Structural differences in the cerebral cortex of healthy female and male subjects: a magnetic resonance imaging study

Sex differences in brain activation elicited by humor

With recent investigation beginning to reveal the cortical and subcortical neuroanatomical correlates of humor appreciation, the present event-related functional MRI (fMRI) study was designed to elucidate sex-specific recruitment of these humor related networks. Twenty healthy subjects (10 females) underwent fMRI scanning while subjectively rating 70 verbal and nonverbal achromatic cartoons as funny or unfunny. Data were analyzed by comparing blood oxygenation-level-dependent signal activation during funny and unfunny stimuli. Males and females share an extensive humor-response strategy as indicated by recruitment of similar brain regions: both activate the temporal-occipital junction and temporal pole, structures implicated in semantic knowledge and juxtaposition, and the inferior frontal gyrus, likely to be involved in language processing. Females, however, activate the left prefrontal cortex more than males, suggesting a greater degree of executive processing and language-based decoding. Females also exhibit greater activation of mesolimbic regions, including the nucleus accumbens, implying greater reward network response and possibly less reward expectation. These results indicate sex-specific differences in neural response to humor with implications for sex-based disparities in the integration of cognition and emotion.

Sex differences in prefrontal cortical brain activity during fMRI of auditory verbal working memory

Functional imaging studies of sex effects in working memory (WMEM) are few, despite significant normal sex differences in brain regions implicated in WMEM. This functional MRI (fMRI) study tested for sex effects in an auditory verbal WMEM task in prefrontal, parietal, cingulate, and insula regions. Fourteen healthy, right-handed community subjects were comparable between the sexes, including on WMEM performance. Per statistical parametric mapping, women exhibited greater signal intensity changes in middle, inferior, and orbital prefrontal cortices than men (corrected for multiple comparisons). A test of mixed-sex groups, comparable on performance, showed no significant differences in the hypothesized regions, providing evidence for discriminant validity for significant sex differences. The findings suggest that combining men and women in fMRI studies of cognition may obscure or bias results.

Voxel-based morphometry versus region of interest: a comparison of two methods for analyzing gray matter differences in schizophrenia

Many previous studies exploring cortical gray matter (GM) differences in schizophrenia have used "region of interest" (ROI) measurements to manually delineate GM volumes. Recently, some investigators have instead employed voxel-based morphometry (VBM), an automated whole-brain magnetic resonance image measurement technique. The purpose of the current study was to compare the above methods in calculating GM distributions in schizophrenia patients relative to matched controls. Using ROIs, Buchanan et al. (Buchanan, R.W., Francis, A., Arango, C., Miller, K., Lefkowitz, D.M., McMahon, R.P., Barta, P.E. and Pearlson, G.D., 2004. Morphometric assessment of the heteromodal association cortex in schizophrenia. Am J Psychiatry. 161 (2), 322-331.) found decreased dorsolateral prefrontal GM volume and altered symmetry of inferior parietal GM in schizophrenia patients. We hypothesized that VBM analyses of the same data would complement the ROI findings. As predicted, VBM analyses replicated results of less left inferior and right superior frontal cortical GM in schizophrenia. Additionally, VBM uncovered a significantly lower concentration of GM in the middle and superior temporal gyri, sought but not detected using ROIs, but did not replicate the parietal changes. The principal explanation for these differences may be the methodological differences between voxel-averaged, landmark-based ROI analyses and the single, voxel-by-voxel whole brain VBM measurements. Although VBM is rapid and fully automated, it is not a replacement for manual ROI-based analyses. Both methods provide different types of information and should thus be used in tandem.

Chronic active heavy drinking and family history of problem drinking modulate regional brain tissue volumes

The goals of this study were to measure if chronic active heavy drinking is associated with brain volume loss in non-treatment seeking men and women, and to assess the effect of positive family history of problem drinking on brain structure in heavy drinkers. Automated image processing was used to analyze high-resolution T1-weighted magnetic resonance images from 49 active heavy drinkers and 49 age- and sex-matched light drinkers, yielding gray matter, white matter and cerebrospinal fluid (CSF) volumes within the frontal, temporal, parietal and occipital lobes. Regional brain volume measures were compared as a function of group, sex and their interaction. Within heavy drinkers, volumes were correlated with measures of alcohol consumption and compared as a function of family history of problem drinking. Deformation morphometry explored localized patterns of atrophy associated with heavy drinking or severity of drinking. We found significant gray matter volume losses, but no white matter losses, in active heavy drinkers compared with light drinkers. Women had greater gray matter and smaller white matter and CSF volumes as a percentage of intracranial vault than men. Within heavy drinkers, smaller gray matter volumes were associated with higher current levels of drinking and older age, while a positive family history of problem drinking was associated with smaller CSF volumes. Community-dwelling heavy drinkers who are not in alcoholism treatment have dose-related gray matter volume losses, and family history of problem drinking ameliorates some structural consequences of heavy drinking.

The neuroanatomy of general intelligence: sex matters

We examined the relationship between structural brain variation and general intelligence using voxel-based morphometric analysis of MRI data in men and women with equivalent IQ scores. Compared to men, women show more white matter and fewer gray matter areas related to intelligence. In men IQ/gray matter correlations are strongest in frontal and parietal lobes (BA 8, 9, 39, 40), whereas the strongest correlations in women are in the frontal lobe (BA10) along with Broca's area. Men and women apparently achieve similar IQ results with different brain regions, suggesting that there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs may manifest equivalent intellectual performance.

