The Open Psychology Journal


ISSN: 1874-3501 ― Volume 10, 2017

Why Do Healthy Men Experience Morning Erections?



Gahyun Youn*
Department of Psychology, Chonnam National University, 77 Yongbong-Ro, Gwangju 61186, Korea

Abstract

People begin the sleep cycle with a period of non-rapid eye movement (NREM) sleep, followed by a very short period of rapid eye movement (REM) sleep. During a normal night of sleep, humans usually experience about four or five periods of REM sleep. Penile erections have generally been considered to be an epiphenomenon of REM sleep-related physiological changes for healthy males. Thus, men are very likely to awaken in the morning with a REM sleep-related erection, which is also known as nocturnal penile tumescence (NPT). Men who are physically under great strain or serious psychological stress may find it difficult to maintain a psychogenic erection. The best time for them to have sex would be during sleep time, such as when they are experiencing REM sleep-related erections. It is reasonable to assume that the NPT phenomena might have evolved as a tool for having sex, in the context of both procreation and recreation.

Keywords : REM sleep, Morning erection, Nocturnal penile tumescence, Sexual intercourse, Procreation, Recreational sex.


Article Information


Identifiers and Pagination:

Year: 2017
Volume: 10
First Page: 49
Last Page: 54
Publisher Id: TOPSYJ-10-49
DOI: 10.2174/1874350101710010049

Article History:

Received Date: 04/03/2017
Revision Received Date: 15/03/2017
Acceptance Date: 10/04/2017
Electronic publication date: 16/05/2017
Collection year: 2017

© 2017 Gahyun Youn.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence to this author at the Department of Psychology, Chonnam National University, 77 Yongbong-Ro, Gwangju 61186, Korea; Tel: +82 62-530-2655, +82 10 6612-2655; Fax: +82 62 530-2659; Emails: ghyoun@jnu.ac.kr, you90900@naver.com




REM SLEEP

Mammalian sleep consists of natural cycles of activity in the brain and has distinct states: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep which consists of Stages 1 through 3 [1Iber C, Ancoli-Israel S, Chesson A, Quan SF. The AASM manual for the scoring of sleep and associated events: rules, terminology and technical specifications. Westchester, Illinois: AASM 2007; Vol. 1.]. Typically, people begin the sleep cycle with a period of NREM sleep followed by a very short period of REM sleep. Dreams generally occur in the REM state of sleep [2Carskadon MA, Dement WC. Monitoring and staging human sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. St. Louis: Elsevier Saunders 2011; pp. 16-26.
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, 3Hobson JA, Stickgold R, Pace-Schott EF. The neuropsychology of REM sleep dreaming. Neuroreport 1998; 9(3): R1-R14.
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]. Usually, REM sleep occurs 90 minutes after sleep onset. The first period of REM typically lasts 10 minutes, with each recurring REM state lengthening, and the final one lasting up to an hour. That is, the proportion of REM sleep in total sleep time in humans increases as morning approaches. During a normal night of sleep, humans usually experience about four or five periods of REM sleep. REM sleep in adult humans occupies approximately 20-25% of total sleep, or about 90-120 minutes. Some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM [2Carskadon MA, Dement WC. Monitoring and staging human sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. St. Louis: Elsevier Saunders 2011; pp. 16-26.
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].

