Reconceptualizing Sexual Arousal

by Mary Hrovat

Researchers generally view the activation of the sexual response system as dependent on the effectiveness of the exciting stimulus. Until recently, they have virtually ignored the idea that activation of arousal might also depend on a reduction of central inhibition. Erick Janssen, an assistant scientist at the Kinsey Institute for Research in Sex, Gender, and Reproduction, and Dr. John Bancroft, a clinical professor of psychiatry at Indiana University Bloomington and director of the institute, are exploring a new conceptual model of dual control and working to establish a methodology for investigating inhibition, as well as excitation, of sexual response. In their model, the occurrence of a sexual response depends on the balance between excitation and inhibition.

Work with the new model builds on Janssen's earlier work in the department of psychology at the Universiteit van Amsterdam in the Netherlands and on Bancroft's earlier research at the Medical Research Council's Reproductive Biology Unit at the University of Edinburgh in Scotland. The story begins with the study of sexual dysfunction in men, yet the study of an inhibitory system that operates parallel to the excitatory system has potential social importance well beyond such origins since it could explain why some people are more prone to high-risk sexual behavior than others.

Part of Janssen's work in Amsterdam involved the diagnostic assessment of men with erectile difficulties. One of the main goals was to understand the relative roles of organic causes (e.g., a vascular problem) and psychological causes. In his work, which eventually resulted in a psychophysiological protocol that makes this determination much simpler and less expensive than some of the alternatives, Janssen traced the outlines of his current understanding of sexual arousal. He describes the basis of the new model as going back to the work of William H. Masters and Virginia E. Johnson.

Masters and Johnson, whose study of human sexual behavior focused on the physiology of sexual response, viewed anxiety (e.g., performance anxiety) as playing a key role in causing sexual dysfunction. Later researchers tested this idea using psychophysiological methods and found that anxiety indeed has a negative effect on sexual response in sexually dysfunctional men. However, they also found that in men without sexual dysfunction, anxiety was often associated with an enhancement of response to sexual stimuli. In looking for an explanation for this intriguing difference, researchers explored the idea that the negative effects of anxiety may be mediated by cognitive processes. A man who has difficulty becoming sexually aroused may be worrying about whether or not he will become aroused. This thought interferes with the excitatory mechanisms that would normally cause a sexual response. Researchers tested this theory by observing how distractions affect responses to sexual stimuli. The surprising result was that for normal men, distractions did impair ability to become aroused, but for the men with erectile difficulties, in some cases the distractions actually enhanced this ability. This result seemed to indicate that for men with erectile difficulties the distractions provided in the laboratory setting (sexually neutral distractions, like having to mentally solve a puzzle or work out a problem) reduced the attention paid to the sexually negative distractions the man was giving himself, and hence facilitated erectile responses.

Janssen developed a screening test (currently in use in the Academic Medical Center of the Universiteit van Amsterdam) based on this understanding of sexual dysfunction. Before administering costly and uncomfortable physical tests to men with erectile difficulties, a clinician uses a diagnostic process in which both sexual stimuli (erotic films and vibrotactile stimulation) and suitable distractions are presented. This process provides an optimum setting for inducing an erection, and while absence of an erection isn't proof of physiological problems, the test does identify the men who do respond and who are thus spared the more invasive physical testing.

However, researchers have recently encountered data indicating that cognitive mechanisms are only part of the explanation of erectile dysfunction. A few years ago, for example, surgeons discovered that injections of smooth muscle relaxants into the penis cause an erection. The erection occurs because the penis consists largely of spongelike smooth muscle tissue that is contracted when the penis is flaccid. The injected drug leads to relaxation of this smooth muscle and thus to erection. This injection-induced erection seemed to be beyond conscious control, a purely physiological response, and as such, a valuable, though limited, diagnostic tool. Surprisingly, however, sexually dysfunctional men sometimes do not respond to such an injection, even if there is other evidence (e.g., nocturnal erections or erections during masturbation but not with a partner) that there aren't any organic problems. The cognitive model "fails in a situation like this, because there is no sexual stimulus, there's nothing to be distracted from," Janssen explains. Something else is going on.

