Gender-related differences in regional cerebral glucose metabolism in normal volunteers

Exploring sex differences: insights into gene expression, neuroanatomy, neurochemistry, cognition, and pathology

Increased knowledge about sex differences is important for development of individualized treatments against many diseases as well as understanding behavioral and pathological differences. This review summarizes sex chromosome effects on gene expression, epigenetics, and hormones in relation to the brain. We explore neuroanatomy, neurochemistry, cognition, and brain pathology aiming to explain the current state of the art. While some domains exhibit strong differences, others reveal subtle differences whose overall significance warrants clarification. We hope that the current review increases awareness and serves as a basis for the planning of future studies that consider both sexes equally regarding similarities and differences.

Regional sex differences in neurochemical profiles of healthy mice measured by magnetic resonance spectroscopy at 9.4 tesla

Objective

To determine sex differences in the neurochemical concentrations measured by in vivo proton magnetic resonance spectroscopy (1H MRS) of healthy mice on a genetic background commonly used for neurodegenerative disease models.

Methods

1H MRS data collected from wild type mice with C57BL/6 or related genetic backgrounds in seven prior studies were used in this retrospective analysis. To be included, data had to be collected at 9.4 tesla magnetic field using advanced 1H MRS protocols, with isoflurane anesthesia and similar animal handling protocols, and a similar number of datasets from male and female mice had to be available for the brain regions analyzed. Overall, 155 spectra from female mice and 166 spectra from male mice (321 in total), collected from six brain regions (brainstem, cerebellum, cortex, hippocampus, hypothalamus, and striatum) at various ages were included.

Results

Concentrations of taurine, total creatine (creatine + phosphocreatine), ascorbate, glucose and glutamate were consistently higher in male vs. female mice in most brain regions. Striatum was an exception with similar total creatine in male and female mice. The sex difference pattern in the hypothalamus was notably different from other regions. Interaction between sex and age was significant for total creatine and taurine in the cerebellum and hippocampus.

Conclusion

Sex differences in regional neurochemical levels are small but significant and age-dependent, with consistent male-female differences across most brain regions. The neuroendocrine region hypothalamus displays a different pattern of sex differences in neurochemical levels. Differences in energy metabolism and cellular density may underlie the differences, with higher metabolic rates in females and higher osmoregulatory and antioxidant capacity in males.

The need of radiotherapy optimization for glioblastomas considering immune responses

Glioblastoma is the most common of malignant primary brain tumors and one of the tumors with the poorest prognosis for which the overall survival rate has not significantly improved despite recent advances in treatment techniques and therapeutic drugs. Since the emergence of immune checkpoint inhibitors, the immune response to tumors has attracted increasing attention. Treatments affecting the immune system have been attempted for various tumors, including glioblastomas, but little has been shown to be effective. It has been found that the reason for this is that glioblastomas have a high ability to evade attacks from the immune system, and that the lymphocyte depletion associated with treatment can reduce its immune function. Currently, research to elucidate the resistance of glioblastomas to the immune system and development of new immunotherapies are being vigorously carried out. Targeting of radiation therapy for glioblastomas varies among guidelines and clinical trials. Based on early reports, target definitions with wide margins are common, but there are also reports that narrowing the margins does not make a significant difference in treatment outcome. It has also been suggested that a large number of lymphocytes in the blood are irradiated by the irradiation treatment to a wide area in a large number of fractionations, which may reduce the immune function, and the blood is being recognized as an organ at risk. Recently, a randomized phase II trial comparing two types of target definition in radiotherapy for glioblastomas was conducted, and it was reported that the overall survival and progression-free survival were significantly better in a small irradiation field group. We review recent findings on the immune response and the immunotherapy to glioblastomas and the novel role of radiotherapy and propose the need to develop an optimal radiotherapy that takes radiation effects on the immune function into account.

Current and Emerging Techniques in Neuroimaging of Sport-Related Concussion

SUMMARY

Sport-related concussion (SRC) affects an estimated 1.6 to 3.8 million Americans each year. Sport-related concussion results from biomechanical forces to the head or neck that lead to a broad range of neurologic symptoms and impaired cognitive function. Although most individuals recover within weeks, some develop chronic symptoms. The heterogeneity of both the clinical presentation and the underlying brain injury profile make SRC a challenging condition. Adding to this challenge, there is also a lack of objective and reliable biomarkers to support diagnosis, to inform clinical decision making, and to monitor recovery after SRC. In this review, the authors provide an overview of advanced neuroimaging techniques that provide the sensitivity needed to capture subtle changes in brain structure, metabolism, function, and perfusion after SRC. This is followed by a discussion of emerging neuroimaging techniques, as well as current efforts of international research consortia committed to the study of SRC. Finally, the authors emphasize the need for advanced multimodal neuroimaging to develop objective biomarkers that will inform targeted treatment strategies after SRC.

Sex-specific radiomic features of L-[S-methyl-11C] methionine PET in patients with newly-diagnosed gliomas in relation to IDH1 predictability

Introduction

Amino-acid positron emission tomography (PET) is a validated metabolic imaging approach for the diagnostic work-up of gliomas. This study aimed to evaluate sex-specific radiomic characteristics of L-[S-methyl-¹¹Cmethionine (MET)-PET images of glioma patients in consideration of the prognostically relevant biomarker isocitrate dehydrogenase (IDH) mutation status.

Methods

MET-PET of 35 astrocytic gliomas (13 females, mean age 41 ± 13 yrs. and 22 males, mean age 46 ± 17 yrs.) and known IDH mutation status were included. All patients underwent radiomic analysis following imaging biomarker standardization initiative (IBSI)-conform guidelines both from standardized uptake value (SUV) and tumor-to-background ratio (TBR) PET values. Aligned Monte Carlo (MC) 100-fold split was utilized for SUV and TBR dataset pairs for both sex and IDH-specific analysis. Borderline and outlier scores were calculated for both sex and IDH-specific MC folds. Feature ranking was performed by R-squared ranking and Mann-Whitney U-test together with Bonferroni correction. Correlation of SUV and TBR radiomics in relation to IDH mutational status in male and female patients were also investigated.

