Sexual Behavior
Electrical stimulation of specific sites of the human brain can cause sexual pleasure and desire, erection, orgasm, and romantic feelings.
These sites include the septal area, amygdala, subthalamic nucleus, and thalamus.
Electrical stimulation of specific sites of the animal brain can cause mating, erection, masturbation, ejaculation, ovulation, and uterine contractions (and childbirth/miscarriage).
These sites include the septal area, amygdala, preoptic area, medial forebrain bundle, ventral tegmental area, putamen, periaqueductal gray, hypothalamus, and pituitary gland.
If abused, this would make it possible to cause individuals with no tendency toward committing sexual crimes to do so.
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Circuitry
Male Sexual Behavior
Regions involved in male sexual behavior include the medial preoptic area, lateral septum, medial amygdala, medial forebrain bundle (MFB), and ventral tegmental area.
The medial preoptic area is a critical integrative site for male sexual behavior, facilitating both sexual motivation and copulation. (Hull and Rodríguez-Manzo 2017)
The lateral septum is also an important site in male sexual behavior, involved in both sexual satiety and motivation. (He et al. 2013)
It is also a site activated during erection and ejaculation, and rich in testosterone receptors. (Gulia et al. 2018, Mallick et al. 2007, Menon et al. 2022)
There is a connection from the lateral septum to the medial preoptic area via the MFB. (Swanson and Cowan 1979)
The medial amygdala is a site at a higher level of the medial preoptic area and lateral septum and is involved in regulating male sexual behavior. (Jennings and de Lecea 2020, Hull et al. 2002, Caffé et al. 1987)
As explained on the previous page, the ventral tegmental area is a site that contains dopamine neurons that are important with respect to desire.
Both the medial preoptic area and lateral septum activate the ventral tegmental area via the MFB in the lateral hypothalamus, facilitating male sexual behavior. (Bayless et al. 2023, Sheehan et al. 2004, Conrad and Pfaff 1976)
Electrical stimulation of the regions described above has been shown to facilitate male sexual behavior.
Regions involved in male sexual behavior: medial amygdala, medial preoptic area, lateral septum, medial forebrain bundle, and ventral tegmental area
(The brain image from Vanderah 2018)
MeA = medial nucleus of the amygdala; MFB = medial forebrain bundle; VTA = ventral tegmental area.
Female Sexual Behavior
In female sexual behavior, the ventromedial nucleus of the hypothalamus (VMH) is the most important brain region for regulating female sexual behavior. (Yin and Lin 2023)
Activation of the VMH can rapidly increase female sexual receptivity, whereas lesion of this region inhibits it.
The VMH is also a region that produces aggression, but it is subdivided into topographically distinct subregions for sexual behavior and aggression.
Electrical stimulation of the VMH has been shown to facilitate female sexual behavior.
Humans
Electrical stimulation of the septum, amygdala, subthalamic nucleus, and thalamus has been shown to produce sexual pleasure and desire, and sometimes can even lead to orgasm.
The induced responses can be so intense that they become uncontrollable, as can be seen, for example, in patients who compulsively self-stimulate these brain sites.
It has also been observed that electrical stimulation of the temporal lobe and amygdala can produce something like romantic feelings.
Heath's Human Experiments
Sexual Pleasure and Desire
Psychiatrist Robert Heath of Tulane University repeatedly conducted human experiments of electrical brain stimulation, mainly on patients with schizophrenia. (Heath and Hodes 1954, Heath 1964)
The patients received electrical stimulation primarily to the septal area, but after all, it was concluded that this had no therapeutic effect on schizophrenia.
What is remarkable is that electrical stimulation of the septal area produced pleasure and, to varying degrees, that the patients were consistently sexually motivated.
For example, one patient on the verge of tears described his father's near-fatal illness and condemned himself as somehow responsible.
But when the septal area was stimulated, he immediately terminated this conversation and within 15 seconds exhibited a broad grin as he discussed plans to date and seduce a girl friend.
When asked why he had changed the conversation so abruptly, he replied that the plans concerning the girl suddenly came to him. This phenomenon was replicated with each repeated stimulation.
Another patient was severely agitated and depressed and expressed self-condemnation and hopelessness for over 2 years.
But when the septal area was stimulated, he smiled broadly and related a sexual experience of his youth within a minute.
Three male patients experienced penile erection during septal stimulation.
On the other hand, when stimulation was applied to the lateral hypothalamus or midbrain tegmentum, the patients reported feeling pleasure, such as "This is a good feeling," but they were not sexually motivated.
Self-Stimulation
A 28-year-old male patient with narcolepsy, "B-7," had electrodes attached to the septum, hippocampus, and midbrain, allowing him to self-stimulate these sites using a portable stimulation device. (HEATH 1963)
The patient wore the stimulation device for 17 weeks, during which time he almost exclusively pressed the septal button.
When asked why he pressed the septal button with such frequency, the patient stated that the feeling was “good”; it was as if he were building up to a sexual orgasm.
He reported that he was unable to achieve the orgasmic end point, however, explaining that his frequent, sometimes frantic, pushing of the button was an attempt to reach the end point.
Additionally, the septal stimulation had an alerting effect, and thereby the patient could combat the narcolepsy by this.
A 25-year-old male epileptic patient, "B-10," self-stimulated a total of 17 different brain regions. (HEATH 1963)
These regions were selected at random, and the device design permitted 3 regions to be hooked up at any one time.
Most frequently pushed was a button that stimulates the centromedian thalamus. This stimulation did not, however, induce the most pleasurable response; in fact, it induced irritability.
He reported that he was almost able to recall a memory during this stimulation, but he could not quite grasp it. The frequent self-stimulation was an endeavor to bring this elusive memory into clear focus.
The patient most consistently reported pleasurable feelings with stimulation to two electrodes in the septal area and one in the midbrain tegmentum.
With the pleasurable response, septal stimulation frequently produced sexual thoughts in the patients. Actual content varied considerably, but was unrelated to his original emotional state or the topic of conversation in the room.
With a broad grin, the patient introduced a sexual subject that came to his mind.
When questioned about this, he would say, “I don’t know why that came to mind—I just happened to think of it.”
Midbrain stimulation produced the “happy feelings," but they were not accompanied by sexual thoughts.
