Gender differences in white matter microstructure.
BACKGROUND
Sexual dimorphism in human brain structure is well recognised, but little is known about gender differences in white matter microstructure. We used diffusion tensor imaging to explore differences in fractional anisotropy (FA), an index of microstructural integrity.


METHODS
A whole brain analysis of 135 matched subjects (90 men and 45 women) using a 1.5 T scanner. A region of interest (ROI) analysis was used to confirm those results where proximity to CSF raised the possibility of partial-volume artefact.


RESULTS
Men had higher fractional anisotropy (FA) in cerebellar white matter and in the left superior longitudinal fasciculus; women had higher FA in the corpus callosum, confirmed by ROI.


CONCLUSIONS
The size of the differences was substantial--of the same order as that attributed to some pathology--suggesting gender may be a potentially significant confound in unbalanced clinical studies. There are several previous reports of difference in the corpus callosum, though they disagree on the direction of difference; our findings in the cerebellum and the superior longitudinal fasciculus have not previously been noted. The higher FA in women may reflect greater efficiency of a smaller corpus callosum. The relatively increased superior longitudinal fasciculus and cerebellar FA in men may reflect their increased language lateralisation and enhanced motor development, respectively.
Department of Psychological Medicine, King's College London, Institute of Psychiatry, London, United Kingdom. richard.kanaan@kcl.ac.uk
Richard A
RA
Kanaan
Matthew
M
Allin
Marco
M
Picchioni
Gareth J
GJ
Barker
Eileen
E
Daly
Sukhwinder S
SS
Shergill
James
J
Woolley
Philip K
PK
McGuire
D000328:Adult; D000704:Analysis of Variance; D016880:Anisotropy; D002531:Cerebellum / Q000033:anatomy & histology; D003337:Corpus Callosum / Q000033:anatomy & histology; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D008131:London; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure*; D012727:Sex Characteristics