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Male-typical visuospatial functioning in gynephilic girls with gender dysphoria — Organizational and activational effects of testosterone

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Background: Sex differences in performance and regional brain activity during mental rotation have been reported repeatedly and reflect organizational and activational effects of sex hormones. We investigated whether adolescent girls with gender dysphoria (GD), before and after 10 months of testosterone treatment, showed male-typical brain activity during a mental rotation task (MRT). Methods: Girls with GD underwent fMRI while performing the MRT twice: when receiving medication to suppress their endogenous sex hormones before onset of testosterone treatment, and 10 months later during testosterone treatment. Two age-matched control groups participated twice as well. Results: We included 21 girls with GD, 20 male controls and 21 female controls in our study. In the absence of any group differences in performance, control girls showed significantly increased activation in frontal brain areas compared with control boys (pFWE = 0.012). Girls with GD before testosterone treatment differed significantly in frontal brain activation from the control girls (pFWE = 0.034), suggesting a masculinization of brain structures associated with visuospatial cognitive functions. After 10 months of testosterone treatment, girls with GD, similar to the control boys, showed increases in brain activation in areas implicated in mental rotation. Limitations: Since all girls with GD identified as gynephilic, their resemblance in spatial cognition with the control boys, who were also gynephilic, may have been related to their shared sexual orientation rather than their shared gender identity. We did not account for menstrual cycle phase or contraceptive use in our analyses. Conclusion: Our findings suggest atypical sexual differentiation of the brain in natal girls with GD and provide new evidence for organizational and activational effects of testosterone on visuospatial cognitive functioning.
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J Psychiatry Neurosci 1
©2016 8872147 Canada Inc.
Research Paper
Male-typical visuospatial functioning in gynephilic
girls with gender dysphoria — organizational and
activational effects of testosterone
Sarah M. Burke, PhD; Baudewijntje P.C. Kreukels, PhD; Peggy T. Cohen-Kettenis, PhD;
Dick J. Veltman, MD, PhD; Daniel T. Klink, MD, PhD; Julie Bakker, PhD
Introduction
The mental rotation task (MRT),1,2 a visuospatial working
memory task, has consistently been shown to elicit robust sex
differences in performance, with men outperforming
women.3,4 Accordingly, fMRI studies have found that men
and women use different cerebral networks when they have
to determine whether 2 differently rotated 3-dimensional g-
ures are identical or mirrored. Stronger superior parietal acti-
vations during mental rotation have been observed in men,
whereas women recruit (inferior) frontal and temporal brain
areas more than men.5
The classical theory of organizational and activational effects
of sex hormones on the brain6 assumes that functional (i.e., be-
havioural) differences between men and women reect sex
differences at the structural (morphological) level, which have
been established (“organized”) during prenatal development.
Sex differences in visuospatial cognition evolve during early
development under the organizational inuence of sex hor-
mones.7 Evidence for these early hormonal effects on later
visuospatial abilities comes from studies in individuals with
congenital adrenal hyperplasia,8–10 idiopathic hypogonado-
tropic hypogonadism,11 or complete androgen insensitivity
syndrome.12 These conditions are all characterized by aberrant
androgen action from early development onwards. In addi-
tion, sex differences in mental rotation performance have al-
ready been found in children,13–16 suggesting that sex differ-
ences in spatial functioning observed in adulthood reect sex
differences in exposure to androgens during the perinatal
period of sexual differentiation.
However, some studies have failed to observe sex differences
in mental rotation functions in children in contrast to older par-
ticipants,17–19 which suggests that postnatal factors, such as pu-
berty, cognitive development and experience, may also affect
the sex-specic development in mental rotation functioning.
Signicant effects of age and age × sex interactions in studies
Correspondence to: S.M. Burke, Karolinska Institute, Department of Women’s and Children’s Health, Karolinska Hospital, Q2:07, SE-171 76
Stockholm, Sweden; sarah.burke@ki.se
Submitted Apr. 27, 2015; Revised Nov. 19, 2015; Revised Dec. 20, 2015; Accepted Dec. 20, 2015
DOI: 10.1503/jpn.150147
Background: Sex differences in performance and regional brain activity during mental rotation have been reported repeatedly and reflect
organizational and activational effects of sex hormones. We investigated whether adolescent girls with gender dysphoria (GD), before and
after 10 months of testosterone treatment, showed male-typical brain activity during a mental rotation task (MRT). Methods: Girls with GD
underwent fMRI while performing the MRT twice: when receiving medication to suppress their endogenous sex hormones before onset of
testosterone treatment, and 10 months later during testosterone treatment. Two age-matched control groups participated twice as well.
Results: We included 21 girls with GD, 20 male controls and 21 female controls in our study. In the absence of any group differences in
performance, control girls showed significantly increased activation in frontal brain areas compared with control boys (pFWE= 0.012). Girls
with GD before testosterone treatment differed significantly in frontal brain activation from the control girls (pFWE = 0.034), suggesting a
masculinization of brain structures associated with visuospatial cognitive functions. After 10 months of testosterone treatment, girls with
GD, similar to the control boys, showed increases in brain activation in areas implicated in mental rotation. Limitations: Since all girls with
GD identified as gynephilic, their resemblance in spatial cognition with the control boys, who were also gynephilic, may have been related
to their shared sexual orientation rather than their shared gender identity. We did not account for menstrual cycle phase or contraceptive
use in our analyses. Conclusion: Our findings suggest atypical sexual differentiation of the brain in natal girls with GD and provide new
evidence for organizational and activational effects of testosterone on visuospatial cognitive functioning.
Early-released on Apr. 12, 2016; subject to revision
Burke et al.
2 J Psychiatry Neurosci
on mental rotation performance during adolescence20,21 have
suggested that activational effects of sex hormones, starting at
puberty, reinforce sex differences in visuospatial functioning.
Furthermore, several studies22,23 have indicated effects of
gonadal hormone uctuations in girls on visuospatial cogni-
tive functioning.
Individuals with gender dysphoria (GD; DSM-524) are char-
acterized by distress due to a profound feeling of incongru-
ence between their natal sex and experienced gender. It has
been hypothesized that atypical levels of pre- and perinatal
sex steroids during a critical period of sexual differentiation of
the brain may be involved in the development of GD.25
Neuropsychological studies involving adults with GD have
yielded some support for both organizational and activational
effects of testosterone on mental rotation performance.
