Nocturnal penile tumescence

Nocturnal penile tumescence is a spontaneous erection of the penis during sleep or when waking up. Along with nocturnal clitoral tumescence, it is also known as sleep-related erection, morning glory or morning wood. Men without physiological erectile dysfunction or severe depression experience nocturnal penile tumescence, usually three to five times during a period of sleep, typically during rapid eye movement sleep. Nocturnal penile tumescence is believed to contribute to penile health.

History

The history of the scientific study of nocturnal penile erections is related in an article by Frank Heynick (1984). In 1944 P. Ohlmeyer, H. Brilmayer, and H. Hüllstrung published in a German journal of physiology an article with the cautiously neutral title “Periodische Vorgänge im Schlaf” (Periodic processes in sleep). The researchers, having observed recurrent erections in sleeping soldiers, let their subjects wear a snug ring around their penises with an electric contact which would be broken when the rings expanded. The authors reported nightly erections about every 85 minutes lasting on average 25 minutes.

Although in the 1930s something was known about the cyclic nature of brain wave patterns of sleeping subjects, it wasn’t until the 1950s, that William Dement and his colleagues Eugene Aserinski and Nathaniel Kleitman at the University of Chicago established – with the use of electroencephalographic and electrooculographic monitoring on multiple subjects – the correlation between stage 1 brain wave patterns, rapid eye movements, and detailed reports from awakened subjects of vivid dreaming. These periods, termed “REM” for rapid eye movement, apparently regulated by an internal biological clock, recurred on average at about 90-minute intervals, getting progressively longer in the course of the night. Reports from subjects awakened from the intervening non-REM periods, which take up most of a night’s sleep, generally show comparatively far less vivid mental activity, if any, though there are exceptions.

In 1960, professor of psychiatry at the University of Edinburgh Ian Oswald came across the article by Ohlmayer et al. (Having been published during the war, the journal had had little distribution outside of Germany.) A prominent sleep researcher, Oswald was familiar with Dement’s findings and he asked himself whether the nightly erections might be yet another synchronous periodic process. “The atmosphere in Edinburgh was such that I was worried about hurting my career,” Oswald explained when interviewed by Heynick at the session on nocturnal penile tumescence at the Congress of the Association for the Psychophysiological Study of Sleep (APPS) in Bologna, Italy, in 1982. Oswald proceeded cautiously, using himself as nightly subject, hooked up to the appropriate monitoring devices. When the suspected correlation of erections with REM-periods was confirmed, Oswald made only passing and cautious mention of it in his 1962 book Sleeping and Waking (keeping his own role as subject anonymous).

A few years later, the American researchers Charles Fisher, Joseph Gross, and Joseph Zurch of Mt. Sinai Hospital in New York, inspired by the suggestion in Oswald’s book, conducted experiments with 17 subjects using brain wave and eye movement monitoring plus measurement of erectile activity with a modified plethysmograph (cuff), a mercury strain gauge, penile skin temperature sensors, and direct visual observation. The researchers reported their results in their 1965 article “Cycle of penile erections synchronous with dreaming (REM) sleep,” where the recorded overlap (full or partial erections) was about 95 percent.

Psychoanalytic interpretation

In his historical consideration, Heynick found it remarkable that until the mid-twentieth century such a universal phenomenon as regular penile erections in sleep should have gone unmentioned in the scientific (or other) literature. Prof. Ismet Karacan, then head of the Sleep Disorders Center of the VA Medical Center in Houston and chair of the nocturnal penile tumescence session at the APPS Congress in Bologna, recalled when interviewed by Heynick seeing an ancient Chinese print of the sleeping emperor with a cord around his penis on which a few courtesans were pulling. “There was a myth that the fate of the Empire depended on the emperor’s potency,” Karacan explained. “The emperor was assumed to have a particular capacity for nightly erections. If they were to diminish or stop, the Empire would crumble.” Apparently, no one realized that even the humblest of the Emperor’s peasant subjects had the same wonderous capacity.

Perhaps the first reference – a guarded allusion – to nocturnal penile tumescence in the scientific literature is found in the 1867 book Les Rêves et les Moyens de les Diriger (Dreams and ways to direct them) by the Marquis Léon d’Hervey de Saint-Denys in which he wrote of “les rêves supersensuels” and the interplay in sleep between the organism and the mind.