Results

There were no significant features in either SUV or TBR radiomics to distinguish female and male patients. In contrast, intensity histogram coefficient of variation (ih.cov) and intensity skewness (stat.skew) were identified as significant to predict IDH +/-. In addition, IDH+ females had significant ih.cov deviation (0.031) and mean stat.skew (-0.327) differences compared to IDH+ male patients (0.068 and -0.123, respectively) with two-times higher standard deviations of the normal brain background MET uptake as well.

Discussion

We demonstrated that female and male glioma patients have significantly different radiomic profiles in MET PET imaging data. Future IDH prediction models shall not be built on mixed female-male cohorts, but shall rely on sex-specific cohorts and radiomic imaging biomarkers.

Gender-Related Differences in Regional Cerebral Glucose Metabolism in Normal Aging Brain

Objectives: This study was aimed to investigate the gender-related differences of regional cerebral glucose metabolism in healthy people along the age using 18F-FDG PET/CT.

Methods: We recruited 344 healthy volunteers, including 217 males and 127 females (age range: 40–89 years old). All subjects underwent fluorine-18 fluorodeoxyglucose(18F-FDG) positron emission tomography (PET). All the data were divided into four groups for every 10 years old. Each participant was carefully screened from PET, MR, and other examinations in order to exclude the abnormalities, such as neurodegenerative or psychiatric disorders, alcohol/abuse, cerebral vascular disorders, metabolic diseases like diabetes mellitus and hyperthyroidism, and other systemic malignancies. The 40–50 years old group was set as the baseline group. Statistical parametric mapping (SPM) analysis was employed to illustrate the differences among groups.

Results: Compared to the baseline group, whether in a cohort or different gender groups, the decrease of brain glucose metabolism was shown in the bilateral frontal lobe, anterior cingulate gyrus, and the bilateral temporal lobe. In males, the regions of decreased metabolism were bilateral frontal lobe, caudate nucleus, and cingulate gyrus, whereas that of females were left occipital lobe, cerebellum, and the thalamus. However, the overall decrease of brain metabolism in men and women began from the age of 60s, an aggravated decrease from 70s was only observed in males.

Conclusion: (1) An obviously decreased brain metabolism was found from 60 years old, especially in the bilateral frontal lobe, bilateral temporal lobe, and inferior cingulate gyrus; (2) We found specific brain metabolic differences between genders, including the caudate nucleus region in males and the occipital lobe region in females; and (3) The aging trend is different between genders.

Sex Differences in the Outcomes of Mild Traumatic Brain Injury in Children Presenting to the Emergency Department

Sex differences after concussion have been studied largely in high school and college athletes, often without reference to comparison groups without concussion. This study sought to evaluate sex differences in outcomes among all children and adolescents presenting to the Emergency Department (ED) for either mild traumatic brain injury (TBI) or orthopedic injury (OI), regardless of mechanism of injury. The study involved a concurrent cohort, prospective study design with longitudinal follow-up. Participants were eight to 16 years old with mild TBI (n = 143) or OI (n = 73). They were recruited and completed an initial assessment at EDs at two children's hospitals. They returned for a post-acute assessment within two weeks of injury and for follow-up assessments at three and six months. Outcomes included child and parent proxy ratings of somatic and cognitive symptoms, and standardized tests of cognitive functioning and balance. Sex did not moderate group differences in balance, fluid or crystallized cognitive ability, or child or parent proxy ratings of somatic or cognitive symptoms. Both parents and children reported more somatic symptoms in girls than boys, but in both groups. Compared with the OI group, the mild TBI group showed significantly lower fluid cognitive ability at the post-acute assessment and significantly higher somatic and cognitive symptoms according to both child and parent proxy ratings across the first two weeks post-injury. The results suggest that sex does not moderate the outcomes of mild TBI in a pediatric ED population. Previous research pointing to sex differences after concussion may reflect the lack of comparison groups, as well as a focus on adolescents and young adults and sport-related concussion. Future research should investigate whether sex moderates the outcomes of pediatric mild TBI in adolescents but not in pre-adolescent children.

The effects of cerebral amyloidopathy on regional glucose metabolism in older adults with depression and mild cognitive impairment while performing memory tasks

Co-occurring depression and mild cognitive impairment (MCI) in older adults are important because they have a high risk of conversion to dementia. In the present study, task-related F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) was used to analyse older adults with concomitant depression and MCI. We recruited 20 older adults with simultaneous depression and MCI and 10 older adults with normal cognition (NC). The Verbal Paired Associates test and digit span test were used for the task-related FDG-PET. The 20 older adults with depression and MCI were classified into two groups based on the F-18 florbetaben PET results: depressed MCI patients with (LLD-MCI-A[+]; n = 11) and without amyloid accumulation (LLD-MCI-A[-]; n = 9). Reduced regional cerebral glucose metabolism (rCMglc) in the left superior frontal region was observed in the LLD-MCI-A(-) group compared with the NC group. Analyses of the NC and LLD-MCI-A(+) groups showed significantly decreased rCMglc in the right inferior parietal and left middle frontal regions in the LLD-MCI-A(+) group. rCMglc in the left precuneus was lower in the LLD-MCI-A(+) group than in the LLD-MCI-A(-) group. Significant correlations between the rCMglc in the right inferior parietal/left precuneus regions and memory task scores were observed based on correlation analyses of NC and LLD-MCI-A(+) groups. The findings in the present study indicate the presence of amyloid accumulation influences glucose metabolism in depressed elderly subjects with MCI while performing cognitive tasks. Task-related FDG-PET examinations may help differentiate MCI associated with depression from comorbid depression in patients with prodromal Alzheimer's disease.

