Sex is a natural phenomenon experienced by both humans and animals. The sexual response of humans can be divided into the desire, excitement, and orgasm phases (Kaplan, 1977). There are several definitions of sexual desire, including it being seen as “an appetitive state, an innate psychological drive which shapes the personality, an instinct, a need, and most generally as 'lust'” (Beck et al., 1991). It is a mental process, but it also drives the need for a physical stimulus in return for satisfaction. It functions the same as any biological function humans and animals may experience, with biological undercurrents. Sexual desire, along with the need for food and water, are housed within the brain and processed by neural transmitters (Kaplan, 1977). Leiblum and Rosen (1988) state that sexual desire is “a subjective feeling state that may be triggered by both internal and external cues, and may or may not result in overt sexual behavior”. It is generally agreed upon that desire is subjective in nature, a process that exists in a person's mind.
	Research on desire and the other phases of sexual response has been a fairly recent development within the last century. Each response—desire, excitement, and orgasm—are subject to ruin by emotional states (Kaplan, 1977). However, despite all three phases being subjected to such impairments, there is a large gap between research on disorders, or impairments, on desire than there is on the excitement or orgasm phases. While there is literature with the focus of the material on the orgasm and excitement phase disorders, desire and its disorders have been neglected (Kaplan, 1977).  Literature pertaining to desire disorders is much smaller in comparison than to the other phases of sexual response. It's not a topic that has been ignored, however. The recognition of disorders of sexual desire has prompted considerable attention (Beck et al., 1991). Regardless of the fact that it's been agreed upon that there is a need to discover more about sexual desire, few data exists to tie it into the psychological aspect (Beck et al., 1991). Despite there being some research, overall, this is an aspect of sexual response that has been wholly under-investigated.
	“A number of sex therapists (e.g., Kaplan, 1974, 1979; Masters and Johnson, 1970) have long argued that anxiety is the primary psychological mechanism underlying the interference with sexual arousal . . .” (Hale & Strassberg, 1990). It's not uncommon for a person to feel anxiety at least once in their life, depending on the number of stressors a person may have in their lives. Anxiety has been used to refer to emotional states such as doubt, boredom, mental conflict, disappointment, bashfulness, and feelings of unreality (Barlow, 2002), as well as a blend of fear with such emotions as distress/sadness, anger, shame, guilt, and interest/excitement (Barlow, 2002). There isn't just one strict definition for the term, since it encompasses so many emotional states a person could be feeling at any given time.  Anxiety occurs in reaction to the possibility of being overwhelmed by a threat and rendered helpless (Barlow, 2002). It excites the sympathetic nervous system, a branch of the autonomic nervous system of the body. There are two categories for categorizing anxiety: state anxiety and trait anxiety. State anxiety is an acute emotional response characterized by subjective feelings of apprehension and increased activation of the SNS (Bradford & Meston, 2006). Trait anxiety, by contrast, just reflects a person's tendency to experience state anxiety (Bradford & Meston, 2006). So while there is a heavy emphasis on a mental or emotional reaction to anxiety, it can also affect the body physically.
	Kaplan's model (of hypoactive sexual desire) postulates that sexual desire can be interrupted or “shut off” by emotional conflicts, particularly by feelings of anxiety and anger (Beck & Bozman, 1995). For as little attention as sexual desire disorders have received, the most focused upon area of research has been anxiety and concerns about sex. Beck and Bozman (1995) say that sources of anxiety can include performance fear, fear of pleasure, and “unconscious” fear of injury. Anxiety can play an important role in the body's physical functions. This is a narrow focus of the topic, however. Research on the role of anxiety in sexual arousal has primarily focused on anxiety arising from specific concerns about sexual performance, but there is ample evidence to justify a broader study of this relation (Bradford & Meston, 2006). From the sources of anxiety that can include performance fears, research has the basic structure to find other emotional states, such as general anxiety, to study.
