MRIs of Stimulation to the clitoris, Cervix, and Vagina - A Journal Article I Read

Share

Tweet

Yes, another Journal Article I Read. This one is pretty simple, really.

Women's clitoris, vagina, and cervix mapped on the sensory cortex: fMRI evidence. Komisaruk BR1, Wise N, Frangos E, Liu WC, Allen K, Brody S. J Sex Med. 2011 Oct;8(10):2822-30. doi: 10.1111/j.1743-6109.2011.02388.x. Epub 2011 Jul 28.

"The aim of this study was to map the sensory cortical fields of the clitoris, vagina, cervix, and nipple toward an elucidation of the neural systems underlying sexual response." Basically, they used fMRI to investigate what parts of the brain received increased blood flow (which assumes neurons in that part of the brain are getting activated) when the cervix, vagina, clitoris, and nipples were being stimulated. All this in an effort to better understand sexual response.

The verdict? "As seen in the present findings, using fMRI, in which the women applied clitoral, vagina, or uterine cervical self-stimulation, there is clear evidence of activation in the medial region of the paracentral lobule, in the sensory genital region of the homuncular map of Penfield and Rasmussen. In addition, there is an occasional secondary activation in the dorsolateral paracentral loule, indicative of groin stimulation."


Background

• "The original map of the representation of the genitals in the sensory cortex in humans was generated by applying roving electrical stimulation to the brain in awake men, and asking the men from which part of the body the stimulation seemed to emanate" It was mapped to the medial cortex.
• The medial cortex was associated to the penis in a couple more studies, and it was assumed, given some indirect evidence, that this is the same area that would be associated to the clitoris
• However, more recent PET and fMRI studies associated the penis to "a more dorsolateral portion of the paracentral lobule rather than its medial region." The studies include one in which the researcher stimulated the penis with a toothbrush while recording fMRI, one in which the subjects partner manually stimulated the penis while recording PET, and one in response to electrical stimulation of the penis.
• This discrepancy about where penis stimulation is associated in the brain (more dorsolateral or more medial) is not fully understood or rectified.
• Recently PET and MRI studies associated the clitoris to the dorsolateral rather than the medial region of the paracentral lobule - matching the more modern penis studies. The studies include one in which the subjects partner manually stimulated the clitoris while recording PET, and one using fMRI recordings are taken in response to electrical stimulation of the clitoris.
• To the researcher's knowledge, an investigation of where stimulation of the vagina and cervix projects onto the human brain has not been done until now.

The Experiment

• 11 women were recruited by word-of mouth. They were healthy, right-handed, 23-56 years old, and not pregnant. They were also pre-screened with the Symptoms Checklist-90-R questionnaire to "rule out any psychological contraindications."
• Their heads were stabilize with individually fitted frames to limit head motion while fMRI was being recorded.
• The trials for each body part were 5 minutes long with 5 repeated sequences of 30 seconds of rest followed by 30 seconds of stimulation. The subjects wore headphones through which the researchers would give them instructions.

The Stimulation

• "Control trials consisted of an experimenter rhythmically tapping a participant's thumb or toe in separate trials to establish reference points on the sensory cortex."
• "Experimental mapping trials consisted of participants self-stimulating, by hand or personal device, using 'comfortable' intensity, the clitoris, anterior wall of the vagina, the cervix, or the nipple in separate, randomized-sequence trials."
• "Clitoral self-stimulation was applied using rhythmic tapping with the right hand."
• "Vaginal self-stimulation (of the anterior wall) was applied using the participants own stimulator (typically a 15 mm-diameter S-shaped acrylic rounded-top cylinder)."
• "Cervical self-stimulation was applied using a similar diameter, glass or acrylic straight, rounded-tip cylinder brought to the study by each participant."
• "Nipple self-stimulation was applied using the right hand to tap the left nipple rhythmically."

The fMRI

• During each 5-minute sensory session, 150 image sets of 32 slices per Repetition Time were obtained. (If you want more details about the fMRI situation, put it in the comments, and I'll update).
• "Group maps" were created for each anatomical trial. It doesn't say specifically what that means, but I am assuming from context that this is a combination of all 11 women's MRI recordings per each trial...so, all the clitoral stimulation tests for all 11 women were combined, and so on. (If you know this to be incorrect, let me know).
• A software program called MRIcro was used "for visualization of group maps on a standardized anatomical template."