Heynick pointed to the irony that Sigmund Freud was apparently unaware of such a ubiquitous phenomenon as nocturnal penile tumescence even in himself, which would have lent much support to his dream theory. In brief: Freud theorized in The Interpretation of Dreams (1900) and subsequent writing that dreaming had evolved in humans as the guardian of sleep (which, it was taken for granted, is a biological necessity). Its function is to render disruptive stimuli harmless by incorporating them into a dream story and thus allow the sleeper to sleep on. The disruptive stimulus can be of an external sensory nature (e.g., a ringing telephone); but far more often it is of an internal psychological nature relating to the fulfilment of instinctual, particularly sexual drives and wishes. Not, however, run of the mill sex, according to Freud, but taboo sex of an incestuous and aggressive nature stemming from the first years of infancy and childhood, which have been suppressed as complexes in the adult unconscious but continue to influence one’s thought and behavior in wakefulness. These sexual drives and wishes press for gratification during sleep, but explicit representation would shock the sleeper’s sensibility into wakefulness, which would defeat the very function of dreams as the guardian of sleep. Thus dreams are a compromise formation, presenting the gratification in symbolic, camouflaged representation. As fully obvious from Freud’s analysis of his own dreams, everyday concerns abound in dreams, and the hypothesized wish-fulfilling nature of dreaming also functions on this mundane level. Still, according to Freud, almost all dreams are powered ultimately by sexual drives, though due to camouflaging few dreams are explicitly sexual in content and fewer still are explicitly of the repressed taboo sexual nature.

Freud died in 1939, before the above-mentioned discovery was made of the cyclical nature of REM-periods in the course of the night regulated by an internal biological clock and the strong correlation – although there are exceptions – with the phenomenological experience of vivid dreaming. This discovery, Heynick points out, would have presented a theoretical problem for Freud in that “there is little variation in sleep-stage patterns from one person to the next, and the same person over time; and that the variations that do appear can hardly be viewed as following Freud’s basic biological principle” that the generation of dreams results from a given individual’s psychological complexes.

The subsequent discovery of the nocturnal penile tumescence cycle synchronous with REM periods and dreaming would however have offered unexpected ammunition to Freud’s concept of sexual drive as the motive power behind almost all dreams. But there are theoretical complications. For example, cyclical erections have been found in human male infants and even fetuses and in other mammals – beings which presumably have not (yet) developed unconscious taboo sexual complexes which are pressing for expression in the form of dreams. Furthermore, there are reports that when REM periods (and thus dreaming) are pharmacologically suppressed, the erection cycle continues. To complicate the matter, Fisher, Gross, and Zurch in their groundbreaking article pointed to the research of the American sexologist Alfred Kinsley that non-sexual stimuli ranging from the hearing of the national anthem to seeing one’s name in print can cause erections in pre-pubescent boys. Indeed, as Freud himself wrote in his Three Essays on Sexuality (1905) “[T]here are arrangements in the organism which induce sexual excitement as a subsidiary action in a large number of inner processes as soon as the intensity of these processes has risen above certain quantitative limits. […] It is possible that nothing of any considerable significance occurs in the organism that does not contribute its components to the excitement of the sexual impulse.” The pioneering researcher Prof. Ian Oswald when interviewed by Heynick in 1982 summed up the then current situation with regard to nocturnal penile erections thus: “Freud would have loved this. There are obscure mechanisms operating in our psyches and who’s to say exactly how they relate to one another?”

Mechanism

The cause of nocturnal penile tumescence is not known with certainty. In a wakeful state, in the presence of mechanical stimulation with or without an arousal, erection is initiated by the parasympathetic division of the autonomic nervous system with minimal input from the central nervous system. Parasympathetic branches extend from the sacral plexus of the spinal nerves into the arteries supplying the erectile tissue; upon stimulation, these nerve branches release acetylcholine, which in turn causes release of nitric oxide from endothelial cells in the trabecular arteries, that eventually causes tumescence. Bancroft (2005) hypothesizes that the noradrenergic neurons of the locus ceruleus in the brain are perpetually inhibitory to penile erection, and that the cessation of their discharge that occurs during rapid eye movement sleep may allow testosterone-related excitatory actions to manifest as nocturnal penile tumescence. Suh et al. (2003) recognizes that in particular the spinal regulation of the cervical cord is critical for nocturnal erectile activity.

