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Eotrontat-
Sexand the CerebralCortex
"Whycan'tawomanbemorelikeaman?"RexHarrisonsanginthemusical'MyFair
Lady.Butcanshe,orwhyshould'.h"?l"guinui"n"tundentandingofthedifferential
But for various
*" n"ffio itudy ttrebraindirectly'
role of genderin braindevelopment
studiesof the
longitudinal
feasibleto .oiAuo ltngtime
resonance
reasonsit has so f* no, been
magnetic
of
noninvasiveltechnique
of ,n.lu*uo brain.Eventhe
cerebral
as
development
features
,"
of resolutionnecessary
iil_:lth
sections
imagingdoesnot "fi;;;'Gee
histological
measuring
u"lur""y achievedby actually
ln
cortical thicknessffi;;;
differences
sex
of
studies
.t,o'ough
is ,ut,y our
senes'
my
from, say, rodentuiuin,. That
in
rats
'o,.
700
over
done on the rat-actually
cortical devetopmenthave been
astechnology
ror-ii"tuter srudyof humanbrains
Hopefully tn"." nl"y ,.*" "r-r"io"rin.,
in nine
*tffit;
cortical thicknesswas first measured
recentsrudy of this question,
samplesfromthefrontal,somatosensorY,andoccipitalcortexofmaleratsatSuccessrve
seeDiamond 1988)' An
to 900 d"y;;
lfor {etaifs 26 and41 daysof age'
intervalsover the period of 6
"g;
birth uiiit ,o'i"',rttere beo'eenregionsOro, .Ouu,f,;*O1l after
lives' The overall
a..rin" ior ,rr" t".ander of their
when they *run u'i"",i.J", ,i."av
reachedand the
was
peak
* avout+sqobeforcthe
postnatalcorticali'il;:";;;;";
a different
followed
developm"it or tn" femalecortex
decline began.,n'.on*rr, the
by 18
course,withsomeregionalvariation.Thefrontalcortexwasquitewelldevelopedat
t+ auyt or age,reachinga peak
birth, growingonly by 2Vo\n the:r*k-f;;tio
daysofag".erea,39,ho,""u",'tt.eareuteastdevelopedatbirth,grewby40Toduring
of age' The female
*, ..u"f io p.at untr 33 days
that 7 to 14 day period, and did
of
Uirttrthanthat the male' In other
.o.t"* was also .or" O"i.iofA'at
somatosensory
thoseof the male
."nl- g".* u, ,u,., differentfrom
words. variousregionsof the female
co r te x.
, I A on\
.,.:--
?
lnahumancorticalstudyChuganietal.(1987),using2-deoxy-glucosePoslron
duringthe first 5-6
increased
tne upiJe oi glucose
"u"gun
emissiontomography,found that
t9 qraoyllv decrease'indicating
g-10 yearstn" *t" ii ,put"
yearsafterunn. dy
apatlernsimilartothedeveloPment,""nintherat.Unfoffunatelyinthishumanstudy
the databy sex'
there was no separateanalysisof
that the femalecortexis morehighly
ui"*'ii;;;;;
From an evolutionarypoint of
species'The fact
t,*'t"i the ,eprodu.tionof the
developedat birth to "nru." a better
thatshehasfeweroppornrnitiest"pJut"(f"th:li:,lbout420ovulationsper
ejaculation)suggeststhe
to zo.,odo,ooosp€nnper single
reproductrvepJ;
",ilpu,.a
for the female'
importanceof eu'ty adaitive.succel
Sincethe middle of the
-J*are i-"i * noted'
to
other sex differencesin brain d"t;i";;;;
of the relevanceof brain asymmetry
u"en
nineteenthcenruryscientistst uu"
speech.UoOya"L"ness'andotn"'fun"tions'Uutsexdifferencesinasymmetryofthe
We now know that in
late in the twentiethcentury'
cerebralcortexwere not noteduntil
and this
is typicaily thickerthanthe left'
the newbornmale rat the right ."r"urJ"on.x
0m632?3i89ls03 50
I 1989socicty of BiologrcalPsvchiary
il
'i
b.dl torl s t
3)L
.; -: ',:_
Editorial
BIOL PSYCHIAT RY
I 9 8 9 ;1 5 :8 2 3 - 3 1 5
very old age' 900 days' the
maturity' However' at a
panern persists lnto advanced
cortex' showsthe most
oiea lT, the primayrisual
differencesur. no ,onrl, ,ig",n.^",.
