Monday, May 08, 2006

Sweat, Urine, and Sexual Orientation

Sexual Orientation May Affect Brain Response to Human Pheromones

May 8, 2006 -- Lesbian women and heterosexual women respond differently to the scent of human pheromones, a new study shows.

. . .

The researchers studied brain scans of lesbian women, heterosexual women, and heterosexual men while those people smelled scents including two potential human pheromones.

Brain scans taken while smelling those pheromones were more similar for lesbian women and heterosexual men than for lesbian women and heterosexual women, the researchers report. Their study appears in the online early edition of Proceedings of the National Academy of Sciences. [Not yet, check back tomorrow.]

Last year, Savic's team published a study showing that homosexual men and heterosexual women had similar brain activity patterns when smelling those same human pheromone candidates. [See below.]

Brain response to putative pheromones in homosexual men
Ivanka Savic, Hans Berglund, and Per Lindström
PNAS | May 17, 2005 | vol. 102 | no. 20 | 7356-7361

The testosterone derivative 4,16-androstadien-3-one (AND) and the estrogen-like steroid estra-1,3,5(10),16-tetraen-3-ol (EST) are candidate compounds for human pheromones. AND is detected primarily in male sweat, whereas EST has been found in female urine. In a previous positron emission tomography study, we found that smelling AND and EST activated regions covering sexually dimorphic nuclei of the anterior hypothalamus, and that this activation was differentiated with respect to sex and compound. In the present study, the pattern of activation induced by AND and EST was compared among homosexual men, heterosexual men, and heterosexual women. In contrast to heterosexual men, and in congruence with heterosexual women, homosexual men displayed hypothalamic activation in response to AND. Maximal activation was observed in the medial preoptic area/anterior hypothalamus, which, according to animal studies, is highly involved in sexual behavior. As opposed to putative pheromones, common odors were processed similarly in all three groups of subjects and engaged only the olfactory brain (amygdala, piriform, orbitofrontal, and insular cortex). These findings show that our brain reacts differently to the two putative pheromones compared with common odors, and suggest a link between sexual orientation and hypothalamic neuronal processes.
. . .

Savic's latest study included 12 heterosexual men, 12 lesbian women, and 12 heterosexual women. All were healthy and not taking medication.

The lesbian women had normal hormonal levels. Regardless of sexual orientation, the women were studied at the same point in their menstrual cycle.

Participants were given glass bottles containing scents including AND, EST, lavender oil, or cedar oil. Each bottle only contained one scent.

Meanwhile, the researchers scanned participants' brains with magnetic resonance imaging (MRI) and positron emission tomography (PET) technology. Afterward, participants rated the scents for pleasantness, irritability, intensity, and familiarity.

Lesbian and heterosexual women showed different patterns of brain activity while sniffing AND and EST, the study shows.

While smelling AND and EST, the brain activity pattern for lesbian women was closer to that of heterosexual men than heterosexual women, Savic and colleagues note.

However, the previously reported similarities between brain activity for heterosexual women and homosexual men while sniffing the pheromones were stronger than those between lesbian women and heterosexual men.

The pheromones didn't necessarily have a sexy smell. "None of our subjects reported sexual arousal" while whiffing any of the scents, the researchers write.

[with a "straight" face, I presume??]

See also:

Lesbians Respond Differently to "Human Pheromones"

Lesbians' Brains React Differently
. . .

Heterosexual women found the male and female pheromones about equally pleasant, while straight men and lesbians liked the female pheromone more than the male one. Men and lesbians also found the male hormone more irritating than the female one, while straight women were more likely to be irritated by the female hormone than the male one.

All three groups rated the male hormone more familiar than the female one. Straight women found both hormones about equal in intensity, while lesbians and straight men found the male hormone more intense than the female one.

The brains of all three groups were scanned when sniffing male and female hormones and a set of four ordinary odors. Ordinary odors were processed in the brain circuits associated with smell in all the volunteers.

In heterosexual males the male hormone was processed in the scent area but the female hormone was processed in the hypothalamus, which is related to sexual stimulation. In straight women the sexual area of the brain responded to the male hormone while the female hormone was perceived by the scent area.

In lesbians, both male and female hormones were processed the same, in the basic odor processing circuits, Savic and her team reported.
While we're at it:
Sex-specific influences of vasopressin on human social communication
R. R. Thompson, K. George, J.C. Walton, S.P. Orr, and J. Benson
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0600406103

Published online before print May 8, 2006

Arginine vasopressin (AVP) and related peptides affect social behaviors in numerous species, but AVP influences on human social functions have not yet been established. Here, we describe how intranasal AVP administration differentially affects social communication in men and women, and we propose a mechanism through which it may exert those influences. In men, AVP stimulates agonistic facial motor patterns in response to the faces of unfamiliar men and decreases perceptions of the friendliness of those faces. In contrast, in women, AVP stimulates affiliative facial motor patterns in response to the faces of unfamiliar women and increases perceptions of the friendliness of those faces. AVP also affected autonomic responsiveness to threatening faces and increased anxiety, which may underlie both communication patterns by promoting different social strategies in stressful contexts in men and women.

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At May 17, 2006 7:27 PM, Blogger Dan Dright said...

I have a few questions:

1. Although mammals have a specific vomeronasal organ (fed by the palatine nasal duct, I think) nobody has ever been able to find one in humans.