There are many theories about the functions of REM sleep, but they are not understood well. It has been hypothesized that the REM state serves a sentinel function, bringing about a brief, but periodic, awakening after preparing the organism for immediate fight or escape [7Horne J. Why REM sleep? Clues beyond the laboratory in a more challenging world. Biol Psychol 2013; 92(2): 152-68.
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, 8Horne JA. Human REM sleep: influence on feeding behaviour, with clinical implications. Sleep Med 2015; 16(8): 910-6.
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]. That is, REM sleep activates an animal periodically to scan the environment for possible predators. Such a built-in physiological mechanism presumably would provide maximal security from external danger compatible with minimal disturbance to the continuity of sleep. Apparently, humans are more alert when aroused from REM sleep than NREM sleep [2Carskadon MA, Dement WC. Monitoring and staging human sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. St. Louis: Elsevier Saunders 2011; pp. 16-26.
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, 8Horne JA. Human REM sleep: influence on feeding behaviour, with clinical implications. Sleep Med 2015; 16(8): 910-6.
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]. Many researchers argue that REM sleep serves an important function for the survival of mammalian and avian species. In both humans and experimental animals, REM sleep loss leads to several behavioral and physiological abnormalities [2Carskadon MA, Dement WC. Monitoring and staging human sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. St. Louis: Elsevier Saunders 2011; pp. 16-26.
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, 8Horne JA. Human REM sleep: influence on feeding behaviour, with clinical implications. Sleep Med 2015; 16(8): 910-6.
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, 11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
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]. In addition, some researchers state that REM sleep may function to influence and promote social bonding or attachment in the developing organism and in adults [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
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].

NOCTURNAL PENILE TUMESCENCE

Penile Erections During Sleep

Spontaneous awakening from sleep is significantly associated with the erection cycle [5Schulz H, Salzarulo P. Forerunners of REM sleep. Sleep Med Rev 2012; 16(1): 95-108.
[http://dx.doi.org/10.1016/j.smrv.2011.05.006] [PMID: 21906979]
] and the association had already documented in the early 1940s [15Halverson H. Genital and sphincter behavior of the male infant. Pedagog Semin J Gen 1940; 56: 95-136.
[http://dx.doi.org/10.1080/08856559.1940.9944066]
]. Sleep is different for each individual, but most men have four to five full erections during REM sleep, with each erection lasting about 25-35 minutes. The erections are a normal part of REM sleep for males of all ages, even in infants and children. The relationship between REM sleep and erections is the reason that men are likely to awaken directly from REM sleep, or soon after a long morning REM period has ended. Thus, even though men do not always wake up at the end of each episode of REM sleep, they are very likely to awaken in the morning with an REM sleep-related erection [5Schulz H, Salzarulo P. Forerunners of REM sleep. Sleep Med Rev 2012; 16(1): 95-108.
[http://dx.doi.org/10.1016/j.smrv.2011.05.006] [PMID: 21906979]
, 16Schmidt MH. Neural mechanisms of sleep-related penile erections. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. Philadelphia: Saunders 2005; pp. 305-18.
[http://dx.doi.org/10.1016/B0-72-160797-7/50032-X]
]. Morning erections are scientifically defined as involuntary sleep-related erections (SREs) or nocturnal penile tumescence (NPT) and are a healthy and normal physiological response that most men experience [5Schulz H, Salzarulo P. Forerunners of REM sleep. Sleep Med Rev 2012; 16(1): 95-108.
[http://dx.doi.org/10.1016/j.smrv.2011.05.006] [PMID: 21906979]
, 16Schmidt MH. Neural mechanisms of sleep-related penile erections. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. Philadelphia: Saunders 2005; pp. 305-18.
[http://dx.doi.org/10.1016/B0-72-160797-7/50032-X]
-19Jung J, Jo HW, Kwon H, Jeong NY. Clinical neuroanatomy and neurotransmitter-mediated regulation of penile erection. Int Neurourol J 2014; 18(2): 58-62.
[http://dx.doi.org/10.5213/inj.2014.18.2.58] [PMID: 24987557]
].