il^:n" study this area
tn
preponderanceat every ugt'
lut'll
marked and consistentright
w a s s h o w n to b e 5 v o g," ut" ,i ntheri ghtn:.l ncortei
thani nthel eft,agai ni ndi cati ng
for thesebrain measures'
,f,l*f,"urit,i. value of rat studies
p"ti"""t tr'":".T:1",::'
j:;,'tii:i:;;ffi;1o.::::""I
not
are
rheasymmet'""r
'lni'li i"i"- Lt"n"'"lTl,:n:.:*llllji,i',lifrerences
becomes
.\
-
.nJ,l:'::1TlT."i:;""# i" in" agingfemalethe right occipitalcortex
sisnificant.Qult" intt'"""i"trt'
his right dominance
In otherwords,the maieloses
ini'r"t.
tr,un
thicker
si-enificantly
region'theoccipitai'
rightdominan."'inon" particuiar
with aging,whilethef;;;"i",
with aging'
ue reversed
that somegi"o"t"rt"*"i may
suggesting
but thehippocampaldifferences,
g"no"r
ti,.r"
It is notoniytr,. .on.* iiu, J"*onrou,",
duringthe
rightd-ominance
maleshowsa utty"pronounced
The
well'
as
complex
dentate
+txio"vt of age'the femalehippocampalfirstthreeweeksof [r";;ilJisgnear1u-v
for mostof her liie' exceptat
lefi^dominance
rh"*r;;;;rignifi;t
complex
dentate
significant'
becomes
whenleft dominance
the initial periodof *-""f'rn"*?iry
"fr'-*
;
.i"a'+*'m'
or""::'::;;;"",-_"r*.
ur
preces
pieces
severar
Several
i',llJ;
estrogen
.1"!l^,'"::ln:T:[",11i%lJl
";il"*
ln the male, developingcortex
patterns of cortical asymmetry'
"4t
a:,).
tr.,
.$
\a'
,1 ."*
termining these
re c e p to rs e x i s ti n g ,.u* ," .on" " n.,ati oni nthel efthemi sphere;i nthefemal ethep at t er n
isreversed.Furthermore,exogenousestro€en.uno"",.u."corticalthickness'Thisfinding
side of the cortex'
nu[nu", of receptorsin the thinner
*i;;;;.';r;,
positively
pattern
correlates
masculineright dominant cortical
,"r""".0 iifinn, u rypically
male
lf the ovanes
the
of age in
"r,
months. r.o;-fittrt to ttfee months
female;i;;;r""
the
in
leftdevelops
cortlcal areas'show the female
*d
frontai
anterior
the
testes
another
lacking
'otuto'"nsory
ia right dominance' ln
uut tr,e occipital .ort"* r"tuin,
sreater-than-rigr,tpaneri,
e x a mp l e o fth e e ffe ctofsexhormonesoncorti cal domi nancepatterns,Fl emi n get al.
;;'*. f:jt::ti"::"f,
ecrttutrrti"ilffi ;;;;;;
pups
6)show
(1e8tliffi.l
J:: ffi:
mare
these
iorairv
urpun.*.Behav
;i.
"lT"[::,'ilT::'J
Jhtffi
:Xill
being
:tJrt
u., by displayinglordosisand
the ,"^uut
iater simuiatefemalei.f,uulo. during
a biologicalbasis
thattheie'*iy
findings
These
maies'
!:
other
the
to
submissive
'ugg""
importanceof cortical
and ,r*. ,o-i""*ind us of the
homosexuality,
of
form
one
for
b"lulio:
u.Vrntn".y in its relationship,to
---,
overtheyearswehavelearnedthatcorticalthicknesscanbeaccountedforbya
the areaof perikaryon
nu*u., of neuronsandglialcells,
ir,"
in.ruaing
factors,
of
number
numberof dendntic
lengthof O""atiii. brinches,the
und
nu*i"i,
tn.
nucleus,
its
and
ln otherwords,everymeasured
ttrictcening.
spines,and the r"ngri,oiii"-for,ryiup,i.
conelatedwith corticaithickening'
part of the neuron'nt*t tituttges
gIiaI ui'"i::
;;;;;J and
lnourgende.,t"o'
":
," ilJLi;1ff:"'lJl'l';;;;;;'ons
T;,
with
compared
: :t51ff
:f :?