He also described as “good,” but somewhat less in pleasurable-yielding quality, stimulation of two sites, the amygdala and the caudate nucleus.
The patient noted that the frustration and anger resulting from stimulation of the centromedian thalamus was alleviated with stimulation to the septal area and to the midbrain tegmentum.
When stimulation to the septal area was introduced without his knowledge, almost instantly his behavioral state changed from one of disorganization, rage, and persecution to one of happiness and mild euphoria.
Orgasm
A 34-year-old female epileptic patient, "B-5," instead of electrical stimulation, received chemical stimulation of the septal area with acetylcholine and norepinephrine . (HEATH 1972)
In 1-2 minutes after completion of the injection, the patient's mood would gradually begin to change. It consisted of gradual elevation of mood, culminating, within 10 to 15 minutes, in a state of mild euphoria accompanied by increased level of awareness.
The degree of change was dependent on the patient's condition at the time the stimulation was given.
If she had been in a low mood, the change was dramatic, whereas if she had already been feeling pleasant at the onset of treatment, the change was less profound.
The elevation in mood and heightened awareness involved development in sexual motivation and in most instances, within another 5 to 10 minutes, this culminated in repetitive orgasms.
Not only did the patient describe the response when questioned, but her sensuous appearance and movements offered confirmation.
Gay Conversion Experiment
In 1972, Heath conducted an infamous experiment in which he attempted to convert a homosexual man into a heterosexual through electrical brain stimulation. (HEATH 1972)
Heath claimed that this "treatment" was successful.
The subject was a 24-year-old man with epilepsy, "B-19," and had a 5-year history of homosexuality and a 3-year history of drug abuse.
He had repeatedly remarked, "I live with the idea of suicide daily" and had made several abortive suicidal attempts.
The subject had never engaged in heterosexual intercourse, and when shown a film displaying heterosexual intercourse, he responded with revulsion to the film, registering angry protests.
A program involving both passive stimulation from the experimenter and self-stimulation to the septal area was begun the following day. (Moan and Heath 1972)
During and following the initial three periods of passive stimulation, the subject exhibited an improved mood, smiled frequently, stated that he could think more clearly, and reported a sense of generalized muscle relaxation.
He likened these responses to the pleasurable states he had sought and experienced through the use of amphetamines.
Moreover, he reported an increase in sexual motivation.
In the next two sessions the patient was allowed to self-stimulate the septal area.
During these sessions of self-stimulation, he was experiencing an almost overwhelming euphoria and elation and had to be disconnected, despite his vigorous protests.
Over the next 4 days the subject showed a notable improvement in disposition and behavior.
He was less recalcitrant and more cooperative both at the laboratory and in his hospital ward, and reported increasing interest in female personnel. He also experienced feelings of sexual arousal with a compulsion to masturbate.
The next afternoon he agreed without reluctance to re-watch the heterosexual film and during its showing became sexually aroused, had an erection, and masturbated to orgasm.
At the conclusion of this session the subject stated that he "felt great" and was highly pleased with himself.
The behavior of the subject over the ensuing 4 days showed increased self-satisfaction, preoccupation with sex, and a continued growing interest in women.
When passive stimulation of the septal area was resumed, it resulted in the subject reporting feelings of alertness, elation, and being quite "high." Consequent self-stimulation also produced an experience of warmth, a flushing sensation, and sexual arousal.
At this time, the patient was maintaining an active interest in females, culminating in an expressed desire to attempt heterosexual activity in the near future.
At last, he was introduced to a prostitute and engaged in two hours of sexual activity in a laboratory specially prepared to afford complete privacy.
Despite the awkward situation and being hooked up to leads to measure deep brainwaves, the subject actively participated in intercourse and achieved a very satisfying orgasm.
After the termination of the program, he met a married woman and formed a close sexual relationship with her for almost 10 months.
He reported that homosexual behavior had occurred only twice, when he needed money and was out of work.
Delgado's Human Experiments
Romantic Feelings
Neurophysiologist Jose Delgado of Yale University also conducted human experiments of electrical brain stimulation on patients with schizophrenia and epilepsy. (Delgado and Hamlin 1960)
He showed that electrical stimulation of the temporal lobes of several epileptic patients produced pleasure.
In three patients, in addition to pleasure, something like romantic feelings was induced, specifically, fondness for a male interviewer they had met for the first time and a desire to marry him.
The first patient was a 36-year-old woman, and electrical stimulation 1.2 in (3 cm) below the surface of the right temporal lobe induced a pleasant tingling sensation in the left side of her body, from her face down to the bottom of her legs. (Delgado 1970)
She started giggling and making funny comments, stating that she enjoyed the sensation very much.
Repetition of these stimulations made the patient more communicative and flirtatious, and she ended by openly expressing her desire to marry the interviewer she had met for the first time.
During interviews before and after stimulation, her behavior was quite proper, without familiarity or excessive friendliness.
The second patient was a 30-year-old woman, and electrical stimulation of the amygdala induced a pleasant sensation of relaxation.
Her verbal output considerably increased, which took on a more intimate character.
She openly expressed her fondness for the interviewer she had met for the first time, kissed his hands, and talked about her immense gratitude for what was being done for her.
A similar increase in verbal and emotional expression was repeated when the same point was stimulated on a different day.
During interviews without stimuation she was rather reserved and poised.
The third patient was an 11-year-old boy with a somewhat greater tendency to identify with women. (HIGGINS 1956, Delgado 1970)
For example, at an interview before stimulation he said such things toward a male interviewer as "You smell like perfume on you—you look cute," or he sniffed, licked, kissed, and bit the interviewer.
During an interview a point located on the surface of the left temporal lobe was stimulated, and there was an open and precipitous declaration of pleasure.
The patient had been silent before this stimulation, but immediately after the stimulation he exclaimed, “Hey! You can keep me here longer when you give me these; I like those.”
He went on to insist that the ongoing brain tests made him feel good.
Similar statements with an emphatic expression of “feeling good” followed eight of a total sixteen stimulations of this point.
Several of these manifestations were accompanied by a statement of fondness for the male interviewer, and the last one was accompanied by a voluptuous stretch.
None of these manifestations appeared during the interviews before stimulation.
In another interview, after stimulation at the same point, he expressed confusion about his own sexual identity.
And he suddenly began to discuss his desire to get married.