Erections are considered a normal part of sleep physiology in men. Evaluation of NPT is one of the earlier tests devised to study erectile dysfunction (ED). After demonstrating that NPT was a general phenomenon in healthy males 3 to 79 years old, Karacan, in the early 1970s, suggested that NPT could be used to evaluate ED [4Karacan I, Hursch CJ, Williams RL, Littell RC. Some characteristics of nocturnal penile tumescence during puberty. Pediatr Res 1972; 6(6): 529-37.
[http://dx.doi.org/10.1203/00006450-197206000-00001] [PMID: 4340042]
, 20Karacan I. Clinical value of nocturnal erection in the prognosis and diagnosis of impotence. Med Aspects Hum Sex 1970; 27: 382.]. The mechanism of NPT is presumed to rely on neurovascular response mechanisms similar to those seen in erotically induced erections. Thus, men who are documented to have normal NPT are presumed to have a normal capacity for spontaneous, erotically induced erections. As a matter of fact, the primary function of NPT tests is to distinguish psychogenic causes of ED from organic causes [18Hirshkowitz M, Schmidt MH. Sleep-related erections: clinical perspectives and neural mechanisms. Sleep Med Rev 2005; 9(4): 311-29.
[http://dx.doi.org/10.1016/j.smrv.2005.03.001] [PMID: 15994100]
, 21Kaneko S, Bradley WE. Evaluation of erectile dysfunction with continuous monitoring of penile rigidity. J Urol 1986; 136(5): 1026-9.
[PMID: 3773061]
-23Shamloul R, Ghanem H. Erectile dysfunction. Lancet 2013; 381(9861): 153-65.
[http://dx.doi.org/10.1016/S0140-6736(12)60520-0] [PMID: 23040455]
]. Men who do not have erections because of psychological problems can still have erections during deep sleep. If a lack of morning erections is accompanied by a lack of overall erections, a physical cause is suggested rather than a psychological cause [21Kaneko S, Bradley WE. Evaluation of erectile dysfunction with continuous monitoring of penile rigidity. J Urol 1986; 136(5): 1026-9.
[PMID: 3773061]
, 23Shamloul R, Ghanem H. Erectile dysfunction. Lancet 2013; 381(9861): 153-65.
[http://dx.doi.org/10.1016/S0140-6736(12)60520-0] [PMID: 23040455]
, 24Papagiannopoulos D, Khare N, Nehra A. Evaluation of young men with organic erectile dysfunction. Asian J Androl 2015; 17(1): 11-6.
[http://dx.doi.org/10.4103/1008-682X.139253] [PMID: 25370205]
].

Physiology of NPT

Although it has been known for some time that every REM cycle is associated with penile erections in males and clitoral engorgement in females, it is not known why this sexual excitation occurs. The erections are not related to erotic content of dreams, previous sexual activity, or a full or empty bladder [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
]. Oddly enough, the erections have generally been considered as mere epiphenomena of REM sleep-related physiologic changes [3Hobson JA, Stickgold R, Pace-Schott EF. The neuropsychology of REM sleep dreaming. Neuroreport 1998; 9(3): R1-R14.
[http://dx.doi.org/10.1097/00001756-199802160-00033] [PMID: 9512371]
, 11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
, 16Schmidt MH. Neural mechanisms of sleep-related penile erections. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. Philadelphia: Saunders 2005; pp. 305-18.
[http://dx.doi.org/10.1016/B0-72-160797-7/50032-X]
]. That is, morning erections have been connected to some hormones and neurotransmitters.