Proton therapy reduces the likelihood of high-grade radiation-induced lymphopenia in glioblastoma patients: phase II randomized study of protons vs photons

BACKGROUND

We investigated differences in radiation-induced grade 3+ lymphopenia (G3+L), defined as an absolute lymphocyte count (ALC) nadir of <500 cells/µL, after proton therapy (PT) or X-ray (photon) therapy (XRT) for patients with glioblastoma (GBM).

METHODS

Patients enrolled in a randomized phase II trial received PT (n = 28) or XRT (n = 56) concomitantly with temozolomide. ALC was measured before, weekly during, and within 1 month after radiotherapy. Whole-brain mean dose (WBMD) and brain dose-volume indices were extracted from planned dose distributions. Univariate and multivariate logistic regression analyses were used to identify independent predictive variables. The resulting model was evaluated using receiver operating characteristic (ROC) curve analysis.

RESULTS

Rates of G3+L were lower in men (7/47 [15%]) versus women (19/37 [51%]) (P < 0.001), and for PT (4/28 [14%]) versus XRT (22/56 [39%]) (P = 0.024). G3+L was significantly associated with baseline ALC, WBMD, and brain volumes receiving 5‒40 Gy(relative biological effectiveness [RBE]) or higher (ie, V5 through V40). Stepwise multivariate logistic regression analysis identified being female (odds ratio [OR] 6.2, 95% confidence interval [CI]: 1.95‒22.4, P = 0.003), baseline ALC (OR 0.18, 95% CI: 0.05‒0.51, P = 0.003), and whole-brain V20 (OR 1.07, 95% CI: 1.03‒1.13, P = 0.002) as the strongest predictors. ROC analysis yielded an area under the curve of 0.86 (95% CI: 0.79-0.94) for the final G3+L prediction model.

CONCLUSIONS

Sex, baseline ALC, and whole-brain V20 were the strongest predictors of G3+L for patients with GBM treated with radiation and temozolomide. PT reduced brain volumes receiving low and intermediate doses and, consequently, reduced G3+L.

Cerebral Small Vessel Disease

Cerebral small vessel disease (CSVD) represents a cluster of various vascular disorders with different pathological backgrounds. The advanced vasculature net of cerebral vessels, including small arteries, capillaries, arterioles and venules, is usually affected. Processes of oxidation underlie the pathology of CSVD, promoting the degenerative status of the epithelial layer. There are several classifications of cerebral small vessel diseases; some of them include diseases such as Binswanger’s disease, leukoaraiosis, cerebral microbleeds (CMBs) and lacunar strokes. This paper presents the characteristics of CSVD and the impact of the current knowledge of this topic on the diagnosis and treatment of patients.

Women's higher brain metabolic rate compensates for early Alzheimer's pathology

INTRODUCTION

The female advantage in brain metabolic function may confer cognitive resilience against Alzheimer's disease (AD).

METHODS

A total of 1259 participants (44% women; 52% mild cognitive impairment; 18% AD) aged 55 to 90 from the Alzheimer's Disease Neuroimaging Initiative (ANDI) completed tests of global cognition, verbal memory, and executive function, and neuroimaging assessments of regional glucose metabolism, hippocampal volume (HV), and amyloid beta (Aβ). We examined sex differences in brain metabolism and cognition by AD biomarker quartiles (Aβ, HV). We then examined if metabolism mediates sex differences in cognition.

RESULTS

Metabolism was higher in women versus men when pathology was mild-to-moderate (quartiles 2 to 3). Women outperformed men on all cognitive outcomes at ≥1 biomarker quartile, reflecting minimal-to-moderate pathology; however, these differences were eliminated/attenuated after adjusting for metabolism. The female advantage in verbal memory was also observed at minimal pathology quartiles but was unchanged after metabolism adjustment.

DISCUSSION

Women's greater brain metabolism may confer cognitive resilience against early AD.

Sex differences in health and disease: A review of biological sex differences relevant to cancer with a spotlight on glioma

The influence of biological sex differences on human health and disease, while being increasingly recognized, has long been underappreciated and underexplored. While humans of all sexes are more alike than different, there is evidence for sex differences in the most basic aspects of human biology and these differences have consequences for the etiology and pathophysiology of many diseases. In a disease like cancer, these consequences manifest in the sex biases in incidence and outcome of many cancer types. The ability to deliver precise, targeted therapies to complex cancer cases is limited by our current understanding of the underlying sex differences. Gaining a better understanding of the implications and interplay of sex differences in diseases like cancer will thus be informative for clinical practice and biological research. Here we review the evidence for a broad array of biological sex differences in humans and discuss how these differences may relate to observed sex differences in various diseases, including many cancers and specifically glioblastoma. We focus on areas of human biology that play vital roles in healthy and disease states, including metabolism, development, hormones, and the immune system, and emphasize that the intersection of sex differences in these areas should not go overlooked. We further propose that mathematical approaches can be useful for exploring the extent to which sex differences affect disease outcomes and accounting for those in the development of therapeutic strategies.