2. Where is the imaging data to show what happens in hetero/homo male and female brains during arousal generally? Is this at all related to "sex" per se, or just to differing levels of hormones in people of different sexual orientations?

3. I guess it seems to me that the sexual orientation of the participants is being conflated with the meaning of the imaging data.

Nice post. Keep up the good work.

PS: I put a link to your fabulous blog up after a spell of bloggy inactivity caused by finals and papers.

At May 17, 2006 7:30 PM, Blogger Dan Dright said...

By the way, I think Peter Brunjes, (one of my profs at UVA. Brilliant. Does olfaction and he's funny as hell, too), would like these posts. I will send him over if I can get in touch with him.

At May 18, 2006 6:58 PM, Blogger The Neurocritic said...

Thanks, Dan. Too bad that things like finals and papers (and grant progress reports and manuscript submissions) keep us from blogging! I'm behind on my posts this week, but I'll get to your interesting questions soon.

At May 22, 2006 4:47 PM, Blogger The Neurocritic said...

Here are some musings on Dan's questions:

(1) Oooh, the human VNO... I don't know anything about that. I defer to this review article:

Michael Meredith
Human Vomeronasal Organ Function: A Critical Review of Best and Worst Cases
Chem. Senses 26: 433-445, 2001

The human vomeronasal organ (VNO) has been the subject of some interest in the scientific literature and of considerable speculation in the popular science literature. A function for the human VNO has been both dismissed with ridicule and averred with conviction. This question of VNO function has been needlessly tied to the separate question of whether there is any place for pheromone communication among humans, a topic that is itself bogged down in conflicting definitions. This review is an attempt to weigh the evidence for and against human VNO function, to deconvolve that question from the question of pheromone communication and finally to provide a working definition of ‘pheromone’. Further experimental work is required to resolve the conflicting evidence for and against human VNO function but chemical communication does appear to occur among humans. However, several examples reported in the literature do not meet the proposed definition for communication by pheromones: ‘chemical substances released by one member of a species as communication with another member, to their mutual benefit’.

(2a) Imaging data to show what happens in hetero/homo male and female brains during arousal: it's not out there. The Neurocritic found 3 papers that directly compared brain activity in heterosexual men and heterosexual women viewing porn clips. In one of these, men showed greater activation in the amygdala and hypothalamus, even when women reported greater arousal [Hamann S, Herman RA, Nolan CL, Wallen K (2004) Men and women differ in amygdala response to visual sexual stimuli. Nature Neurosci 7:411–416]. Another paper reported greater hypothalamic activation in men than women [Karama S, Lecours AR, Leroux JM, Bourgouin P, Beaudoin G, Joubert S, Beauregard M. (2002). Areas of brain activation in males and females during viewing of erotic film excerpts. Hum Brain Mapp. 16:1-13], but a more recent experiment by the same group did not find a difference between men and women in the hypothalamus [Gizewski ER, Krause E, Karama S, Baars A, Senf W, Forsting M. There are differences in cerebral activation between females in distinct menstrual phases during viewing of erotic stimuli: a fMRI study. Exp Brain Res. 2006 Apr 8].

Gizewski et al. say, "According to common sense women should have greater sexual arousal during the mid-luteal phase but contradictory results in the literature are reported (Karama et al. 2002). Due to hormonal influences on sexual arousal, we assumed differences in brain activation during the emotional task of viewing erotic film excerpts. Therefore, in the present study, only women in midluteal phase were entered into the experimental group
and were measured again during menstrual phase vice versa respectively according to randomization. We revealed superior activation for women in mid-luteal phase in the anterior cingulate, the left insula, and left orbitofrontal cortex compared to women in menstrual phase." [NOTE: but no difference in hypothalamus]


"This study cannot clarify the relationship between hormonal influences on the one hand and sexual arousal and patterns of brain activation on the other, as interactions between social and hormonal influences have to be considered (Breedlove et al. 1999)."

At May 22, 2006 11:35 PM, Blogger The Neurocritic said...

More musings:

(2B) ...differing levels of hormones in people of different sexual orientations?

There's a lot more on that topic; many of the recent studies use the relative lengths of the 2nd and 4th fingers as a proxy for prenatal testosterone levels:

McFadden D, Loehlin JC, Breedlove SM, Lippa RA, Manning JT, Rahman Q. (2005). A reanalysis of five studies on sexual orientation and the relative length of the 2nd and 4th fingers (the 2D:4D ratio). Arch Sex Behav. 34:341-56.

How this may (or may not) relate to adult hormone levels doesn't seem to be on the agenda (or at least it wasn't discussed in the review article).

Savic et al. state in the PNAS article that hormone levels (LH, FSH, prolactin, testosterone) were normal in their lesbian population.

(3) Here I'll point out a caveat mentioned by the authors, and one I wondered about: PET can't really resolve different hypothalamic nuclei.

"The centers of the hypothalamic clusters in He[tero]M and He[tero]W were ~10 mm apart. Because registration and repositioning of PET clusters on individual reformatted magnetic resonance images revealed similar locations in all subjects and no systematic shifts between the groups, attention was paid to the more precise location of the respective local maxima. It should, however, be emphasized that their relationship to the specific hypothalamic nuclei should be viewed with caution and that the localization of atlas coordinates to a specific hypothalamic nucleus does not imply that only this nucleus was activated. Rather, it indicates that an area of 10mm around this coordinate was maximally involved."

At January 19, 2011 3:38 AM, Anonymous Anonymous said...

Can Humas detect pheromones?


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