	As with research on sexual function being a relatively recent development, so is the idea of both research and treatment on sexual inadequacy or dysfunctions. Masters and Johnson (1970) say of their work on sexual inadequacy therapy, “. . .permission to constitute the program was granted upon a research premise which stated categorically that the greatest handicap to successful treatment of sexual inadequacy was a lack of reliable physiological information in the area of human sexual response.” In order for the two researchers to begin even properly looking into the inner workings of sexual dysfunction, they first had to learn about the human sexual response. A drawback to their proposed therapies, however, was the fact that it was based on married couples. The concept and basic building block introduced was that there was no such thing as an uninvolved partner where sexual dysfunction was present (Masters & Johnson, 1970). Regardless of this downside to their research, Masters and Johnson did provide the foundation for later research. Attitudes and states of mind can cause several dysfunctions (Masters & Johnson, 1970). The fear of failing sexual could cause the person's mental and emotional involvement to cease existing (Masters & Johnson, 1970). They were the first to begin connecting a pattern between a person's own emotions and how their sexual response would function together.
	From the sexual inadequacy research and therapy conducted by Masters and Johnson came other researchers and therapists who saw these ideas and began to theorize. Helen Kaplan came to coin the term “hypoactive sexual desire”. Hypoactive sexual disorder is also called low libido, and can be associated with hindrance of the other phases (Kaplan, 1977). Low libido means that a person exhibits little to no sexual desire. It was recognized that desire and disorders associated with this phase were largely ignored, not even receiving mention in works by Masters and Johnson or her own previous work (Kaplan, 1977). In the face of learning how to properly treat those in sexual therapy, this is an oversight that needs attention. Earlier, sexual desire was described as an “appetite”. Kaplan (1977) says, “Naturally, psychic forces, such as conflict or fear, can also inhibit an appetite.” As such, a force like anxiety can effectively shut off desire. Anxiety is the basic cause of sexual dysfunction (Kaplan, 1977). This thought relates back to Masters and Johnson's work about attitudes and is cited by later researchers in their own works. Ultimately, there is an issue that can effect this view of thought. A few points are posed by Kaplan regarding the concern. What is considered as normal sexual desire is unknown (Kaplan, 1977). Another is that desire is a subjective process with pitfalls in its definition (Kaplan, 1977). While it is believed that anxiety can impact the flow of sexual desire, and therefore possibly interrupt the other phases of sexual response, there is not much known about desire.
	Studies have been conducted from the research of both Masters and Johnson and Kaplan concerning sexual dysfunction and hypoactive sexual desire. There is a contradiction, however, between research and laboratory evidence. The argument by sex therapists is that anxiety inhibits desire, but experimental results are inconsistent at best (Hale & Strassberg, 1990). In an experiment using men and threat of electrical shock, it was found that anxiety either decreased, had no effect, or even facilitated sexual arousal (Hale & Strassberg, 1990). This is what researchers Valerie Hale and Donald Strassberg wanted to test while exploring the relationship of anxiety and sexual desire. Could empirical data be found to support the report of anxiety being a factor of erectile dysfunction?
	This particular study was created to assess the effects of performance anxiety and if it connected to self-esteem concerns centering around sex (Hale & Strassberg, 1990). Hale and Strassberg (1990) tested fifty-four males with no medical or sexual dysfunctions to test whether threats to self-esteem (false feedback about performance) or a physical threat (threat of shock) will have lower levels of penile tumescence (an erection). A 30-min series of erotic videos were shown to the participants. Arousal was recorded with a mercury-in-rubber strain gauge and a penile plethysmograph. Prior to the experiment, and after, the participants were asked to fill out a State Anxiety Inventory, to get a measurement of their level of anxiety before and after the conditions. The participants were then put into three conditions: the control, the shock threat, and the self-esteem threat. Both strategies were effective in creating anxiety and also in reducing arousal within the subjects. These findings, however, are the opposite of Barlow et al. (1983), who found that shock threat actually facilitated objective sexual arousal, although it is assumed that the number of differences between the two studies can account for difference in results (Hale & Strassberg, 1990). With the significant results of the study on penile tumescence, it does provide the support of anxiety being a factor for low desire, regardless of the nature of the anxiety. Even sexually functional men with no history of arousal issues were concerned enough about their sexual performance that it interfered with their arousal (Hale & Strassberg, 1990). Despite the findings, there are still limitations on this particular study. The subjects were all men who were sexually functional and only made temporarily dysfunctional, and therefore the need for further research is needed.