Sex-related developmental differences in the lateralized activation of the prefrontal cortex and amygdala during perception of facial affect

The lateralization of cognitive abilities is influenced by a number of factors, including handedness, sex, and developmental maturation. To date, a small number of studies have examined sex differences in the lateralization of cognitive and affective functions, and in only few of these have the developmental trajectories of these lateralized differences been mapped from childhood through early adulthood. In the present study, a cross-sectional design was used with healthy children (n=7), adolescents (n= 12), and adults (n= 10) who underwent functional magnetic resonance imaging (fMRI) during a task that required perceiving fearful faces. Males and females differed in the asymmetry of activation of the amygdala and prefrontal cortex across the three age groups. For males, activation within the dorsolateral prefrontal cortex was bilateral in children, right lateralized in adolescents, and bilateral in adults, whereas females showed a monotonic relationship with age, with older females showing more bilateral activation than younger ones. In contrast, amygdala activation was similar for both sexes, with bilateral activation in children, right-lateralized activation in adolescents, and bilateral activation in adults. These results suggest that males and females show different patterns of lateralized cortical and subcortical brain activation across the period of development from childhood through early adulthood.

Mapping brain structure and personality in late adulthood

Cerebral gray matter (GM) volume decreases in normal aging with a parallel increase in intracranial cerebrospinal fluid (CSF) volume. There is considerable interindividual variation in these changes, and the consequences of age-related GM shrinkage and CSF expansion are unclear. The present study examined whether late adulthood brain structural differences are related to differences in temperament and character. Personality structures of 42 healthy aged adults (mean age 60 years) were examined together with global and regional GM, CSF, and white matter (WM) volumes calculated from structural magnetic resonance images using voxel-based morphometry (VBM). A positive relationship was seen between GM volume at the border of the temporal, parietal, and frontal cortices, and self-transcendence, a character personality trait that reflects mature creativity and spiritualism. The relationship remained significant after a conservative correction for multiple comparisons and it was seen both using uncorrected raw values and after a correction for the effects of age and sex. The results suggest that high self-transcendence, which has adaptive advantages in the later part of life, is associated with relatively greater temporal cortical GM volumes.

Age-associated changes of cerebral glucose metabolic activity in both male and female deaf children: parametric analysis using objective volume of interest and voxel-based mapping

Quantitative analysis of brain activity in the brains of children requires the establishment of age-associated norms. We investigated regional differences in age-associated changes in fluorodeoxyglucose (FDG) uptake in the developmental brains. From 87 (44 male and 43 female) deaf children from the age of 1 to 15, brain FDG positron emission tomography (PET) images were examined after spatial normalization, smoothing, and global normalization to identify brain regions showing a correlation between FDG uptake and age. Using population-based probabilistic volume of interests (VOIs), an objective VOI analysis was performed where normalized relative FDG uptake was measured and their correlations with age were examined in both genders. For the voxel-based analyses, the correlations with age were examined in a general linear model using statistical parametric mapping (SPM99). Both methods revealed that FDG uptake linearly increases with age both in the bilateral inferior prefrontal/orbitofrontal gyri and the right dorsomedial frontal gyrus and decreases in the inferior temporal gyrus and internal capsule white matter. Male children showed age-associated increases of FDG uptake in the right dorsomedial frontal gyrus, and female children in the left dorsolateral prefrontal cortex and thalamus. These changes in FDG uptake in various brain regions may suggest changes in synaptic density or regional activity resulting from normal maturation or deaf-induced adaptation. Caution should be exercised in interpreting the differences in the brain of child patients when compared with adult control's or with a different gender. Further research will be needed to examine if gender difference is manifested in the development rate of behavioral/cognitive functions in association with the age-associated changes of the right medial frontal (male) or the left dorsolateral prefrontal cortices.

The genetic basis for sex differences in human behaviour: role of the sex chromosomes

The nature of the mechanisms underlying observed sex differences in human behaviour continues to be debated. This review concentrates on the thesis that genes on the sex chromosomes other than those directly controlling sex determination, and whose functions are, at least in part, independent from hormonal influences, play a significant role in determining gender differences in behaviour. To provide an adequate basis for examining this issue, the current understanding of the nature of sex determination, differences in behaviour and the influences of sex hormones are evaluated. The possible contribution to behavioural differences of those X-linked genes which escape inactivation, or which may be subjected to imprinting, is discussed. The review concludes with a summary of the genetic basis for two sexually disparate types of behaviour.

Brain function and structure in adults with attention-deficit/hyperactivity disorder

Cross-sectional data suggest that brain dysfunctions are a central component of attention-deficit/hyperactivity disorder (ADHD) in children, and a growing literature is suggesting the same for adults. This article reviews the current state of the literature pertaining to the structural and functional brain abnormalities that are found in adults with ADHD. Because the literature on ADHD in children is more extensive than that reported heretofore in ADHD in adults,the authors include brief summaries of the child literature to help inform that found in adults.