When asked, “To whom?” he did not immediately reply, but after a 1-minute, 20-second silence, the patient said, “I was thinking—there’s—I was saying this to you (male interviewer).”
The topic was then completely dropped.
Over the next 40 minutes, other points were tested, but the patient spoke about several topics of completely different and unrelated content.
When that point was stimulated again, he then again expressed doubt about his sexual identity, saying, “I was thinkin’ if I was a boy or a girl—which one I'd like to be.”
Following further stimulation he remarked with evident pleasure, “You're doin’ it now,” and then he said, “I’d like to be a girl.”
Sem-Jacobsen's Human Experiments
Sexual Pleasure
Norwegian neurophysiologist Sem-Jacobsen also repeatedly conducted human experiments of electrical brain stimulation on patients with schizophrenia and Parkinson's disease. (Sem-Jacobsen 1968)
Electrical stimulation of the ventromedial parts of the forebrain and of the limbic system induced positive changes in mood like a feeling of well-being and euphoria.
The positive responses induced were classified into three types:
- The patient becomes relaxed and at ease, has a feeling of well-being, and/or may be a little sleepy.
- The patient is definitely changed, is in a good mood, and feels good. He is relaxed, at ease, and enjoying himself. He frequently smiles. There is slight euphoria, but the behavior is within normal limits. He may want more stimulation.
- The euphoria is definitely beyond normal limits. The patient laughs out loud, enjoys himself, positively likes the stimulation and wants more.
Two men experienced clearly recognizable sexual pleasure.
One patient obtained a strong sexual pleasure.
The patient liked it and wanted to be stimulated again, but when suddenly he became satisfied, he did not want any more electrical stimulation.
Then one day, he volunteered information as follows:
- Relaxed, pleasant.
- It is pleasant.
- It's like a sexual pleasure.
- No smell.
- No taste.
- I feel it in the whole body.
Upon realizing that this was definitely a sexual response, no further stimulation was made.
Another patient was a rather quiet, untalkative man. He liked the stimulation and asked for more. His responses were as follows:
- Moves head.
- Takes a deep breath.
- Moves around on bed.
- Moves leg—flushing—constant trembling—deep breathing.
- Sudden relaxation—smiling.
- Stopped—flushing—wet the bed.
- Ejaculation.
- Later, eyes watered and moved around.
Several other patients also showed orgasm-like reactions.
Self-Stimulation
Just like Heath, Shem-Jacobsen had his patients self-stimulate their brains as well. (Sem-Jacobsen and Torkildsen 1960)
The way in which the patients are stimulating themselves varies from site to site.
In some sites they like to keep the stimulation on for a prolonged period, only interrupted by short breaks. In other sites, they seem to get the most pleasure by frequently starting and stopping the stimulation.
From strong pleasure sites it was found that the patients stimulate themselves into a convulsion.
After the convulsion, these patients were lying relaxed, smiling happily.
Bekhtereva's Human Experiments
Sexual Pleasure and Desire
Natalia Bekhtereva, a Soviet neuroscientist and psychologist, administered electrical coagulation of the brain on patients with hyperkinesia such as Parkinson's disease. (Bekhtereva 1969)
Prior to the operation, experiments on electrical brain stimulation were conducted, and she discovered that electrical stimulation of the thalamus, hypothalamus, and midbrain tegmentum produced sexual pleasure and desire.
A 37-year-old female patient suffered from Parkinson's disease.
When the ventral lateral nucleus of the thalamus and its adjacent sites were electrically stimulated, the patient experienced sexual excitement with extremely pleasant sensations, which turned into orgasm.
This ceased after the stimulation was terminated.
The voluptuous experiences were accompanied by characteristic facial expressions and autonomic changes.
The patient began to visit the laboratory more frequently, where she initiated conversations with the staff; she also waited for them at the ward entrance, in the corridor, or in the hospital garden and tried to find out from them when the next electrical stimulation was to take place.
She asked for the treatments to be performed more frequently, expressed dissatisfaction when they had to be postponed, and showed impatience until she was asked to go to the laboratory.
The patient actively sought a way to repeatedly receive the stimulation.
She showed particular attention to the person who administered electrical stimulation. For this person, the patient developed a feeling of a peculiar infatuation with a certain sexual overtone.
She was ashamed of the urge, didn't want others to know about it, paid close attention to her behavior, disguised the manifestations of the urge, and tried to distract herself and concentrate on some activity. (She actively helped care for other patients, read, listened to music, etc.)
A 49-year-old female patient suffered from Parkinson's disease.
Electrical stimulation of the left midbrain tegmentum, subthalamic nucleus, and ventral lateral nucleus of the thalamus produced a pleasant sensation in the patient.
This was an extraordinarily pleasant sensation accompanied by unusual sensations of warmth in the right side of the body, especially in the arm. The intensity of these sensations increased with higher stimulation intensity.
Stimulation of the ventral lateral nucleus also resulted in the tremor stopping and rigidity being reduced.
The phenomena disappeared simultaneously with the end of stimulation.
The patient's urge was most striking in the first few hours after the electrical stimulation, and the patient experienced a joyful, elated mood.
She began to joke and flirt with men, addressing them with ambiguous remarks, sometimes of an obviously erotic nature.
She persistently requested that the stimulation be repeated, declaring that she wanted to experience the pleasant sensation once more.
The patient tried to attract attention, made herself pretty, puckered her lips up, etc.
Gradually, these manifestations diminished, but after a few days, the patient besieged the doctors, requesting that the stimulation with the "pleasant electrodes" be repeated.
The next electrical stimulation then intensified the urge and revived the characteristic behavioral pattern.
The stronger the pleasant sensations during the stimulation, the more pronounced and the longer lasting the manifestations of the urge were.
Other Studies
Sexual Experiential Phenomenon
Dr. Pierre Gloor of the Montreal Neurological Institute reported a case in which electrical stimulation of the amygdala produced a sexual experiential phenomenon. (Gloor 1986)
The subject was a 40-year-old female patient with epilepsy, and the response was produced by right amygdala stimulation. The patient looked perplexed and was reluctant to talk about what she felt.
She had an abdominal feeling like nausea, but in addition she experienced a pleasant feeling in her vulva and on the inner surface of her thighs, as if she were having sexual intercourse.
She did not see her partner, but knew it was “X,” the boyfriend with whom she had had her first sexual intercourse, and subsequently many times more.