Treatment-naive study participants with GD performed com-
parably to their experienced gender control groups (e.g., per-
formance in women with GD was similar to control men),26,27
and cross-sex hormone (CSH) treatment (i.e., natal women re-
ceive testosterone, natal men receive estrogen) improved per-
formance in natal women and had detrimental effects in natal
men.28–30 However, other studies failed to observe early or late
sex hormone–dependent changes or differences in spatial abil-
ities between individuals with GD and controls.31–33
Three fMRI studies34–36 investigated sex-typical (in accor-
dance with natal sex) and sex-atypical (in accordance with ex-
perienced gender) brain functioning during mental rotation in
treatment-naive individuals with GD as well as in participants
receiving CSH treatment. However, these reports focused
mostly on adult men with GD and thus on the activational ef-
fects of estrogen treatment, whereas the association between
testosterone and neuroimaging correlates of spatial cognition
in women with GD remains understudied.
In the present prospective fMRI study, the rst aim was to
investigate whether a carefully selected, highly homogeneous
(in terms of GD onset age, sexual orientation, dosage and type
of the CSH treatment) group of adolescent natal girls with GD
would show a male- or female-typical brain activation pattern
during an fMRI MRT before the start of the testosterone treat-
ment. At the Center of Expertise on Gender Dysphoria at the
VU University Medical Center in Amsterdam, the Nether-
lands, adolescents with persisting GD may start treatment
with gonadotropin-releasing hormone analogues (GnRHa) at
the age of 12 years to suppress endogenous gonadal stimula-
tion and thus the irreversible development of sex characteris-
tics of the natal sex. Then, at the age of 16 years, as a rst step
in the actual sex reassignment, they receive CSH treatment.37,38
Our second aim was to investigate the effects of testosterone
on MRT performance and associated brain functioning. Thus,
girls with GD participating in the present study were tested
twice: shortly before receiving testosterone while their endo-
genous sex hormones were suppressed, and then again
10months later while receiving testosterone treatment. We hy-
pothesized that girls with GD, based on the assumption that
they have undergone a more masculinized early neuronal sex-
ual differentiation, would show male-typical mental rotation
functioning (organizational effects). In addition, we expected
to observe a testosterone-dependent improvement in task per-
formance and a more male-typical cerebral activation pattern
during mental rotation when receiving testosterone (activa-
tional effects).
Methods
Participants
Adolescent girls with GD who had been gender dysphoric
since childhood were recruited via the Center of Expertise on
Gender Dysphoria. Age-matched controls were recruited via
several secondary schools in the Netherlands and by inviting
friends of the participants with GD. Exclusion criteria for par-
ticipation in the study were any form of neurologic or psychiat-
ric disorder and continuous psychotropic medication use.
When scanned for the rst time (session 1), girls with GD had
been treated monthly with 3.75 mg of triptorelin (Decapeptyl-
CR, Ferring) by injection for on average 24 (range 2–48)months,
resulting in complete suppression of gonadal hormone produc-
tion. At scan session 2, girls with GD had been receiving testos-
terone treatment for on average 10 (range 6–15) months. All
girls with GD either received a testosterone ester mixture (Sus-
tanon 250 mg/mL Merck Sharp & Dohme bv) every 2 weeks or
testosterone undecanoate (Nebido, 250 mg/mL, Bayer) every
12 weeks. The starting dosage varied with the patient’s age.
Until the age of 16.5 years, the starting dosage was 25 mg/m2
body surface area every 2 weeks. When older than 16.5 years
the dosage was 75 mg every 2 weeks.39 Controls were exposed
to their endogenous sex hormones during both test sessions.
Female controls were tested randomly according to their men-
strual cycles, and we assessed use of hormonal contraceptives,
but this was not an exclusion criterion.
Procedure
Before the session 1 fMRI scan, all participants underwent a
neuropsychological assessment and olfactory function test (re-
sults published elsewhere40) lasting approximately 90 min.
Participants completed 4 subtests (arithmetic, vocabulary, pic-
ture arrangement and block design) of the Wechsler Intelli-
gence Scale for Children41 or, if older than 16years, the
Wechsler Intelligence Scale for Adults.42 Each 4-subtest sum
score was converted to an individual’s estimated IQ. We as-
sessed sexual orientation by asking whether the participant
had ever been in love with somebody and whether that per-
son was a boy or a girl. Pubertal stages were assessed in the
control participants by means of self-report,43 and in girls with
GD by a pediatric endocrinologist (D.T.K.) as part of their
clinical assessments.44,45
Participants were instructed on the fMRI paradigm and
performed 2 practice trials of the MRT before the scan. The
fMRI session also included 2 other fMRI tasks,40 a resting
state and diffusion tensor imaging scan. The whole scanning
session lasted approximately 1 hour.
All participants and their legal guardians gave their in-
formed consent according to the Declaration of Helsinki, and
the study was approved by the Ethics Committee of the VU
University Medical Center Amsterdam.
Male-typical visuospatial functioning in gynephilic girls with gender dysphoria
J Psychiatry Neurosci 3
Hormone assessments
At both test sessions for the control groups and at session 2
for the girls with GD, testosterone levels were measured in sa-
liva, which provides an index of the free (i.e., unbound, or
biologically available) fraction of testosterone in circulation.46
Participants were asked to collect saliva samples at home by
salivating at least 1 mL into a polypropylene tube, directly af-
ter waking up on the day of the MRI scan. Samples were
brought to the clinic and stored at –80°C until analysis. Tes-
tosterone levels were determined with an isotope dilution-
liquid chromatography-tandem mass spectrometry (ID-LC-
MS/MS) method. For further details on the analysis see the
study by Bui and colleagues.47
Functional MRI mental rotation
Participants were presented with Shepard and Metzler–type
3-dimensional (3D) white drawings on a black background
taken from the mental rotation stimulus library, provided by
Peters and Battista.48 In the mental rotation condition, partici-
pants were presented 40 pairs of 3D shapes, with 1 shape ro-
tated along the x-plane (half of the presented pairs) or the z-
plane relative to the other shape. Stimuli could be rotated at
9different angles, with at least 80° difference between the
2presented shapes. Participants had to indicate (by pressing a
button) whether the 2 shapes were identical or mirror images.