Results

• In Figure 2 below, the arrows "indicate sensory cortical brain regions activated by the specific stimuli."
• Not all the "lighting up" going on in the pictures below is related to the part of the body being specifically investigated. Since the vagina, clit, and cervix are all self-stimulated, you are also seeing areas of the brain involved in hand-movement.

• "Note the absence of hand movement in the case of experimenter-applied thumb stimulation."
• Although the participants only used their right hands to apply self-stimulation, the areas in the brain for both hands were activated - which surprised the researchers. Although they later point out that there is substantial evidence in the literature for "bilateral sensory cortical response to unilateral hand stimulation."
• In the case of the investigator-applied toe stimulation, hand areas in the participants brains were also activated - which also surprised the researchers. They later guess that this maybe has something to do with a "stumble" response in which the hands subtly twitch in response to foot stimulation so that the hands are ready to catch a person when the feet falter, but it's only a speculation.
• Cervical, Vaginal, and Clitoral activation sites, "are all in the medial paracentral lobule, but are regionally differentiated." The researchers hypothesize that the different brain areas affected by clitoris, vagina, cervix could be due to the different nerves that serve each of those anatomical structures.
• There is some overlap between the parts of the brain activated during vaginal and cervical stimulation. The researchers think this must be due at least in part to the stretching of the vagina that happens when the dildo is inserted for both cervical and vaginal stimulation.
• "Nipple self-stimulation not only, as expected, activated the thoracic (rib) region...but also, unexpectedly, the genital sensory cortex, i.e., the genital (medial) region of the paracentral lobule."
• Nipple self-stimulation and vaginal self-stimulation each activated both the genital area and  activated the rib area. The authors wonder if this has to do with fact that both types of stimulation release oxytocin and the connection between nipple stimulation and uterine contractions that nursing mothers would certainly recognize.

• So in relation to the discrepancy between earlier studies (and this study) indicating penis/clit projecting to the medial and later studies showing the projection in the dorsolateral paracentral lobule, the authors posit the following. "...based on the present findings, the discrepancy in the literature may be due to the responses to indirect stimulation of the perinial (groin) region rather than to adequate stimulation of the genital per se."
• "Under the conditions of the present study, it is not possible to discern whether the overlap among regions of the sensory cortex activated in response to self-stimulation of each of these three genital regions is due to true overlap of the brain regions that would be activated by 'pure' stimulation of each of these three genital regions separately, or whether the overlap is due to incidental stimulation of one genital region (e.g., vagina) during self-stimulation of a different genital region (e.g., cervix). What is clear, however, is that the sensory cortical regions activated by each of these three genital regions are to some extent separable and distinct."
• "The cerebellum activation observed in the present study during vaginal and cervical self-stimulation is a common observation during genital stimulation, especially during orgasm. It is likely this is involved in controlling muscle tension during genital stimulation."

Concluding Statements

• * "The present findings provide evidence that, rather than vaginal stimulation being just an indirect means of stimulating the clitoris [18,25], vaginal and cervical stimulation per se activate specific sensory cortical regions that are distinct from the clitoral sensory projection." *
• "While the present study mapped the primary sensory field of genital input to the sensory cortex, it would be of interest in future studies to extend this analysis to brain fields beyond the sensory cortex that are activated when genital stimulation is perceived as "erotic" vs. when it is perceived as "just pressure."

My Thoughts
There's not too much to say about this one. It is certainly a worthwhile study that added to the scientific discussion on where genital sensation is projected in the sensory cortex, and could be useful to reference in further investigation.

I do wonder why self-stimulation was chosen in this particular study. It adds the extra variable of intentional body movement into the brain activity. Also, the self-stimulation for the vagina and cervix (moving a dildo inside the vagina) seems to me to be much more complicated than the self-stimulation involved with the clitoral and nipple self-stimulation (simply tapping). So, I wonder if the more complicated holding and moving actions involved with the dildos affected the ability to compare cervix and vagina results with the nipple and clit stimulation results. I also wonder if there was any discrepancy among the 11 women about where the different stimulations were projected. I honestly don't know anything about how the fMRIs are combined, but I know the authors didn't discuss any discrepancies that might affect the study's outcome, so I assume all 11 women were quite similar. Just a thought, but overall I don't have complaints about the experimental design.

Extra things that I just want to talk about....
I think that the authors of this study (with the statement starred * above) are specifically weighing in on an argument that relates to female orgasm. Although female orgasm was not specifically mentioned in the statement, I believe, based on the works they cite in that statement, they are pointing out that their work here is contrary to 2 different hypotheses about how orgasm can happen during intercourse with no extra manual clitoral stimulation.

