Well, my friend, this is another installment of A Journal Article I Read - a segment in which I read a lady-gasm related peer-reviewed journal article and try my damndest to summarize the article here for you without taking away too much of the detail and subtlety, yet making it readable and not too long. I do my best to achieve those goals, and that's all I can say.
In these summaries, you can assume that anything I write is a genuine attempt to reflect what is said in the paper - even if it's shortened or summarized. My opinions, if I have any to add will either be inside brackets likes these [me:], or in a section headed in a way that clearly lets you know these are my opinions. All quotes are from this article unless specifically noted.
You can check out the list of all the past 'A Journal Article I Read' Summaries HERE.
My Quick Take On This Article (for those preferring a quicker read)
Regional cerebral blood flow changes associated with clitorally induced orgasm in healthy women. Georgiadis JR1, Kortekaas R, Kuipers R, Nieuwenburg A, Pruim J, Reinders AA, Holstege G. Eur J Neurosci. 2006 Dec;24(11):3305-16.
What they did...very basically This lovely article investigates what parts of the brain are activated (by observing where blood flow is increased or decreased in the brain) during 1) non-sexual relaxation 2) imitation of orgasm 3) clitoral stimulation (performed by the male partner of the participant) and 4) orgasm. The study includes 12 different women, and each woman is allowed 3 tries to have an orgasm during the correct timeframe for being able to measure what's happening in the brain. 6 orgasms were ill-times and 2 did not have muscle activity that was distinct from the orgasm imitation, so those 8 were not used, leaving a total of 20 orgasms actually used for this study.
They physically verified orgasms with rectal pressure readings!
The beauty of this study is that the researchers didn't just take the participants' word for if and when an orgasm happened. Way too many lady-gasm researchers do that, and it severely lessens the usefulness of their data because there are so many reasons women may say they orgasm when they really did not physically orgasm - ranging from simply faking because they feel like they should be orgasming to not really understanding that 'orgasm' doesn't necessarily mean any old feeling of climax - which may lead a woman to say she orgasmed when she actually was experiencing something else like an emotional peak or a highly aroused state without orgasm. It'd be nice to say that a woman's say so is the best resource for whether she had an orgasm or not, but that's just not true - not in any way that works in a scientific study of the physical elements of orgasm. There's just too damn much confusion and misinformation permeating our culture about female orgasm that muddies women's understanding of their own sexual functioning.
Plus, frankly, this is science, and if a scientist is investigating what effect a particular event has on a body, they better be damn sure that the 'event' is happening before they see how the body reacts. That's just good scientific method, and not ensuring the event happened would muddy and confuse any results that came of it. It's like studying the body's reaction to a heart attack in people who say they've had a heart attack, but not verifying if they actually had heart attack and inadvertently mixing into the study people who had a panic attack but thought it was a heart attack. It's bad science, and it's really bullshit that lady-gasm scientists indulge in this regularly...so again, very pleased that these scientists did their scientific due diligence here.
Anyway, in this study the researchers verified orgasm by physically checking rectal pressure (basically the women had a small probe in their anus that was constantly measuring the pressure from the pelvic muscle). This way, they were able to observe the rhythmic pelvic muscular activity during the time the women claimed orgasm and could see if it was different than the muscular activity when the women were imitating orgasm (including imitation of the rhythmic pelvic muscle activity), becoming aroused, or resting.
What they found...very basically
In the end their research indicated that there were particular areas of the brain that became more or less activated during orgasm as compared to resting or to the controls of arousal by clitoral stimulation and of imitating orgasm. The prefrontal cortex and left temporal lobe showed large decreases in blood flow during orgasm that would indicate, from previous research, that inhibitions were lowered and sexual arousal was high. There were also increases found in the left deep cerebellar nuclei indicating, from previous research, that there was increased motion in the central body muscles such as the pelvic muscles. These results were comparable to brain activation during orgasm/ejaculation and arousal seen in previous studies on men.
My thoughts
I am no neuroscientist and cannot comment on the specifics of the statistical analysis and methodology details, but as with all of these studies, I go with the assumption that they are using their tools well. What I can and do comment on is the broader use of the scientific method to make the conclusions they make about female orgasm. So, it's not really a high bar I set for these studies. They just need to not over-reach and not ignore important fundamentals. Happily, this study easily reached above my bar for a solid lady-gasm study.
The only thing I would have liked to see is probably a bit beyond the scope of this study, but I'll mention it anyway. It seems that 2 of the 28 orgasms claimed by the women in this study happened at the correct time to record brain activity, but were dropped from the analysis because their rectal pressure readings (which indicate pelvic muscle activity) were indistinct from the controls - i.e. those 2 claims of orgasms cannot confidently be categorized as orgasms like the others because they didn't show rectal pressure readings that were distinct from the women's imitation of orgasm.