During the control condition 1 of the 3D stimuli was presented
next to an arrow pointing either to the left or right. Participants
were asked to indicate the side to which the arrow was point-
ing. Stimuli were presented using a classical block design, with
16 alternating rotation/control blocks, and each block con-
tained 5 mental rotation or control trials. Presentation duration
of each stimulus varied depending on the participant’s per-
form ance, with a maximum stimulus presentation of 20 s. Out-
come parameters were the percentage of trials correctly identi-
ed and mean reaction time per trial.
Imaging protocol
All scans for session 1 were performed on a 3.0 T GE Signa
HDxt scanner. A gradient-echo echo-planar imaging sequence
was used for functional imaging. The parameters included a
24cm2 eld of view (FOV), repetition time (TR) of 2100 ms, echo
time (TE) of 30 ms, an 80° ip angle, isotropic voxels of 3mm,
and 40 slices. Before each imaging session a local high-order
shimming technique was used to reduce susceptibility artifacts.
For coregistration with the functional images we obtained a T1-
weighted scan (3D FSPGR sequence, 25cm2 FOV, TR of 7.8 ms,
TE of 3.0 ms, slice thickness of 1mm, and 176 slices). During the
course of the project, a major scanner upgrade (hardware and
software) was performed. Although all settings of the scanning
protocol remained unchanged, in order to account for possible
effects of the upgrade, we counterbalanced session 2 scans over
groups. Thus, for all session 2 scans, approximately half of the
participants of each group were tested before the upgrade was
carried out and the other half of each group was scanned with
the upgraded GE scanner, type MR750.
Data analysis
Behavioural data
Demographic, self-report, and performance data as well as the
hormone assessments were analyzed using the Statistical Pack-
age for the Social Sciences, version 20 (SPSS Inc.). Differences
in group characteristics and performance were analyzed using
1-way analysis of variance (ANOVA). A repeated-measures
ANOVA was conducted to assess session effects in MRT per-
formance, with accuracy and mean reaction time per trial as
within-subjects factors and group as a between-subjects fac-
tor, including IQ as a covariate. The signicance level was set
at p < 0.05.
Neuroimaging data
We performed fMRI data analysis using SPM8 software (Well-
come Department of Imaging Neuroscience, Institute of Neur-
ology at the University College London) implemented in Mat-
lab R2012b (MathWorks Inc.). Functional images were
slice-timed, realigned to the mean image, and coregistered with
the individual anatomic image. Applying the ‘New Segment’
and ‘Create Template’ options of the DARTEL toolbox, struc-
tural images were segmented. Then we used grey matter and
white matter images to create a group-specic template regis-
tered in Montreal Neurological Institute (MNI) space. Func-
tional images were spatially normalized to the group template,
applying each individual’s DARTEL flow field, and finally
images were smoothed using an 8mm full-width at half-
maximum isotropic Gaussian kernel. First-level contrast images
were built by subtracting control trial blocks from mental rota-
tion blocks. Based on the image realignment process, individ-
ual head jerks were identied (>1 mm displacement).49 To-
gether with the 6 motion parameters, these so-called scan
nulling regressors were included in every rst-level design ma-
trix to account for the effects of excessive head motion.
We conducted second-level random effects analyses, enter-
ing all individual contrast images (mental rotation > control
condition) from session 1 into a 1-way ANOVA in order to
test for sex differences (control boys > / < control girls), and
to determine whether girls with GD at baseline (i.e., during
hormonal suppression and before CSH treatment) compared
with the control boys and control girls, showed a female- or
male-typical mental rotation activation pattern.
By means of a flexible factorial design, testing within-
group differences between sessions and group × session
inter action effects, we investigated the effects of the testos-
terone treatment in girls with GD (session 2 v. session 1)
while controlling for possible cognitive developmental and/
or learning effects. Thus, adding both control groups to the
design controlled for possible within-subject effects other
than the testosterone treatment. In case of signicant interac-
tions, we used post hoc paired-sample t tests to explore
within-group session effects.
In order to further explore the effects of the testosterone
treatment on visuospatial brain functioning in girls with GD,
we extracted brain activation (using MarsBaR50). We specif-
ically focused on those clusters in which girls with GD
showed male-typical effects and investigated correlations
Burke et al.
4 J Psychiatry Neurosci
between MRT brain activation and testosterone levels of the
girls with GD for these clusters.
According to a meta-analysis of neuroimaging studies on
brain regions implicated in mental rotation,51 we focused our
imaging analyses on predened regions of interest (ROI), en-
compassing the intraparietal sulcus, the precentral sulcus and
the inferior frontal sulcus. These 3 bilateral ROIs were selected
from Nielsen and Hansen’s52 volume of interest BrainMap
data base. Using the MarsBaR tool,50 the anatomic ROIs were
masked with the control groups’ MRT main effect (applying a
whole-brain threshold of p < 0.05, family-wise error [FWE]–
corrected) in order to create 4 separate ROIs: the precentral
and the inferior frontal sulcus combined were defined as
“frontal ROI,” for the right (4240 mm3) and left hemisphere
(5728 mm3), respectively; the right parietal (20744mm3) and
left parietal (16288 mm3) ROI. All group comparisons were co-
varied for IQ, and effects were considered statistically signi-
cant at p < 0.05, voxel-wise FWE- corrected for the spatial ex-
tent of the ROI and a minimum cluster size of 20 voxels.
Results
Participant characteristics
Twenty-one adolescent girls (mean age 16.1 ± 0.8 yr) with
GD, 20 control boys (mean age 15.9 ± 0.6 yr) and 21 control
girls (mean age 16.3 ± 1.0 yr) participated in the study.
Among the girls with GD, 14 received Sustanon every
2weeks and 7 received Nebido every 12 weeks during the
testosterone treatment phase. One control girl and 4 control
boys dropped out of the study after the rst session, thus
16control boys, 20 control girls and all 21 girls with GD par-
ticipated in session 2.
The demographic, self-report data and testosterone levels
of participants are presented in Table 1. The IQ scores of the
girls with GD were signicantly lower than those of both
control groups, therefore we included IQ scores as a covari-
ate in all further between-groups analyses. At session 1, all
participants were in pubertal stage 4 or higher (1 = pre-
pubertal, 5 = postpubertal). For the subscale pubic hair
growth, the control girls on average rated themselves half a
stage lower than the control boys and the girls with GD,
which resulted in a signicant effect for the overall group
comparison (F2,59 = 3.9, p = 0.027). With regard to genital and
breast development, there were no group differences, there-
fore we decided not to include puberty stage as a covariate
in the further analyses. Saliva samples of 2 control girls and
1 control boy were missing, and 1 control girl had an ex-
tremely high testosterone value in comparison to all other
control girls and was therefore excluded from all analyses.
