Where Does Touch To the Clit Activate In The Brain - A Journal Article I Read

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Welcome back to 'A Journal Article I Read,' a series where I summarize a lady-gasm related journal article in a way that is hopefully both comprehensive and also not too long. You can find a list of all the journal articles in this series HERE.

Here is what I'll be summarizing today.

The Somatosensory Representation of the Human Clitoris: An fMRI Study 
LarsMichels, UlrichMehnert, SönkeBoy, BrigitteSchurch, SpyrosKollias
NeuroImage 2010 Jan. Vol.49 Issue 1, p.177-184

And lucky you, you can find this full article HERE, so if you're into fMRIs and know some shit about that stuff, you can get the full details there.

Quick Summary
The researchers here are trying to identify where in the brain clitoral stimulation activates. There was a famous study done about 80 years ago that identified where stimulation of different body parts activated the brain. It had a place for the genitals, but there's been a lot of disagreement on that since.  Some more recent studies have used fMRI to identify a different area of the brain related to penis stimulation than that original study, and this study hypothesized the clitoral stimulation would activate a similar area using fMRI. They tested 15 women by putting electrodes on either side of the clit and giving them a gentle electrical pulse while in an fMRI machine that takes particular types of pictures of the brain. For 8 of these women, they also did the same thing, but this time the electrode is on their right big toe (which they refer to as the hallux). They use this as a type of control because in that original old study, foot/toe area was said to activate the brain very near where the genitals were said to. However, these researchers did in fact find that stimulation of the clitoris activated a similar area to where the more modern fMRI study showed activation from penis stimulation. It was also different from the area of activation from the toe stimulation, even though the original study showed the toe and the genitals quite close.

**I will from now on just be summarizing to the best of my ability, what is actually said in the article. If I want to give you my opinion, I'll clearly mark it with a heading or in a [Me:...] parenthesis. Things in quotes are actual quotes from this article.**

Introduction
My quick description of this old study they reference a lot
Okay, so this old study, by Penfield and Boldray from the scientific journal Brain in 1937 which I will refer to from now on as P&B 1937, was about mapping the somatosensory system on the brain. They did the mapping by using electrical stimulation on the brains of people undergoing open brain surgery for control of epilepsy, and continued doing the research for years after. My understanding is that they stimulated areas and asked the awake patients where they felt the stimulation in their body. Through this, they created an incredibly famous and much used depiction of the human body on the brain (the somatosensory homunculus which you can check out below). The size of the body part represents the density of the receptors in the brain for that body part and not necessarily the size of the brain area where the receptors are. Also notice that the genitals are right next to the toes.

homunculus picture from EBN Consult (which is a cool site to get free core medical education information)

Okay, now the actual study intro

• P&B 1937 has been "virtually a standard reference for various somatotopical studies" for the last 70 years.
• P&B 1937 "relied on reported sensation of different body parts after electrical stimulation of the cortex. Assessment of the exact location was generally difficult and sometimes led to conflicting results."
• "The genital region was especially hard to assess due to difficulties with sense of shame." The location of genital sensation has been subject to lots of discussion and conflicting results over the years. Penile representation has been reported from some studies in the mesial wall as expected from the P&B 1937 and in other studies in the lateral surface of the postcentral gyrus using fMRI.
• Though it's fair to assume the clit would be represented in the brain in the same area as the penis given that they are anatomically homologous, little has actually been studied of it. A 1991 study showed the penis represented in the inter-hemispheric fissure, "though they were not able to distinguish it's location from that of the posterior tibial nerve," which these researchers say makes sense because of the low spacial resolution of the type of testing done in this study. There was also a 2006 study (that I summarized HERE) about brain activation during orgasm caused by manual clitoral stimulation that howed the activation area in a somewhat different area.
• Based on recent studies of penile sensation, the researchers hypothesize they will find clitoral stimulation on the lateral surface of the postcentral gyrus (not the mesial wall as predicted by P&B 1937).
• The researchers also believe this is an important line of study because electrical dorsal genital nerve (i.e. dorsal clitoral nerve) stimulation emerged as a promising therapeutic approach for improving neurgenic and non-neurogenic lower urinary tract dysfunction such as sphincter weakness or overactive bladder." [Me: I can't help but imagine that the researchers had to throw in this link to medical relevance for research grant purposes, because, I think, getting money and permission to do research simply for research sake - especially related to sex or genitals, is not a smart or easy bet.]