She affirmed that the experience was an evocation of an old memory, and although she subsequently had had intercourse with other men, she was positive that the feeling evoked by amygdaloid stimulation was the feeling of having sexual relations with her old boyfriend “X.”
Self-Stimulation
At the Albert Einstein College of Medicine, they administered electrical stimulation of the ventral posterolateral nucleus of the thalamus as treatment to a 48-year-old female patient with hernia pain. (Portenoy et al. 1986)
The patient was given a self-stimulation device, and the stimulation provided adequate analgesia.
The patient noted, however, that stimulation also produced erotic sensations. This pleasurable response was heightened by continuous stimulation.
Though sexual arousal was prominent, no orgasm occurred.
Although arrhythmia and neurological symptoms occurred, the patient developed compulsive use of the self-stimulation device.
At its most frequent, the patient self-stimulated throughout the day, neglecting personal hygiene and family commitments.
A chronic ulceration developed at the tip of the finger used to adjust the amplitude dial and she frequently tampered with the device in an effort to increase the stimulation amplitude.
At times, she implored her family to limit her access to the stimulation device, each time demanding its return after a short hiatus.
Sexual Pleasure and Desire
Indian researchers reported cases of two patients in which electrical stimulation of the subthalamic nucleus as a treatment for Parkinson's disease resulted in excessive sexual desire. (Bhargava and Doshi 2008)
First was a 70-year-old male patient, and one month after starting electrical stimulation, his wife noted that he had become hypersexual.
He would insist on sexual gratification every night and would become very aggressive if denied. Once satisfied he would return back to his normal self.
The patient realized that though this was exhausting for him, he could not control his urge.
His hypersexual behavior continued for almost four years after the surgery after which it abruptly stopped without any intervention. However, his wife attributed this change to his recent interaction with a religious “guru.”
The second was a 58-year-old female patient, and she post-operatively began forcing herself into her husband’s room to demand sex.
In addition to this, losing all inhibitions, she also exposed herself to other males in the family and demanded sex.
Pre-operatively, she had had no sexual relationship with her husband for several years except for occasional instances.
Post-operatively, she became more vocal in expressing her sexual desires and frustration to the nurses looking after her.
Also, though she had a liking for sweets, in spite of being diabetic, her craving increased post-operatively.
The therapeutic effect on motor disorders was remarkable, but aberrant behavior continued for a period of five years, requiring intervention with an antipsychotic drug.
Chinese researchers administered electrical stimulation of the anterior limb of the internal capsule as a treatment to a 28-year-old male patient with obsessive-compulsive disorder. (Chang et al. 2010)
In the test stimulation, the patient reported mild euphoria and decreased obsessive thoughts. These feelings rapidly dissipated when the stimulation was switched off.
Continuous electrical stimulation started at 3 V, and after about three weeks, he reported energy improvement, a decreased need for sleep, an increased sexual desire, and frequent thoughts of lovemaking, although his obsessive-compulsive symptoms persisted.
The patient said that he was a conservative Christian and that he was uncomfortable with his increased sexual urge.
To try to relieve his obsessive-compulsive symptoms, they increased the stimulation intensity to 4 V.
On his visit 2 weeks later, he reported that his moods changed quickly, and an unstoppable sexual desire had compelled him into a one-night stand with a pub woman. His mother reported that he was quicker to anger than before.
Since his obsessive-compulsive symptomatology persisted , they increased the stimulation to 4.5 V.
A few days later, he suffered from severe suicidal ideation due to persistent symptoms and hypersexuality.
He was then readmitted to decrease the stimulation to 1 V, and his hypersexuality subsided. Unfortunately, he felt depressed because his condition was the same as before surgery.
Erection Sensation
Researchers at Stanford University reported cases in which electrical stimulation of the anterior cingulate cortex induced an erection sensation as well as sexual arousal. (Yih et al. 2019)
In the experiment, they investigated subjective experiences and emotional states induced by electrical stimulation of the anterior cingulate cortex, insular cortex, and orbitofrontal cortex in 18 patients with epilepsy.
They found that electrical stimulation of the anterior cingulate cortex induced sexual arousal in two male subjects.
The first subject reported a "sexually excited" feeling at 4 mA stimulation, and an "erotic" feeling became stronger and exclaimed "whoa!" at 6 mA.
Stimulation at another point produced an erection sensation without an actual erection.
The second subject reported a "very sexually aroused" feeling at 5 mA electrical stimulation. The stimulation at this site also elicited visceral and somatic sensations.
Males
In male animals, electrical stimulation of the septal area, medial preoptic area, medial forebrain bundle, ventral tegmental area, and medial amygdala has been shown to induce and facilitate various sexual behaviors, including erection, ejaculation, masturbation, and mating.
Erections, Ejaculation
Septal Area and Preoptic Area
The National Institutes of Health extensively explored regions that induce erections in the brains of squirrel monkeys. (MacLean and Ploog 1962)
They found that electrical stimulation of the septal area and medial preoptic area produced erections.
Electrical stimulation at 20-30 Hz was most effective, resulting in immediate erections within 3-6 seconds after the stimulation.
Erections were also obtained in the medial forebrain bundle, subthalamic nucleus, and ventral tegmental area, and stimulation at 60-100 Hz was effective.
In addition, erections were sometimes accompanied by urination, vocalization, and arrhythmia.
The Yerkes National Primate Research Center succeeded in inducing ejaculation in rhesus monkeys by electrical stimulation of the erection-inducing sites in the preoptic area repeatedly in a specific pattern. (Robinson and Mishkin 1966)
The semen contained motile sperm in high concentration.
The evoked ejaculation resembled the normal response in several important respects: it was preceded and accompanied by a full penile erection; it was often accompanied by hip thrusting; and the discharge of semen was projectile.
Following ejaculation, the animal usually sat quietly, often dozing.
The most effective was a series of stimulation trains, each lasting 10-20 seconds and separated by 20-60 seconds.
When stimulation trains were applied in this manner the erection would gradually grow in size, and ejaculation, accompanied by hip thrusting, might occur during trains 5-10.
Erections could not be evoked at a rate less than 20 Hz or higher than 100 Hz, and large erections followed by ejaculation occurred only at 40-50 Hz.
One monkey was allowed to self-stimulate the same brain site using a lever.