The 1st way was proposed (and observed) by Masters and Johnson. The say that the clitoral glans can be indirectly stimulated through vulva movement during intercourse that pulls the clitoral hood and gently stimulates the clitoral glans so that a weak orgasm may occur.

The second is what I would say is one of the most pop hypotheses for understanding how a vaginally activated orgasm might work. This hypothesis goes something like this: 'All orgasms are clitoral, actually. What we call vaginal orgasms are really just clitoral orgasms caused by stimulation of the inner clitoral legs through the vagina.'

Another opposing (and I'd say a bit less currently popular among sexperts) view on how a vaginal orgasm might occur is that there is some aspect of the vagina or cervix themselves that cause an orgasm to happen when stimulated. This less pop one is the one these authors seem to throw their weight towards. Their reasoning is that if cervical or vaginal stimulation is projected to a different part of the brain than the clit stimulation, then vaginal orgasms are likely caused by something specific about stimulation of the vagina, not just indirect stimulation of the clitoris. I must point out, though, that no orgasm from stimulation inside the vagina has ever been observed anyway - be it through the inner clitoral legs or through something specific about the vagina itself, so speculating about what might cause this thing that might not exist is maybe not so useful.

Okay - one final thing about a possible Freud obsession
At the end of the discussion - directly after the starred statement we just discussed, the authors write this:

"The differential routes of entry into the brain are undoubtedly of significance in activating the diverse and differential consequences of clitoral, vaginal or cervical stimulation; they include differential physiological effects (e.g., on prolactin secretion [26], analgesia [27], and blood pressure reactivity to stress [28]) and differential behavioral effects (e.g., on orgasm [29], sexual satisfaction [30], and intimate relationship quality [31.32]).

I bring this passage up because, if I may be blunt, it seems like it has an agenda.The authors concluded that stimulation of the clitoris, vagina and cervix activate different areas of the sensory cortex and are trying to point out that this finding is in line with the idea that stimulation of the vagina, the cervix, and the clitoris each have different effects on women. It's not the craziest speculation to make, I guess. However what bothers me is that most of these citations are from the study's 6th author, Stuart Brody, who if I may be blunt again, seems to definitely have an agenda. He's a little obsessed with proving that Freud was not just making shit up about lady-gasms, and that penis-in-vagina sex and vaginally stimulated orgasms (which, let's review, haven't actually been observed in scientific literature) are basically the bestest, most healthy things a woman could ever have.

I've linked all the citations and you can see the titles, authors and sometimes a smart ass description from me below. Feel free to judge for yourself, but I thought this passage seemed at best to be a tagged on way to get more of their own previous work into the citations (which I heard recently is pretty important for researchers - and that sometimes citations get added into papers a little shadily) or at worst an indication that the rest of these authors also have a bit of an obsession or at least a professional stake in preserving a Freudian idea of vaginal orgasm.

You might also be interested in some of Brody's other studies not listed below: A Woman's History of Vaginal Orgasm is Discernible from Her Walk (2008) because, obviously, right? and Vaginal Orgasm Is Associated with Less Use of Immature Psychological Defense Mechanisms (2008) - He wanted to test Freud's theory that women who couldn't orgasm vaginally were immature....and guess what? He found that they were. That ol' dog Freud was right!

 [26] The post-orgasmic prolactin increase following intercourse is greater than following masturbation and suggests greater satiety. Brody S1, Krüger TH. 

[27] Analgesia produced in women by genital self-stimulation. Whipple B1, Komisaruk BR.

[28] Blood pressure reactivity to stress is better for people who recently had penile-vaginal intercourse than for people who had other or no sexual activity. Brody S1.

[29] Sexual response in women Winnifred B. Cutler, PhDa, Millicent Zackera (DO), Norma McCoy, PhDa, Elizabeth Genovese-Stone, MDa, Erika Friedman, PhDa - the only article here not written by one of these authors.

[30] Sexual behavior predictors of satisfaction in a Chinese sample. Tao P1, Brody S.  - Guess what? Satisfaction was associated with P-in-V sex and vaginal orgasm for the ladies!

[31] Women's relationship quality is associated with specifically penile-vaginal intercourse orgasm and frequency. Costa RM1, Brody S. - I think you get the gist.

[32] The Relative Health Benefits of Different Sexual Activities Stuart Brody PhD - A little surprise ending.... P-in-V sex? Associated with better mental AND physical health! All them other ways to do it? Don't have nothin' to do with health...OR associated with worse mental and physical health (I'd stay away from anal sex and masturbation, ya'll).