There were no differences in mean testosterone levels be-
tween session 1 and session 2 for the control groups. The
post-treatment testosterone levels of the girls with GD were
comparable to those of the control boys. At session 1, 11 of
21 control girls, and at session 2, 15 of 20 control girls re-
ported using hormonal contraception. The groups did not
differ with regard to age during either test session and were
homogeneous with regard to sexual orientation (i.e., all con-
trol boys and girls with GD were gynephilic, and all control
girls were androphilic).
Behavioural data
One-way ANOVA yielded no signicant group differences in
MRT performance (Table 2). The repeated-measures
ANOVA, corrected for group differences in IQ, revealed a
signicant main effect of session in mental rotation accuracy
(F1,53 = 11.9, p = 0.001). No main effect of group or any group ×
session interaction was observed. Cohen d effect sizes sug-
gested moderate to strong improvements in reaction time
Table 1: Demographic and clinical characteristics of study participants
Group; mean ± SD*
Characateristic Session Girls with GD Control girls Control boys Statistic p value
No. of participants 1 21 21 20
2 21 20 16 — —
Age, yr 1 16.1 ± 0.8 16.3 ± 1.0 15.9 ± 0.6 F2,59 = 1.1 0.34
2 17.1 ± 0.7 17.6 ± 0.8 17.2 ± 0.7 F2,54 = 1.9 0.16
Puberty stages†
Pubic hair growth 1 4.7 ± 0.6 4.2 ± 0.7 4.7 ± 0.7 F2,59 = 3.9 0.027
Genital development‡/
breast development§
1 4.1 ± 1.1 4.1 ± 0.8 4.1 ± 0.8 F2,59 <0.1 0.98
IQ 1 100.5 ± 12.7 110.3 ± 14.7 113.4 ± 14.5 F2,59 = 5.1 0.009
Sexual orientation 1 100% gynephilic 100% androphilic 100% gynephilic
Testosterone levels,
median (range), pmol/L
1 39.0 (13–130)¶ 307.0 (158–552)
2 285.0 (130–545) 30.0 (13–109)¶ 323.5 (186–630)**
GD = gender dysphoria; SD = standard deviation.
*Unless indicated otherwise.
†Pubertal stages were assessed using the 5-point (1 = prepubertal, 5 = post-pubertal) Tanner Maturation Scale.
‡Applies to natal boys.
§Applies to natal girls.
n = 19.
**n = 15.
Male-typical visuospatial functioning in gynephilic girls with gender dysphoria
J Psychiatry Neurosci 5
and accuracy for both the girls with GD and the control girls
(mainly in reaction times), whereas the performance of the
control boys remained stable (Table 2).
Neuroimaging data
During mental rotation all 3 groups showed widespread
task-related bilateral activations, recruiting parieto-occipital
and frontal networks (Fig. 1).
Group differences in mental rotation
The between-group comparisons at baseline (session 1) re-
vealed significant sex differences in mental rotation–
associated brain activation. Control girls showed several
clusters of increased activation compared with control boys
in the right frontal and left parietal ROIs. The reverse con-
trast, testing for any increased activation during mental rota-
tion in control boys versus control girls yielded no signicant
Table 2: Performance data for the mental rotation task
Group; mean ± SD*
Variable Session Girls with GD Control girls Control boys Statistic p value
% correct 1 66.7 ± 15.9 67.0 ± 11.6 70.2 ± 10.7 F2,59 = 0.5 0.64
2 74.2 ± 9.0 71.7 ± 8.2 71.6 ± 10.3 F2,54 = 0.5 0.60
Cohen d –0.59 –0.48 –0.14
RT/trial 1 8.0 ± 2.2 8.2 ± 1.5 8.1 ± 1.6 F2,59 = 0.04 0.96
2 6.7 ± 2.1 6.8 ± 1.7 7.5 ± 2.0 F2,54 = 1.0 0.39
Cohen d 0.62 0.90 0.35
GD = gender dysphoria; RT = reaction time; SD = standard deviation.
*Unless indicated otherwise.
†Effect sizes were calculated for group means at session 1 versus session 2 using the pooled SD of the 2 means.
Fig. 1: Brain activation pattern during mental rotation at session 1 in
(A) control boys, (B) girls with gender dysphoria (GD) and (C) con-
trol girls. Statistical parametric maps were rendered on an SPM8
template image showing the left and right hemisphere in sagittal
view. For illustrative purposes, whole brain results are displayed at
an uncorrected threshold of p < 0.005.
Control boys
Girls with GD
Control girls
A
B
C
Burke et al.
6 J Psychiatry Neurosci
effects. Comparing control girls and girls with GD revealed a
signicant activation in the right frontal ROI, similar to the
sex difference observed between the control groups (Fig. 2
and Table 3). No other between-group differences were
signicant.
Testosterone-induced effects
Two of the contrasts testing group × session interactions
(control boys > control girls and girls with GD > control girls)
revealed signicant effects in the left frontal and both parietal
ROIs (Table 4). No other signicant interaction effects were
found. Post hoc within-group comparisons conrmed that
both the control boys and the girls with GD showed stronger
frontal and parietal activations at session 2 than at session 1,
whereas no signicant changes in brain activation between
sessions were found in the control girls (Table 4 and Fig. 3).
None of the regression analyses revealed any signicant
correlations between male-typical MRT brain activation and
post-treatment saliva testosterone levels in the girls with GD.
Discussion
In the present study, we demonstrated sex differences in
brain activation during mental rotation. Control girls had sig-
nicantly increased right inferior frontal (precentral gyrus
and frontal inferior operculum) and left parietal (cuneus) ac-
tivation during mental rotation compared with control boys.