I completely agree with not including those 2 claimed orgasms in with the others for this study. They are possibly not physically the same things as the others. The researchers were absolutely on point with that. What would be cool, though, is if they also reported some data on those two sans-physical-marker-orgasms. A woman or two in this study did call whatever happened those 2 times an orgasm, and we know that sometimes women do claim orgasm when an orgasm cannot be physically detected. So lets start parsing out how to understand women's claims of orgasms vs. what's happening physically during the claimed orgasms. It'd be fantastic to get some details on that so scientists can begin having some data based answers for what women mean when they say orgasm.
For instance, I'd love if this study could answer a few things: Was it the same women that claimed both these orgasms or was it one orgasm a piece from two women? Were these sans-physical-marker-orgasms either of the women's 2nd or 3rd orgasm attempt? What exactly was their rectal pressure readings like compared to the control? Was the brain activity that happened during these 2 thrown-out orgasms more similar to imitation of orgasm, to arousal, to rest? Did it have any similarities to the readings during other women's orgasms who did have distinct rectal pressure readings? Did the women who claimed these sans-physical-marker-orgasms say anything about the experience that set it apart from the other orgasm experiences? We absolutely need to look at claims of orgasm with and without the distinct pelvic muscle activity separately, but we should be investigating both so we can clear some shit up.
But these are hopes and dreams for the future. Now on to the summary.
-------------------------------------
Introduction
The authors then go over different methods in the past that have been used to study the brain during orgasm:
"We aimed to investigate orgasm-related brain activity in healthy women. PET was used because it is more robust to motion artifact than fMRI."
Hypothesis for brain activity during female orgasm:
Materials and Method
Participants
[Me: quick background: To get these readings of brain activity measured through PET, a radiotracer has to be injected into the blood. After injection, reading of regional cerebral blood flow (rCBF) can be detected in the brain for a very short amount of time, and this increase or decrease of blood flow is the 'brain activity' they are looking at. This study detects for only 120 seconds after each injection.]
Scan 2: IMITATION: "voluntary repetitive contractions of the hip, buttock, abdominal and pelvic floor in a rhythmic 'orgasm-like' fashion, while receiving stimulation to the clitoris. This condition was included to control for the motor output during orgasm."
Scan 3: Another round of IMITATION
Scan 4: STIMULATION: "receiving clitoral stimulation without executing bodily movements. The subjects were encouraged to enjoy the stimulation, but were also explicitly instructed not to have an orgasm. This condition was included to control for the clitoral stimulation and high sexual arousal during orgasm."
Scan 5: Another round of STIMULATION
Scan 6: ORGASM: "orgasm induced by clitoral stimulation. The subject tried to reach orgasm in the first minute after tracer injection. After each orgasm attempt, volunteers reported whether they had reached orgasm and, if so, when they thought it had occurred relative to the moment of tracer injection."
Scan 7: Another round of ORGASM
Scan 8: Another round of ORGASM
Data analysis
RP (rectal pressure) and PSA (perceived sexual arousal)
The women's claims of orgasm were only used in the study if:
1. "according to the subject, orgasm was unambiguous and occurred in the first minute of the scan"
2. "the orgasm report was supported by the rectal pressure of the same scan"
3. "within a subject the rectal pressure pattern of a reported orgasm and that of an imitation were clearly distinct, because both involved contraction of the same muscles, but probably with different frequency characteristics." (they cited Bohen et al for this)
PET measurements
(The authors also describe a bunch of statistical analysis for how they do it, but that is too out of my realm to describe here.)
Results
Number of orgasms studied
"Six women reached one orgasm, four women reached two orgasms and two women reached three orgasms each. Six orgasms were ill-timed and two had an indistinct rectal pressure pattern. Therefore of the 28 orgasms reported, 20 were included in the analysis. There was a high intersubject variability with regard to the orgasmic rectal pressure patterns, but in multi orgasmic women, rectal pressure patterns looked consistent between orgasms. Figure 1 demonstrated that orgasmic rectal pressure patterns were clearly distinct from those during imitation."
PSA (perceived level of sexual arousal) results:
shown as: median rating (lowest rating, 3rd quartile rating)
REST: 0 (0,0)
IMITATION: 4 (3,5)
STIMULATION: 6 (6,7)
ORGASM: 9 (8.1, 10)
RPstd (rectal pressure variability) results:
shown as: median ratings (lowest rating, 3rd quartile rating)
REST: 0.31932 (0.14852, 0.55158)
IMITATION: 0.91827 (0.5398, 1.4363)
STIMULATION: 0.45855 (0.3753, 0.65063)
ORGASM: 1.811 (1.3366, 2.1299)
PET measurement results
"...changes in rCBF are called significant in the case of a corrected cluster P<0.05. Subsignificant rCBF changes (P>0.05 corrected) are called trends."