-coina sampre
rightcortex
of T"il":.';
giia
a',nd
i ts c o u n te rp a rto n thel eft;i nthefemal ei tw as.thel eftsampl
ethatcontai
ecells
the number
due in part tonedmor
that cortical asymmeriei are
These
nght.
the
than
'";;i;';"tctst
"t fi:T,ffffi:;x":l;|,|:HllT;
instandard
orratsriving
intherorebrain
d'rrerencls
rat cortlceswete
in OTl"t how maie and female
coiony condittons' *" *-"'" *"rested
In the enriched
o, in]pou"rirnid living environmenrs'
affected by exposureto enriched
to explore'
(toys)
many.objects
t"itli
in u iurg" luge
together
il*J
,o,,
dozen
a
condirion
in small cageswithout
condition, rats tiied individuaily
rmpovensr,ed
the
in
conrrasr.
ln
..to y s .,i o e x p i o re.tn,* o," p* uteexperi mentsmal eandt.emal eratsw erepl acedineit her
BIOL PSYCHIATRY
1989;25:823-825
Editorial
.', 9 0 0 daY s , t he
tl: mosl
,t'o,ut
i.j,,.'*,
' .^a study this area
1,u'.rg.in' i"aicating
thoseseen ln
- ..^m
tt""'
are not
;c Jrfferences
becomes
j:9ltalcortex
irs right dominance
occiPitai,
i :egion,the
il
butthehiPPocamPallominanceduring the
lemalehiPPocamPalr oi her life, excePtat
:nesplaYa role in deing cortex estrogen
ihefemalethe Pattern
juckness.
This finding
rnersideof the cortex'
inantcortical Pattern
of aee in the male
showthe female leftlominance.In another
rrirerns,Fleming et al.
.rsttrimester.her male
orallythesemale pups
r-.rri
nglordosis
lvlu vo lJ
sand
rru
being
vvtrr6
:rr bea biologicalbasis
.nponanceof cortical
)e accountedfor by a
i. $e areaof perikaryon
:e numberof dendritic
iords,every measured
:.l oS.
-'sr,19of the rat cortex.
:l .ortexcompared with
:.1t.onlainedmore cells
:reln partto the number
'I nts living in standard
'.nale
rat corticeswere
:nents.In
the enriched
:'ects(toys)to
expiore.
n smallcageswithout
....
"r ''tereplacedin either
825
o fth e s e tw o e n v i ro n m entsforthesameperi odofti me.Inthemal etheocci pi tal cor t ex
c h a n g e d mo re th a n theothercorti cal areas' Thefrontal cortexshow edl esschange, and
th e So ma to s e n ,o ,l -* n" * show ednosi gni fi cantchangeatal l .Inthei
emal ethese t hr ee
with the ottipid cortex changing significantly
cortical regionschangedabout equally,
cortex changingt"*
ll:,:':"'T"::
less than in the male, but with the somatosensory
maleshave a more responsivevisual
conditions
indicatethat undersimilar environmental
one
a more resPonsivegeneralSensorycortex.
cortex than females,while femaleshave
visual'
findings, "It just showsthat men are more
professorquipp"a-in ,.rponr" to these
and women more feeling'"
differencei representaverages'some signifrcant
One needs* t."p i" ,,'ind that these
a n d s o me n o t,a n d thevari ati onsi rremany:i nhumantei ngsthevari
ati onsw oul
no
of dreal
possibility
as.a whole these data alert us to the
T"";
doubt be .".h ;;;;.
findings
of the brain' Nloredetailson these
genderdifferencJsin highercognitivefunctions
the
Any manied couple working together in
can be found elsewhere(Diamond l9s8).
te d i o u s ta s k o fu " ." " .' i ngthebi ol ogi cal basesofourbehavi orcandraw
S omeencour
job instead .
have four well-balancedbrainsdoing the
agementfro,o tn" iu., thaithey may
left-right'
oi t*o, a male right-left and a female
arian CleevesDiamond
I
References
ChuganiFfT,PhelpsME'MazziottaJC(1987):Humanbrainfuncdonaldevelopment.AnnNeurol
22.48'7497
'
York: The FreePress'
DiamondMC (1988):EnrichingHerediry'New
F l e m i n g D E' An d e rsonR H ,R heesR W ,K i nghornE ,B akai ti sJ(1986):B rai nR e sBulI 16: 395_
398.