Similarly, control girls showed increased right frontal activa-
tion compared with girls with GD who had not yet started
testosterone treatment. Thus, girls with GD showed a priori
masculinized mental rotation–associated brain activations,
and were thus atypical for their natal sex in terms of visuo-
spatial cognitive functioning. In addition, the group compari-
sons between control boys and girls with GD revealed no sig-
nificant differences in brain activation during mental
rotation, supporting the notion of masculinized cognitive
functioning of girls with GD. Testing girls with GD on
GnRHa enabled us to control for possible activational effects
of endogenous sex hormones on spatial abilities in this
group. However, we cannot rule out that the suppression of
endogenous gonadal sex steroids may have contributed to
the differences found between girls with GD and control
girls. In behavioural studies, estrogen treatment in adult men
with GD was shown to have detrimental effects on their
mental rotation performance.25,26 It is therefore possible that
the girls with GD, in contrast to control girls, were not af-
fected by the inhibiting effects of circulating estrogens on
visuospatial cognitive functions. Nonetheless, in line with
previous research,23,24 our study suggests a masculinization of
Fig. 2: Between-group differences in brain activation in right frontal and left parietal areas during mental rotation at session 1. Red = control girls
> control boys; blue = control girls > girls with gender dysphoria. Numbers indicate xaxis coordinates in Montreal Neurological Institute space,
displayed in sagittal view. See Table 3 for further details.
–1650 54 60
Table 3: Group differences in brain activation during mental rotation at baseline (session 1)
MNI space
Comparison ROI AAL label x, y, zNo. of voxels Zmax pFWE value
Control girls > control boys Frontal R Precentral/inferior frontal operculum 52, 3, 24 50 3.2 0.012
Mid-frontal/frontal superior 26, 6, 48 174 2.8 0.08
Frontal L Precentral –24, –9, 42 87 3.2 0.07
Parietal R Supramarginal gyrus 55, –28, 42 89 3.4 0.07
Parietal L Cuneus –15, –78, 37 164 3.5 0.038
Precuneus –12, –67, 57 263 3.3 0.08
Control girls > girls with GD Frontal R Precentral/inferior frontal operculum 57, 6, 24 43 3.2 0.034
AAL = automated anatomic labelling; FWE = family-wise error; GD = gender dysphoria; L = left hemisphere; MNI = Montreal Neurological Institute; R = right
hemisphere; ROI = region of interest.
Male-typical visuospatial functioning in gynephilic girls with gender dysphoria
J Psychiatry Neurosci 7
brain structures associated with visuospatial cognitive func-
tions in girls with GD, presumably originating from a critical
perinatal period of sexual differentiation in the brain.
Our prospective design of testing girls with GD before and
after 10 months of testosterone treatment and also testing
male and female controls twice, allowed for the specic in-
vestigation of the effects of testosterone on MRT-associated
brain activation. After 10 months of testosterone exposure,
girls with GD showed signicantly increased bilateral pari-
etal and left frontal activation during mental rotation. We ob-
served a similar pattern of increased frontal and parietal acti-
vation in the control boys at session 2, whereas in the control
girls, brain activations during mental rotation remained un-
changed between sessions. Interestingly, we found signi-
cant and very similar group × session interaction effects
when comparing control boys with control girls and when
comparing girls with GD with control girls. Thus, the in-
crease in parietal and frontal activation in session 2 compared
with session 1 in the girls with GD mirrored those effects
found in the male controls. The control boys, of course, aged
(from a mean age of 15.9 to 17.2yr) and matured physically
between both test sessions, which is accompanied by an
Fig. 3: Clusters of significant increases in brain activation during mental rotation for session 2 compared with session 1. Left parietal and left
frontal regions are shown. Yellow = session 2 > session 1 in girls with gender dysphoria; purple = session 2 > session 1 in control boys. See
Table 4 for further details.
–42–30–21 –52
Table 4: Session effects and session × group interactions
MNI space
Effect ROI AAL atlas x, y, zNo. of voxels Zmax pFWE value
Group × session interactions
Control boys > control girls Frontal L Supplementary motor area/superior frontal –15, –3, 51 40 3.5 0.021
Parietal L Precuneus/superior occipital –15, –64, 31 77 3.7 0.024
Superior parietal/inferior parietal –23, –54, 51 121 3.7 0.049
Girls with GD > control girls Parietal R Superior parietal/inferior parietal 27, –58, 61 26 3.5 0.06
Parietal L Cuneus/superior occipital –15, –79, 37 51 4.4 0.002
Session (2 > 1)
Control boys Frontal R Mid-frontal/precentral 24, –1, 48 202 3.5 0.016
Frontal L Superior frontal/precentral –51, 8, 34 101 4.0 0.004
Parietal R Superior parietal/angularis 27, –58, 48 342 4.0 0.013
Supra marginal/postcentral 58, –27, 45 31 4.0 0.013
Inferior parietal/superior parietal 36, –40, 49 106 3.5 0.06
Parietal L Superior parietal/inferior parietal –21, –57, 52 1381 4.7 0.001
Mid-occipital/superior occipital –26, –73, 31 130 4.2 0.004
Girls with GD Frontal L Precentral/inferior frontal triangularis –56, 6, 33 61 3.9 0.005
Parietal R Superior parietal/inferior parietal 24, –60, 61 300 3.9 0.018
Parietal L Postcentral/superior parietal –42, –40, 57 366 4.5 0.001
Superior parietal/precuneus –17, –67, 57 341 3.9 0.012
AAL = automated anatomic labelling; FWE = family-wise error; GD = gender dysphoria; L = left hemisphere; MNI = Montreal Neurological Institute; R = right hemisphere; ROI = region of
interest.
Burke et al.
8 J Psychiatry Neurosci
increase in endogenous testosterone secretion.53 The increase
in parietal and frontal brain activations in the male controls
may therefore be testosterone-dependent as well.
Similar to our results, Sommer and colleagues36 found na-
tal women with GD to have increased brain activation in
MRT-implicated brain areas after 3 months of testosterone
treatment. However, this nding did not reach statistical sig-
nicance, possibly owing to the limited sample size of only
6women with GD. In contrast, Carrillo and colleagues34
found no group differences between 19 adult women with
GD receiving testosterone treatment and control men or
women. In their study, pretreatment data were not reported,
therefore within-group effects of the testosterone treatment
could not be determined. The authors noted that they did not
control for menstrual cycle effects, which might have inu-
enced their results.
At odds with our ndings, another study testing the effects
of testosterone treatment in 9 postmenopausal women indi-
cated decreased parietal activation during mental rotation af-
ter 26 weeks of transdermal testosterone treatment.54
The present study, suggesting a masculinization of the
functional neuroanatomy of visuospatial working memory in
natal girls with GD, are in line with 2 recent reports showing
testosterone treatment effects on morphological brain meas-
ures: cortical thickness, subcortical volumes,55 and white mat-
ter microstructure.56
Next to the group comparisons, we aimed to explore the
association between the testosterone treatment and visuospa-
tial brain functioning in girls with GD by means of regression
analyses. However, we found no signicant correlations be-
tween their post-treatment testosterone levels and their male-
typical parietal and frontal activation during mental rotation
at session 2, which suggests that within-group variations in
brain activation in girls with GD were not related to the acti-
vational effects of current testosterone levels.