Sex-related hormones have been selectively associated with REM sleep. Testosterone modulates nearly every component involved in erectile function, from pelvic ganglions to smooth muscle and the endothelial cells of the corpora cavernosa. Testosterone also regulates the timing of the erectile process as a function of sexual desire, coordinating penile erection with sex [25Gupta SK, Lindemulder EA, Sathyan G. Modeling of circadian testosterone in healthy men and hypogonadal men. J Clin Pharmacol 2000; 40(7): 731-8.
[http://dx.doi.org/10.1177/00912700022009486] [PMID: 10883414]
-27Luboshitzky R, Herer P, Levi M, Shen-Orr Z, Lavie P. Relationship between rapid eye movement sleep and testosterone secretion in normal men. J Androl 1999; 20(6): 731-7.
[PMID: 10591612]
]. Testosterone levels are higher early in the morning compared to the afternoon or evening in males. In general, the levels rise on falling asleep, are highest at the transition from non-REM to REM sleep state, peak around the time of the first REM sleep period, and remain constant until awakening. Testosterone has been found to be the cause of NPT [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
, 17Foresta C, Caretta N, Rossato M, Garolla A, Ferlin A. Role of androgens in erectile function. J Urol 2004; 171(6 Pt 1): 2358-62.
[http://dx.doi.org/10.1097/01.ju.0000124323.02868.68] [PMID: 15126821]
, 18Hirshkowitz M, Schmidt MH. Sleep-related erections: clinical perspectives and neural mechanisms. Sleep Med Rev 2005; 9(4): 311-29.
[http://dx.doi.org/10.1016/j.smrv.2005.03.001] [PMID: 15994100]
, 27Luboshitzky R, Herer P, Levi M, Shen-Orr Z, Lavie P. Relationship between rapid eye movement sleep and testosterone secretion in normal men. J Androl 1999; 20(6): 731-7.
[PMID: 10591612]
-29Resko JA, Eik-nes KB. Diurnal testosterone levels in peripheral plasma of human male subjects. J Clin Endocrinol Metab 1966; 26(5): 573-6.
[http://dx.doi.org/10.1210/jcem-26-5-573] [PMID: 5938372]
]. Prolactin is also known to be crucial for the development of reproductive and sexual behaviors. It stimulates an array of testicular functions in males and ovarian functions in females [30Dzaja A, Wehrle R, Lancel M, Pollmächer T. Elevated estradiol plasma levels in women with restless legs during pregnancy. Sleep 2009; 32(2): 169-74.
[http://dx.doi.org/10.1093/sleep/32.2.169] [PMID: 19238803]
]. Its release is dependent on REM sleep, with its level rising rapidly at sleep onset and peaking around 3-5 a.m. when REM sleep dominates [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
, 30Dzaja A, Wehrle R, Lancel M, Pollmächer T. Elevated estradiol plasma levels in women with restless legs during pregnancy. Sleep 2009; 32(2): 169-74.
[http://dx.doi.org/10.1093/sleep/32.2.169] [PMID: 19238803]
].

Penile erection is neurologically controlled by the autonomic nervous system. Several neurotransmitters, especially norepinephrine and acetylcholine, are well-known regulators of penile erection [19Jung J, Jo HW, Kwon H, Jeong NY. Clinical neuroanatomy and neurotransmitter-mediated regulation of penile erection. Int Neurourol J 2014; 18(2): 58-62.
[http://dx.doi.org/10.5213/inj.2014.18.2.58] [PMID: 24987557]
]. During REM sleep, high levels of acetylcholine in the hippocampus suppress feedback from the hippocampus to the neocortex, and lower levels of acetylcholine and norepinephrine in the neocortex encourage the spread of associational activity within neocortical areas, without control from the hippocampus [31Hasselmo ME. Neuromodulation: acetylcholine and memory consolidation. Trends Cogn Sci (Regul Ed) 1999; 3(9): 351-9.
[http://dx.doi.org/10.1016/S1364-6613(99)01365-0] [PMID: 10461198]
, 32Vazquez J, Baghdoyan HA. Basal forebrain acetylcholine release during REM sleep is significantly greater than during waking. Am J Physiol – Reg I 2001; 280: R598-601.]. This leads to the cessation of histamine, norepinephrine, and serotonin neuron activity during REM sleep [3Hobson JA, Stickgold R, Pace-Schott EF. The neuropsychology of REM sleep dreaming. Neuroreport 1998; 9(3): R1-R14.
[http://dx.doi.org/10.1097/00001756-199802160-00033] [PMID: 9512371]
, 6Siegel JM. REM sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. Philadelphia: Saunders 2005; pp. 120-35.
[http://dx.doi.org/10.1016/B0-72-160797-7/50017-3]
]. The erections in REM sleep occur when neurological stimulators cause blood to flow into the penis. This ensures that oxygen is properly delivered to the penis and helps keep penile tissue healthy [2Carskadon MA, Dement WC. Monitoring and staging human sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. St. Louis: Elsevier Saunders 2011; pp. 16-26.
[http://dx.doi.org/10.1016/B978-1-4160-6645-3.00002-5]
, 33Padmanabhan P, McCullough AR. Penile oxygen saturation in the flaccid and erect penis in men with and without erectile dysfunction. J Androl 2007; 28(2): 223-8.
[http://dx.doi.org/10.2164/jandrol.106.001313] [PMID: 17021333]
].

