the mammalian body quite apart from the genital and pelvic areas may bring some sort of sexual response, and even full and complete sexual response to the point of orgasm, it becomes difficult to believe that the stimulation of the upper end of the trunk of the animal or of the mouth or other portions of the head of the animal is transmitted to the sacro-lumbar areas of the cord before it brings response. It is more reasonable to believe that the stimulation of end organs in the upper end of the mammalian body is mediated through thoracic or cervical spinal centers, and that these directly effect sexual response not only of the upper end of the body itself, but of the whole of the animal body which is involved during the sexual response. Because of the complexity of the neural anatomy at this point, and because of the lack of specific experimental work in this area, we can do no more than draw attention to the possibility and hope that additional data may be gathered on the point.

We have already drawn attention to the evidence which suggests that the stimulation of any area of the cord spreads throughout the length of the cord, and that this effects the movement of muscles in the upper portions of the body by way of the spinal nerves which lead out of corresponding portions of the cord. These nerves connect directly with the muscles in the upper portions of the body and are apparently responsible for their action during sexual response and orgasm.

One body of data which shows something of the function of the upper end of the cord comes from a single case of a human female paraplegic in whom an operation had severed the damaged cord above the sacro-lumbar area. While psychologic stimulation did not bring any pelvic reactions from the subject, she claimed that tactile stimulation of the upper end of her body (apparently centered about the breasts) did bring sexual response which led to complete orgasm. There appeared to be a build-up of neuromuscular tensions and the explosive release which characterizes orgasm, although the orgasm involved only the upper parts of the body and did not involve the pelvic area. Because the portion of the body which was involved in orgasm was connected with the brain, the subject was conscious of the sexual arousal and found satisfaction in the orgasm.
This case was brought to our attention by Dr. L. W. Freeman of the Indiana University Medical Faculty.

There are some other cases in which an awareness of tactile stimulation remains in the intact portion of the body even though no erotic satisfaction is derived from such tactile stimulation. It would be very important to accumulate data on these points from additional cases of true paraplegics.

Unfortunately, the medical literature is badly confused by the fact that many of these supposedly paraplegic cases may have had some injury which did not sever the cord. Some of the reported cases of paraplegics suddenly becoming capable of full sexual function when there is a sufficient stimulus, probably depend upon the fact that the cord, although it may have been considerably damaged, was never completely severed. 14 It is doubtful whether any true paraplegic ever maintained voluntary control over the lower portion of his or her body. Consequently it is important to sharply distinguish the records on the sexual performances of supposed paraplegics from the records of individuals in whom the cord is definitely known to have been severed.
Without additional operations or autopsy it is difficult to determine if transection is complete, and information on sexual function is confusing. For example, Talbot, J. Nerv. Ment. Dis. 1952:360-361, states that 20 per cent of a group of paraplegics and quadriplegics experienced erection from psychologic stimulation. Note that Talbot 1949:266-268 states that complete transection precludes all cortical influence but found 8 presumably complete transection cases experiencing erection from psychologic stimuli.

Role of Autonomic Nervous System
While the central nervous system, meaning the brain and the spinal cord, is directly connected by afferent nerves with the peripheral end organs which receive sensory stimuli, and by efferent nerves which transmit impulses to other organs of the body and consequently effect muscular action, the autonomic nervous system (Figures 141, 142) is not directly connected with any peripheral end organs and cannot be brought into direct action by the stimulation of end organs of touch or other types of sense organs. The activities which animals voluntarily undertake are controlled by the central nervous system. There is ordinarily no voluntary control of the action of the autonomic nervous system.

The main trunks of the sympathetic division of the autonomic nervous system lie parallel and close to the spinal cord. Throughout the length of the cord there are nerve connections between it and the autonomic system, and consequently the autonomic system may be brought into action by the stimulation of the cord at various levels. It may also be brought into action by the direct stimulation of blood-circulated substances such as adrenaline. Most of the autonomic nervous system consists of fine and highly branched nerves that spread throughout the body in a fashion that sometimes makes it very difficult for the neurologist to determine with any exactitude what nerves are connected with a given organ.

