The hypothalamus mPOA medial preoptic area lesion both sexes stop having sex males no change in hormones in motivation females cycle stops sex resumes with added E P mPOA contains several nuclei SDN Sexually Dimorphic Nucleus of the mPOA larger in males more neurons in males Development of the SDN of the mPOA same number of neurons at birth T apoptosis males have more neurons as adults AVPV anteroventral periventricular nucleus of the mPOA females males in size and number of neurons female cycle feedforward same number of neurons at birth T apoptosis females have more neurons Humans INAH 1 4 Interstitial Nuclei of the Anterior Hypothalamus INAH 3 SDN size of INAH3 males females and homosexual males number of neurons males male homosexuals females Homosexuality male monozygotic twins 60 concordance higher incidence in some families maternal line homosexual brothers same X number of older biological brothers Other animals some examples domestic sheep primates bonobo chimps bisexuality Human situations CAH congenital adrenal hyperplasia prenatal adrenals T XX external genitalia in between male and female at birth stop secretion later alter genitalia outcome female mostly AI androgen insensitivity defective androgen receptors XY SRY gene testes external genitalia female internal genitalia none outcome female T but no receptor T Menopause Women s Health Initiative clinical trial with E and P behavior and dementia start hormones at 65 years or older need to start at beginning of menopause Rats E helps behavioral performance Sex differences in cognitive areas Brain size Cellular components rat corpus callosum males larger more myelinated axons males females in number of axons Many differences appear during adolescence Role of hormones Sex differences in connections B Child C Adolescent D Adult Ingalhalikar et al 2013 Sex differences in math Green female Purple male The top 0 01 of math SAT 1980 13 males 1 female 2010 4 males 1 female Males more variable more at high and low end