Utilizing bursts of 8-10 presses separated by rests of 2-5 minutes, large erections were evoked, terminating on the eighth burst with an ejaculation and pelvic thrusting.
Lever pressing then ceased completely.
The entire sequence lasted 25 minutes, during which only 76 presses were recorded, nonetheless, repetition of the phenomenon on two other occasions suggests that the monkey was indeed self-stimulating at a very low rate but with a specific temporal pattern.
A joint Indian-Japanese study investigated the role of the septal area in erection. (Gulia et al. 2008)
Electrical stimulation of the septal area was performed on rats while they were awake and during REM sleep, and in both cases, erections were induced.
In most cases, full erections occurred, equivalent to spontaneous ones, but in some cases abnormal erections accompanied by urination also occurred.
Stimulation during REM sleep could produce prolonged erections lasting up to 16 minutes with a single 3-second stimulation.
Erection was effectively induced from the lateral septum but not from the medial septum.
Putamen
The Yerkes National Primate Research Center used rhesus monkeys to explore the brain sites that induce erections. (Robinson and Mishkin 1968)
Although the majority of the erection-inducing sites were located in the preoptic area, but unexpectedly, erection-inducing sites were also found in the putamen and anterior cingulate cortex.
In addition, several erection-inducing sites were found in the hypothalamus and amygdala.
Medial Forebrain Bundle
A researcher at Oxford University noticed that two rats were discharging semen during an experiment on self-stimulation of the brain. (Herberg 1963)
The rats had had electrodes attached to the medial forebrain bundle of the lateral hypothalamus.
The researcher tested this phenomenon using 12 rats with electrodes attached to the same brain site.
They found that 10 of them regularly discharged semen from their penises while continuing to self-stimulate.
The discharge of semen showed some unusual features. First, no penile erection was seen at any time before, during, or after self-stimulation.
The discharge itself usually took the form of a prolonged dribble rather than a frank ejaculation, and the rats usually continued lever pressing without interruption.
In those instances where clear-cut ejaculation was seen, it always occurred about 5 seconds after a spontaneous or imposed ending of self-stimulation, and was accompanied by arching of the spine, and one or two convulsive lurches, after which the rat remained quiescent and unresponsive for 1-3 minutes.
But the stereotyped oral grooming of the genitalia that characteristically follows ejaculation in normal copulation was never observed.
Male Mating
Medial Preoptic Area/Anterior Hypothalamus
A study at the University of Michigan found that electrical stimulation of the anterior hypothalamus in male rats produced a marked increase in sexual capacity. (Vaughan and Fisher 1962)
However, these effects occurred only in 3 out of 30 rats.
After the male rats were accompanied by female rats, electrical stimulation of the anterior hypothalamus was delivered.
Within seconds after the onset of stimulation, mounting began and continued at a high rate.
The refractory period was significantly shortened, and the male's behavior remained oriented toward the female during the refractory period. Penile erection was virtually constant during stimulation.
The sexual behavior stopped immediately on termination of stimulation.
In some rats, the refractory period was shortened to 27 seconds, from the normal average of more than 5 minutes. This rat had as many as four ejaculations during one 5-minute stimulation period.
A joint Dutch-Swedish study showed that the medial preoptic area, located anterior to the anterior hypothalamus, is important for male sexual behavior. (Van Dis and Larsson 1971)
As the male rats were accompanied by the female rats, electrical stimulation of the medial preoptic area was delivered, resulting in a dramatic increase in the sexual behavior in the male rats.
These changes were indicated by a dramatic increase in the number of ejaculations, a shortening of the time taken to ejaculate, a reduction in the number of intromissions to ejaculation, and extremely shortened refractory periods.
However, these effects occurred only in 2 out of 11 rats.
One had 12 ejaculations in a single 30-minute test, and the other ejaculated 17 times during this period.
The time taken to ejaculate was often shortened to less than 10 seconds, and in some tests the rats started to copulate immediately again after having ejaculated.
The behavioral changes closely followed the onset and termination of electrical stimulation.
When one rat was castrated, it no longer showed any sexual activity. Upon electrical stimulation, however, the castrated male again displayed a large number of mounts and even a few intromissions.
During the stimulation the sexual behavior of the castrated male returned to its pre-castration level.
In addition, when the rats were allowed to self-stimulate the medial preoptic area in the absence of females, half of them dribbled from the penis a small amount of what appeared to be seminal fluid.
An experiment with opossums has also shown that electrical stimulation of the medial preoptic area facilitates sexual behavior. (Roberts et al. 1967)
The stimulated opossums displayed mating behavior toward a stuffed dog.
The principal elements of the mating pattern were mounting, rubbing, biting, relaxing, clicking, and penile erection, all of which are also seen in spontaneous sexual behavior.
Except for the erections, these were induced in both the females and males.
If the dog was removed while the stimulation was on, the opossum clung to it tenaciously and endeavored to pursue it.
In a few cases, the grip was so strong at high-intensity stimulation that the experimenter was forced to turn off the stimulation to extract the dog.
When three males were introduced to the females and given brain stimulation, all three exhibited behavior similar to that exhibited by the stuffed toys, and in addition, two sniffed or licked the female's anogenital area.
In the absence of stimulation, two of the males did not display any spontaneous mating behavior, and the third mounted once, but did not bite or rub.
Medial Forebrain Bundle
A research group at the University of Pittsburgh showed that electrical stimulation of the medial forebrain bundle facilitates sexual behavior. (Caggiula and Hoebel 1966)
The medial forebrain bundle is a bundle of nerve fibers that runs through the lateral hypothalamus, and along it are located brain regions important for desire.
First, in the absence of females, when the male rats were allowed to self-stimulate the medial forebrain bundle of the lateral hypothalamus, it was sometimes accompanied by a penile discharge containing motile sperm.
This usually occurred several seconds after releasing the self-stimulation lever, and penile erection was usually absent during self-stimulation.
Next, in the presence of the females, the male rats continuously received electrical stimulation that turned on and off every 3 minutes.
They found that copulation became stimulation-bound, that is, the males copulated repeatedly when stimulation was on but seldom when it was off.
At a session the male was resting far from the female while the stimulation was left off for 12 minutes; when the stimulation was again turned on, the male began copulating within 10 seconds.