This phenomenon offered a method for identifying and studying direct inhibition, a mechanism that Bancroft had assumed existed, but never had the means to study. When other sex researchers used the term "inhibition," they typically meant "lack of excitation." That is, they conceived of inhibition as a result of worries or distractions, thought processes that interfere with activation of sexual arousal. In this view, the sexual response is either activated or it is not. However, the injection results indicated that inhibition can occur when no sexual stimuli are involved. Janssen and Bancroft discussed this and the results of some of Bancroft's work in Scotland, and from this conversation developed the idea that "we should look at sexual arousal as under dual control; there are both excitatory and inhibitory influences, and it's the balance between these two that determines whether a response occurs," Janssen says.

This is a relatively new view of sexual response, but in other aspects of psychophysiology, the idea of a mechanism or system that evokes a response and one that suppresses a response working simultaneously is common, as is the idea that people vary in their propensity for these mechanisms. "In psychophysiological theories of emotion, there is always a force and some kind of regulating counterforce," Janssen says, offering the example of the sympathetic and parasympathetic nervous systems, which scientists believe play complex opposing roles in mediating responses to outside stimuli. The new model of sexual arousal could explain why some people experience sexual dysfunction and others don't, even in similar circumstances--perhaps there is an inherent tendency toward high levels of inhibition that increases the vulnerability of some people in difficult circumstances.

Janssen and Bancroft's next question arose after developing the idea of an axis along which a researcher could measure inhibition independently from excitation. "We thought, first, that there is a continuum, and then, we thought about what the other end might look like," Janssen states. Given the evidence for an inhibitory mechanism causing problems for men who are highly prone to inhibition, what happens to men who are much less prone to inhibition? Inhibition in moderation could be a valuable and adaptive mechanism that can keep a person out of trouble and away from riskier sexual situations. Sexual intercourse has always involved some vulnerability: attention is focused away from external cues for danger, one's partner can transmit a disease, and sexual activity can lead to destructive social consequences. This vulnerability is a key to what might happen in a person who is inherently less prone to inhibition.

To explore the nature of inhibition and verify and examine its role in sexual arousal, Janssen and Bancroft decided to start by developing a questionnaire to measure the propensity for inhibition. They worked with Peter Finn, an associate professor of psychology at IUB, to devise the questionnaire, which Janssen has so far administered to four hundred psychology student volunteers for validation. The questionnaire asks men about their sexual response in certain situations, how easily it is triggered, and how it is affected by factors such as an unknown partner who doesn't want the man to use a condom or an unwilling partner. Janssen also gives subjects several other established questionnaires that index general propensities for excitation or inhibition of emotional responses. Preliminary analysis of the results to date is promising. Subjects display varying combinations of inhibitory and excitatory proneness, and some score high or low in both areas, demonstrating the independent nature of the two.

The next step involves study of the actual physiological responses of some of the men at the extreme ends of the inhibition scale, as well as some in the middle, as they view movies with sexual content, some of which is threatening. Janssen explains that it is not enough to present a stimulus and see what happens because inhibition would be indistinguishable from a lack of excitation. To demonstrate active inhibition, a lack of response must be associated with other evidence of inhibition (e.g., physiological evidence that the stimulus has a negative valence). Some of the films presented to the subjects contain a coercive sexual element, although none goes beyond the bounds of what can be seen at any mainstream movie theater, and this coercive element might trigger inhibition in some subjects. Other films present a more emotionally positive view of sexuality. A range of more independent inhibitory stimuli are also presented, all of which center around some perceived threat (e.g., the fear of not being able to attain an erection during the test).