Gender Differences Are Encoded Differently in the Structure and Function of the Human Brain Revealed by Multimodal MRI

Despite widely reported gender differences in both brain structure and brain function, very few studies have examined the relationship between the structural differences and the functional differences between genders. Here, different imaging measures including both structural [i.e., gray matter volume (GMV)] and functional [i.e., regional homogeneity (ReHo) and functional connectivity (FC)] measures were employed to detect the gender differences in the human brain based on univariate and multivariate approaches with a sample of 290 healthy adults (155 females). The univariate analyses revealed that gender differences were detected in both structural (i.e., GMV) and functional (ReHo or FC) imaging measures, mainly manifested as greater values in females than in males in regions of the frontal, parietal, occipital lobes and cerebellum. Importantly, there was little overlap between the differences detected in GMV and those detected in ReHo and FC, and their differences between genders were not correlated with each other. The multivariate pattern analyses revealed that each of these measures had discriminative power to successfully distinguish between genders (classification accuracy: 94.3%, 90.73%, and 83.89% for GMV, ReHo, and FC, respectively) and their combination further improved the classification performance (96.6%). Our results suggest that gender differences are encoded in both brain structure and brain function, but in different manners. The finding of different and complementary information contained in structural and functional differences between genders highlights the complex relationship between brain structure and function, which may underlie the complex nature of gender differences in behavior.

Test-Retest Stability of Cerebral 2-Deoxy-2-[18F]Fluoro-D-Glucose ([18F]FDG) Positron Emission Tomography (PET) in Male and Female Rats

PURPOSE

An important issue in rodent imaging is the question whether a mixed population of male and female animals can be used rather than animals of a single sex. For this reason, the present study examined the test-retest stability of positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in male rats and female rats at different phases of the estrous cycle.

PROCEDURES

Long-Evans rats (age 1 year) were divided into three groups: (1) males (n = 6), (2) females in metestrous (low estrogen levels, n = 9), and (3) females in proestrous (high estrogen levels, n = 7). Two standard [¹⁸F]FDG scans with rapid arterial blood sampling were made at an interval of 10 days in subjects anesthetized with isoflurane and oxygen. Body temperature, heart rate, and blood oxygenation were continuously monitored. Regional cerebral metabolic rates of glucose were calculated using a Patlak plot with plasma radioactivity as input function.

RESULTS

Regional metabolic rate of glucose (rCMR_glucose) in male and female rats, or [¹⁸F]FDG uptake in females at proestrous and metestrous, was not significantly different, but females showed significantly higher standardized uptake values (SUVs) and Patlak flux than males, particularly in the initial scan. The relative difference between the scans and the test-retest variability (TRV) were greater in females than in males. Intra-class correlation coefficients (ICCs) of rCMR_glucose, SUV, normalized SUV, and glucose flux were good to excellent in males but poor to moderate in females.

CONCLUSIONS

Based on these data for [¹⁸F]FDG, the mixing of sexes in imaging studies of the rodent brain will result in an impaired test-retest stability of PET data and a need for larger group sizes to maintain statistical power in group comparisons. The observed differences between males and females do not indicate any specific gender difference in cerebral metabolism but are related to different levels of non-radioactive glucose in blood plasma during isoflurane anesthesia.

First-Time Sports-Related Concussion Recovery: The Role of Sex, Age, and Sport

Background

Concussion is one of the most common injuries in athletes. Current concussion consensus statements propose that female sex may be a modifying factor in concussion management and recovery.

Objective

To determine whether female athletes in middle school and high school with a first-time, sports-related concussion remained symptomatic longer than their male counterparts.

Methods

A retrospective medical record analysis was performed among athletes who sustained a concussion between 2011 and 2013. Inclusion criteria consisted of age between 11 and 18 years and diagnosis of first-time concussion sustained while playing organized sports. Using the documented notes in the medical record, length of time that each athlete was symptomatic from his or her concussion was calculated.

Results

A total of 110 male and 102 female athletes (N=212) met the eligibility criteria for the study. A significant difference was found in the median number of days female athletes remained symptomatic (28 days) when compared with male athletes (11 days) (P<.001). No statistically significant difference was found in symptom duration between age groups. When matched for sex, no statistically significant differences were found in symptom duration between the type of sports played.

Conclusion

Female athletes aged 11 to 18 years with first-time, sports-related concussions remained symptomatic for a longer period when compared with male athletes of similar age, regardless of sport played. The mechanism behind this difference needs to be further elucidated.

Sex differences in the association between apolipoprotein E ε4 allele and Alzheimer's disease markers

Introduction

We determined whether the effect of apolipoprotein E (APOE)-ε4 genotype on Alzheimer's disease (AD) markers differs in men and women across AD stages.

Methods

Among normal control (NC) participants (N = 702) and participants with mild cognitive impairment (N = 576) and AD (N = 305), we examined the associations of sex and APOE-ε4 carrier status with cortical amyloid-β (Aβ) burden, hippocampal volume ratio (HpVR; hippocampal volume/intracranial volume × 10³), brain glucose metabolism, and verbal memory.

Results

In NC, APOE-ε4 related to greater Aβ burden and poorer verbal memory across sex but to smaller HpVR and hypometabolism in men only. In mild cognitive impairment, APOE-ε4 related to smaller HpVR, hypometabolism, greater Aβ burden, and poorer verbal memory across sex. In AD, APOE-ε4 related to greater Aβ burden in men only and smaller HpVR across sex and showed no association with hypometabolism or verbal memory.

Discussion

Sex differences in the association between APOE-ε4 and AD markers vary by disease stage.

Gender-Based Cerebral Perfusion Differences in 46,034 Functional Neuroimaging Scans

BACKGROUND

Studies have reported that females have widespread increases in regional cerebral blood flow, but the studies were relatively small and inconsistent.

OBJECTIVE

Here we analyzed a healthy and a very large clinical psychiatric population to determine the effect of gender, using single photon emission computed tomography (SPECT).

METHODS

Whole brain and region of interest (ROI) gender differences were analyzed in a total of 46,034 SPECT scans at baseline and concentration. The sample included 119 healthy subjects and 26,683 patients (60.4% male, 39.6% female); a subset of 11,587 patients had complete diagnostic information. A total of 128 regions were analyzed according to the AAL Atlas, using ROI Extract and SPSS statistical software programs, controlling for age, diagnoses, and correcting for multiple comparisons.

