Editing Amygdala (section)

==<span id="Development"></span><span id="Sex distinction"></span>Development and sex distinction==
{{See also|Neuroscience of sex differences}}

The amygdala is one of the best-understood brain regions with regard to [[sexual dimorphism|differences between the sexes]]. The amygdala is larger in males than females, in children aged 7 to 11,<ref>{{cite journal|vauthors=Caviness VS, Kennedy DN, Richelme C, Rademacher J, Filipek PA|year=1996|title=The human brain age 7-11 years: a volumetric analysis based on magnetic resonance images|journal=Cerebral Cortex|volume=6|issue=5|pages=726–36|doi=10.1093/cercor/6.5.726|pmid=8921207|doi-access=}}</ref> adult humans,<ref>{{cite journal|vauthors=Goldstein JM, Seidman LJ, Horton NJ, Makris N, Kennedy DN, Caviness VS, Faraone SV, Tsuang MT|date=June 2001|title=Normal sexual dimorphism of the adult human brain assessed by in vivo magnetic resonance imaging|journal=Cerebral Cortex|volume=11|issue=6|pages=490–7|doi=10.1093/cercor/11.6.490|pmid=11375910|doi-access=free}}</ref> and adult rats.<ref>{{cite journal|vauthors=Hines M, Allen LS, Gorski RA|s2cid=171083|date=May 1992|title=Sex differences in subregions of the medial nucleus of the amygdala and the bed nucleus of the stria terminalis of the rat|journal=Brain Research|volume=579|issue=2|pages=321–6|doi=10.1016/0006-8993(92)90068-K|pmid=1352729}}</ref>

There is considerable growth within the first few years of structural development in both male and female amygdalae.<ref name="Development">{{cite journal | vauthors = Uematsu A, Matsui M, Tanaka C, Takahashi T, Noguchi K, Suzuki M, Nishijo H | title = Developmental trajectories of amygdala and hippocampus from infancy to early adulthood in healthy individuals | journal = PLOS ONE | volume = 7 | issue = 10 | pages = e46970 | year = 2012 | pmid = 23056545 | pmc = 3467280 | doi = 10.1371/journal.pone.0046970 | bibcode = 2012PLoSO...746970U | doi-access = free }}</ref> Within this early period, female limbic structures grow at a more rapid pace than the male ones. Amongst female subjects, the amygdala reaches its full growth potential approximately 1.5 years before the peak of male development. The structural development of the male amygdala occurs over a longer period than in women. Because of the early development of female amygdalae, they reach their growth potential sooner than males, whose amygdalae continue to develop. The larger relative size of the male amygdala may be attributed to this extended developmental period.

Hormonal factors may contribute to these sex-specific developmental differences. The amygdala is rich in [[Androgen receptor|androgen receptors]]—nuclear receptors that bind to [[testosterone]]. Androgen receptors play a role in the DNA binding that regulates [[gene expression]]. Though testosterone is present within the female hormonal systems, women have lower levels of testosterone than men. The abundance of testosterone in the male hormonal system may contribute to development. In addition, the grey matter volume on the amygdala is predicted by testosterone levels, which may also contribute to the increased mass of the male amygdala.

There are observable developmental differences between the right and left amygdala. The left amygdala reaches its developmental peak approximately 1.5–2 years prior to the right amygdala. Despite the early growth of the left amygdala, the right increases in volume for a longer period of time. The right amygdala is associated with response to fearful stimuli as well as face recognition. For the left amygdala, it is inferred that the early development of it functions to provide infants the ability to detect danger due to its reported responds predominantly to fearful events and faces.<ref>{{Cite journal |last=Hardee |first=Jillian E. |last2=Thompson |first2=James C. |last3=Puce |first3=Aina |date=2008-01-31 |title=The left amygdala knows fear: laterality in the amygdala response to fearful eyes |url=https://doi.org/10.1093/scan/nsn001 |journal=Social Cognitive and Affective Neuroscience |volume=3 |issue=1 |pages=47–54 |doi=10.1093/scan/nsn001 |issn=1749-5024|hdl=2022/22747 |hdl-access=free }}</ref><ref>{{Cite journal |last=Phelps |first=Elizabeth A. |last2=O'Connor |first2=Kevin J. |last3=Gatenby |first3=J. Christopher |last4=Gore |first4=John C. |last5=Grillon |first5=Christian |last6=Davis |first6=Michael |date=2001 |title=Activation of the left amygdala to a cognitive representation of fear |url=https://doi.org/10.1038/86110 |journal=Nature Neuroscience |volume=4 |issue=4 |pages=437–441 |doi=10.1038/86110 |issn=1097-6256|url-access=subscription }}</ref> In childhood, the amygdala is found to react differently to same-sex versus opposite-sex individuals. This reactivity decreases until a person enters adolescence, where it increases dramatically at puberty.<ref>{{cite journal | vauthors = Telzer EH, Flannery J, Humphreys KL, Goff B, Gabard-Durman L, Gee DG, Tottenham N | title = "The Cooties Effect": Amygdala Reactivity to Opposite- versus Same-sex Faces Declines from Childhood to Adolescence | journal = Journal of Cognitive Neuroscience | volume = 27 | issue = 9 | pages = 1685–96 | date = September 2015 | pmid = 25848681 | pmc = 5723398 | doi = 10.1162/jocn_a_00813 }}</ref>

Other functional and structural differences between male and female amygdalae have been observed. Subjects' amygdala activation was observed when watching a horror film and [[subliminal stimuli]]. The results of the study showed a different lateralization of the amygdala in men and women. Enhanced memory for the film was related to enhanced activity of the left, but not the right, amygdala in women, whereas it was related to enhanced activity of the right, but not the left, amygdala in men.<ref>{{cite journal | vauthors = Cahill L, Haier RJ, White NS, Fallon J, Kilpatrick L, Lawrence C, Potkin SG, Alkire MT | display-authors = 6 | title = Sex-related difference in amygdala activity during emotionally influenced memory storage | journal = Neurobiology of Learning and Memory | volume = 75 | issue = 1 | pages = 1–9 | date = January 2001 | pmid = 11124043 | doi = 10.1006/nlme.2000.3999 | s2cid = 25492047 }}</ref> Similarly, a study of decision-making ability in patients with unilateral amygdala damage suggested that men with right (but not left) amygdala damage were more likely to be impaired in decision-making ability, while women with left (but not right) amygdala damage were more likely to be impaired in decision-making ability.<ref>{{cite journal | vauthors = Tranel D, Bechara A | title = Sex-related functional asymmetry of the amygdala: preliminary evidence using a case-matched lesion approach | journal = Neurocase | volume = 15 | issue = 3 | pages = 217–34 | date = June 2009 | pmid = 19308794 | pmc = 2829120 | doi = 10.1080/13554790902775492 }}</ref><ref>{{cite journal | vauthors = Gupta R, Koscik TR, Bechara A, Tranel D | title = The amygdala and decision-making | journal = Neuropsychologia | volume = 49 | issue = 4 | pages = 760–6 | date = March 2011 | pmid = 20920513 | pmc = 3032808 | doi = 10.1016/j.neuropsychologia.2010.09.029 }}</ref> One study found evidence that, on average, women tend to retain stronger memories for emotional events than men.<ref>{{cite journal | vauthors = Hamann S | title = Sex differences in the responses of the human amygdala | journal = The Neuroscientist | volume = 11 | issue = 4 | pages = 288–93 | date = August 2005 | pmid = 16061516 | doi = 10.1177/1073858404271981 | s2cid = 15324475 }}</ref>