Cerebral volume loss, cognitive deficit and neuropsychological performance: comparative measures of brain atrophy: I. Dementia

There are several magnetic resonance (MR) imaging methods to measure brain volume and cerebral atrophy; however, the best measure for examining potential relationships between such measures and neuropsychological performance has not been established. Relationships between seven measures of MR derived brain volume or indices of atrophy and neuropsychological performance in the elderly subjects of the population-based Cache County, Utah Study of Aging and Memory (n = 195) were evaluated. The seven MR measures included uncorrected total brain volume (TBV), TBV corrected by total intracranial volume (TICV), TBV corrected by the ratio of the individuals TICV by group TICV (TBVC), a ventricle-to-brain ratio (VBR), total ventricular volume (TVV), TVV corrected by TICV, and a measure of parenchymal volume loss. The cases from the Cache County Study were comprised of elderly individuals classified into one of four subject groups based on a consensus diagnostic process, independent of quantitative MR imaging findings. The groups included subjects with Alzheimer's disease (AD, n = 85), no dementia but mild/ambiguous (M/A) deficits (n = 30), a group of subjects with non-AD dementia or neuropsychiatric disorder including vascular dementia (n = 60), and control subjects (n = 20). Neuropsychological performance was based on the Mini-Mental Status Exam (MMSE) and an expanded neuropsychological test battery (consortium to establish a registry for Alzheimer's disease (CERAD). The results demonstrated that the various quantitative MR measures were highly interrelated and no single measure was statistically superior. However, TBVC, TBV/TICV and VBR consistently exhibited the more robust relationships with neuropsychological performance. These results suggest that a single corrected brain volume measure or index is sufficient in studies examining global MR indicators of cerebral atrophy in relation to cognitive function and recommends use of either TBVC, TBV/TICV, or VBR.

Sex-Linked Differences in the Anatomy of the Perisylvian Language Cortex: A Volumetric MRI Study of Gray Matter Volumes

Perisylvian regions important for auditory processing include Heschl's gyrus (HG), the planum temporale (PT), the posterior superior temporal gyrus (pSTG), and the posterior ascending ramus (PAR). Sex-linked differences in language functions and anatomy have been suggested. To examine sex-linked differences, the authors used MRI to measure HG, PT, pSTG, and PAR volumes. Sex differences were found in right HG and right pSTG volumes but not in the left volumes of these structures. For the PT, there were sex differences in asymmetry; women exhibited leftward asymmetry of the PT, whereas men did not exhibit PT asymmetry. These findings suggest that there are sex-linked differences in the anatomy of primary and association auditory cortices.

Gender-specific Differences of Hypometabolism in mTLE: Implication for Cognitive Impairments

PURPOSE

To determine gender differences of hypometabolism and their implications for cognitive impairment in patients with medically refractory mesial temporal lobe epilepsy (mTLE).

METHODS

Regional cerebral glucose metabolism (rCMRGlu) was studied in 42 patients (21 male, 21 female) with either left- or right-sided mTLE (22 left, 20 right) and in 12 gender- and age-matched healthy controls during resting wakefulness and in 12 sex- and age-matched healthy controls. Clinical characteristics were balanced across the patient subgroups. All patients were subjected to neuropsychological assessment: 41 patients had histologic changes of definite or probable hippocampal sclerosis.

RESULTS

Data analysis based on pixel-by-pixel comparisons and on a laterality index of regions of interest (ROIs) showed significant depressions of the mean rCMRGlu extending beyond the mesiotemporal region and temporolateral cortex to extratemporal regions including the frontoorbital and insular cortex in mTLE patients. Extramesiotemporal hypometabolism prevailed in the male patients. Metabolic asymmetry in temporal and frontal regions was related to performance in the Trail-Making Test and WAIS-R subitems.

CONCLUSIONS

Our data showed a gender-specific predominance of extramesiotemporal hypometabolism in male patients with mTLE related to abnormalities of temporal and frontal lobe functions.

Sex differences in frontal lobe white matter microstructure: a DTI study

There is evidence that the brains of men and women are structurally different, but there are few data regarding possible sex differences in white matter microstructure. Using diffusion tensor imaging we assessed fractional anisotropy (FA) in the frontal lobe white matter on contiguous 5 mm slices in nine healthy male and 11 healthy female adults. Overall, women had higher FA in the left frontal lobe compared to men and a leftward asymmetry of FA in contrast to men, who showed no hemispheric asymmetry. Among women, greater leftward asymmetry of frontal lobe FA correlated significantly with better verbal comprehension and memory functioning. Our findings may be indicative of increased directional coherence and/or density of left hemisphere white matter fibers and a leftward asymmetry of this structural integrity among women compared to men.

Sex differences in mouse cortical thickness are independent of the complement of sex chromosomes

Although the morphology of the cerebral cortex is known to be sexually dimorphic in several species, to date this difference has not been investigated in mice. The present study is the first to report that the mouse cerebral cortex is thicker in males than in females. We further asked if this sex difference is the result of gonadal hormones, or alternatively is induced by a direct effect of genes encoded on the sex chromosomes. The traditional view of mammalian neural sexual differentiation is that androgens or their metabolites act during early development to masculinize the brain, whereas a feminine brain develops in the relative absence of sex steroids. We used mice in which the testis determination gene Sry was inherited independently from the rest of the Y chromosome to produce XX animals that possessed either ovaries or testes, and XY animals that possessed either testes or ovaries. Thus, the design allowed assessment of the role of sex chromosome genes, independent of gonadal hormones, in the ontogeny of sex differences in the mouse cerebral cortex. When a sex difference was present, mice possessing testes were invariably masculine in the morphology of the cerebral cortex, independent of the complement of their sex chromosomes (XX vs. XY), and mice with ovaries always displayed the feminine phenotype. These data suggest that sex differences in cortical thickness are under the control of gonadal steroids and not sex chromosomal complement. However, it is unclear whether it is the presence of testicular secretions or the absence of ovarian hormones that is responsible for the thicker male cerebral cortex.