	It has been observed that much of the material on this subject has dealt in specific performance anxiety issues. There is cause to believe that this is not the only case in low libido. In the absence of sexual-specific concerns, high levels of anxiety may be associated with distractions that can interfere with sexual response (Bradford & Meston, 2006). This is the idea that, outside of anxieties associated with sexual performance and others, anxiety can still have an effect on the sexual desire of people. Bradford and Meston (2006) say that “high-normal levels of anxiety in normal populations may also be a risk factor for sexual problems.” In particular, their study focused on women and anxiety. It was reported that women with anxiety disorders also had a high prevalence of sexual dysfunction (Bradford & Meston, 2006). There is evidence to suggest that there is a physiological connection to sexual dysfunction and anxiety, as both are mediated by changes in autonomic arousal (Bradford & Meston, 2006). Anxiety can have impacts on the body, the same as desire helps to facilitate sexual action, should the person wish to act upon their need. With that in mind,  it would stand to reason that people with high anxiety sensitivity would react anxiously to even the physical experience of arousal (Bradford & Meston, 2006).
	These ideas led researchers Andrea Bradford and Cindy Meston to study the effects of state and trait anxiety on both the physiological and subjective sexual desire in women. It was expected that state anxiety would be associated with greater physiological sexual arousal, based on previous research, while subjective sexual arousal was expected to decrease as a function of state anxiety (Bradford & Meston, 2006). Thirty-eight women with no medical conditions known to affect sexual response, sexual dysfunctions, or history of sexual abuse participated in the study (Bradford & Meston, 2006). Physiological sexual arousal was measured with an infrared vaginal photoplethysmograph to record vasocongestion, or the swelling of tissue from blood flow, during the presentation of the film stimulus (1-min display of the word “relax”, 3-min clip of a travel documentary, and 10-min clip of an erotic film). Participants then took questionnaires and surveys to rate themselves on subjective sexual desire, sexual function, and their level of anxiety. What was found in this study both led to consistent predictions and also did not adhere to what the researchers expected. Those with moderate state anxiety scores had a greater physiological response to the erotic stimuli, but there was an unexpected result with both low and high state anxiety scores being associated with lower physiological responses than the moderate (Bradford & Meston, 2006). Bradford and Meston (2006) believe that it's possible to attribute the different results to previous manipulations on anxiety in previous studies, but it's speculative at best because no other prior study had any laboratory research using such comprehensive measures of state anxiety. There are many potential explanations for this finding, however, that can be attributed to other bodily functions and SNS activation. As for the results of the subjective sexual arousal, the findings were much more predictable. The relationship between the two provides tentative support to the hypothesis that anxiety negatively affects arousal (Bradford & Meston, 2006). However, it should be kept in mind that there were potential issues, including the fact that study was invasive with the use of the photoplethysmograph and the different reactions participants could experience (Bradford & Meston, 2006). The study does lay precedence for the need for further study of general anxieties and its relationship with sexual desire.
	Being relatively new research, there are still plenty of uncertainties in what has already been studied and learned. Thus far, the information on sexual desire has been gathered by studies relying on methodologies that give only descriptive data (Beck & Bozman, 1995). While the information has helped the basic understanding of sexual desire, there is still a gap between understanding the influence it has on the arousal response and sexual behavior (Beck & Bozman, 1995). The lack of information does not end here. Gender differences are highly under-investigated when it comes to sexual desire as well. Beck and Bozman (1995) have noticed this problem, stating that “many studies assessing correlates of sexual desire have relied on exclusively female samples, thus limiting our ability to understand gender differences in the phenomenon of sexual desire”. It's not to say that men haven't been studied before, as was shown in the previous study conducted by Hale and Strassberg, but that women have been dominant subjects.