Functions of NPT

What are fundamental functions of NPT? It is reported that REM sleep is present during a considerably higher percentage of the sleeping time of infants and children than adults. Since penile erections tend to be synchronous with REM sleep, this again suggests that the erections may not be primarily a sexual phenomenon, at least to infants and children [34Chodoff P. A critique of Freud's theory of infantile sexuality. Am J Psychiatry 1966; 123(5): 507-18.
[http://dx.doi.org/10.1176/ajp.123.5.507] [PMID: 5331925]
]. There are two types of erections. One is a psychogenic erection which occurs due to the stimulation of some parts of the brain, and the other is reflex erection which may spontaneously appear at any time, such as NPT [35Andersson KE, Wagner G. Physiology of penile erection. Physiol Rev 1995; 75(1): 191-236.
[PMID: 7831397]
]. A psychogenic erection is triggered by sexual stimulation and sexual arousal [19Jung J, Jo HW, Kwon H, Jeong NY. Clinical neuroanatomy and neurotransmitter-mediated regulation of penile erection. Int Neurourol J 2014; 18(2): 58-62.
[http://dx.doi.org/10.5213/inj.2014.18.2.58] [PMID: 24987557]
].

The major functions of sexual interaction are both procreation and recreation [36Benagiano G, Mori M. The origins of human sexuality: procreation or recreation? Reprod Biomed Online 2009; 18(Suppl. 1): 50-9.
[http://dx.doi.org/10.1016/S1472-6483(10)60116-2] [PMID: 19281665]
]. A man should maintain either a psychogenic or reflex erection for penile-vaginal intercourse. If he wants sex with a psychogenic erection, he should be awake and sexually aroused by the erotic and/or emotional stimuli. He could, however, have sex with an REM sleep-related erection, even without stimuli. Here, it is possible to surmise the reason why men experience REM sleep-related erections spontaneously, in the context of procreation. The brain of every man instinctively seeks to eternal generation. On the instinctive level, this leads to a man looking for a sexual partner to transfer his genes to create future generations [37Cartwright J. Evolution and human behavior: Darwinian perspectives on human nature. Cambridge, Massachusetts: MIT Press 2000.]. This is the most important role played by erections, as they are one of the most necessary tools for sexual intercourse.

Sexual Intercourse with NPT

In general, men who are physically under great strain may have difficulty maintaining a psychogenic erection [38Rosen RC. Psychogenic erectile dysfunction: Classification and management. Urol Clin North Am 2001; 28(2): 269-78.
[http://dx.doi.org/10.1016/S0094-0143(05)70137-3] [PMID: 11402580]
]. For instance, monogamous men, in prehistoric societies, might come back home with physically fatigued from gathering and/or hunting. If so, it might not be pertinent for them to have sexual intercourse immediately after coming back from work early in the evening. The best time for them to have sex would be after getting enough rest during sleep time, such as experiencing REM sleep. Thus, men’s REM sleep-related erections during sleep might have evolved to allow procreation irrespective of their will or intention [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
].