Even after ejaculation, the male remained sexually excited, often sniffing, nudging, and, in several instances, mounting the female until stimulation terminated.
If a male in the process of eating was stimulated, it stopped eating and mounted the female.
The males electrically stimulated in the medial forebrain bundle were highly motivated to mate.
A male and a female were separated by a partition, and the partition could be opened by pressing a bar inside the cage. The stimulated male frequently pressed the bar to open the partition, indicating its desire to mate with the female.
Ventral Tegmental Area
The research group also showed that the electrical stimulation of the ventral tegmental area, one of the brain regions along the medial forebrain bundle, facilitates sexual behavior. (Eibergen and Caggiula 1973)
The male rats continuously received electrical stimulation that turned on and off every 2 minutes in the presence of females.
As with stimulation of the medial forebrain bundle, copulation of the male rats was bound by the stimulation, and 70-100% of the copulation occurred during the periods of stimulation. And especially ejaculations occurred almost invariably during the on periods.
Electrical stimulation produced intense sexual arousal as gauged by constant pursuit of the female, anogenital licking and other approach patterns.
Furthermore, stimulation caused the male to constantly follow the female even during the refractory period.
During this time, the male showed partial mounting, i.e., causing the female to exhibit mating posture by placing a forelimb on the female's back or clasping the female's flanks, without licking or hip thrusting.
Up to thirty such incidents in a two-minute period of stimulation were not uncommon. Such behaviors rarely occurred during periods without stimulation.
Termination of stimulation led to immediate reduction, and often complete cessation of both copulation and signs of sexual arousal.
An experiment with rhesus monkeys has also shown that electrical stimulation of the ventral tegmental area can facilitate sexual behavior. (Okada et al. 1991)
In the experiment, the males and females were restrained in a position that allowed them to mate.
When the ventral tegmental area was stimulated, the male monkey touched and held the waist of his partner, and then mounted her when she responded by presenting her hip toward him.
However, the mounting did not lead to intromission, thrusting, or ejaculation in any monkeys even if stimulation continued longer.
All the monkeys dismounted and withdrew their hands as soon as the stimulation ended.
Touching and mounting were not induced when the partner was put away from the male or replaced by submissive male monkeys or humans.
When the female partner was changed to the other less attractive female, the threshold current to elicit the touching tended to increase.
Septal Area
A study at the Massachusetts Institute of Technology showed that sexual capacity in castrated rats can be restored by stimulating the septal area or the amygdala. (Baum et al. 1982)
No such effects were observed with the stimulation of the preoptic area/anterior hypothalamus, caudate nucleus/putamen, or the substantia nigra/ventral tegmental area.
In this experiment, instead of electrical stimulation, chemical stimulation was performed by injecting dihydrotestosterone, an androgen, into the septal area or medial amygdala.
The male rats were first castrated.
Then, in the presence of females, the male rats received stimulation of the lateral septum or medial amygdala, resulting in facilitation of copulation.
This was mainly indicated by an increase in the number of mounts and intromissions, which were statistically significant in the lateral septum group of 15 rats and the medial amygdala group of 13 rats, respectively.
There was also a marked recovery in ejaculation rate and some recovery in refractory period.
Ejaculation Rate and
Refractory Period
Medial Amygdala
A research group at the University of Colorado found that stimulating the medial amygdala in male rats can induce sexual behavior toward females not in heat. (Stark et al. 1998)
In the absence of stimulation, the males rarely mounted the females not in heat.
However, when the males received electrical stimulation of the medial amygdala, they came to mount the females.
In addition, there was an increase in the number of chasing females and sniffing the anogenital area.
These were more pronounced at higher stimulation intensities.
The research group investigated the effects of the medial amygdala on sexual behavior in sexually experienced and inexperienced males separately. (Stark 2005)
Electrical stimulation of the medial amygdala of the sexually inexperienced male rats increased sexual behavior toward male rats.
In the absence of stimulation, the male rarely mounted the other male, but when stimulated, he began to mount the male.
In addition, there was an increase in the number of chasing males and sniffing the anogenital area.
On the other hand, the sexually experienced male rats showed no significant changes when the medial amygdala was stimulated.
Dorsomedial Nucleus of the Hypothalamus
Stimulation of the dorsomedial nucleus of the hypothalamus in monkeys has also been shown to facilitate sexual behavior. (Perachio et al. 1979)
This stimulation facilitated sexual behavior more than that of the preoptic area.
Stimulation of the preoptic area or dorsomedial nucleus of the hypothalamus in the male rhesus monkeys produced mounts toward the females, and in some cases intromission.
Mounting occurred within 12 seconds of stimulation.
Furthermore, stimulation of the dorsomedial nucleus of the hypothalamus led to intromission and ejaculation.
Compared to spontaneous sexual activity, stimulation produced prolonged mount duration, increased number and rate of hip thrusting per mount, increased number of ejaculation per trial, and shortened refractory period.
Masturbation
Medulla
The National Institutes of Health discovered a brain site in squirrel monkeys that induces masturbation-like scratching that leads to ejaculation. (MacLEAN et al. 1963)
Stimulation of the site resulted in intensive scratching, pulling, and kneading of the skin of the genitalia and was followed by ejaculation.
The site was at the level of the upper medulla and lay lateral to the medial lemniscus.
Putamen
The Yerkes National Primate Research Center discovered brain sites in rhesus monkeys that induce masturbation-like genital teasing while exploring for erection-inducing sites. (Robinson and Mishkin 1968)
The response was obtained primarily from the putamen and, to a lesser extent, from the anterior cingulate cortex.
The genital teasing was of a masturbatory but not rhythmic character.
Large erections invariably accompanied this activity with occasional contraction of the bulbospongiosus and ischiocavernosus muscles, resulting in momentary expansion and congestion of the glans.
Ejaculation, however, was not seen.
The center then went on to investigate what sexual responses electrical stimulation of the erection-inducing sites produced in unrestrained monkeys. (Perachio et al. 1969)
In this experiment, the anterior hypothalamus and putamen were investigated.
First, the experiment was conducted with the monkeys restrained in chairs.
During electrical stimulation of the anterior hypothalamus, the monkey alerted at the onset, the penis began to erect within 3-5 seconds, and the monkey directed an open-jaw threat toward the experimenter.