	Another problem to note about the research of sexual desire and its connection to anxiety is the use of studies based on Kaplan's research. Kaplan's model of hypoactive sexual desire disorder (HSDD) has been primarily used to study the effect of anxiety interrupting sexual arousal (Beck & Bozman, 1995). This gives rise to another problem in the previous research. The experiments have a unrealistic threat that is used to produce anxiety for performance-based fears, giving rise to criticism (Beck & Bozman, 1995). A previous study done by Beck and Bozman wanted to use a naturalistic emotional manipulation to create anxiety among their male participants. The researchers used three audiotapes containing identical descriptions of a sexual activity: a control condition with appropriate statements and self-statements, an anxiety condition where a female questioned the male's sexual ability and his own self-questioning, and an anger condition where a female made annoying remarks and male self-statements about his irritation towards her (Beck & Bozman, 1991). The results of this study were interesting. There were significant differences in desire in each condition, the highest being in the control condition, followed by anxiety, and the lowest being that of anger (Beck & Bozman, 1991). It seemed that more natural manipulations that caused anxiety proved to be an effective method in reducing sexual desire.
	Using their previous study as a basis, researchers J. Beck and Alan Bozman wanted to investigate the gender differences that occurred in sexual desire when presented with anxiety and anger using the same methodology as their previous study. Unfortunately, no genital measure exists that can compare men and women's physiological results of sexual desire, and the date to compare would have to rely on a continuous measure of subjective sexual desire (Beck & Bozman, 1995). Another addition to the study was given for further investigation. The subjects were given the opportunity to decide when they would have ended each sexual encounter during each of the audiotapes presented to them (Beck & Bozman, 1995). Twenty-four men and twenty-four women with no past or current history of medical conditions or sexual disorders and who were currently sexually active participated in the study.  They were asked to move a subjective rating dial throughout the experiment to provide a continuous measure of subjective sexual desire. Subjects were also asked to not rate their degree of physical arousal, but to indicate the intensity of their desire (Beck & Bozman, 1995). As with the first study done with the men, audiotapes were again utilized; this time, there were six tapes, all gender appropriate depending on the participant. As before, each tape was a different condition. The first was a control condition with partner and self-statements appropriate for a sexual encounter, the second was an anxiety condition with statements on the participant's apparent nervousness of the situation as well as the participant's own self-statements of anxiety, and the third being the anger condition, where the partner became reluctant to participate in sexual behavior despite prior encouragement and a self-statement about the participant's irritation with their partner (Beck & Bozman, 1995). Beck and Bozman (1995) say, “The results indicate that for women, both anger and anxiety significantly reduced desire, with anger showing a more marked effect. For men, similar results were noted, although fewer difference were observed between the anxiety and anger conditions.” There was another interesting result that showed a large gender difference. There were no differences in termination of the sexual encounter with the control and anxiety conditions, but a larger number of the women terminated the encounter during the anger condition than men (Beck & Bozman, 1995). With this information in hand, it seems likely that there is a gender difference in the interrelationship between sexual desire and sexual behavior (Beck & Bozman, 1995). From the results of this study, there is a need to investigate more into the emotional impacts that can affect sexual desire and more into the gender differences to determine why these differences can occur.
	Since the early 1970s, sexual dysfunctions and disorders have been given attention. Beginning with Master and Johnson's work, there have been many new theories and studies based on the idea of attitudes and emotions affecting a person's sexual desire. There is a correlation between anxiety and arousal such as that people who experience higher levels of anxiety, as defined by the Zung Self-Rating Anxiety Scale, will also experience lower levels of subjective desire, based on a self-report measure.