What about the men of today? The life of the modern men is full of stresses and constant strain, both physically and psychologically. If they work all of the time, take care of kids, and stay busy most of the day, it might not be easy to have sex before they fall asleep [39Gager CT, Yabiku ST. Who has the time? The relationship between household labor time and sexual frequency. J Fam Issues 2010; 31(2): 135-63.
[http://dx.doi.org/10.1177/0192513X09348753]
]. Also, there are many men who suffer from ED, owing to psychological strain [22Rew KT, Heidelbaugh JJ. Erectile dysfunction. Am Fam Physician 2016; 94(10): 820-7.
[PMID: 27929275]
, 23Shamloul R, Ghanem H. Erectile dysfunction. Lancet 2013; 381(9861): 153-65.
[http://dx.doi.org/10.1016/S0140-6736(12)60520-0] [PMID: 23040455]
]. Under psychologically serious stress, men become too anxious to get or maintain an erection, and thus, suffer from either the loss of erection and/or premature ejaculation [38Rosen RC. Psychogenic erectile dysfunction: Classification and management. Urol Clin North Am 2001; 28(2): 269-78.
[http://dx.doi.org/10.1016/S0094-0143(05)70137-3] [PMID: 11402580]
]. For instance, men who have relationship problems with female partners do not attempt to have sex owing to anxiety [40Abdo CH. The impact of ejaculatory dysfunction upon the sufferer and his partner. Transl Androl Urol 2016; 5(4): 460-9.
[http://dx.doi.org/10.21037/tau.2016.05.08] [PMID: 27652218]
]. They fear that when they initiate sex, their female partners might reject the initiation. Even though the female partners might not reject the initiation, the men would experience erectile problems and/or premature ejaculation [38Rosen RC. Psychogenic erectile dysfunction: Classification and management. Urol Clin North Am 2001; 28(2): 269-78.
[http://dx.doi.org/10.1016/S0094-0143(05)70137-3] [PMID: 11402580]
].

Women experience clitoral enlargement, as men do penile erections, during the REM sleep state due to increased blood flow to genital organs [6Siegel JM. REM sleep. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. Philadelphia: Saunders 2005; pp. 120-35.
[http://dx.doi.org/10.1016/B0-72-160797-7/50017-3]
, 41Goldstein I. Female sexual arousal disorder: New insights. Int J Impot Res 2000; 12(S4)(Suppl. 4): S152-7.
[http://dx.doi.org/10.1038/sj.ijir.3900596] [PMID: 11035405]
]. This indicates that a woman’s body is ready to have sex during the REM sleep state. It also indicates that women who are semi-awake would be less resistant to their partner, even if they are currently uncomfortable with their partner [42Park J, Youn G. Gender differences in attitudes towards “sleeping in separate rooms” in response to marital conflict. Korean J Androl 2011; 29: 199-205.
[http://dx.doi.org/10.5534/kja.2011.29.3.199]
]. As mentioned earlier, some researchers stated that REM sleep evolved to promote attachment in unattached sexual partners [12McNamara P. REM sleep: A social bonding mechanism. New Ideas Psychol 1996; 14: 35-46.
[http://dx.doi.org/10.1016/0732-118X(95)00023-A]
, 13McNamara P, Andresen J, Clark J, Zborowski M, Duffy CA. Impact of attachment styles on dream recall and dream content: A test of the attachment hypothesis of REM sleep. J Sleep Res 2001; 10(2): 117-27.
[http://dx.doi.org/10.1046/j.1365-2869.2001.00244.x] [PMID: 11422726]
]. That is, men who have relationship problems may try sexual intercourse by genital erections during REM sleep [14Zborowski MJ, McNamara P. Attachment hypothesis of REM sleep: Toward an integration of psychoanalysis, neuroscience, and evolutionary psychology and the implications for psychopathology research. Psychoanal Psychol 1998; 15: 115-40.
[http://dx.doi.org/10.1037/0736-9735.15.1.115]
].