[me: So at this point the researchers write out in detail which parts of the brain show increases or decreases in rCBF between different experimental states (REST, IMITATION, STIMULATION ORGASM). There's a lot of information and a lot of brain words that are pretty foreign to me. So, I'm not going to summarize that here. Luckily the authors themselves kinda summarized it in pictures, so I'm just going to use those, because I think they are pretty simple depictions of pretty complicated results. As always, if you are truly interested in this detail, then you can probably get a hold of this article somewhere, and you should do that, and then please let me know if you have any thought. I'd love to hear them.]
Discussion
In relation to hypothesis
PSA (perceived sexual arousal)
rCBF changes during STIMULATION
"The importance of the clitoris for female sexual pleasure is undisputed. However, this is the first account of brain regions involved in the experience of clitoral stimulation."
The strongest rCBF increase for this study was in the left SII (secondary somatosensory cortex).
"Decreases of rCBF were not statistically significant." (during STIMULATION)
rCBF changes during ORGASM
"Despite liberal statistical thresholds, there was no orgasm-related increased rCBF in the hypothalamus, the brainstem or the striatum, regions known to be key players in the sexual and/or rewarding behaviours." [me: if you recall, the researchers had hypothesized that they would see increased activity int he hypothalamus, but did not]
There was a cluster of increase around the clitoral part of the SI (seen increased during STIMULATION as well), the cluster also included areas corresponding to abdominal, hip, leg and pelvic floor muscle control.
There was also a significant increase in areas of the cerebellum.
STIMULATION and IMITATION as control measures
Changes in dopamine related brain areas
Limitations and considerations
Why measure rectal pressure?
Although orgasm is known to induce a big blood pressure increase, the researchers are not worried that the increased blood flow in the cerebellum (the only area of significant rCBF increase in the brain during orgasm) was merely a result of heightened blood pressure. There is no worry largely because it happened also during the imitation of orgasm, and also because past literature showed activation in that area during voluntary motion of pelvic floor muscles.
Why wasn't hypothalamus activity seen?
The hypothalamus is known for its role in female reproduction, and during orgasm it might release oxytocin or prolactin, but it did not show any significant involvement in orgasm for this study. Here are reasons the researchers think this might be the case:
1. "synthesis of these hormones is unaltered and release requires no metabolic increase and hence no rCBF increase."
2. the PET scan may have not had the resolution to detect the activity
3. Komisaruk's 2004 study suggests that stimulation of the vagina and cervix may actually be better at activating the hypothalamus
4. "there was high intersubject variability in orgasmic RP (rectal pressure) patterns and although no objective proof exists for orgasmic typology (Mah & Binik 2001), these different RP patterns might still reflect a qualitative difference in the orgasmic experience."
Conclusion
"We conclude that the decreased rCBF in the prefrontal cortex and left temporal lobes is the main feature of orgasm in women. In particular, activation in the left lateral OFC seems to reflect the level of behavioural inhibition during sexual behaviour. The deactivation of the temporal lobe is directly related to the level of sexual arousal. As the regressive analyses revealed, the deep cerebellar nuclei appear to be involved in orgasm-specific muscle contractions while the ventral midbrain and right caudate nucleus suggest a role for dopamine in the orgasm. This novel finding might have important implications for the treatment of anorgasmia, a prevalent female sexual disorder which probably originates in the brain." [me: or originates in years of the clit not being touched properly, yet expecting orgasm anyway...Seriously, I know there are cases of anorgasmia that exist despite appropriate sexual touch, but I dare say there is also a portion that originate because we live in a world where women are expected to orgasm from a penis in their vagina and where the clit is all but ignored in most sexual education, sexual depictions, sexual advice/therapy, and sexual interactions.]
***Bonus fun fact: a short list of words I had to look up while writing this: axial, perfusion, salience, conversely, precluded***
What they did...very basically This lovely article investigates what parts of the brain are activated (by observing where blood flow is increased or decreased in the brain) during 1) non-sexual relaxation 2) imitation of orgasm 3) clitoral stimulation (performed by the male partner of the participant) and 4) orgasm. The study includes 12 different women, and each woman is allowed 3 tries to have an orgasm during the correct timeframe for being able to measure what's happening in the brain. 6 orgasms were ill-times and 2 did not have muscle activity that was distinct from the orgasm imitation, so those 8 were not used, leaving a total of 20 orgasms actually used for this study.