Sexual dimorphism and asymmetries in the gray-white composition of the human cerebrum

Using high resolution MRI scans and automated tissue segmentation, gray and white matter (GM, WM) volumes of the frontal, temporal, parietal, and occipital lobes, cingulate gyrus, and insula were calculated. Subjects included 23 male and 23 female healthy, right-handed subjects. For all structures, male volumes were greater than female, but the gray/white (G/W) ratio was consistently higher across structures in women than men. Sexual dimorphism was greater for WM than GM: most of the G/W ratio sex differences can be attributed to variation in WM volume. The corpus callosum, although larger in men, is less sexually dimorphic than the WM as a whole. Several regions demonstrate pair-wise asymmetries in G/W ratio and WM volume. Both the cingulate gyrus and insula exhibit strong asymmetries. The left cingulate gyrus is significantly larger than the right, and the G/W ratio of the left insula is significantly greater than that of the right. Although statistically significant sex differences and asymmetries are present at this level of analysis, we argue that researchers should be wary of ascribing cognitive functional significance to these patterns at this time. This is not to say, however, that these patterns are not important for understanding the natural history of the human brain, and its evolution and development.

Sex differences in semantic language processing: a functional MRI study

Predictions based on two models of sex differences in cerebral organization of language were compared by examining fMRI patterns of 10 females and 9 males during a semantic processing task. Both groups displayed activation of left inferior frontal gyrus (IFG), left superior temporal gyrus (STG), and cingulate. Females, but not males, showed bilateral IFG and STG activation. Further analyses revealed females had less diffuse left activation and greater right posterior temporal and insula region activation than males. Results support both an interhemispheric and an intrahemispheric model of sex differences in language, suggesting that the models may not be mutually exclusive.

Quantitative frontal and temporal structural MRI studies in personality-disordered offenders and control subjects

High rates of temporal and frontal lobe dysfunction have been reported in neuropsychological and EEG studies of incarcerated personality-disordered (PD) offenders, but there have been few quantitative structural magnetic resonance imaging (MRI) studies. We investigated whether impulsive-aggressive male PD patients showed evidence of reduced brain volumes in frontal and temporal brain regions on MRI compared with healthy control subjects. All subjects were screened for axis I pathology and brain abnormalities. Quantitative measures of frontal and temporal lobe volume were computed on MR images of the brain in 19 control subjects and 18 patients who did not show any evidence of brain pathology on diagnostic MRI scans. Temporal lobe volumes were 20% smaller in PD patients than control subjects, but the predicted reductions in frontal lobe volume did not occur, despite evidence of impairments in executive function. There was no evidence of differences in asymmetry of brain structures. The study further implicates temporal lobes in the pathogenesis of severe personality disorder, but does not support the notion that PDs characterised by impulsive-aggressive traits have abnormalities in brain symmetry similar to those reported in mentally ill populations. Higher-resolution MRI studies are needed to localise the abnormalities and to determine their nature.

Abnormal asymmetry in language association cortex in autism

Autism is a neurodevelopmental disorder affecting cognitive, language, and social functioning. Although language and social communication abnormalities are characteristic, prior structural imaging studies have not examined language-related cortex in autistic and control subjects. Subjects included 16 boys with autism (aged 7-11 years), with nonverbal IQ greater than 80, and 15 age- and handedness-matched controls. Magnetic resonance brain images were segmented into gray and white matter; cerebral cortex was parcellated into 48 gyral-based divisions per hemisphere. Asymmetry was assessed a priori in language-related inferior lateral frontal and posterior superior temporal regions and assessed post hoc in all regions to determine specificity of asymmetry abnormalities. Boys with autism had significant asymmetry reversal in frontal language-related cortex: 27% larger on the right in autism and 17% larger on the left in controls. Only one additional region had significant asymmetry differences on post hoc analysis: posterior temporal fusiform gyrus (more left-sided in autism), whereas adjacent fusiform gyrus and temporooccipital inferior temporal gyrus both approached significance (more right-sided in autism). These inferior temporal regions are involved in visual face processing. In boys with autism, language and social/face processing-related regions displayed abnormal asymmetry. These structural abnormalities may relate to language and social disturbances observed in autism.

3D laser surface scanning and geometric morphometric analysis of craniofacial shape as an index of cerebro-craniofacial morphogenesis: initial application to sexual dimorphism

BACKGROUND

Over early fetal life, when disturbances in schizophrenia have been posited and craniofacial dysmorphogenesis reported, cerebral morphogenesis proceeds in embryological intimacy with craniofacial morphogenesis. Digitization technologies now allow 3D recording of craniofacial surface landmarks and modeling of craniofacial shape differences using geometric morphometrics.

METHODS

Using normal sexual dimorphism as an exemplar, facial surfaces of 131 Medical School employees [82 females, 49 males] were recorded in 3D using a portable, hand-held laser scanner; 3D coordinate data were then analyzed using geometric morphometrics.

RESULTS

Males and females differed markedly on an omnibus test of craniofacial shape. Logistic regression analysis of 16 principal components of shape variability, explaining 84.9% of the overall sample variance, generated 8 principal components as significant and independent discriminators. On visualization, the female face is wider and flatter; the eyes are more lateral, anterior and are further apart, and nasal bridge is posterior; the nose is smaller; the lips are fuller and the chin more forward. These findings are complementary to sexual dimorphism in cerebral structures.