RESULTS

Compared to males, healthy females showed significant whole brain (p < 0.01) and ROI increases in 65 baseline and 48 concentration regions (p < 0.01 corrected). Healthy males showed non-significant increases in 9 and 22 regions, respectively. In the clinical group, there were widespread significant increases in females, especially in the prefrontal and limbic regions, and specific increases in males in the inferior occipital lobes, inferior temporal lobes, and lobule 7 and Crus 2 of the cerebellum. These findings were replicated in the subset of 11,587 patients with the effect of diagnoses removed.

CONCLUSIONS

Our results demonstrated significant gender differences in a healthy and clinical population. Understanding these differences is crucial in evaluating functional neuroimaging and may be useful in understanding the epidemiological gender differences among psychiatric disorders.

Sex differences in white matter alterations following repetitive subconcussive head impacts in collegiate ice hockey players

Objective

Repetitive subconcussive head impacts (RSHI) may lead to structural, functional, and metabolic alterations of the brain. While differences between males and females have already been suggested following a concussion, whether there are sex differences following exposure to RSHI remains unknown. The aim of this study was to identify and to characterize sex differences following exposure to RSHI.

Methods

Twenty-five collegiate ice hockey players (14 males and 11 females, 20.6 ± 2.0 years), all part of the Hockey Concussion Education Project (HCEP), underwent diffusion-weighted magnetic resonance imaging (dMRI) before and after the Canadian Interuniversity Sports (CIS) ice hockey season 2011-2012 and did not experience a concussion during the season. Whole-brain tract-based spatial statistics (TBSS) were used to compare pre- and postseason imaging in both sexes for fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). Pre- and postseason neurocognitive performance were assessed by the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT).

Results

Significant differences between the sexes were primarily located within the superior longitudinal fasciculus (SLF), the internal capsule (IC), and the corona radiata (CR) of the right hemisphere (RH). In significant voxel clusters (p < 0.05), decreases in FA (absolute difference pre- vs. postseason: 0.0268) and increases in MD (0.0002), AD (0.00008), and RD (0.00005) were observed in females whereas males showed no significant changes. There was no significant correlation between the change in diffusion scalar measures over the course of the season and neurocognitive performance as evidenced from postseason ImPACT scores.

Conclusions

The results of this study suggest sex differences in structural alterations following exposure to RSHI. Future studies need to investigate further the underlying mechanisms and association with exposure and clinical outcomes.

Distribution of cardiac output to the brain across the adult lifespan

A widely accepted dogma is that about 15-20% of cardiac output is received by the brain in healthy adults under resting conditions. However, it is unclear if the distribution of cardiac output directed to the brain alters across the adult lifespan and is modulated by sex or other hemodynamic variables. We measured cerebral blood flow/cardiac output ratio index in 139 subjects (88 women, age 21-80 years) using phase-contrast magnetic resonance imaging and echocardiography. Body mass index, cardiac systolic function (eject fraction), central arterial stiffness (carotid-femoral pulse wave velocity), arterial pressure, heart rate, physical fitness (VO2 max), and total brain volume were measured to assess their effects on the cardiac output-cerebral blood flow relationship. Cerebral blood flow/cardiac output ratio index decreased by 1.3% per decade associated with decreases in cerebral blood flow ( P < 0.001), while cardiac output remained unchanged. Women had higher cerebral blood flow, lower cardiac output, and thus higher cerebral blood flow/cardiac output ratio index than men across the adult lifespan. Age, body mass index, carotid-femoral pulse wave velocity, and arterial pressure all had negative correlations with cerebral blood flow and cerebral blood flow/cardiac output ratio index ( P < 0.05). Multivariable analysis adjusted for sex, age showed that only body mass index was negatively associated with cerebral blood flow/cardiac output ratio index (β = -0.33, P < 0.001). These findings demonstrated that cardiac output distributed to the brain has sex differences and decreases across the adult lifespan and is inversely associated with body mass index.

Brain: normal variations and benign findings in fluorodeoxyglucose-PET/computed tomography imaging

Brain 18F-fluorodeoxyglucose (18F-FDG) PET allows the in vivo study of cerebral glucose metabolism, reflecting neuronal and synaptic activity. 18F-FDG-PET has been extensively used to detect metabolic alterations in several neurologic diseases compared with normal aging. However, healthy subjects have variants of 18F-FDG distribution, especially as associated with aging. This article focuses on 18F-FDG-PET findings in so-called normal brain aging, and in particular on metabolic differences occurring with aging and as a function of people’s gender. The effect of different substances, medications, and therapy procedures are discussed, as well as common artifacts.

Cocaine reduces cytochrome oxidase activity in the prefrontal cortex and modifies its functional connectivity with brainstem nuclei

Cocaine-induced psychomotor stimulation may be mediated by metabolic hypofrontality and modification of brain functional connectivity. Functional connectivity refers to the pattern of relationships among brain regions, and one way to evaluate this pattern is using interactivity correlations of the metabolic marker cytochrome oxidase among different regions. This is the first study of how repeated cocaine modifies: (1) mean cytochrome oxidase activity in neural areas using quantitative enzyme histochemistry, and (2) functional connectivity among brain regions using inter-correlations of cytochrome oxidase activity. Rats were injected with 15 mg/kg i.p. cocaine or saline for 5 days, which lead to cocaine-enhanced total locomotion. Mean cytochrome oxidase activity was significantly decreased in cocaine-treated animals in the superficial dorsal and lateral frontal cortical association areas Fr2 and Fr3 when compared to saline-treated animals. Functional connectivity showed that the cytochrome oxidase activity of the noradrenergic locus coeruleus and the infralimbic cortex were positively inter-correlated in cocaine but not in control rats. Positive cytochrome oxidase activity inter-correlations were also observed between the dopaminergic substantia nigra compacta and Fr2 and Fr3 areas and the lateral orbital cortex in cocaine-treated animals. In contrast, cytochrome oxidase activity in the interpeduncular nucleus was negatively correlated with that of Fr2, anterior insular cortex, and lateral orbital cortex in saline but not in cocaine groups. After repeated cocaine specific prefrontal areas became hypometabolic and their functional connectivity changed in networks involving noradrenergic and dopaminergic brainstem nuclei. We suggest that this pattern of hypofrontality and altered functional connectivity may contribute to cocaine-induced psychomotor stimulation.