They physically verified orgasms with rectal pressure readings!
The beauty of this study is that the researchers didn't just take the participants' word for if and when an orgasm happened. Way too many lady-gasm researchers do that, and it severely lessens the usefulness of their data because there are so many reasons women may say they orgasm when they really did not physically orgasm - ranging from simply faking because they feel like they should be orgasming to not really understanding that 'orgasm' doesn't necessarily mean any old feeling of climax - which may lead a woman to say she orgasmed when she actually was experiencing something else like an emotional peak or a highly aroused state without orgasm. It'd be nice to say that a woman's say so is the best resource for whether she had an orgasm or not, but that's just not true - not in any way that works in a scientific study of the physical elements of orgasm. There's just too damn much confusion and misinformation permeating our culture about female orgasm that muddies women's understanding of their own sexual functioning.
Plus, frankly, this is science, and if a scientist is investigating what effect a particular event has on a body, they better be damn sure that the 'event' is happening before they see how the body reacts. That's just good scientific method, and not ensuring the event happened would muddy and confuse any results that came of it. It's like studying the body's reaction to a heart attack in people who say they've had a heart attack, but not verifying if they actually had heart attack and inadvertently mixing into the study people who had a panic attack but thought it was a heart attack. It's bad science, and it's really bullshit that lady-gasm scientists indulge in this regularly...so again, very pleased that these scientists did their scientific due diligence here.
Anyway, in this study the researchers verified orgasm by physically checking rectal pressure (basically the women had a small probe in their anus that was constantly measuring the pressure from the pelvic muscle). This way, they were able to observe the rhythmic pelvic muscular activity during the time the women claimed orgasm and could see if it was different than the muscular activity when the women were imitating orgasm (including imitation of the rhythmic pelvic muscle activity), becoming aroused, or resting.
What they found...very basically
In the end their research indicated that there were particular areas of the brain that became more or less activated during orgasm as compared to resting or to the controls of arousal by clitoral stimulation and of imitating orgasm. The prefrontal cortex and left temporal lobe showed large decreases in blood flow during orgasm that would indicate, from previous research, that inhibitions were lowered and sexual arousal was high. There were also increases found in the left deep cerebellar nuclei indicating, from previous research, that there was increased motion in the central body muscles such as the pelvic muscles. These results were comparable to brain activation during orgasm/ejaculation and arousal seen in previous studies on men.
My thoughts
I am no neuroscientist and cannot comment on the specifics of the statistical analysis and methodology details, but as with all of these studies, I go with the assumption that they are using their tools well. What I can and do comment on is the broader use of the scientific method to make the conclusions they make about female orgasm. So, it's not really a high bar I set for these studies. They just need to not over-reach and not ignore important fundamentals. Happily, this study easily reached above my bar for a solid lady-gasm study.
The only thing I would have liked to see is probably a bit beyond the scope of this study, but I'll mention it anyway. It seems that 2 of the 28 orgasms claimed by the women in this study happened at the correct time to record brain activity, but were dropped from the analysis because their rectal pressure readings (which indicate pelvic muscle activity) were indistinct from the controls - i.e. those 2 claims of orgasms cannot confidently be categorized as orgasms like the others because they didn't show rectal pressure readings that were distinct from the women's imitation of orgasm.
I completely agree with not including those 2 claimed orgasms in with the others for this study. They are possibly not physically the same things as the others. The researchers were absolutely on point with that. What would be cool, though, is if they also reported some data on those two sans-physical-marker-orgasms. A woman or two in this study did call whatever happened those 2 times an orgasm, and we know that sometimes women do claim orgasm when an orgasm cannot be physically detected. So lets start parsing out how to understand women's claims of orgasms vs. what's happening physically during the claimed orgasms. It'd be fantastic to get some details on that so scientists can begin having some data based answers for what women mean when they say orgasm.
For instance, I'd love if this study could answer a few things: Was it the same women that claimed both these orgasms or was it one orgasm a piece from two women? Were these sans-physical-marker-orgasms either of the women's 2nd or 3rd orgasm attempt? What exactly was their rectal pressure readings like compared to the control? Was the brain activity that happened during these 2 thrown-out orgasms more similar to imitation of orgasm, to arousal, to rest? Did it have any similarities to the readings during other women's orgasms who did have distinct rectal pressure readings? Did the women who claimed these sans-physical-marker-orgasms say anything about the experience that set it apart from the other orgasm experiences? We absolutely need to look at claims of orgasm with and without the distinct pelvic muscle activity separately, but we should be investigating both so we can clear some shit up.
But these are hopes and dreams for the future. Now on to the summary.