As for Korean couples, some who had relationship problems with their spouses do not choose divorce or separation as a solution. Many of them tend to believe that the problems can be solved if they have sex with their partners [42Park J, Youn G. Gender differences in attitudes towards “sleeping in separate rooms” in response to marital conflict. Korean J Androl 2011; 29: 199-205.
[http://dx.doi.org/10.5534/kja.2011.29.3.199]
]. This means that they believe marital conflicts might be solved through sex, no matter the situation [42Park J, Youn G. Gender differences in attitudes towards “sleeping in separate rooms” in response to marital conflict. Korean J Androl 2011; 29: 199-205.
[http://dx.doi.org/10.5534/kja.2011.29.3.199]
, 43Park J, Youn G. Sleeping in separate rooms due to marital conflict: Psychological characteristics of married Korean women. INT J Psychol Behav Sci 2015; 5(2): 53-61.]. Many couples in marital conflict choose sleeping in separate rooms for a specific period of time (e.g., for a week, month, or even longer than that) as a solution [43Park J, Youn G. Sleeping in separate rooms due to marital conflict: Psychological characteristics of married Korean women. INT J Psychol Behav Sci 2015; 5(2): 53-61., 44Youn G. Marital and sexual conflicts in elderly Korean people. J Sex Marital Ther 2009; 35(3): 230-8.
[http://dx.doi.org/10.1080/00926230802716369] [PMID: 19360521]
]. While researching these couples, the authors met many women who reported having sex with their husbands during the separate room arrangement. Women, who refused their husbands at other times, did not reject their husbands who came to their room while they were sleeping, when they had penile erections [42Park J, Youn G. Gender differences in attitudes towards “sleeping in separate rooms” in response to marital conflict. Korean J Androl 2011; 29: 199-205.
[http://dx.doi.org/10.5534/kja.2011.29.3.199]
-44Youn G. Marital and sexual conflicts in elderly Korean people. J Sex Marital Ther 2009; 35(3): 230-8.
[http://dx.doi.org/10.1080/00926230802716369] [PMID: 19360521]
]. This indicates that their sexual encounters by the REM sleep-related erections would serve a palliative function especially during time of physical and/or psychological stress [14Zborowski MJ, McNamara P. Attachment hypothesis of REM sleep: Toward an integration of psychoanalysis, neuroscience, and evolutionary psychology and the implications for psychopathology research. Psychoanal Psychol 1998; 15: 115-40.
[http://dx.doi.org/10.1037/0736-9735.15.1.115]
].

According to a study of part-time college students who had their sexual partners, some of them reported to have sex early in the morning before getting up. In general, the majority of sexual encounters take place at bedtime, that is, people begin to sleep after having sex, while some of the encounters do occur during the daytime [45Refinetti R. Time for sex: Nycthemeral distribution of human sexual behavior. J Circadian Rhythms 2005; 3(1): 4.
[http://dx.doi.org/10.1186/1740-3391-3-4] [PMID: 15790406]
]. However, approximately 20% of sexual encounters take place early in the morning [46Jankowski KS, Díaz-Morales JF, Randler C. Chronotype, gender, and time for sex. Chronobiol Int 2014; 31(8): 911-6.
[http://dx.doi.org/10.3109/07420528.2014.925470] [PMID: 24927370]
]. It is reasonable to assume that REM sleep-related erections have a function of recreation, such as resolving marital conflict. According to Komsomolskaya Pravda, some Russian women said they had sex during the sleep. Many women who never experienced orgasm before are reported to have achieved peak of sexual satisfaction while having sex half-asleep [47Naumov A. Sexual satisfaction depends greatly on time of the day. Komsomolskaya Pravda 2016 November 20; Available from: http://www.pravdareport.com/society/sex/20-11-2006/85566-sex-0/?mode=print.].