CONCLUSIONS

This technique reliably discriminates geometric features of craniofacial morphology that are associated with aspects of cerebral morphology, and may inform on putative neurodevelopmental disorders characterised by dysmorphogenesis.

Cerebral asymmetry and the effects of sex and handedness on brain structure: a voxel-based morphometric analysis of 465 normal adult human brains

We used voxel-based morphometry (VBM) to examine human brain asymmetry and the effects of sex and handedness on brain structure in 465 normal adults. We observed significant asymmetry of cerebral grey and white matter in the occipital, frontal, and temporal lobes (petalia), including Heschl's gyrus, planum temporale (PT) and the hippocampal formation. Males demonstrated increased leftward asymmetry within Heschl's gyrus and PT compared to females. There was no significant interaction between asymmetry and handedness and no main effect of handedness. There was a significant main effect of sex on brain morphology, even after accounting for the larger global volumes of grey and white matter in males. Females had increased grey matter volume adjacent to the depths of both central sulci and the left superior temporal sulcus, in right Heschl's gyrus and PT, in right inferior frontal and frontomarginal gyri and in the cingulate gyrus. Females had significantly increased grey matter concentration extensively and relatively symmetrically in the cortical mantle, parahippocampal gyri, and in the banks of the cingulate and calcarine sulci. Males had increased grey matter volume bilaterally in the mesial temporal lobes, entorhinal and perirhinal cortex, and in the anterior lobes of the cerebellum, but no regions of increased grey matter concentration.

Frequency dependence and gender effects in visual cortical regions involved in temporal frequency dependent pattern processing

Neural response to flickering stimuli has been shown to be frequency dependent in the primary visual cortex. Controversial gender differences in blood oxygen level dependent (BOLD) amplitude upon 6 and 8 Hz visual stimulation have been reported. In order to analyze frequency and gender effects in early visual processing we employed a passive graded task paradigm with a dartboard stimulus combining eight temporal frequencies from 0 to 22 Hz in one run. Activation maps were calculated within Statistical Parametric Mapping, and BOLD amplitudes were estimated for each frequency within the striate and extrastriate visual cortex. The BOLD amplitude was found to steadily rise up to 8 Hz in BA 17 and 18 with an activation plateau at higher frequencies. In addition, we observed a laterality effect in the striate cortex with higher BOLD contrasts in the right hemisphere in men and in women. BOLD response rises similarly in men and women up to 8 Hz but with lower amplitudes in women at 4, 8, and 12 Hz (30% lower). No frequency effect above 1 Hz was found in the extrastriate visual cortex. There was also a regional specific gender difference. Men activated more in the right lingual gyrus (BA 18) and the right cerebellum compared with women, whereas women showed more activation in the right inferior temporal gyrus (BA 17). The study indicates that frequency dependent processing at the cortical level is limited to the striate cortex and may be associated with a more global information processing (right hemisphere dominance), particularly in men. The finding of significantly lower BOLD amplitudes in women despite previously shown larger VEP (visual evoked potential) amplitudes might suggest gender differences in cerebral hemodynamics (baseline rCBV, rCBF, or neurovascular coupling). The regional distinction points at additional differences in psychological processing even when using a simple visual stimulus.

Sex-specific developmental changes in amygdala responses to affective faces

It is hypothesized that adolescent development involves a redistribution of cerebral functions from lower subcortical structures to higher regions of the prefrontal cortex to provide greater self-control over emotional behavior. We further hypothesized that this redistribution is likely to be moderated by sex-specific hormonal changes. To examine developmental sex differences in affective processing, 19 children and adolescents underwent fMRI while viewing photographs of faces expressing fear. Males and females differed in the pattern of their amygdala vs prefrontal activation during adolescent maturation. With age, females showed a progressive increase in prefrontal relative to amygdala activation in the left hemisphere, whereas males failed to show a significant age related difference. There appear to be sex differences in the functional maturation of affect-related prefrontal-amygdala circuits during adolescence.

Opiate receptor avidity in the thalamus is sexually dimorphic in the elderly

Opiate receptor avidity (B(')(max)/K(D)), was measured in the subcortex of nine females (five healthy subjects, four Alzheimer patients) and 15 males (seven healthy subjects, eight Alzheimer patients), 51-75 years of age, with the opiate receptor antagonist 6-deoxy-6-beta-[(18)F]fluoronaltrexone (cyclofoxy, CF) and a positron emission tomograph. CF avidity was 27.5% less in the thalamus of healthy women compared to healthy men and 48.5% less in Alzheimer disease female patients compared to male patients.

Brain morphological changes and early marijuana use: a magnetic resonance and positron emission tomography study

BACKGROUND

The focus of this report is on the possible role that the age of first use of marijuana may play on brain morphology and function.

METHODS

Magnetic resonance imaging (MRI) and positron emission tomography (PET) were utilized to study 57 subjects. Brain volume measures (whole brain, gray matter, white matter and lateral ventricle volumes), global cerebral blood flow (CBF) and body size were evaluated.

RESULTS

There are three primary findings related to age of first use of marijuana. Subjects who started using marijuana before age 17, compared to those who started later, had smaller whole brain and percent cortical gray matter and larger percent white matter volumes. Functionally, males who started using marijuana before 17 had significantly higher CBF than other males. Both males and females who started younger were physically smaller in height and weight, with the effects being greater in males.

