INAH-3 is the short form for the third
interstitial
An interstitial space or interstice is a space between structures or objects.
In particular, interstitial may refer to:
Biology
* Interstitial cell tumor
* Interstitial cell, any cell that lies between other cells
* Interstitial collagenase ...
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
* Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucl ...
of the
anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...
hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...
, and is the
sexually dimorphic nucleus of humans. The INAH-3 is significantly larger in males than in females regardless of age and larger in heterosexual males than in homosexual males and heterosexual females.
Research
The term INAH (interstitial nuclei of the anterior hypothalamus), first proposed in 1989 by a group of the
University of California at Los Angeles
The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California ...
, refers to 4 previously undescribed cell groups of the preoptic-anterior hypothalamic area (PO-AHA) of the human brain, which is a structure that influences
gonadotropin
Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/ chorioni ...
secretion, maternal behavior, and sexual behavior in several mammalian species. There are four nuclei in the PO-AHA (INAH1-4). One of these nuclei, INAH-3, was found to be 2.8 times larger in the male brain than in the female brain regardless of age.
A study authored by
Simon LeVay
Simon LeVay (born 28 August 1943 in Oxford, England) is a British-American neuroscientist.
He received a bachelor's degree in natural sciences from the University of Cambridge in 1966, a Ph.D. in Neuroanatomy at the University of Göttingen ...
and published in the journal ''
Science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence ...
'' suggests that the region is an important biological
substrate with regard to
sexual orientation
Sexual orientation is an enduring pattern of romantic or sexual attraction (or a combination of these) to persons of the opposite sex or gender, the same sex or gender, or to both sexes or more than one gender. These attractions are generall ...
. This article reported the INAH-3 to be smaller on average in
homosexual
Homosexuality is romantic attraction, sexual attraction, or sexual behavior between members of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" to pe ...
men than in
heterosexual men, and in fact has approximately the same size in homosexual men as in heterosexual women.
Further research has found that the INAH3 is smaller in volume in homosexual men than in heterosexual men because homosexual men have a higher neuronal packing density (the
number of neurons per cubic millimeter) in the INAH3 than heterosexual men; there is no difference in the number or cross-sectional area of
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...
s in the INAH3 of homosexual versus heterosexual men.
It has also been found that there is no effect of HIV infection on the size of INAH3, that is, HIV infection cannot account for the observed difference in INAH3 volume between homosexual and heterosexual men.
[
LeVay noted three possibilities that could account for his findings: 1. The structural differences in INAH3 between homosexual and heterosexual males were present prenatally or in early life and aided in establishment of the men’s sexual orientation; 2. The differences appeared postnatally as a result of the men’s sexual feelings or behavior and; 3. Both the differences in INAH3 and sexual orientation are linked to some third ]confounding variable
In statistics, a confounder (also confounding variable, confounding factor, extraneous determinant or lurking variable) is a variable that influences both the dependent variable and independent variable, causing a spurious association. Con ...
(such as a developmental event in prenatal or early life). LeVay found the first possibility most probable and noted that the second possibility was unlikely in light of various homologous studies in other species.transgender
A transgender (often abbreviated as trans) person is someone whose gender identity or gender expression does not correspond with their sex assigned at birth. Many transgender people experience dysphoria, which they seek to alleviate through ...
individuals by neuroanatomist Dick Swaab found male-to-female transgender people to have a size and number of neurons of INAH-3 closer to a normal female range, and that female-to-male transgender people have a size and number of INAH-3 neurons closer to a normal male range. This finding that the size of the INAH-3 more closely corresponded to the gender the subject identified with rather than their biological or chromosomal gender has since been repeated, but is still controversial due to potential confounds of hormone replacement therapy.
Kay Brown (2010), "the Incredible Shrinking Brain"
See also
* ''
The Sexual Brain''
Notes
References
{{reflist, 30em
Sexual orientation and science