It is customary to think of the autonomic nervous system as consisting of two main parts, the sympathetic and parasympathetic groups of nerves. Although physiologists and neurologists have become increasingly aware that these two parts do not function independently, and that there is no sharp differentiation of the action of the two at many points, the classification has provided a useful basis for thinking in regard to certain points, and there are some of the body functions which may depend primarily upon one or the other of the branches of the autonomic system. Anatomically the two portions of the autonomic system are not wholly discrete, for they lie closely parallel at many points and sympathetic nerves may actually fuse at some points with parasympathetic nerves.

Moreover, the stimulation of the sympathetic branch of the system produces a chemical substance (sympathin) which acts as a hormone, producing many of the same results which follow the secretion of adrenaline from the adrenal glands or the injection of the drug adrenaline. The most specific action of sympathin is its effect upon the parasympathetic system, and this is brought into action whenever the sympathetic system is stimulated. Similarly, however, stimulation of the parasympathetic system leads to the secretion of acetylcholine, which has a specific action on sympathetic nerves and brings that portion of the system into play. This accounts for the fact that in many emotional situations the responses of an animal may involve physiologic changes which may be attributed to both sympathetic and parasympathetic controls. This is exactly what we find in regard to the physiology of sexual response; and we shall not attempt to suggest which aspects of sexual response may depend upon one or the other portion of the autonomic system.

Actually both portions of the autonomic system are usually involved when any portion of the system comes into action in the course of a sexual response, for the parts of the body which are primarily under autonomic control (such as the heart, the glands, and the smooth muscles) are supplied with both sympathetic and parasympathetic nerve fibers. These two types of nerve fibers act antagonistically on the organ and they may thus exert a slight but constant (tonic) effect on it. A given organ, therefore, will be stimulated or inhibited almost instantaneously depending on (1) the strength of the impulse, and (2) whether the impulse reaches it through the sympathetic or parasympathetic system. Because of the complexity of the interrelationships and the delicate balance which exists here, it is not surprising that some organs may be dominated by the parasympathetic system at the same time that other organs are being controlled by the sympathetic system. It is, moreover, to be remembered that most of the organs which are reached by the autonomic nervous system also have sensory nerves which connect with the central nervous system, and may be affected by reflexes which develop in that part of the nervous system.

Many of the physiologic activities which we have found characteristic of sexual response probably do not represent any direct reaction via a reflex arc. The efferent spinal nerves leading from the sacrolumbar areas can account for only some of the genital, pelvic, and lower-limb responses during sexual activity. Most of the activity must depend primarily upon the action of the autonomic nervous system which is brought into play through nerves which originate in the sacro-lumbar areas and in other parts of the cord. The instantaneous involvement during sexual response of those portions of the body, such as the heart, which are for the most part beyond voluntary control, constitutes strong evidence that the autonomic nervous system is involved.
Kuntz 1945:313 is one of the few others who have concluded that the entire autonomic system is involved in sexual response.

The following aspects of the gross physiology of sexual response are among those that apparently depend upon the action of the autonomic system:
Increase in pulse rate
Increase in blood pressure
Vasodilation
Increase in peripheral circulation of blood
Tumescence of distensible parts of body
Reduced rate of bleeding
Hyperventilation
Irregular breathing
Increase in genital secretions
Increase in salivary secretion
Increase in lacrimal secretion
Gastro-intestinal activity inhibited
Hair raised
Eye pupil dilated
Ejaculation

Reference to Table 176f will show that more of the elements in sexual response appear to depend on parasympathetic than on sympathetic function.

The autonomic system, like the sacro-lumbar area, is ancient in mammalian heritage, and the similarities between human and infrahuman sexual responses probably depend, for the most part, upon the fact that these two are the portions of the nervous system which are chiefly responsible for human sexual responses. The physiology of human sexual response depends only to a minimum degree upon the more highly evolved human brain.