Characterizing the normative profile of 18F-FDG PET brain imaging: sex difference, aging effect, and cognitive reserve

The aim of this study was to investigate findings of positron emission tomography with 18F-fluorodeoxyglucose (18F-FDG PET) in normal subjects to clarify the effects of sex differences, aging, and cognitive reserve on cerebral glucose metabolism. Participants comprised 123 normal adults who underwent 18F-FDG PET and a neuropsychological battery. We used statistical parametric mapping (SPM8) to investigate sex differences, and aging effects. The effects of cognitive reserve on 18F-FDG uptake were investigated using years of education as a proxy. Finally, we studied the effect of cognitive reserve on the recruitment of glucose metabolism in a memory task by dichotomizing the data according to educational level. Our results showed that the overall cerebral glucose metabolism in females was higher than that in males, whereas male participants had higher glucose metabolism in the bilateral inferior temporal gyri and cerebellum than females. Age-related hypometabolism was found in anterior regions, including the anterior cingulate gyrus. These areas are part of the attentional system, which may decline with aging even in healthy elderly individuals. Highly educated subjects revealed focal hypermetabolism in the right hemisphere and lower recruitment of glucose metabolism in memory tasks. This phenomenon is likely a candidate for a neural substrate of cognitive reserve.

Estrogen: a master regulator of bioenergetic systems in the brain and body

Estrogen is a fundamental regulator of the metabolic system of the female brain and body. Within the brain, estrogen regulates glucose transport, aerobic glycolysis, and mitochondrial function to generate ATP. In the body, estrogen protects against adiposity, insulin resistance, and type II diabetes, and regulates energy intake and expenditure. During menopause, decline in circulating estrogen is coincident with decline in brain bioenergetics and shift towards a metabolically compromised phenotype. Compensatory bioenergetic adaptations, or lack thereof, to estrogen loss could determine risk of late-onset Alzheimer's disease. Estrogen coordinates brain and body metabolism, such that peripheral metabolic state can indicate bioenergetic status of the brain. By generating biomarker profiles that encompass peripheral metabolic changes occurring with menopause, individual risk profiles for decreased brain bioenergetics and cognitive decline can be created. Biomarker profiles could identify women at risk while also serving as indicators of efficacy of hormone therapy or other preventative interventions.

Common neural mechanisms underlying reversal learning by reward and punishment

Impairments in flexible goal-directed decisions, often examined by reversal learning, are associated with behavioral abnormalities characterized by impulsiveness and disinhibition. Although the lateral orbital frontal cortex (OFC) has been consistently implicated in reversal learning, it is still unclear whether this region is involved in negative feedback processing, behavioral control, or both, and whether reward and punishment might have different effects on lateral OFC involvement. Using a relatively large sample (N = 47), and a categorical learning task with either monetary reward or moderate electric shock as feedback, we found overlapping activations in the right lateral OFC (and adjacent insula) for reward and punishment reversal learning when comparing correct reversal trials with correct acquisition trials, whereas we found overlapping activations in the right dorsolateral prefrontal cortex (DLPFC) when negative feedback signaled contingency change. The right lateral OFC and DLPFC also showed greater sensitivity to punishment than did their left homologues, indicating an asymmetry in how punishment is processed. We propose that the right lateral OFC and anterior insula are important for transforming affective feedback to behavioral adjustment, whereas the right DLPFC is involved in higher level attention control. These results provide insight into the neural mechanisms of reversal learning and behavioral flexibility, which can be leveraged to understand risky behaviors among vulnerable populations.

Relative risk for concussions in young female soccer players

The objective of this study was to determine the relative risk and reported symptoms of concussions in 11- to 13-year-old, female soccer players. For this, a survey to compare the reported incidence of concussion in age-matched female soccer players to nonsoccer players was performed. The survey included 342 girls between the ages of 11 and 13: 195 were involved in an organized soccer team and 147 were not involved in organized soccer but were allowed to participate in any other sport or activity. A total of 94 of the 195 soccer players, or 48%, reported at least one symptom consistent with a concussion. The most prevalent symptom for these girls was headache (84%). A total of 34 of the 147 nonsoccer players, or 23%, reported at least one symptom consistent with a concussion in the previous six months. These results determined that the relative risk of probable concussions among 11- to 13-year-old, female soccer players is 2.09 (p < .001, α = .05, CI = 95%). This demonstrates that the relative risk of probable concussions in young female soccer players is significantly higher than in a control group of nonsoccer players of the same sex and age.

Age- and gender-related regional variations of human brain cortical thickness, complexity, and gradient in the third decade

Brain functional and cytoarchitectural maturation continue until adulthood, but little is known about the evolution of the regional pattern of cortical thickness (CT), complexity (CC), and intensity or gradient (CG) in young adults. We attempted to detect global and regional age- and gender-related variations of brain CT, CC, and CG, in 28 healthy young adults (19-33 years) using a three-dimensional T1 -weighted magnetic resonance imaging sequence and surface-based methods. Whole brain interindividual variations of CT and CG were similar to that in the literature. As a new finding, age- and gender-related variations significantly affected brain complexity (P < 0.01) on posterior cingulate and middle temporal cortices (age), and the fronto-orbital cortex (gender), all in the right hemisphere. Regions of interest analyses showed age and gender significant interaction (P < 0.05) on the temporopolar, inferior, and middle temporal-entorrhinal cortices bilaterally, as well as left inferior parietal. In addition, we found significant inverse correlations between CT and CC and between CT and CG over the whole brain and markedly in precentral and occipital areas. Our findings differ in details from previous reports and may correlate with late brain maturation and learning plasticity in young adults' brain in the third decade.