Approximately one-third of the men who answered the questionnaire indicated that they were willing to be contacted for this next part of the study, and about thirty have so far taken part. In this phase of the research, each subject has his blood pressure continually monitored by a device called a Portapres, which uses two finger cuffs to measure blood pressure on each heartbeat. Also, the study involves the use of a diagnostic device called a RigiScan to monitor the circumference and rigidity of the penis. Use of these two measures helps researchers determine how a person's indices for inhibition and excitation, as measured by the questionnaire, correspond to physiological responses. The subjects also rate their subjective experience of sexual arousal and their emotional state during the data collection process. This combination of psychological and physiological assessment is what makes this work a new venture for the institute.

Psychophysiological studies look at both the physiological response of a subject (changes in heart rate and blood pressure, for example, as well as genital response) and the subject's own reports of his or her experiences. Janssen explains why it is necessary to look at both elements of sexuality: the relationship between them is variable. While women are more likely than men to display differences between their physical and their emotional reactions to sexual stimuli, some men also report subjective experiences that don't match the stories their physical reactions tell. Researchers conducting psychophysiological studies today can make use of new data-gathering technologies to examine data that were unavailable to their predecessors. The institute has just outfitted a new laboratory to take advantage of this new technology.

The psychophysiological research laboratory, located in Morrison Hall, consists of a room for the subject, complete with a comfortable chair and video monitor, and an adjoining room from which the researcher controls and monitors the equipment. Janssen provides subjects with as much privacy as possible, and subjects place the devices such as the RigiScan into position by themselves with no one observing. Janssen notes that there is an inevitable selection effect involved in doing sexual research, in that people with more conservative sexual attitudes who don't feel comfortable about being observed are less likely to volunteer for such studies. All the researcher can do is offer as much comfort and privacy as possible, and allow many "back-out" points along the way should the subject change his mind during the proceedings. With the recent installation of equipment in the lab, Janssen realizes a goal he had when he came to the Kinsey Institute in 1995 and anticipates increasing the scope of research at the institute.

Janssen is also working with Brian Foresman, a clinical assistant professor of medicine at the IU School of Medicine, who runs the school's Sleep Laboratory, in studying nocturnal erections. These occur during the rapid eye movement stage of sleep, during which the central mechanisms for inhibition seem to be switched off. Examining physiological responses (e.g., cardiovascular responses) during this stage of sleep could shed light on the basic neurophysiological processes involved in inhibition.

Although psychophysiological research is new for the institute, there is one important way in which Janssen's work is a return to the type of work done by Alfred Kinsey. "Most of the research on sexual arousal has involved comparison between groups, for example, dysfunctional and functional men," Janssen notes. "What we're doing is looking at variations within the general population, in what often has been viewed as the control group. Basically what we're doing is comparable to what Kinsey did. He was looking at variations in the general population, too."

As Janssen and Bancroft refine the new model for sexual response in men, they also hope to learn how the inhibition/excitation indices relate to behavior. Their theory is that men at the high-inhibition end of the scale will be inherently more prone to sexual dysfunction, while men at the low-inhibition end will be inherently more prone to high-risk and "problem" sexual behavior. Thus this research could help in understanding such problems as date rape, unplanned pregnancy, and the spread of sexually transmitted diseases. Citing the fact that people continue to contract HIV despite prevention efforts, Janssen states, "Although many researchers are studying, for example, the role of personality, the perception of risk, and situational factors such as alcohol usage in high-risk and 'problem' sexual behavior, almost no attention has been paid to the more specifically sexual aspects of these behaviors." Explaining the potential importance of focusing attention on these aspects, Janssen points out that "sexual arousal may mediate the effects of risk perception or alcohol use on high-risk sexual behaviors. Also, the interaction between personality and disposition to sexual arousal may prove to be an important predictor of sexual risk taking." This novel research program, according to Bancroft, "not only promises to broaden our understanding of basic sexual physiology, it may also fill an important gap in the current campaign to understand and modify high-risk sexual behavior."