In contrast to previous studies that showed superior male
performance (reaction time, accuracy) on the MRT,3,57 we did
not nd any signicant group differences on the behavioural
parameters. However, sex differences in brain activation
need not necessarily be reected in sex differences on a be-
havioural level, as has been shown by Jordan and col-
leagues.58 Moreover, particularly in the control boys MRT
task performance remained stable across sessions, whereas
both groups of natal girls showed improvements in accuracy
and reaction times at session 2 (Table 2). Thus, our neuroim-
aging ndings of a testosterone-associated increase in pari-
etal and frontal activation during mental rotation do not
match our MRT performance data. We speculate that the
underlying cause for the task improvement may be different
for the 2 groups of natal girls. The girls with GD may indeed
have beneted from the testosterone treatment in terms of
better visuospatial performance, as has been suggested previ-
ously by Aleman and colleagues.59 In the control girls, better
performance might be related to motivation and striving to
excel at a task, which is generally more difcult to accom-
plish for females. Accordingly, the control girls showed a
strong improvement with regard to reaction times, whereas
their accuracy scores improved only moderately.
Limitations
Our results should be viewed in light of some limitations.
First, by design, the groups differed with regard to the pu-
berty suppressing treatment at baseline. Therefore, we cannot
rule out that any differences in brain activation or behaviour
between the girls with GD and the control girls may have
been due to the hormonal suppression.
Second, we did not account for possible effects of men-
strual cycle or the use of hormonal contraception, which have
previously been shown to affect sex differences in mental ro-
tation performance.60–62 However, these effects of uctuating
endogenous hormone levels on visuospatial performance
were relatively small. In addition, the control girls were
tested randomly according to the phase of their menstrual
cycles, and about half of them were using hormonal contra-
ceptives. Therefore, we do not expect that any systematic dif-
ferences in circulating sex hormone levels might have af-
fected our results.
Third, it should be noted that sexual orientation might
present a confounding factor. Peters and colleagues63 and
Maylor and colleagues64 showed that performance on the
MRT varied as a function of sexual orientation: homosexual
men performed worse than heterosexual men, whereas les-
bian women excelled in mental rotation performance com-
pared with heterosexual women. The majority of natal
women with GD are gynephilic,65–67 which was also found in
our group of adolescent girls with GD. However, effects of
sexual orientation have been shown only for behavioural re-
sponses and have not been investigated using neuroimaging
studies of visuospatial cognitive abilities. Moreover, the ef-
fects of sexual orientation on mental rotation performance
were observed primarily in men, whereas only moderate or
even negligible effects were found in women.68–70 We there-
fore believe that such effects in our young natal female popu-
lation are likely to be small.
Finally, an alternative explanation for our ndings that
girls with GD showed similar visuospatial cognitive func-
tions as control boys may be that both groups share similar
interests and preferences for certain hobbies and activities,
such as video games and sports. Thus, the differences found
between control girls and girls with GD may also be related
to their differential experiences with visuospatial tasks and
may therefore reect, at least in part, training effects.
Conclusion
We found sex-atypical mental rotation–associated brain acti-
vations in adolescent girls with GD, suggesting a masculin-
ization of brain structures associated with visuospatial cogni-
tive functions. Moreover, our prospective fMRI study
provides new insights into the differential organizational and
activational effects of testosterone on visuospatial cognitive
functioning.
Acknowledgments: The authors thank Ms. Willeke Menks for her
help with participant recruitment and support during the fMRI and
neuropsychological data acquisition and Mr. Ton Schweigmann for
his efforts in coordinating and supporting the fMRI data acquisition.
Male-typical visuospatial functioning in gynephilic girls with gender dysphoria
J Psychiatry Neurosci 9
This work was supported by a VICI grant (453-08-003) from the Dutch
Science Foundation (Nederlandse Organisatie voor Wetenschappelijk
Onderzoek) to J. Bakker. J. Bakker is a senior research associate of the
Belgian Fonds National de la Recherche Scientique.
Afliations: From the Center of Expertise on Gender Dysphoria, De-
partment of Medical Psychology, VU University Medical Center, Am-
sterdam, the Netherlands (Burke, Kreukels, Cohen-Kettenis, Bakker);
the Netherlands Institute for Neuroscience, Neuroendocrinology
group, Meibergdreef 47, Amsterdam, the Netherlands (Burke, Bakker);
the Karolinska Institute, Department of Women’s and Children’s
Health, Karolinska Hospital, Stockholm, Sweden (Burke); the Depart-
ment of Psychiatry, VU University Medical Center, De Boelelaan, Am-
sterdam, the Netherlands (Veltman); the Department of Pediatric En-
docrinology, VU University Medical Center, De Boelelaan,
Amsterdam, the Netherlands (Klink); and the GIGA Neuroscience,
University of Liege, Avenue Hippocrate, Liege, Belgium (Bakker).
Competing interests: None declared.
Contributors: S. Burke, P. Cohen-Kettenis and J. Bakker designed the
study. S. Burke and D. Klink acquired the data, which S. Burke,
B.Kreukels, P. Cohen-Kettenis, D. Veltman and J. Bakker analyzed.
S. Burke and J. Bakker wrote the article, which all authors reviewed
and approved for publication.
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... Neuroimaging investigations revealed that during a Mental Rotation Test (MRT), men activate parietal cortex more than women who, in their turn, exhibit a more marked activation in the inferior frontal cortex (Hugdahl et al., 2006). Such activation patterns might depend on divergent strategies adopted to accomplish the task (Burke et al., 2016;Hugdahl et al., 2006). Namely, men might be inclined to use more holistic strategies, while women might prefer verbal or analytical strategies. ...
... Along this line, Burke et al. (2016) investigated visuospatial abilities with functional MRI (fMRI) during execution of the MRT in girls with GD, control girls and boys. They observed that the brain activation patterns of hormone-naive girls with GD were different from those observed in control girls and resembled those in control boys, suggesting a masculinization of functions associated with visuospatial working memory in girls with GD. ...