The nerves that control a man’s ability to have a reflex erection are located in the sacral nerves (S2-S4) of the spinal cord. Evidence supporting the possibility that a full bladder can stimulate an erection has existed for some time and is characterized as a 'reflex erection'. A full bladder is known to mildly stimulate nerves in the same region. The possibility of a full bladder causing an erection, especially during sleep, is perhaps further supported by the beneficial physiological effect of an erection inhibiting urination, thereby helping to avoid nocturnal enuresis . However, given females have a similar phenomenon called nocturnal clitoral tumescence, prevention of nocturnal enuresis (bed-wetting) is not likely a sole supporting cause.

In an old study, during puberty, the average tumescence time per night was 159 min; average REM sleep time was 137 min. Average simultaneous REM sleep and penile tumescence per night was 102 min. Study subjects averaged 6.85 tumescence episodes/night, and, of these, 5.15 occurred during a REM sleep period. Tumescence episodes during REM averaged 30.8 min in duration, whereas episodes which occurred when no REM was present averaged 11.75 min. Study subjects had at least four REM periods per night and at least three tumescence episodes.

In another old study of healthy aging men, frequency and duration of nocturnal penile tumescence decreased progressively with age independent of variations in sleep. In contrast to men in the younger age groups, the majority of men above age 60 did not have full sleep erections even though they and their partners reported regular intercourse.

Unlike physiological penile tumescence, sleep-related painful erections (SRPE) and Stuttering priapism (SP) are much rarer pathological erections, resulting in poor sleep and daytime tiredness, and long term cardiovascular morbidity. SRPE, though also occur predominantly during REM sleep, without an apparent underlying illness are painful and thus interrupt sleep. On the contrary, stuttering priapism can occur spontaneously at any time of the day, but more commonly so during REM sleep. SP is a subtype of ischemic priapism that is characterized by recurrent, self-limiting, painful erections that often require maneuvers (compression, cold packs or a cold shower, voiding, or exercise, etc.) to aid detumescence. In ischemic priapism, most of the penis is hard; however, the glans penis is not. Much rarer priapism is secondary to blunt trauma to the perineum or penis, with laceration of the cavernous artery, which can generate an arterial-lacunar fistula resulting in a high blood flow state, hence the tumescence. Tumescence lasting for more than four hours is a medical emergency.

Diagnostic value

The existence and predictability of nocturnal tumescence is used by sexual health practitioners to ascertain whether a given case of erectile dysfunction is psychological or physiological in origin. A patient presenting with erectile dysfunction is fitted with an elastic device to wear around his penis during sleep; the device detects changes in girth and relays the information to a computer for later analysis. If nocturnal tumescence is detected, then the erectile dysfunction is presumed to be due to a psychosomatic illness such as sexual anxiety; if not, then it is presumed to be due to a physiological cause.

Nocturnal penile tumescence testing

Regularly, men who experience erectile dysfunction are given a nocturnal penile tumescence (NPT) test, usually over a three-day period. Such a test detects the presence of an erection occurring during sleep using either:

1. a small portable computer connected to two bands placed around the shaft of the penis which records penile tumescence,
2. a band of paper tape with perforations (similar to coil postage stamps) that is fit snugly around the shaft of the penis and will break at the perforations during penile tumescence.

The goal of nocturnal penile tumescence testing is to determine whether a man can experience an erection while sleeping after reporting he is unable to experience an erection while awake. The average man has 3–5 episodes of NPT each night, and each episode lasts 30–60 minutes, although the duration is reduced with advanced age. If a man does obtain an erection while sleeping, but cannot obtain one while awake, a psychological cause or a medication side effect is usually suspected. Otherwise, if a man does not obtain an erection in either state, a physiological cause is usually suspected.

See also

• Tumescence
• Swelling (medical)
• Nocturnal clitoral tumescence
• Erection
• Priapism
• Nocturnal emission
• Sleep sex

Bibliography

• Knight, Jane (November 2016). The Complete Guide to Fertility Awareness. Routledge. ISBN 978-1138790100.