Biological and behavioral differences between the sexes range from obvious to subtle or nonexistent. Neuroanatomical differences are particularly controversial, perhaps due to the implication that they might account for behavioral differences. In this sample of 200 men and women, large effect sizes (Cohen's d > 0.8) were found for sex differences in total cerebral gray and white matter, cerebellum, and gray matter proportion (women had a higher proportion of gray matter). The only one of these sex differences that survived adjustment for the effect of cerebral volume was gray matter proportion. Individual differences in cerebral volume accounted for 21% of the difference in gray matter proportion, while sex accounted for an additional 4%. The relative size of the corpus callosum was 5% larger in women, but this difference was completely explained by a negative relationship between relative callosal size and cerebral volume. In agreement with Jancke et al., individuals with higher cerebral volume tended to have smaller corpora callosa. There were few sex differences in the size of structures in Broca's and Wernicke's area. We conclude that individual differences in brain volume, in both men and women, account for apparent sex differences in relative size.

Many structural brain asymmetries accompany left hemisphere language dominance. For example, the cingulate sulcus is larger in the medial cortex of the right hemisphere, while the more dorsal paracingulate sulcus is larger on the left. The functional significance of these asymmetries is unknown because fMRI studies rarely attempt to localize activation to specific sulci, possibly due to difficulties in consistent sulcal identification. In medial cortex, for example, there are many regions of partial sulcal overlap where MRI images do not provide sufficient information to unambiguously distinguish a paracingulate sulcus from a displaced anterior cingulate segment. As large samples of postmortem material are rarely available for cytoarchitectural studies of sulcal variation, we have investigated the effect of variation in boundary and sulcal definition on paracingulate asymmetry in the MRI scans of 200 healthy adults (100 men, 100 women). Although women displayed a reliable asymmetry in the size of the paracingulate sulcus, regardless of boundary definition or technique, asymmetry was greatest when (1) the measurement was limited to the midcingulate region between the genu and the anterior commissure; and (2) the more dorsal of two overlapping sulci was always classified as a paracingulate sulcus (rather than as a displaced cingulate segment). The fact that paracingulate asymmetry is maximal in the midcingulate region suggests that this region may play a particular role in hemispheric specialization for language. Future work should investigate the structural and functional correlates of sulcal variation in this region.

As part of a study investigating commonalities between Prader-Willi syndrome (PWS -a genetic imprinting disorder) and early-onset obesity of unknown etiology (EMO) we measured total cerebral and cerebellar volume on volumetric MRI images. Individuals with PWS (n=16) and EMO (n=12) had smaller cerebellar volumes than a control group of 15 siblings (p=0.02 control vs. EMO; p=0.0005 control vs. PWS), although there was no difference among the groups in cerebral volume. Individuals with PWS and EMO also had impaired cognitive function: general intellectual ability (GIA): PWS 65 ± 25; EMO 81 ± 19; and Controls 112 ± 13 (p<0.0001 controls vs. PWS and controls vs. EMO). As both conditions are characterized by early-onset obesity and slowed cognitive development, these results raise the possibility that early childhood obesity retards both cerebellar and cognitive development.Prader-Willi syndrome (PWS) is a genetic disorder which is associated with developmental delay and learning disabilities. Other associated clinical features include hypotonia, speech delay, language problems, endocrinopathies, behavioral and psychiatric problems, and neonatal failure to thrive followed by early-onset childhood obesity (Goldstone, 2004). PWS is an imprinted condition with approximately 70% of the cases due to a de novo deletion in the paternally inherited chromosome 15q11-q13 region, 25% from a maternal uniparental disomy (UPD) of chromosome 15, and the remaining 5% from either microdeletions or epimutations of the imprinting center in the 15q11-q13 region (i.e. imprinting defects) (Glenn et al, 1997;Nicholls and Knepper, 2001;Bittel and Butler, 2005). Structural brain abnormalities occurring with PWS are thought to be due to the loss of function of several paternally expressed genes in the PWS region. The MKRN3, MAGEL2, NDN, C15orf2, SNURF-SNRPN, and a cluster of 5 sno-RNA genes are all expressed in the brain (Bittel and Butler, 2005;Lee et al, 2005;Lee et al, 2003). The loss of some of these genes may result in misrouting of long projection axons, resulting in abnormalities of cortical development which are thought to be associated with cognitive delay in individuals with PWS (Lee et al, 2005).Before MRI technology was available to allow correlation of structural brain findings with cognition, a retrospective study of individuals with PWS suggested that the degree of mental retardation in this syndrome can be modified by the extent of weight control early in life (i.e. those individuals with PWS who remained lean during early childhood did not have the decline in IQ noted in those who were obese during this time) (Crnic et al, 1980). This study raised the question as the extent to which environmental influences can modify the clinical phenotype in genetic syndromes. With current MRI technology it is now possible to investigate associations between brain structure, genotype, and phenotype in genetic disorders.The clinical phenotype of individuals with PWS, including mental retardation, hypotonia, motor delay, and poor fine ...

Although left hemisphere language specialization is one of the most widely reported findings in human neuropsychology, some studies have found evidence for more bilateral language organization in women. We report findings of a large scale, multi-task investigation of sex differences in both structural asymmetries and lateralization of word reading. Two hundred participants were tested in eight divided visual field lexical tasks, and each received a structural MRI scan. We examined whether there was evidence for sex differences in overall measures of neuroanatomical and behavioral lateralization, in specific language tasks and brain regions, and in variation in asymmetry within and across tasks and brain regions. There was very little evidence for sex differences on any behavioral measure. The few indications of sex differences in the current report accounted for 2% or less of the individual variation in asymmetry and could not be replicated in independent subsamples. No sex differences were observed in the asymmetry of structures in Broca’s and Wernicke’s area such as pars triangularis, pars opercularis, the planum temporale, planum parietale, or Heschl’s gyrus. There were also no sex differences in the variability of neuroanatomical asymmetries within or between brain regions. However, a significant relationship between planum temporale and behavioral asymmetry was restricted to men.

Background An aphasia treatment was designed to shift laterality from the left to right lateral frontal lobe during word production by initiating word-finding trials with complex left-hand movements. Previous findings indicated successful re-lateralization. Objective The current study was designed to ascertain whether the shift was attributable to the left-hand movement. Methods Using stratified random sampling, 14 subjects were equally divided between Intention (IT) and Control (CT) treatments. CT was identical to IT, except with no left-hand movements. Both treatments trained picture naming (phases 1, 2) and category-member generation (phase 3), each phase lasting 10 sessions. fMRI of category member generation occurred at pre-treatment, post-treatment, and 3-month follow-up. Results IT shifted lateral frontal activity rightward compared to pre-treatment both at post-treatment (t=−2.602, df=6, p<.05) and 3-month follow-up (t=−2.332, df=5, p<.05), but CT did not. IT and CT yielded similar changes for all picture-naming and category probes. However, IT patients showed gains for untrained category (t=3.33, df=6, p<.01) and picture-naming probes (t=3.77, df=5, p<.01), but CT patients did not. Conclusions The rightward shift in lateral frontal activity for IT was due to the left-hand movements. IT evoked greater generalization than CT.