... They observed that the brain activation patterns of hormone-naive girls with GD were different from those observed in control girls and resembled those in control boys, suggesting a masculinization of functions associated with visuospatial working memory in girls with GD. To explain these results, the authors speculated that GD females and boys share similar interests and preferences for certain hobbies and activities reflecting different experiences and training of visuospatial abilities (Burke et al., 2016). ...
Article
Full-text available
The contribution of brain regions to visuospatial abilities according to sex differences and gender identity is inconsistently described. One potential explaining factor may be the different tasks employed requiring a variable load of working memory and other cognitive resources. Here we asked to 20 cis and 20 transgender participants to undergo functional Magnetic Resonance Imaging during performance of a judgement line of orientation test that was adapted to explore the basic visuospatial processing while minimizing the working memory load. We show that V1 activation may be viewed as a brain area with enhanced activation in males, regardless of participants’ gender identity. On its turn, gender identity exclusively influences the visuospatial processing of extrastriate visual areas (V5) in women with gender dysphoria. They showed enhanced V5 activation and an increased functional connectivity between V5 and V1. Overall our neuroimaging results suggest that the basic visuospatial abilities are associated with different activations pattern of cortical visual areas depending on the sex assigned at birth and gender identity.
... Such activation patterns might depend on divergent strategies adopted to accomplish the task (Hugdahl et al. 2006;Burke et al. 2016). Namely, men might be inclined to use more holistic strategies, while women might prefer verbal or analytical strategies. ...
... Along this line, Burke et al. (2016) investigated visuospatial abilities with functional MRI (fMRI) during execution of the MRT in girls with GD, control girls and boys. They observed that the brain activation patterns of hormone-naive girls with GD were different from those observed in control girls and resembled those in control boys, suggesting a masculinization of functions associated with visuospatial working memory in girls with GD. ...
... They observed that the brain activation patterns of hormone-naive girls with GD were different from those observed in control girls and resembled those in control boys, suggesting a masculinization of functions associated with visuospatial working memory in girls with GD. To explain these results, the authors speculated that GD females and boys share similar interests and preferences for certain hobbies and activities reflecting different experiences and training of visuospatial abilities (Burke et al. 2016). ...
Preprint
The contribution of brain regions to visuospatial abilities according to sex differences and gender identity is inconsistently described. One potential explaining factor may be the different tasks employed requiring a variable load of working memory and other cognitive resources. Here we asked to 20 cis and 20 trans gender participants to undergo functional Magnetic Resonance Imaging during performance of a judgement line of orientation test that was adapted to explore the basic visuospatial processing while minimizing the working memory load. We show that V1 activation may be viewed as a sexual dimorphic brain area with enhanced activation in males, regardless of participants' gender identity. On its turn, gender identity exclusively influences the visuospatial processing of extrastriate visual areas (V5) in women with gender dysphoria. They showed enhanced V5 activation and an increased functional connectivity between V5 and V1. Overall our neuroimaging results suggest that the basic visuospatial abilities are associated with distinct activations pattern of cortical visual areas depending on the sex assigned at birth and gender identity.
... Sex differences in the human brain have been widely investigated [7]. Not only is there widespread evidence for differences between the sexes in brain morphometric characteristics such as total brain volume [7][8][9] and grey matter and white matter proportions [7,10], but brain function also appears to differ between sexes [11,12]. In general, sex differences take two patterns in the brain: either more male than female or more female than male. ...
... Secondly, even though trans people are often exposed to a variety of social stressors, including stigma and discrimination [46,47,49], this did not appear to play a role in the current study. This is interesting, because the rather limited neuroimaging work on affective function in other brain regions in trans people has not yet assessed the involvement of ostracism in the existence of a possible trans brain phenotype [2,12,95,96]. ...
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Much research has been conducted on sexual differences of the human brain to determine whether and to what extent a brain gender exists. Consequently, a variety of studies using different neuroimaging techniques attempted to identify the existence of a brain phenotype in people with gender dysphoria (GD). However, to date, brain sexual differences at the metabolite level using magnetic resonance spectroscopy (1H-MRS) have not been explored in transgender people. In this study, 28 cisgender men (CM) and 34 cisgender women (CW) and 29 transgender men with GD (TMGD) underwent 1H-MRS at 3 Tesla MRI to characterize common brain metabolites. Specifically, levels of N–acetyl aspartate (NAA), choline (Cho), creatine (Cr), glutamate and glutamine (Glx), and myo-inositol + glycine (mI + Gly) were assessed in two brain regions, the amygdala-anterior hippocampus and the lateral parietal cortex. The results indicated a sex-assigned at birth pattern for Cho/Cr in the amygdala of TMGD. In the parietal cortex, a sex-assigned at birth and an intermediate pattern were found. Though assessed post-hoc, exploration of the age of onset of GD in TMGD demonstrated within-group differences in absolute NAA and relative Cho/Cr levels, suggestive for a possible developmental trend. While brain metabolite levels in TMGD resembled those of CW, some interesting findings, such as modulation of metabolite concentrations by age of onset of GD, warrant future inquiry.
... fMRI studies were conducted under visual stimulation (2), smelling stimulation (1), vocal stimulation (1), a mental rotation task (1), and a verbal fluency test (1). The 17 studies that conducted stereotaxic coordinates analysis involved 195 FtM, 208 MtF, 347 FC, and 346 MC. Figure 4 displays six representative slices showing the foci resultant from the meta-analysis carried out using GingerAle 2.3.6 software using data from 12/17 studies (Burke et al., 2014(Burke et al., , 2016Clemens et al., 2017;Feusner et al., 2017;Gizewski et al., 2009;Hoekzema et al., 2015;Junger et al., 2014;Ku et al, 2013;Manzouri et al., 2017;Santarnecchi et al., 2012;Savic and Arver, 2011;Schöning et al., 2010;Simon et al, 2013) (see Appendix 3 in Supplementary Materials for the labels of each foci and Table 5 for the number of foci related to different brain areas). The meta-analyses conducted ("Transgender_vs_Cisgender Natal Sex", "Transgender_vs_Cisgender Opposite Sex", and "Transgender_vs_Cisgender") showed that transgender people's brain activation differed more frequently in the Brodmann Areas (BA) 18 and 19, which include the occipital visual area along with BA 17, which is involved in visual processing. ...