-------------------------------------
Introduction
- Male orgasms, being linked closely with ejaculation, are coupled with reproduction but there is no strong evidence female orgasm is linked to reproduction in this way...even though ideas for how it might be linked have been proposed.
- Most female orgasm research has focused on physiological parameters. It has been shown that heart rate, blood pressure, respiratory rate and even plasma concentrations of oxytocin and prolactin increase (They cite this Carmichael et al. study I summarized HERE and this Exton et al. one I have not HERE). Also, rectal and vaginal pressure change during orgasm likely due to the involuntary rhythmic contractions of pelvic muscles (They cite Masters and Johnson's Human Sexual Response and this study Bohlen et al. I summarized HERE.
- "Experiencing orgasm is a function of the brain and this is confirmed by clinical studies: brain trauma, epileptic seizures and psychopharmaca may strongly influence the orgasmic ability and/or experience (Lundberg & Brattberg, 1992; Aloni & Katz, 1999)."
- Citing Sholty et al, the authors say conscious action and concentration seems to be needed for women to reach orgasm but things like pleasure and loss of conscious behavioural control are things some women describe during an orgasm (cited from this Mah & Binik study I summarized HERE)
The authors then go over different methods in the past that have been used to study the brain during orgasm:
- EEG on men during ejaculation - no conclusive findings
- SPECT on men during ejaculation - "increased activation in the right prefrontal cortex and decreased activation in all other cortical regions." No deep or subcortical brain regions analyzed.
- PET - on men during ejaculation - "showed various activations during ejaculation, mainly in subcortical parts of the brain." This study was done by this team of researchers.
- "In women only one study exists:" which is the Komisaruk one I've summarized HERE where MRI brain activity was reported for women claiming orgasm during cervical self-stimulation. "Unfortunately, the statistical power of this study was low, which makes the activations, which were scattered throughout the brain in each of the three subjects, very difficult to interpret." So not a lot out there about brain function during female orgasm.
"We aimed to investigate orgasm-related brain activity in healthy women. PET was used because it is more robust to motion artifact than fMRI."
Hypothesis for brain activity during female orgasm:
- Decreased activation of neocortex
- Increased activation of subcortical parts of brain
- Expect "involvement of dopaminergic cell groups in the ventral midbrain and their targets in the striatum" (because orgasms have rewarding nature)
- Activation of the hypothalamus (because that's where prolactin and oxytocin are produced)
Materials and Method
Participants
- 12 women
- mean age 34 (range 21-47)
- volunteered with their male partners
- right handed
- healthy and no history or psychiatric or sexual disorders
- "Genital stimulation was provided by the male partners and was centered on the clitoris, because clitoral stimulation most easily leads to orgasm (Mah & Binik 2001; Lloyd, 2005). An adhesive band was used to restrain the subject's head. During scans the subject had her eyes closed. The couples were allowed to communicate verbally between successive scans."
- "Rectal pressure was measured continuously with a rectal probe ...The probe was positioned in the rectum by an experienced urologist."
- "...after each scan subjects were asked to rate their perceived level of sexual arousal on a 10-point scale (0, not sexually aroused; 10, highest level of sexual arousal ever experienced)."
[Me: quick background: To get these readings of brain activity measured through PET, a radiotracer has to be injected into the blood. After injection, reading of regional cerebral blood flow (rCBF) can be detected in the brain for a very short amount of time, and this increase or decrease of blood flow is the 'brain activity' they are looking at. This study detects for only 120 seconds after each injection.]
- The PET scans were made in 3-D mode
- Each scan was 120 total seconds and was preceded by injection of the radiotracer (32 mL injected at 8mL/s). The 120 seconds of scanning was broken down to 8 dynamic scans; the first 7 lasting 10 seconds each and the final scan lasting 50 seconds.
- Each participant had 8 of these scans consecutively with approximately 8 minutes in between the end of one scan and the injection of radio tracer for the next scan.
Scan 2: IMITATION: "voluntary repetitive contractions of the hip, buttock, abdominal and pelvic floor in a rhythmic 'orgasm-like' fashion, while receiving stimulation to the clitoris. This condition was included to control for the motor output during orgasm."
Scan 3: Another round of IMITATION
Scan 4: STIMULATION: "receiving clitoral stimulation without executing bodily movements. The subjects were encouraged to enjoy the stimulation, but were also explicitly instructed not to have an orgasm. This condition was included to control for the clitoral stimulation and high sexual arousal during orgasm."
Scan 5: Another round of STIMULATION
Scan 6: ORGASM: "orgasm induced by clitoral stimulation. The subject tried to reach orgasm in the first minute after tracer injection. After each orgasm attempt, volunteers reported whether they had reached orgasm and, if so, when they thought it had occurred relative to the moment of tracer injection."