CONCLUSIONS

These findings suggest that the age at which exposure to marijuana begins is important. Early adolescence may be a critical period for effects that are not present when exposure begins later. These results are discussed in light of reported effects of marijuana on gonadal and pituitary hormones.

Measurement of the planum temporale (PT) on magnetic resonance imaging scans: temporal PT alone and with parietal extension

The planum temporale (PT) has been of interest because of (1) its consistent left greater than right asymmetry among right-handed and most left-handed normal individuals; and (2) its relation to language, another variable shown to be highly left-lateralized in normal subjects. Individuals with neurodevelopmental disorders have been reported to show abnormal PT asymmetry (either reversed or absent asymmetry). Several studies have been conducted measuring the PT on MRI scans, although the results do not always concur. We review some of these studies and discuss methodological differences between them. Additionally, we propose a method that has proved to be highly reliable for the measurement of both temporal PT and its parietal extension (PT+).

Volumetric study of lobar atrophy in Pick complex and Alzheimer's disease

BACKGROUND

Lobar atrophy is an important neuroimaging feature of Pick complex (PiC). However, differences in patterns of focal brain atrophy between PiC and Alzheimer's disease (AD), and among PiC subgroups, have not been studied quantitatively.

OBJECTIVE

To compare volumetric measures among primary progressive aphasia (PPA), frontotemporal dementia (FTD) and AD; to assess association between brain atrophy and cognition.

PATIENTS

Seventeen patients with PPA, 11 with FTD and 24 with probable AD were studied.

METHODS

We measured total and regional volume quantitatively using MRI and computerized volumetry. Contributing factors were controlled statistically or by adopting brain volume ratios. We investigated the classifying power of volumetry and correlated regional brain volume with cognitive and language test scores.

RESULTS

The ratio for fronto-temporo-central region was smaller on the left in PPA and on the right in FTD. AD and some PPA patients had smaller parietal lobes. The frontal ratios correctly classified 93% of PPA and FTD patients, but only 50% of the entire PiC and AD patients. Language-dependent examinations correlated with the left fronto-temporal volume.

CONCLUSIONS

Brain atrophy differs in PPA, FTD and AD, but there is some morphological overlap between PiC and AD in parietal volumes. Focal brain atrophy is most consistently associated with language impairments.

Sexual dimorphism in the human brain: evaluation of tissue volume, tissue composition and surface anatomy using magnetic resonance imaging

Magnetic resonance imaging (MRI) was used to evaluate sex differences in brain morphology by comparing measures of brain tissue volume, brain tissue composition (proportions of gray and white matter), and measures of cortical surface anatomy. A large and well-matched sample of healthy women (n=42) and healthy men (n=42) were evaluated. There was a significant gender effect on intracranial volume, males being larger. However, this increase in size was limited to the cerebrum as there was no sex difference in the volume of the cerebellum. The gender difference in size of the cerebral volume was evenly distributed, with all four lobes equally larger in males compared to females. Gray and white matter tissue proportions were similar between the sexes globally. Regional tissue composition analysis showed sex differences within the parietal lobes with females having proportionately more gray matter on the right side. There were no differences between the sexes in cortical surface anatomy measures. Overall, against the background of similarity in morphology, there are differences between the sexes with regard to general and regional brain measures. The functional significance of these sex differences is unclear, but may represent the differential effects of gonadal hormones during brain growth and development.

Sex differences in prefrontal volume with aging and Alzheimer's disease

We used volumetric magnetic resonance imaging to examine sex differences in prefrontal tissue volumes of healthy aged and patients with Alzheimer's disease (AD). Healthy subjects had greater total prefrontal volume than AD, and men had greater total prefrontal volume than women (ps < or = 0.02). This was true for both gray and white matter volumes. There were no interactions between group and sex for total prefrontal volume. An exploratory analysis of each group suggested that sex differences in both gray and white matter in healthy aging are not sustained in AD.

Spatial working memory: absence of gender differences in schizophrenia patients and healthy control subjects

BACKGROUND

Spatial working memory dysfunction has been suggested to be a cardinal feature of schizophrenia. But schizophrenia is heterogeneous in its clinical profile, course, and outcome. One fundamental contributor to this heterogeneity may be gender. No report has yet addressed gender differences in spatial working memory, as measured by the delayed-response task (DRT).

METHODS

We aggregated data from three previously published studies of spatial working memory in schizophrenia and also collected DRT data from a new sample of subjects in order to examine potential gender differences in DRT performance.

RESULTS

As previously reported, schizophrenia patients (n = 71) showed deficits in spatial working memory relative to normal control subjects (n = 213), however, no within-group or between-group gender differences were present.

CONCLUSIONS

These findings provide evidence for the absence of gender differences in spatial working memory function.

