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Lecture 16

HMB200H1 Lecture Notes - Lecture 16: Limbic System, Amygdala, Vasopressin

Human Biology
Course Code
John Yeomans

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HMB200H1S L16; March. 7, 2012
Sex, Gender and the Brain (continued)
Gender Identity
Some homosexual males feel male, some feel female
Central subdivision of Bed N. of Stria Terminalis (BNST) 44%
larger in males than females
6 transgendered males have smaller cBNST like females
o A transgendered female showed a larger cBNST like males
o Transgendered males have no change in their hypothal
o Swaab
No BNST difs in homosexual males
o But have difs in hypothal
No INAH difs in transgendered males
o No relation to preference
Are these correlations causal?
o Only a correlation noticed, not causal relationships
o Hypothal dictates sexual bhvrs
o Limbic system dictates your gender identity difs in BNST
BNST Size Difs dictate gender identity
Bed N. of Stria Terminalis (BNST): in deep limbic system, involved in
emotional learning
o Darker, more oval-shaped in males
A,B: Indicates BNST size dictates gender
o Since o dif in hypothal of subjects
o Bigger BNST = Male
C: Homosexual male w same size BNST as Heterosexual male
o Bhvr’al dif, not a gender identity dif
D: Transgendered male w same size BNST as Heterosexual female
o Believe they are meant to be women gender identity
Conclude: BNST doesn’t control sexual choice or bhvr; instead
affects gender identity way person feels about self
Pair Bonding in Voles
Expt: Adding Vasopressin neurons in Ventral Pallidum Made
polygamous animals into monigamous animals
Vasopressin 1a recs in Ventral Pallidum:
o Long-term relationships
o Higher expression monogamous
o Lower expression polygamous
Conclude: Vasopression 1a recs in VP affect long-term pair bonding
Oxytocin & Attachment
Oxytocin in mother helps her feel bonding to child
o Or else: mother wouldn’t want to help child get milk
Suckling tactile pathway released in nursing (let-down reflex)
maternal bonding in rodents & sheep (can smell offspring thru
Intranasal oxytocin in humans greater “trust” in evaluating
faces, less amygdala activity
o Oxytocin recs in Amygdala (central nucleus) inhibit amygdala
fear responses greater trust of strangers
Central n: where all output sent from
o Humans aren’t influenced that highly by this because need a lot
of it so a little can get thru
But shows we are still affected by chemicals & aren’t as
independent from chemical processes as we first believed
Oxytocin recs in Amygdala & Hippocampus
o Pathways from Paraventricular n (PVN) & Supraoptic n.
Females have higher oxytocin recs than males??
o Rate of anxiety very high in females, could be related to a
decrease in oxytocin recs
Males more oriented in directions via 2D/3D map info, while females
use landmarks to give directions
o Male & female brains very similar
Birds have much greater difs:
o Song sparrows males are only ones that sing & only in spring
due to left hemi structures that grow in spring & shrink in
in spring the areas that are growing have more inputs &
outputs neurogenesis get increase in hormones
needed to sing regrown during times of copulation
Also happens in zebra finches within left hemisphere shrinks in
winter & regrows in summer
o Therefore the hemisphere is testosterone-dependent
Cognitive Difs
Males & females differ in verbal/spatial abilities & preferences
o Ex. most males prefer to read maps while navigating; most
females prefer to receive verbal instructions on where to turn
Related to hormonal effects on hippocampus & cortex?
o Important in Schizophrenia & anxiety
Males more prone to Schizophrenia & females more prone
to depression
o Hypothalamic difs are greatest in males
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