Table 176f. Physiologic Elements in the Sexual Syndrome, Anger, Fear, Epilepsy, and Pain
Physiologic element Neural
mech.		Sexual
resp.		Anger Fear Epi-
lepsy		Pain
Increase in pulse rate symp. vv v mayv
Increase in blood pressure symp.? vv v mayv
Vasodilation para. vmay no v 
Increased periph. circ. of blood para. vmay no may 
Tumescence para. vrare rare rarerare
Reduced rate of bleeding symp. vv v  v
Hyperventilation symp. vv v  v
Breathing irregularity  v v vmay v
Anoxia  ?   v  
Diminished sensory perception  v v vv v
Increase in genital secretions  v no no  
Increase in salivary secretion para. vv no vno
Increase in lacrimal secretion  v     v
Increase in perspiration para.+symp. occas.  v  v
Adrenaline secretion symp. v ?v v  v
Increase in muscular tensions spinal vv v vv
 symp.       
Increase in muscular capacity  v v v  
Involuntary muscular activity spinal vv v vv
Rhythmic muscular movements spinal vno no mayno
Gastro-intest. activ. inhibited symp. v ?v v  v
Hair raised symp. mayv v  may
Eye pupil dilated symp. vv v vv
Ejaculation spinal vrare rare may 
 symp.       
Involuntary vocalization  v v vv v

v = physiologic element is present. No = element is absent. May = element sometimes but not always present.
Symp. = sympathetic division of autonomic system. Para. = parasympathetic portion of autonomic system.
Blanks = data not available.


The Sexual Syndrome
We have already pointed out that the most distinctive aspect of any sexual response is the fact that it is a group, a cluster, a syndrome of physiologic elements, all of which usually appear whenever there is any sort of sexual response. But nearly all of the elements of sexual response are found in other situations, particularly in other emotional responses and most particularly in anger (Table 176f). Actually the sexual elements which are not found in anger are to be found in epilepsy, but there is no other sort of behavioral response which involves all of the elements which may be found in sexual response. One might hypothesize that if certain of the physiologic elements were prevented from developing in a sexual response, or taken away from a sexual response, the individual might be left in a state of anger or fear, or in some other emotional state. The fact that frustrated sexual responses so readily turn into anger and rage might thus be explained. On the other hand, it not infrequently happens, both in the lower mammals and in man, that anger, fighting, and quarrels suddenly turn into sexual responses.
The physiology of the emotions is summarized in such sources as: Prince 1914. Cannon 1927. Bard 1934, 1939. Shock in Reymert 1950.

The close relationship of sexual responses and these other emotional states can best be seen by a more detailed examination of the physiology of anger, fear, and epilepsy.

Anger. The closest parallel to the picture of sexual response is found in the known physiology of anger. Table 176f shows fourteen items which usually appear in both situations. There is, of course, some variation under differing conditions, but the items which are usually identical or closely parallel in anger and the sexual syndrome are the following:
Increase in pulse rate
Increase in blood pressure
Vasodilation (sometimes)
Increase in peripheral circulation of blood
Reduced rate of bleeding
Hyperventilation
Anoxia (probably)
Diminution of sensory perception
Adrenaline secretion (probably)
Increase in muscular tensions
Reduction of fatigue and/or increased muscular capacity
Gastro-intestinal activity inhibited (in sex?)
Hair raised (at least in other mammals)
Involuntary vocalization

There are four respects in which the physiology of anger does not fit the known physiology of sex.
     1.    In sexual response there is an invariable increase in surface temperatures, color, and tumescence during sexual arousal; but in anger there is sometimes (but not always) a vasoconstriction which makes the face of the angry person white, although this may alternate with a flushing of the face which indicates a peripheral flow of blood. Genital tumescence is the more or less inevitable outcome of sexual response in the uninhibited adult animal, short of old age, and while penile erections may sometimes appear in anger, particularly among the infra-human mammals and among pre-adolescent human males, they are not usual.
     2.    Genital (Cowper's, Bartholin, and cervical) secretions appear with sexual arousal, but apparently not in anger.
     3.    The most distinctive aspect of sexual physiology is the rhythmic muscular movement which develops when an individual is sexually aroused. These movements include the pelvic thrusts which constitute the copulatory movements among mammals. Such muscular movements do not appear when one is simply angry.
     4.    Orgasm is a phenomenon which is unique to sexual response. On those rare occasions in which it develops in anger, it is possible that it represents the development of a true sexual response.