Materials and Methods

• 15 right-handed subjects (22-34 years old) were tested. Subjects were not pregnant and had no medical, mental, surgical, or drug-related issues that might interfere with the test.
• To ensure privacy, a trained female assistant attached the electrodes to either side of the clitoral glans "so that they were able to stimulate the fibers of the dorsal clitoral nerve," behind a curtain and then the subject wore pants over it and a blanket. They were also alone in the room when the test was taking place, and their names and data were kept anonymous. [Me: I assume they were careful about privacy because they felt a problem with older studies was related to shame over genital sensation. Also note this study happened in Zurich and the truth is orgasm and clit studies almost always happen not in the USA]
• Before the experiment electrical tests were performed to make sure the subject could feel the stimulation directly on their clitoris. The strength of the electrical stimulation was also set specifically for each subject so that it neither was painful nor elicited sexual arousal [Me: But, I mean, it's on the clit, it'd be hard to not feel a little sexual, right????] 
• fMRI images were created using a Phillips Achieva 3.0 MT R Scanner. It lists out the settings, and if you are interested in them, then please do checkk out the full article linked up top.
• The scan began for each subject with 18 seconds of rest then 12 seconds of electrical stimulation. This altering between rest and stimulation happened 10 times, for a total scan of 5 minutes for each subject.
• For 8 of the subjects, a 2nd experiment was also preformed in which the same type of electrodes were put on the right toe instead of the clit. The rest/stimulation altering and scanning were set up the same.
• The researchers also assessed the discomfort and the sexual arousal caused by the electrodes by asking the subjects to use a Visual Analog Scale. [Me: The scale for pain you often see in hospitals is a Visual Analog Scale - see below]. "the scale ranged form -10 (e.g. unbearable pain) to 10 (e.g. pleasure). For sexual arousal, the scale ranged form -10 (strong sexual arousal) to 10 (no arousal at all/sleepiness).
• 2 subjects had too much head movement to use the data, so their data was thrown out of the study, leaving 13 subjects in the final results.
• There's information about the software used and how the images were aligned, etc. Again, if you're interested and know about that, check out the link to the full article up top.
• [Me: Again - a lot of information about how the resulting data was complied and analyzed. I do not have the expertise to relay any information about this to you except copy what was written, so I'll just give the big-picture stuff that I basically understand.] The images during rest were compared to images during clitoral stimulation, and for the 8 subjects who also took part in the experiment with the big toe stimulation test - the images during rest were compared to images during stimulation of the big toe.
• Potential affects of the co-variates (sexual arousal or discomfort) on the brain were assessed statistically as well - in order to see if that may affect activation areas in the brain.

a type of Visual Analog Scale (VAS)

Results

• The median Visual Analog Score (VAS) for sexual arousal was 0 (which is right in the middle of strong sexual arousal at -10 and none at all at 10). The median VAS score for discomfort was -2 (which is a bit closer to unbearable pain at -10 than the rating of pleasure at 10).
• "Electrical clitoral stimulation produced significant activations predominantly in bilaterally prefrontal areas..., the precentral, parietal and postcentral gyri...In addition distributed activations were also seen in the anterior and posterior parts of the insula and the putamen. This activation pattern was seen in most of the single subjects and therefore also on the group activation map."
• "Most importantly, we found no activation on the mesial surface of S1 on either side even when using unconventionally low thresholds. [Me: So didn't find what P&B 1937 found].
• [Me: There are then 2 paragraphs about specific coordinates of activation for both clitoral stimulation and toe stimulation. It's too complicated and technical for me to understand or summarize. That's the truth.]

Discussion

• The P&B 1937 study placement of genital activation in the brain has been more or less unchallenged for over 70 years, and lots of theories have arisen about why it is as it is. For instance, there is an idea that the feet and the genitals as well as the hands and the face are represented in the brain so close together because during development in the womb, the fetus' feet are tucked up near the genitals and the hands are up near the face. Only in recent fMRI studies have the penis representation been shown in another location.
• The researchers used electrical rather than air pressure or touch-with-brush stimulation for a variety of reasons including that it's easily attachable to the clit and it's easier to adjust the stimulation.
• The researchers found stronger activation in the left somatosensory cortex for the clit stimulation, which they found odd because the clit was being stimulated from both sides. They suggest this could indicate a left-hemispheric dominance of clitoral representation in the brain, although they admit they have no convincing explanation for that.
• They found no evidence for clitoral representation on the Mesial wall like the P&B 1937 study suggested.
• The representation of the big toe was along the mesial wall and thus different from the clitoral representation.
• There is overlapping activity in the operculum (O1-O4) regions, which has also been found in other studies. The researchers do not believe this is a result of discomfort or surprise related to the electrical stimulation, but to the stimulus itself

Conclusion

"In contrast to previous studies using SEPs that were not able to clearly discriminate the location of cortical sensory representation of the genitals in humans, we found a significant activation on the convexity of the postcentral and inferior parietal cortex (S1 and S2) for electrical clitoral stimulation. These findings support the assumption that the S1 representation of the clitoral afferents may be different from the somatosensory homunculus introduced decades ago. The distinct activation locations for the central representation of the clitoris and the hallux indicated that fMRI and electrical stimulation can be used to study the specific organization of small body areas and their somatosensory representation in humans. Apart from its scientific interest, the precise location of the genitalia in humans may have important implications for studying cortical reorganization patterns in various urogenital, sexual and neurological disease processes."