The electrical stimulation of the putamen induced an erection and a rhythmic movement of the hand occasionally accompanied the erection.
Since it was difficult for the monkey to reach through the waist fence to his genitals, the movement of the hand was confined to the lower portion of his body above the fence.
Next, the experiment was conducted with the monkeys unrestrained.
Electrical stimulation of the putamen resulted in the rhythmic hand movements translating into masturbation.
On the other hand, electrical stimulation of the anterior hypothalamus caused a large erection in the same monkey but no masturbation. The monkey ran, smacked, frowned, and after stimulation offset, lip-smacked and flattened his ears.
Then, the male was introduced to the female.
The male was not willing to mate with a female he did not like spontaneously without stimulation.
Electrical stimulation of the putamen induced mounting toward the female within 5–20 seconds of the onset of stimulation.
In contrast, when the male was placed with a favored female, putamen stimulation seemed to enhance the sexual behavior, increasing the number and length of mounts and rapidly leading to ejaculation.
On the other hand, stimulation of the anterior hypothalamus resulted in larger erections but reduced sexual performance and no mounting.
Females
In female animals, electrical stimulation of the ventromedial nucleus of the hypothalamus (VMH) and periaqueductal gray (PAG) has been shown to facilitate mating.
In addition, electrical stimulation of the pituitary gland, hypothalamus, and medial amygdala has been shown to induce ovulation and uterine contractions, which can in turn lead to childbirth or miscarriage.
Female Mating
VMH
A research group at Rockefeller University found that electrical stimulation of the ventromedial nucleus of the hypothalamus (VMH) in rats can increase female sexual receptivity. (Pfaff and Sakuma 1979)
This was shown by a behavior called lordosis, in which a female raises her hips and arches her back, assuming the posture to accept the male's intromission.
First, the ovaries of the female rats were removed and then estrogen was administered systemically.
The females displayed lordosis in response to either skin stimulation by the experimenter or mounting by the male rats.
Here, electrical stimulation of the VMH increased the frequency and intensity of lordosis.
The frequency of lordosis increased considerably from 4 in 10 before stimulation to 9 in 10 during stimulation.
On the contrary, electrical stimulation of the medial preoptic area, which is important for male sexual behavior, suppressed lordosis.
Lordosis
Stimulation of the VMH has been shown to increase not only sexual receptivity but also proceptivity (female active engagement in sexual interaction). (RUBIN and BARFIELD 1980)
First, the ovaries of the female rats were removed.
Next, chemical stimulation was performed by injecting estrogen selectively into the VMH.
Then, progesterone was administered systemically, and the male rats were introduced.
They found that the females displayed lordosis in response to mounting by the males.
Not only that, the female rats showed solicitation behavior, such as darting, hopping, and ear wiggling.
Stimulation of the sites adjacent to the VMH had a mild effect, whereas that of the sites away from there had no effect.
Sexual Behavior
An experiment with monkeys has also shown that electrical stimulation of the VMH in females can increase proceptivity. (Koyama et al. 1988)
This was shown by a behavior called presenting, in which a female spontaneously presents her rear end to the male, assuming the posture to seek the male's intromission.
In the experiment, Japanese monkeys and rhesus monkeys were used, and both the males and females were restrained.
It was arranged so that females could present themselves, but males could not mate unless females did so.
Experimental arrangement (Oomura et al. 1988)
Here, electrical stimulation of the VMH in the females induced presenting.
The electrically induced presenting was identical to that of the normal, that is, the female, with her head fixed to a holder, lifted her hip and turned her hindquarters toward the male.
This posture, like spontaneous presenting, incited a sequence of male sexual behavior such as touching, mounting, and thrusting.
When the male partner was removed, or replaced with a female, a non-living object or the experimenter, presenting was no longer induced by stimulation even with high intensity.
Without stimulation, the female responded to touching by the male but showed almost no spontaneous presenting.
PAG
The Rockefeller University research group found that electrical stimulation of the periaqueductal gray (PAG) can also increase sexual receptivity in females. (Sakuma and Pfaff 1979)
First, the ovaries of the female rats were removed and then estrogen was administered systemically.
The females displayed lordosis in response to either skin stimulation by the experimenter or mounting by the male rats.
Here, electrical stimulation of the PAG of the midbrain increased the frequency and intensity of lordosis.
Stimulation of the PAG induced lordosis more rapidly than that of the VMH.
Lordosis
Ovulation
Ovulation occurs spontaneously in most mammalian species on a periodic basis, but in some species, such as cats and rabbits, ovulation occurs in response to mating stimuli. (Dixson 2021)
In both species, electrical brain stimulation has been shown to induce ovulation.
Ovulation is induced by stimulating several brain sites, but the pathway in common appears to be that at the anterior pituitary gland was eventually released luteinizing hormone, which triggers ovulation, acting on the ovaries via the bloodstream.
Hypothalamus
A Cambridge University study discovered that electrical stimulation of the hypothalamus can induce ovulation. (Harris 1937)
Rabbits are a species that ovulates during the estrus phase in response to mating stimuli.
Electrical stimulation of the tuber cinereum in the hypothalamus in the rabbits in the estrus phase induced ovulation after 15-40 hours.
The tuber cinereum is the inferior expansion of the hypothalamus, which contains the arcuate nucleus, which regulates hormone release in the anterior pituitary gland.
A UCLA study explored the sites that induce ovulation by electrical stimulation in the tuber cinereum of the hypothalamus in rats. (Critchlow 1958)
Rats are a species that spontaneously ovulates during the estrus phase.
When electrical stimulation of the tuber cinereum region was delivered to the rats in the proestrus phase (the prior phase to estrus), ovulation was confirmed the next morning.
The sites that induced ovulation were located in the arcuate nucleus, ventromedial nucleus, and supraoptic nucleus of the hypothalamus.
The conditions of the uteri, vaginas, and oviducts after electrically induced ovulation were similar to those observed after normal ovulation.
Open circle = successful ovulation, numbers indicate stimulation voltage; solid circle = failed ovulation.
An experiment with female sheep showed that ovulation can be induced by electrical stimulation of the anterior hypothalamus, as well as the ventromedial nucleus of the hypothalamus. (PRZEKOP and DOMAŃSKI 1970)
Sheep are a species that spontaneously ovulates during the estrus phase, and the females in the experiment were in the anestrus phase (the resting phase of estrus).