Broca's region revisited: cytoarchitecture and intersubject variability

The sizes of Brodmann's areas 44 and 45 (Broca's speech region) and their extent in relation to macroscopic landmarks and surrounding areas differ considerably among the available cytoarchitectonic maps. Such variability may be due to intersubject differences in anatomy, observer-dependent discrepancies in cytoarchitectonic mapping, or both. Because a reliable definition of cytoarchitectonic borders is important for interpreting functional imaging data, we mapped areas 44 and 45 by means of an observer-independent technique. In 10 human brains, the laminar distributions of cell densities were measured vertical to the cortical surface in serial coronal sections stained for perikarya. Thousands of density profiles were obtained. Cytoarchitectonic borders were defined as statistically significant changes in laminar patterns. The analysis of the three-dimensional reconstructed brains and the two areas showed that cytoarchitectonic borders did not consistently coincide with sulcal contours. Therefore, macroscopic features are not reliable landmarks of cytoarchitectonic borders. Intersubject variability in the cytoarchitecture of areas 44 and 45 was significantly greater than cytoarchitectonic differences between these areas in individual brains. Although the volumes of area 44 differed across subjects by up to a factor of 10, area 44 but not area 45 was left-over-right asymmetrical in all brains. All five male but only three of five female brains had significantly higher cell densities on the left than on the right side. Such hemispheric and gender differences were not detected in area 45. These morphologic asymmetries of area 44 provide a putative correlate of the functional lateralization of speech production.

Structural brain imaging in schizophrenia: a selective review

Structural neuroimaging studies have provided some of the most consistent evidence for brain abnormalities in schizophrenia. Since the initial computed tomography study by Johnstone and co-workers, which reported lateral ventricular enlargement in schizophrenia, advances in brain imaging technology have enabled further and more refined characterization of abnormal brain structure in schizophrenia in vivo. This selective review discusses the major issues and findings in structural neuroimaging studies of schizophrenia. Among these are evidence for generalized and regional brain volume abnormalities, the specificity of anatomic findings to schizophrenia and to men versus women with schizophrenia, the contribution of genetic influences, and the timing of neuroanatomic pathology in schizophrenia. The second section reviews new approaches for examining brain structure in schizophrenia and their applications to studies on the pathophysiology of schizophrenia.

A brain sexual dimorphism controlled by adult circulating androgens

Reports of structural differences between the brains of men and women, heterosexual and homosexual men, and male-to-female transsexuals and other men have been offered as evidence that the behavioral differences between these groups are likely caused by differences in the early development of the brain. However, a possible confounding variable is the concentration of circulating hormones seen in these groups in adulthood. Evaluation of this possibility hinges on the extent to which circulating hormones can alter the size of mammalian brain regions as revealed by Nissl stains. We now report a sexual dimorphism in the volume of a brain nucleus in rats that can be completely accounted for by adult sex differences in circulating androgen. The posterodorsal nucleus of the medial amygdala (MePD) has a greater volume in male rats than in females, but adult castration of males causes the volume to shrink to female values within four weeks, whereas androgen treatment of adult females for that period enlarges the MePD to levels equivalent to normal males. This report demonstrates that adult hormone manipulations can completely reverse a sexual dimorphism in brain regional volume in a mammalian species. The sex difference and androgen responsiveness of MePD volume is reflected in the soma size of neurons there.

Sex differences in brain gray and white matter in healthy young adults: correlations with cognitive performance

Sex-related differences in behavior are extensive, but their neuroanatomic substrate is unclear. Indirect perfusion data have suggested a higher percentage of gray matter (GM) in left hemisphere cortex and in women, but differences in volumes of the major cranial compartments have not been examined for the entire brain in association with cognitive performance. We used volumetric segmentation of dual echo (proton density and T2-weighted) magnetic resonance imaging (MRI) scans in healthy volunteers (40 men, 40 women) age 18-45. Supertentorial volume was segmented into GM, white matter (WM), and CSF. We confirmed that women have a higher percentage of GM, whereas men have a higher percentage of WM and of CSF. These differences sustained a correction for total intracranial volume. In men the slope of the relation between cranial volume and GM paralleled that for WM, whereas in women the increase in WM as a function of cranial volume was at a lower rate. In men the percentage of GM was higher in the left hemisphere, the percentage of WM was symmetric, and the percentage of CSF was higher in the right. Women showed no asymmetries. Both GM and WM volumes correlated moderately with global, verbal, and spatial performance across groups. However, the regression of cognitive performance and WM volume was significantly steeper in women. Because GM consists of the somatodendritic tissue of neurons whereas WM comprises myelinated connecting axons, the higher percentage of GM makes more tissue available for computation relative to transfer across distant regions. This could compensate for smaller intracranial space in women. Sex difference in the percentage and asymmetry of the principal cranial tissue volumes may contribute to differences in cognitive functioning.

Cerebral CT findings in male opioid-dependent patients: stereological, planimetric and linear measurements

Cerebrospinal fluid (CSF) space enlargement has been demonstrated in substance-related disorders like alcohol and cocaine dependence. Experimental animal studies showed a reduction in shape and size of mesolimbic dopaminergic neurons after chronic morphine administration. Other studies indicated a change of neurofilament and glial fibrillary acid proteins after chronic opiate administration. Furthermore, frequent overdosing and toxicological effects of 'street'-heroin may lead to CSF space enlargement in opioid dependence. In our study the pericortical and ventricular CSF space of 21 male opioid-dependent patients was compared with an age- and sex-matched normal control group. Considering serious problems with ratio and proportion measures, we used a battery of linear (cella media index, Huckman number, frontal horn index), planimetric (cortical atrophy score) and stereological volumetric measures in order to detect differences in cranial computerized tomography scans. We found a significant ventricular and cortical volume loss of the brain in opioid-dependent patients. A higher degree of frontal lobe volume loss seemed to be associated with a shorter period of abstinence before relapse. However, the etiology of volume loss of the brain in opioid-dependent patients is still unclear, but experimental animal studies provide some evidence that long-term, chronic opiate exposure is associated with visible changes of specific structures in the brain.