Moreover, sex with an REM sleep-related erection could be advantageous to procreation. If a man has sex with his partner who is in a sleepy state, she may lie back for sex and not move her body much. It is more suitable for sperm to reach her cervix, and thus she can retain more sperm [48Singh D, Meyer W, Zambarano RJ, Hurlbert DF. Frequency and timing of coital orgasm in women desirous of becoming pregnant. Arch Sex Behav 1998; 27(1): 15-29.
[http://dx.doi.org/10.1023/A:1018653724159] [PMID: 9494687]
]. This means the chances of getting pregnant might be somewhat higher in sex with the REM sleep-related erections than other times. That is, if REM sleep might have compensatory and reproductive functions, then the REM sleep-related erections may exert a strong influence on the reproductive success that has greater evolutionary importance [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
-14Zborowski MJ, McNamara P. Attachment hypothesis of REM sleep: Toward an integration of psychoanalysis, neuroscience, and evolutionary psychology and the implications for psychopathology research. Psychoanal Psychol 1998; 15: 115-40.
[http://dx.doi.org/10.1037/0736-9735.15.1.115]
].

CONCLUSION

Healthy men experience erections owing to physiological changes such as sex-related hormonal release during REM sleep. The hormone release leads to REM sleep-related erections. Men are able to have sex with these erections, which may have the benefits of enabling sexual excitation, couples resolving marital conflicts, and their partners getting involved [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
, 16Schmidt MH. Neural mechanisms of sleep-related penile erections. In: Kryger MH, Roth T, Dement WC, Eds. Principles and practice of sleep medicine. Philadelphia: Saunders 2005; pp. 305-18.
[http://dx.doi.org/10.1016/B0-72-160797-7/50032-X]
, 19Jung J, Jo HW, Kwon H, Jeong NY. Clinical neuroanatomy and neurotransmitter-mediated regulation of penile erection. Int Neurourol J 2014; 18(2): 58-62.
[http://dx.doi.org/10.5213/inj.2014.18.2.58] [PMID: 24987557]
, 42Park J, Youn G. Gender differences in attitudes towards “sleeping in separate rooms” in response to marital conflict. Korean J Androl 2011; 29: 199-205.
[http://dx.doi.org/10.5534/kja.2011.29.3.199]
, 49Rampin O, Giuliano F, Benoit G, Jardin A. Central nervous system control of erection. Prog Urol 1997; 7(1): 17-23.
[PMID: 9116734]
]. In conclusion, it can be said that REM sleep promotes development of both attachable and/or recreational and reproductive strategies in human beings [11McNamara P, Dowdall J, Auerbach S. REM sleep, early experience, and the development of reproductive strategies. Hum Nat 2002; 13(4): 405-35.
[http://dx.doi.org/10.1007/s12110-002-1001-x] [PMID: 26193088]
-13McNamara P, Andresen J, Clark J, Zborowski M, Duffy CA. Impact of attachment styles on dream recall and dream content: A test of the attachment hypothesis of REM sleep. J Sleep Res 2001; 10(2): 117-27.
[http://dx.doi.org/10.1046/j.1365-2869.2001.00244.x] [PMID: 11422726]
], while REM sleep-related erection has been observed to be helpful for couples who are under stress physically or psychologically to have sex [13McNamara P, Andresen J, Clark J, Zborowski M, Duffy CA. Impact of attachment styles on dream recall and dream content: A test of the attachment hypothesis of REM sleep. J Sleep Res 2001; 10(2): 117-27.
[http://dx.doi.org/10.1046/j.1365-2869.2001.00244.x] [PMID: 11422726]
, 14Zborowski MJ, McNamara P. Attachment hypothesis of REM sleep: Toward an integration of psychoanalysis, neuroscience, and evolutionary psychology and the implications for psychopathology research. Psychoanal Psychol 1998; 15: 115-40.
[http://dx.doi.org/10.1037/0736-9735.15.1.115]
]. Accordingly, it is said that sex with an REM sleep-related erection would be the best opportunity for both procreation and recreation.

CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

ACKNOWLEDGEMENTS

Declared none.

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