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Objectives: This study focuses on sexual health aspects in partnered gender-dysphoric individuals at the start of medical treatment by examining their partnership constellations, sexual experiences, and reports of psychological problems. Methods: As part of the cross-national European Network for the Investigation of Gender Incongruence Study, 168 adult male-to-females (MFs) and female-to-males (FMs; MF:FM sex ratio = 1:1.2) were surveyed by means of self-administered questionnaires prior to any gender-confirming hormonal and surgical interventions. Results: MFs were often found to have androphilic (female) partners (sexually oriented toward males), noncomplementary with their female gender identity. In contrast, FMs frequently had androphilic (female) partners, complementary with their male gender identity and sexual orientations toward females. Conclusions: In both genders, complementary partnership constellations were associated with more avoidance of sexual experiences and more negative sexual experiences.
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It is still unclear to what extent cross-gender identity is due to pre- and perinatal organising effects of sex hormones on the brain. Empirical evidence for a relationship between prenatal hormonal influences and certain aspects of gender typical (cognitive) functioning comes from pre- and postpubertal clinical samples, such as women suffering from congenital adrenal hyperplasia and studies in normal children. In order to further investigate the hypothesis that cross-gender identity is influenced by prenatal exposure to (atypical) sex steroid levels we conducted a study with early onset, adult, male-to-female and female-to-male transsexuals, who were not yet hormonally treated, and nontranssexual adult female and male controls. The aim of the study was to find out whether early onset transsexuals performed in congruence with their biological sex or their gender identity. The results on different tests show that gender differences were pronounced, and that the two transsexual groups occupied a position in between these two groups, thus showing a pattern of performance away from their biological sex. The findings provide evidence that organisational hormonal influences may have an effect on the development of cross-gender identity.
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The 3D cube figures used by Shepard and Metzler [Shepard, R. N., & Metzler, J. (1971). Mental rotation of three-dimensional objects. Science, 171, 701-703] have been applied in a broad range of studies on mental rotation. This note provides a brief background on these figures, their general use in cognitive psychology and their role in studying spatial behavior. In particular, it is pointed out that large sex differences with the 3D mental rotation figures tend to be observed only in particular tasks, such as the Vandenberg and Kuse test [Vandenberg, S. G., & Kuse, A. R. (1978). Mental rotations, a group test of three-dimensional spatial visualization. Perceptual and Motor Skills, 47, 599-604] that involve multiple figures within a single problem. In contrast, pairwise presentation of the same 3D figures yields either small or no significant sex differences. In the context of the very broad range of ongoing research done with 3D figures, and the desirability of uniformity in the stimulus material used, we introduce a library of 16 cube mental rotation figures, each presented in orientations ranging from 0 to 360 degr in 5 degr steps, and with its mirror image, for a total of 2336 figures. This library, freely available to researchers, will help in the creation of mental rotation tasks both for presentation on the computer screen and for pencil and paper applications.
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The strongest sex differences on any cognitive task, favoring men, are found for tasks that require the mental rotation of three-dimensional objects. A number of studies have explored functional brain activation during mental rotation tasks, and sex differences have been noted in some. However, in these studies there was a substantial confounding factor because male and female subjects differed in overall performance levels. In contrast, our functional brain activation study examined cortical activation patterns for males and females who did not differ in overall level of performance on three mental rotation tasks. This allowed us to eliminate any confounding influences of overall performance levels. Women exhibited significant bilateral activations in the intraparietal sulcus (IPS) and the superior and inferior parietal lobule, as well as in the inferior temporal gyrus (ITG) and the premotor areas. Men showed significant activation in the right parieto-occitpital sulcus (POS), the left intraparietal sulcus and the left superior parietal lobule (SPL). Both men and women showed activation of the premotor areas but men also showed an additional significant activation of the left motor cortex. No significant activation was found in the inferior temporal gyrus. Our results suggest that there are genuine between-sex differences in cerebral activation patterns during mental rotation activities even when performances are similar. Such differences suggest that the sexes use different strategies in solving mental rotation tasks.
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The sexual behavior of male and female guinea pigs from mothers receiving testosterone propionate during most of pregnancy was studied after the attainment of adulthood. As a part of the investigation, the responsiveness of the females to estradiol benzoate and progesterone and to testosterone propionate was determined. The larger quantities of testosterone propionate produced hermaphrodites having external genitalia indistinguishable macroscopicalty from those of newborn males. Gonadectomized animals of this type were used for tests of their responsiveness to estradiol benzoate and progesterone and to testosterone propionate. The capacity to display lordosis following administration of estrogen and progesterone was greatly reduced. Male-like mounting behavior, on the other hand, was displayed by many of these animals even when lordosis could not be elicited. Suppression of the capacity for displaying lordosis was achieved with a quantity of androgen less than that required for masculinization of the external genitalia. The hermaphrodites receiving testosterone propionate as adults displayed an amount of mounting behavior which approached that displayed by the castrated injected males receiving the same hormone. The data are uniform in demonstrating that an androgen administered prenatally has an organizing action on the tissues mediating mating behavior in the sense of producing a responsiveness to exogenous hormones which differs from that of normal adult females. No structural abnormalities were apparent in the male siblings and their behavior was essentially normal. The results are believed to justify the conclusion that the prenatal period is a time when fetal morphogenic substances have an organizing or “differentiating” action on the neural tissues mediating mating behavior. During adulthood the hormones are activational. Attention is directed to the parallel nature of the relationship, on the one hand, between androgens and the differentiation of the genital tracts, and on the other, between androgens and the organization of the neural tissues destined to mediate mating behavior in the adult.
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Sex hormones, androgens in particular, are hypothesized to play a key role in the sexual differentiation of the human brain. However, possible direct effects of the sex chromosomes, that is, XX or XY, have not been well studied in humans. Individuals with complete androgen insensitivity syndrome (CAIS), who have a 46,XY karyotype but a female phenotype due to a complete androgen resistance, enable us to study the separate effects of gonadal hormones versus sex chromosomes on neural sex differences. Therefore, in the present study, we compared 46,XY men (n = 30) and 46,XX women (n = 29) to 46,XY individuals with CAIS (n = 21) on a mental rotation task using functional magnetic resonance imaging. Previously reported sex differences in neural activation during mental rotation were replicated in the control groups, with control men showing more activation in the inferior parietal lobe than control women. Individuals with CAIS showed a female-like neural activation pattern in the parietal lobe, indicating feminization of the brain in CAIS. Furthermore, this first neuroimaging study in individuals with CAIS provides evidence that sex differences in regional brain function during mental rotation are most likely not directly driven by genetic sex, but rather reflect gonadal hormone exposure. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.