Anterior brain glucose hypometabolism predates dementia in progranulin mutation carriers

OBJECTIVE

In this prospective cohort study, we investigated cerebral glucose metabolism reductions on [(18)F]-fluorodeoxyglucose (FDG)-PET in progranulin (GRN) mutation carriers prior to frontotemporal dementia (FTD) onset.

METHODS

Nine mutation carriers (age 51.5 ± 13.5 years) and 11 noncarriers (age 52.7 ± 9.5 years) from 5 families with FTD due to GRN mutations underwent brain scanning with FDG-PET and MRI and clinical evaluation. Normalized FDG uptake values were calculated with reference to the pons. PET images were analyzed with regions of interest (ROI) and statistical parametric mapping (SPM) approaches.

RESULTS

Compared with noncarriers, GRN mutation carriers had a lowered anterior-to-posterior (AP) ratio of FDG uptake (0.86 ± 0.09 vs 0.92 ± 0.05) and less left-right asymmetry, consistent with an overall pattern of right anterior cerebral hypometabolism. This pattern was observed regardless of whether they were deemed clinically symptomatic no dementia or asymptomatic. Individual ROIs with lowered FDG uptake included right anterior cingulate, insula, and gyrus rectus. SPM analysis supported and extended these findings, demonstrating abnormalities in the right and left medial frontal regions, right insular cortex, right precentral and middle frontal gyri, and right cerebellum. Right AP ratio was correlated with cognitive and clinical scores (modified Mini-Mental State Examination r = 0.74; Functional Rating Scale r = -0.73) but not age and years to estimated onset in mutation carriers.

CONCLUSION

The frontotemporal lobar degenerative process associated with GRN mutations appears to begin many years prior to the average age at FTD onset (late 50s-early 60s). Right medial and ventral frontal cortex and insula may be affected in this process but the specific regional patterns associated with specific clinical variants remain to be elucidated.

Cerebral blood flow and glucose metabolism measured with positron emission tomography are decreased in human type 1 diabetes

Subclinical systemic microvascular dysfunction exists in asymptomatic patients with type 1 diabetes. We hypothesized that microangiopathy, resulting from long-standing systemic hyperglycemia and hyperinsulinemia, may be generalized to the brain, resulting in changes in cerebral blood flow (CBF) and metabolism in these patients. We performed dynamic [(15)O]H2O and [(18)F]-fluoro-2-deoxy-d-glucose brain positron emission tomography scans to measure CBF and cerebral glucose metabolism (CMRglu), respectively, in 30 type 1 diabetic patients and 12 age-matched healthy controls after an overnight fast. Regions of interest were automatically delineated on coregistered magnetic resonance images and full kinetic analysis was performed. Plasma glucose and insulin levels were higher in patients versus controls. Total gray matter CBF was 9%, whereas CMRglu was 21% lower in type 1 diabetic subjects versus control subjects. We conclude that at real-life fasting glucose and insulin levels, type 1 diabetes is associated with decreased resting cerebral glucose metabolism, which is only partially explained by the decreased CBF. These findings suggest that mechanisms other than generalized microangiopathy account for the altered CMRglu observed in well-controlled type 1 diabetes.

Cardiovascular risk in cognitively preserved elderlies is associated with glucose hypometabolism in the posterior cingulate cortex and precuneus regardless of brain atrophy and apolipoprotein gene variations

Cardiovascular risk factors (CVRF) possibly contribute to the emergence of Alzheimer's disease (AD). Fluorodeoxyglucose-positron emission tomography (FDG-PET) has been widely used to demonstrate specific patterns of reduced cerebral metabolic rates of glucose (CMRgl) in subjects with AD and in non-demented carriers of the apolipoprotein ε4 (APOE ε4) allele, the major genetic risk factor for AD. However, functional neuroimaging studies investigating the impact of CVRF on cerebral metabolism have been scarce to date. The present FDG-PET study investigated 59 cognitively preserved elderlies divided into three groups according to their cardiovascular risk based on the Framingham 10-year risk Coronary Heart Disease Risk Profile (low-, medium-, and high-risk) to examine whether different levels of CVRF would be associated with reduced CMRgl, involving the same brain regions affected in early stages of AD. Functional imaging data were corrected for partial volume effects to avoid confounding effects due to regional brain atrophy, and all analyses included the presence of the APOE ε4 allele as a confounding covariate. Significant cerebral metabolism reductions were detected in the high-risk group when compared to the low-risk group in the left precuneus and posterior cingulate gyrus. This suggests that findings of brain hypometabolism similar to those seen in subjects with AD can be detected in association with the severity of cardiovascular risk in cognitively preserved individuals. Thus, a greater knowledge about how such factors influence brain functioning in healthy subjects over time may provide important insigths for the future development of strategies aimed at delaying or preventing the vascular-related triggering of pathologic brain changes in the AD.

A quantitative systematic review of domain-specific cognitive impairment in lacunar stroke

OBJECTIVE

To quantitatively characterize domain-specific cognition in individuals with symptomatic lacunar stroke in a systematic review.

METHODS

Systematic searches of MEDLINE and EMBASE were conducted. Inclusion criteria were all articles published prior to December 2011 evaluating domain-specific cognitive status in individuals with a symptomatic lacunar infarct. Data extraction identified cognitive domains with reported impairment and effect size calculations and heterogeneity analyses were completed to assess the magnitude of this impairment for all studies with control group data.