Scan 7: Another round of ORGASM
Scan 8: Another round of ORGASM
Data analysis
RP (rectal pressure) and PSA (perceived sexual arousal)
The women's claims of orgasm were only used in the study if:
1. "according to the subject, orgasm was unambiguous and occurred in the first minute of the scan"
2. "the orgasm report was supported by the rectal pressure of the same scan"
3. "within a subject the rectal pressure pattern of a reported orgasm and that of an imitation were clearly distinct, because both involved contraction of the same muscles, but probably with different frequency characteristics." (they cited Bohen et al for this)
- Because past data has shown rectal pressure (RP) fluctuation to be an important feature of orgasm, the standard deviation in rectal pressure (RPstd) over the 1st minute of each woman's 8 scans were calculated and each woman's RPstd were normalized.
- Their ratings of perceived level of sexual arousal (PSA) were not normalized
PET measurements
- The researchers describe the software etc. used for the PET measurements in the brain - things like spacial pre-processing, global blood flow normalization, etc., but details weren't added to this summary.
(The authors also describe a bunch of statistical analysis for how they do it, but that is too out of my realm to describe here.)
- Main effect - this was investigating "which were the primary brain regions involved in any of the experimental conditions."
- Comparison between conditions: Compared rCBF (regional cerebral blood flow, or loosely, 'brain activity') between stimulation vs. rest and orgasm vs. rest. Then orgasm vs. stimulation (which helps control for sexual arousal since sexual arousal should be part of both the stimulation and orgasm) and orgasm vs. imitation (which helps control for motor output since pelvic movement and rectal/pelvic muscle contractions are part of both). For the last 2 comparisons, "A less stringent significance threshold (P<0.0001, uncorrected) was used in order to be more sensitive to smaller brain regions that may be involved in female orgasm, such as the hypothalamus and ventral midbrain."
- Regression analysis - the women's self-reported sexual arousal levels (PSA) were correlated with the rCBF in each area of the brain [me: the researchers mention there was only 8 women who provided the sexual arousal info instead of 12, but don't say why]. Also the RPstd (rectal pressure variability) was correlated with rCBF in the same way.
Results
Number of orgasms studied
"Six women reached one orgasm, four women reached two orgasms and two women reached three orgasms each. Six orgasms were ill-timed and two had an indistinct rectal pressure pattern. Therefore of the 28 orgasms reported, 20 were included in the analysis. There was a high intersubject variability with regard to the orgasmic rectal pressure patterns, but in multi orgasmic women, rectal pressure patterns looked consistent between orgasms. Figure 1 demonstrated that orgasmic rectal pressure patterns were clearly distinct from those during imitation."
 |
| from Georgiadis et al 2006 p.3307 |
PSA (perceived level of sexual arousal) results:
shown as: median rating (lowest rating, 3rd quartile rating)
REST: 0 (0,0)
IMITATION: 4 (3,5)
STIMULATION: 6 (6,7)
ORGASM: 9 (8.1, 10)
RPstd (rectal pressure variability) results:
shown as: median ratings (lowest rating, 3rd quartile rating)
REST: 0.31932 (0.14852, 0.55158)
IMITATION: 0.91827 (0.5398, 1.4363)
STIMULATION: 0.45855 (0.3753, 0.65063)
ORGASM: 1.811 (1.3366, 2.1299)
PET measurement results
"...changes in rCBF are called significant in the case of a corrected cluster P<0.05. Subsignificant rCBF changes (P>0.05 corrected) are called trends."
[me: So at this point the researchers write out in detail which parts of the brain show increases or decreases in rCBF between different experimental states (REST, IMITATION, STIMULATION ORGASM). There's a lot of information and a lot of brain words that are pretty foreign to me. So, I'm not going to summarize that here. Luckily the authors themselves kinda summarized it in pictures, so I'm just going to use those, because I think they are pretty simple depictions of pretty complicated results. As always, if you are truly interested in this detail, then you can probably get a hold of this article somewhere, and you should do that, and then please let me know if you have any thought. I'd love to hear them.]
 |
| from Georgiadis et al 2006 p.3310 |
 |
| from Georgiadis et al 2006 p.3310 |
Discussion
In relation to hypothesis
- The decreased rCBF in the neocortex during orgasm was observed and was consistent with the hypothesis.
- "Active limbic and subcortical involvement in female orgasm was less than anticipated"..."however, significant orgasm-related increased rCBF was found in the deep cerebellar nuclei."