Fear. The physiology of fear involves a number of the elements which appear in sexual activity, but fear is not as close as anger is to the sexual syndrome (Table 176f). There are nine items in the physiology of fear that are identical with those in a sexual response:
Increase in pulse rate
Increase in blood pressure
Hyperventilation
Diminution of sensory perception
Adrenaline secretion (probably)
Increase in muscular tensions
Reduction of fatigue and/or increased muscular capacity
Hair raised
Involuntary vocalization

On the other hand there are five aspects of the sexual syndrome which are opposites of those found in fear: a peripheral circulation of blood, a vasodilation, genital secretions, salivary secretions, and involuntary and rhythmic muscular movements. The most distinctive aspect of fear which is lacking in a sexual response, is the vasoconstriction which causes the blanching of the face. The rhythmic muscular flow which is so characteristic of a sexual response is lacking in fear. Genital erections only occasionally appear when an individual is afraid, and orgasm is still more rare. In such a case, it is possible that the fear has given way to a sexual response.
Ejaculation from fright was noted as early as Aristotle [384-322 B.C.] : Problems, Bk. IV:877a; Bk. XXVII:949a. We have a few instances in our own case histories.

Epilepsy. The physiology of epilepsy includes eight or more elements of the sexual syndrome (Table 176f).
For the symptoms of epilepsy, see such a standard work as Penfield and Erickson 1941.

In both epilepsy and sexual response there are:
Increase in pulse rate (sometimes)
Increase in blood pressure
Vasodilation
Anoxia
Diminution of sensory perception
Increase in salivary secretion
Increase in muscular tensions
Rhythmic muscular movements
Involuntary vocalization

The most remarkable parallel lies in the similarity of the spasmodic muscular movements in epilepsy and the tensions and muscular movements which are part of the build-up toward orgasm. The extreme rigidity which develops in the build-up to orgasm, and particularly just before orgasm, provides an especially close parallel to the states of tension in epilepsy. On at least some (rare?) occasions orgasm may occur during epilepsy. An even more striking similarity to epileptic movements is to be seen in the more extreme types of spasm which may follow orgasm. Persons who have seen both epileptic seizures and the more extreme types of orgasm have invariably been impressed by the similarities between the two. The electroencephalograms which are now available show a striking resemblance between sexual response and epileptoid reactions (Figure 140f). This is true in the period of the build-up toward orgasm, in the rigidity which precedes orgasm, and in the often violent, convulsive movements which follow orgasm.
Some of the earliest writers to draw attention to the similarities between epilepsy and sexual response included Democritus (ca. 420 B.C.), who was quoted as saying that orgasm is like a small epileptic seizure (see: Clement of Alexandria; Paedagogus Bk. II, ch. X, and K. Freeman 1949:306). Aretaeus (2nd-3rd cent. A.D.) cites the similarity in “On the Cure of Chronic Diseases’’ Bk. I, ch. IV. The latter also noted erection and ejaculation in epilepsy in his “On the Causes and Symptoms of Acute Diseases” Bk. I, ch. V. Erection and ejaculation are sometimes listed as epileptic sequelae in modern medical literature, as in: Hyman 1945:1515.

If the cerebrum is considerably damaged in an accident or by some operation, the body of the individual may become continuously rigid in what is known as a tonic decerebrate rigidity. Such a rigid state is described as a true release phenomenon which results from an interference with the function that the brain ordinarily exercises in controlling muscular tension. The situation in which muscular tensions alternate with movements of the sort which characterize an epileptic seizure has been interpreted to be a “transient decerebrate rigidity.” Persons in a state of tonic decerebrate rigidity present the most striking parallel we have seen with certain moments in sexual activity, and particularly in the tensions which immediately precede orgasm. In decerebrate rigidity the body is stretched out to its maximum, the gluteal muscles are tensed and the buttocks tightly appressed, the legs and the arms are usually extended and stiffly held under tension, the feet may be pointed in line with the legs, the toes may be curled or spread, the fingers are flexed and strongly tensed, the back may be arched, and the neck may be so tensed that the head is held at a stiff angle. In all of these respects, tonic decerebrate rigidity matches what may be seen, in a transient state, in both epilepsy and in sexual activity.
The concept of the spasms in epilepsy depending on a transient decerebrate rigidity is introduced, for example, in Penfield and Erickson 1941:87. The postural and muscular similarities existing between decerebrate rigidity and the body just before orgasm are exemplified by the photograph in Penfield and Erickson 1941: fig. 21, p. 86. The rotation of the arm, so characteristic of decerebration, is not, however, a part of the sexual syndrome.

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