Electrical stimulation of the ventromedial nucleus of the hypothalamus or the anterior hypothalamus (supraoptic nucleus and anterior hypothalamic nucleus) induced ovulation within 72 hours.
Preoptic Area
Electrical stimulation of the medial preoptic area, located in front of the anterior hypothalamus, has also been shown to induce ovulation. (EVERETT 1965)
When electrical stimulation of the medial preoptic area was delivered to the rats in the proestrus phase (the prior phase to estrus), ovulation induction was confirmed the next morning.
In contrast, electrical stimulation of the lateral preoptic area had no effect.
In addition, the number of ovulation increased in proportion to the duration of electrical stimulation.
10 minutes of stimulation did not induce ovulation, but as stimulation time was prolonged, the number of ovulation gradually increased, and an average of as many as 10 eggs were induced by 60 minutes of stimulation.
Number of Ovulation
The number of ovulation increased in proportion to the duration of electrical stimulation.
Medial Amygdala
Japanese anatomist Dr. Haruyoshi Koikegami found that electrical stimulation of the amygdala can also induce ovulation. (Koikegami et al. 1954)
Electrical stimulation of the medial nucleus of the amygdala in rabbits in the estrus phase induced ovulation 24-48 hours later.
Besides this, hemorrhagic follicles and a freshly formed corpus luteum were also observed.
The doctor speculated that the signal from the medial nucleus of the amygdala traveled via the ventromedial nucleus of the hypothalamus to the anterior pituitary gland, where ovulation-triggering hormones were released, acting on the ovaries.
An experiment with rats has also confirmed that electrical stimulation of the medial nucleus of the amygdala can induce ovulation. (VELASCO and TALEISNIK 1969)
When electrical stimulation of the medial nucleus of the amygdala was delivered to the rats in the proestrus phase (the prior phase to estrus), ovulation induction was confirmed the next morning.
In addition, three hours after electrical stimulation, the blood concentration of luteinizing hormone, which triggers ovulation, was found to have increased significantly.
Furthermore, electrical stimulation-induced ovulation was prevented by severing the stria terminalis, nerve fibers connecting the medial nucleus of the amygdala and the ventromedial nucleus of the hypothalamus.
Therefore, the result supported the idea that the signal travels through the amygdala-hypothalamus-anterior pituitary gland, where ovulation-triggering hormones are released, acting on the ovaries.
Uterine Contractions (and Childbirth/Miscarriage)
Unlike ovulation, uterine contractions induced by electrical brain stimulation appear to occur through two different pathways.
One is a pathway via the bloodstream through the release of oxytocin from the posterior pituitary gland, and the other is a pathway via the nervous system through the activation of the sympathetic nervous system.
Pituitary Gland
An Ohio State University study found that electrical stimulation of the pituitary gland can induce uterine contractions. (Haterius and Ferguson 1938)
Electrical stimulation of the pituitary stalk in post-delivery rabbits augmented uterine motility, and marked increases in frequency and amplitude of contractions were observed.
The induced uterine responses, which persisted for as long as 50 minutes or even an hour, were strikingly similar to those seen after injection of oxytocin.
Hypothalamus
Electrical stimulation of the hypothalamus has also been shown to induce uterine contractions. (Cross 1958)
Uterine contractions were observed when electrical stimulation of the paraventricular nucleus or the supraoptic nucleus of the hypothalamus, as well as the pituitary stalk, was delivered to lactating rabbits.
The stimulation of the paraventricular nucleus sometimes produced responses equivalent to those resulting from an injection of 25-30 mU of oxytocic extract.
Since the experiment was conducted on the rabbits with severed spinal cords, these responses were attributed to the release of oxytocin at the posterior pituitary gland.
Oxytocin-producing neurons are present in the supraoptic nucleus and paraventricular nucleus, and pass through the pituitary stalk to terminate in the posterior pituitary gland.
A researcher at Oslo University confirmed similar findings. (Setekleiv 1964)
In the experiment, the rabbits were first spayed and then treated with the synthetic estrogen diethylstilbestrol continuously.
Electrical stimulation was then delivered to the paraventricular nucleus or supraoptic nucleus of the hypothalamus of the rabbits.
They found that an initial uterine contraction occurred 15-25 seconds later, followed by several contractions of the same or somewhat smaller amplitude.
These uterine responses also had a similar pattern as those seen after injection of oxytocin.
Medulla
The researcher also showed that electrical stimulation of the medulla can induce uterine contractions. (Setekleiv 1964)
Electrical stimulation of the lateral part of the medulla in rabbits caused a uterine response consisting of a contraction followed by inhibition of the rhythmic activity.
This was a characteristic pattern of sympathetic activation.
The time it took to occur was 2-4 seconds, suggesting direct nervous activation of the uterus.
Amygdala
Dr. Koikegami showed that electrical stimulation of the amygdala can cause uterine contractions.(Koikegami et al. 1954)
Upon electrical stimulation applied to the medial nucleus of the amygdala in rabbits, dogs, and cats, remarkable changes in the motility of both horns of the uterus were noticed immediately or several seconds after the stimulation .
Namely, there were increases in frequency and amplitude of contractions, followed by either a decrease or a temporary cessation of movements.
The speed of the responses suggested that this was via the nervous system rather than the bloodstream.
A Duke University study showed that electrical stimulation of the amygdala to induce uterine contractions in pregnant animals can result in either childbirth or miscarriage. (Shealy and Peele 1957)
First, an experiment was conducted on three non-pregnant cats.
Upon electrical stimulation of the medial nucleus and central nucleus of the amygdala, increases in frequency and amplitude of uterine contractions were observed.
In two cats, there was a 30-second delay, and the effect lasted for 2-3 minutes after the stimulation had ended.
In the other cat, stimulation for 1-2 minutes resulted in a single, stronger, and more sustained contraction 20 seconds later. Four minutes later the contractions began to increase in frequency and amplitude to reach a maximum in 12-15 minutes and a return to normal about 17 minutes after the end of the stimulation.
Next, an experiment was conducted on two pregnant cats.
Electrical stimulation for one minute to the medial nucleus or central nucleus of the amygdala started uterine contractions.
One cat aborted the next morning.
The other, not having aborted the next morning, was stimulated for 20 minutes and she delivered four kittens during the next night.