- "the perceived level of sexual arousal was positively correlated with rCBF in the ventral midbrain and right caudate nucleus." [me: the caudate nucleus is linked to dopamine production, so the researchers did, with a little extra statistical oomph, find correlation between dopamine related brain areas and orgasm as they hypothesized]
- [me: the researchers did not find activity in the hypothalamus as expected, but they discuss why they might not have later in this paper.]
PSA (perceived sexual arousal)
- Orgasm was the condition where the women claimed the highest level of PSA
- PSA was much higher after stimulation than after imitation of orgasm, and actually most of the women later said that the act of intentional pelvic muscle contractions during imitation actually kinda prevented sexual arousal - even though they were getting clit stim during imitation. However, the women said the stimulation phase was quite enjoyable, and they often had to restrain themselves from coming during this phase.
- "Indeed PRstd was significantly greater during orgasm than during the other conditions, despite the fact that during imitation there were strong rhythmical contractions of muscles in the pelvic region."
rCBF changes during STIMULATION
"The importance of the clitoris for female sexual pleasure is undisputed. However, this is the first account of brain regions involved in the experience of clitoral stimulation."
The strongest rCBF increase for this study was in the left SII (secondary somatosensory cortex).
- In past studies rCBF increase in left and right SII has been associated with blood increase in the penis and increase in the right SII has been associated with stimulation of the erect penis.
- Increases in the SII is also consistently associated with visual erotica, and has been associated with non-sexual stimulation of the dorsal penile nerve, penile skin, and in women, the vaginal vestibulum.
- In fact, the SII increase in that past vaginal vestibulum study was stronger when the vestibular stimulation was perceived as painful. The researchers wonder if SII might assign a particular conscious label to stimulus - in the present study the sensation being 'sexual.'
- This result adds to the variety of results creating a controversy about the location of the external genitals on the SI.
- Originally and in some later studies the genitals were said to be located ion the paracentral lobule of the SI, but this study agrees with some others that place it dorsally on the SI.
"Decreases of rCBF were not statistically significant." (during STIMULATION)
rCBF changes during ORGASM
"Despite liberal statistical thresholds, there was no orgasm-related increased rCBF in the hypothalamus, the brainstem or the striatum, regions known to be key players in the sexual and/or rewarding behaviours." [me: if you recall, the researchers had hypothesized that they would see increased activity int he hypothalamus, but did not]
There was a cluster of increase around the clitoral part of the SI (seen increased during STIMULATION as well), the cluster also included areas corresponding to abdominal, hip, leg and pelvic floor muscle control.
There was also a significant increase in areas of the cerebellum.
- Activation of this area was also seen in a previous study by these authors during male ejaculation/orgasm.
- These areas are also known to be crucial for axial (central part of body) sensorimotor control and be associated tightly with the primary region of motor system (primary motor cortex).
- In previous studies, similar increases were found with voluntary contraction of the pelvic floor indicating these activations are probably related to control of the central body muscles.
- In previous studies similar decreases were found in men during sexual arousal and orgasm.
- There is also lots of clinical evidence (like cases where there is damage to these areas) that show less blood flow (similar to decreased rCBF) to these areas of the brain affecting orgasmic and sexual behaviour - particularly showing that these areas have inhibitory control over sexual behaviour.
- Thus, it seems lowered blood flow (decreased rCBF) to these areas "would release the inhibition and enable sexual behaviour."
STIMULATION and IMITATION as control measures
- Comparing "rest" in the brain to any "activity" in the brain can be problematic because you're not just seeing the "activity." You may also be seeing other things your brain needs to be involved in to do that "activity," like focusing on a goal or something like that. So, that's why the researchers added the states of "STIMULATION" and "IMITATION" into the study as controls for the activity "orgasm." "More specifically, stimulation served as a control for the genital stimulation and heightened sexual arousal during orgasm whereas imitation served as a control for the orgasm-related motor output."
- The large rCBF increase in the area of cerebellum related to central body (axial) motor function between STIMULATION vs. ORGASM was not there between IMITATION (motor output control) and ORGASM. "We therefore conclude the rCBF increases in deep cerebellar nuclei were related to axial motor output, regardless of the behavioural and emotional context."
- An interesting result was the particularly large decrease of rCBF in the OFC from STIMULATION to ORGASM (because it had actually increased from REST to STIMULATION even though it was also expected to decrease). If you remember, this area is known to be related to sexual inhibitions. So increase means more inhibited (less sexually aroused) and decrease means less inhibited (more sexually aroused). During ORGASM, it decreased a lot which made sense with previous studies indicating that type of decrease correlates with less inhibition and more sexual arousal. However, it was strange that there was actually an increase from REST to STIMULATION. That does not make sense given that the women said they were very aroused, and past data has shown genital stimulation and arousal decrease rCBF in that area. The authors think there is a simple explanation for this though: A previous study showed a similar increase in men watching erotica who "voluntarily suppressed emerging feelings of sexual arousal." These men intentionally were inhibiting their arousal. In the same way, most women in this study said (off the record) that during the STIMULATION portion, they often had to intentionally 'hold-back' from orgasming because they were specifically asked not to orgasm. These women's brains, like the men's in the previous study, may have been showing us the intentional inhibition.