Unsolved problems in comparing brain sizes in Homo sapiens

When brain size is compared across taxonomic levels, there is a clear relation between body parameters and brain size. It is generally stated that the correlation between brain size and body parameters becomes very small at the species level (Aboitiz, 1996), but this is not the case for Homo sapiens where there is a strong correlation between brain size and body size across racial groups that differ in body size. The control for body size across racial groups (and sexes) is rendered difficult because bodies do not just differ only in height and weight. Within groups different studies show weak and inconsistent brain size/body height correlations. A better understanding of brain size/body height relations must await better quality data and a better understanding of how exactly body parameters should be scaled between groups and sexes. We attribute the clear between-group and weak within-group correlations to the large variety of body sizes and body types in our species, a variety which is only equalled in selectively bred species of animals. At present, there is no meaningful basis for the comparison of brain sizes within and between racial groups and sexes.

Sexual dimorphism of the developing human brain

1. Sexual dimorphism of human brain anatomy has not been well-studied between 4 and 18 years of age, a time of emerging sex differences in behavior and the sexually specific hormonal changes of adrenarche (the predominantly androgenic augmentation of adrenal cortex function occurring at approximately age 8) and puberty. 2. To assess sex differences in brain structures during this developmental period volumes of the cerebrum, lateral ventricles, caudate, putamen, globus pallidus temporal lobe, amygdala, and hippocampus, and midsagittal area measurements of the corpus callosum were quantified from brain magnetic resonance images of 121 healthy children and adolescent and examined in relation to age and sex. 3. Males had a 9% larger cerebral volume. When adjusted for cerebral volume by ANCOVA only the basal ganglia demonstrated sex differences in mean volume with the caudate being relatively larger in females and the globus pallidus being relatively larger in males. The lateral ventricles demonstrated a prominent sex difference in brain maturation with robust increases in size in males only. A piecewise-linear model revealed a significant change in the linear regression slope of lateral ventricular volume in males after age 11 that was not shared by females at that or other ages. 4. Amygdala and hippocampal volume increased for both sexes but with the amygdala increasing significantly more in males than females and hippocampal volume increasing more in females. 5. These sexually dimorphic patterns of brain development may be related to the observed sex differences in age of onset, prevalence, and symptomatology seen in nearly all neuropsychiatric disorders of childhood.

Sex differences in olfactory identification and Wisconsin Card Sorting performance in schizophrenia: relationship to attention and verbal ability

We investigated the hypothesis that different prefrontal brain systems (i.e., dorsal vs. ventral) and sex contribute differentially to cognitive deficit in schizophrenia. Performance was assessed among clinically stable, chronic schizophrenic outpatients and matched normal control subjects on olfactory identification [on the University of Pennsylvania Smell Identification Test (UPSIT)] and on executive functions [using the Wisconsin Card Sorting Test (WCST)]. Patients were impaired on both tests compared to controls, and male schizophrenics were impaired on the WCST compared to female schizophrenics. The pattern of results suggests that gender differences on the UPSIT are mildly accentuated in schizophrenia. The data support our previous study indicating that UPSIT performance is largely independent of the executive or attentional deficits typically associated with schizophrenia, with the exception of verbal ability. Further research with larger samples is required to test the hypothesis that there is a severely impaired subgroup of male patients with diffuse prefrontal dysfunctions.

Sex differences in neuropsychological function in non-psychotic relatives of schizophrenic probands

Some recent studies suggest that men with schizophrenia may have greater neuropsychological deficits than women. It is not known, however, whether similar sex differences may be present in biological relatives of schizophrenic patients. We evaluated neuropsychological functioning of 54 relatives of schizophrenic patients and 72 normal volunteers. It was hypothesized that, if sex differences were present, they would be accounted for largely by deficits in male relatives. We were particularly interested in three neuropsychological functions that we previously identified as putative neuropsychological vulnerability indicators for schizophrenia: (1) abstraction/executive function; (2) verbal memory; and (3) auditory attention. There were significant group x sex interactions for verbal memory and motor function, and trends toward significant interactions for auditory attention and mental control/encoding. However, with the exception of motor function, it was the female relatives who accounted for most of the impairment. A speculative explanation for the findings is that women may have a higher threshold than men for developing schizophrenia. If so, female relatives might be able to withstand greater impairments than men before developing psychotic symptoms. Consequently, in a sample that was limited to non-psychotic relatives--as in the present study--there could be over-representation of both less impaired men and more impaired women. Alternative explanations and limitations of the study are also discussed.

The anatomy of mood disorders--review of structural neuroimaging studies

The structural neuroimaging findings in mood disorders were reviewed, to evaluate evidence for a neuroanatomic model of pathophysiology, involving the prefrontal cortex, the basal ganglia, the amygdala-hippocampus complex, thalamus, and connections among these structures. Global atrophy is not consistently found. The best replicated finding is an increased rate of white matter and periventricular hyperintensities. A smaller frontal lobe, cerebellum, caudate, and putamen appear present in unipolar depression. A larger third ventricle, and smaller cerebellum and perhaps temporal lobe appear present in bipolar disorder. These localized structural changes involve regions that may be critical in the pathogenesis of mood disorders. Generalized and localized anatomic alterations may be related to age or vascular disease. The clinical and biological correlates of these changes need to be investigated to allow development of a more complete model of pathophysiology of mood disorders.