- Although the decrease in rCBF was greatest between STIMULATION>ORGASM, it was also present when ORGASM was compared to REST and to IMITATION. So, no matter what, the decrease of rCBF in the OFC was a clear quality of ORGASM.
- "From these control comparisons a very interesting distinction emerged regarding the rCBF decrease during orgasm: rCBF decrease were predominately 'prefrontal' for the sexual arousal control comparison (orgasm <stimulation) and mainly 'temporal' for the output control comparison (orgasm<imitation). These control comparisons provide evidence that the temporal lobe deactivation is related to the level of sexual arousal, but that the prefrontal cortex deactivation causes the behavioural release that characterises orgasm."
- "RPstd reflects activity of the muscles in the rectal vicinity. RPstd correlated positively with rCBF in the left deep cerebellar nuclei, confirming the results from the t-contrasts that this region is related to axial motor output."
Changes in dopamine related brain areas
- After some small-volume corrections with the data, areas of the ventral midbrain and caudate nucleus showed increased rCBF in relation to increased perceived sexual arousal (PSA).
- The A10 dopaminergic cell group is located in the vental midbrain and plays a role in rewarding behaviours including; euphoric states induced by drugs of abuse, pleasurable music, and even eating chocolate.
- "In the present study PSA was highest during orgasm and because PSA correlated positively with rCBF in the ventral midbrain, this finding underlines the reinforcing nature of orgasm in women."
Limitations and considerations
Why measure rectal pressure?
- Because the reports of orgasm in this study are crucial to getting appropriate results, the researchers felt that the measuring of the rectal pressure helped in two ways.
- First, since the women knew it was being recorded, it may dissuade from them giving false reports.
- Second, of the reported orgasms, the researchers could check to see if the rectal pressure during the reported orgasm could be discerned from the imitation. It could in all but 2 of the reported orgasm, which were then thrown out.
- So, the researchers feel that, "the orgasms included in the present study are likely to be 'real'."
Although orgasm is known to induce a big blood pressure increase, the researchers are not worried that the increased blood flow in the cerebellum (the only area of significant rCBF increase in the brain during orgasm) was merely a result of heightened blood pressure. There is no worry largely because it happened also during the imitation of orgasm, and also because past literature showed activation in that area during voluntary motion of pelvic floor muscles.
Why wasn't hypothalamus activity seen?
The hypothalamus is known for its role in female reproduction, and during orgasm it might release oxytocin or prolactin, but it did not show any significant involvement in orgasm for this study. Here are reasons the researchers think this might be the case:
1. "synthesis of these hormones is unaltered and release requires no metabolic increase and hence no rCBF increase."
2. the PET scan may have not had the resolution to detect the activity
3. Komisaruk's 2004 study suggests that stimulation of the vagina and cervix may actually be better at activating the hypothalamus
4. "there was high intersubject variability in orgasmic RP (rectal pressure) patterns and although no objective proof exists for orgasmic typology (Mah & Binik 2001), these different RP patterns might still reflect a qualitative difference in the orgasmic experience."
Conclusion
"We conclude that the decreased rCBF in the prefrontal cortex and left temporal lobes is the main feature of orgasm in women. In particular, activation in the left lateral OFC seems to reflect the level of behavioural inhibition during sexual behaviour. The deactivation of the temporal lobe is directly related to the level of sexual arousal. As the regressive analyses revealed, the deep cerebellar nuclei appear to be involved in orgasm-specific muscle contractions while the ventral midbrain and right caudate nucleus suggest a role for dopamine in the orgasm. This novel finding might have important implications for the treatment of anorgasmia, a prevalent female sexual disorder which probably originates in the brain." [me: or originates in years of the clit not being touched properly, yet expecting orgasm anyway...Seriously, I know there are cases of anorgasmia that exist despite appropriate sexual touch, but I dare say there is also a portion that originate because we live in a world where women are expected to orgasm from a penis in their vagina and where the clit is all but ignored in most sexual education, sexual depictions, sexual advice/therapy, and sexual interactions.]
***Bonus fun fact: a short list of words I had to look up while writing this: axial, perfusion, salience, conversely, precluded***
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