RESULTS

Results of the search yielded 12 cross-sectional and 5 longitudinal studies that met inclusion criteria. Effect size calculations revealed small to medium effect sizes (ES) estimations for impairment after stroke in the domains of executive function (ES -0.44, 95% confidence interval [CI] -0.83, -0.50), memory (ES -0.55, 95% CI -0.96, -0.13), language (ES -0.63, 95% CI -0.92, -0.33), attention (ES -0.37, 95% CI -0.67, -0.07), and visuospatial abilities (ES -0.61, 95% CI -1.03, 0.19), and large effect sizes for global cognition (ES -0.90, 95% CI -1.48, -0.31) and information processing speed (ES -0.93, 95% CI -1.63, -0.23). Heterogeneity analyses revealed that a subset of these domains were heterogeneous and identified moderating factors accounting for this heterogeneity.

CONCLUSIONS

Results of this systematic review are consistent with previous characterizations of cognitive impairment associated with lacunar strokes. However, impaired cognition in this stroke subtype appears less selective than previously thought, involving all major cognitive domains.

Interactions between age, sex, and hormones in experimental ischemic stroke

Age, sex, and gonadal hormones have profound effects on ischemic stroke outcomes, although how these factors impact basic stroke pathophysiology remains unclear. There is a plethora of inconsistent data reported throughout the literature, primarily due to differences in the species examined, the timing and methods used to evaluate injury, the models used, and confusion regarding differences in stroke incidence as seen in clinical populations vs. effects on acute neuroprotection or neurorepair in experimental stroke models. Sex and gonadal hormone exposure have considerable independent impact on stroke outcome, but these factors also interact with each other, and the contribution of each differs throughout the lifespan. The contribution of sex and hormones to experimental stroke will be the focus of this review. Recent advances and our current understanding of age, sex, and hormone interactions in ischemic stroke with a focus on inflammation will be discussed.

Gonadal steroids, brain, and behavior: role of context

The nature and extent of the impact of gender and reproductive function on mood has been the subject of speculation and controversy for centuries. Over the past 50 years, however, it has become increasingly clear that not only is the brain a major target of reproductive steroid hormones, but additionally, the steroid hormones, as neuroregulators, create a context thai influences a broad range of brain activities; ie, neural actions and resultant behaviors are markedly different in the presence and absence of gonadal steroids. In turn, the actions of gonadal steroids are themselves context-dependent. Thus, even where it can be demonstrated thai gonadal steroids trigger mood disorders, the triggers are normal levels of gonadal steroids (to be contrasted with the mood disturbances accompanying endocrinopathies), and the mood disorders appear only in a subset of susceptible individuals. The context specificity and differential susceptibility to affective dysregulation seen in women with reproductive endocrine-related mood disorders are undoubtedly important underlying characteristics of a wide range of psychiatric disorders in which the triggers have not yet been identified. Consequently, reproductive endocrine-related mood disorders offer unparalleled promise for the identification of those contextual variables that permit biological stimuli to differentially translate into depression in individuals at risk.

Cognitive impairment in lacunar strokes: the SPS3 trial

OBJECTIVE

Lacunar strokes are a leading cause of cognitive impairment and vascular dementia. However, adequate characterization of cognitive impairment is lacking. The aim of this study was to estimate the prevalence and characterize the neuropsychological impairment in lacunar stroke patients.

METHODS

All English-speaking participants in the Secondary Prevention of Small Subcortical Strokes (SPS3) trial (National Clinical Trial 00059306) underwent neuropsychological testing at baseline. Raw scores were converted to z scores using published norms. Those with impairment (z ≤ -1.5) in memory and/or nonmemory domains were classified as having mild cognitive impairment (MCI).

RESULTS

Among the 1,636 participants, average z scores on all tests were < 0, with the largest deficits seen on tests of episodic memory (range of means, -0.65 to -0.92), verbal fluency (mean, -0.89), and motor dexterity (mean, -2.5). Forty-seven percent were classified as having MCI (36% amnestic, 37% amnestic multidomain, 28% nonamnestic). Of those with modified Rankin score 0-1 and Barthel score = 100, 41% had MCI. Younger age (odds ratio [OR] per 10-year increase, 0.87), male sex (OR, 1.3), less education (OR, 0.13-0.66 for higher education levels compared to 0-4 years education), poststroke disability (OR, 1.4), and impaired activities of daily living (OR, 1.8) were independently associated with MCI.

INTERPRETATION

In this large, well-characterized cohort of lacunar stroke patients, MCI was present in nearly half, including many with minimal or no physical disabilities. Cognitive dysfunction in lacunar stroke patients may commonly be overlooked in clinical practice but may be as important as motor and sensory sequelae.

The role of age and sex in symptoms, neurocognitive performance, and postural stability in athletes after concussion

BACKGROUND

Researchers have begun to focus on age and sex differences in concussion outcomes. Results suggest that younger athletes and female athletes may take longer to recover from a concussion. However, little is known about the interactive effects of age and sex on symptoms, neurocognitive testing (NCT), and postural stability.

HYPOTHESIS/PURPOSE

The purpose of the study was to examine sex and age differences in symptoms, NCT, and postural stability following concussion. We hypothesized that high school and female athletes would have worse symptoms, NCT, and postural stability than college and male athletes, respectively.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

A total of 296 concussed athletes from a multistate, 2-year study were enrolled in this study. Participants completed the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT) and Post-Concussion Symptom Scale (PCSS) at baseline and again at 2, 7, and 14 days after concussion. Participants completed the Balance Error Scoring System (BESS) at 1, 2, and 3 days after concussion.

RESULTS

Female athletes performed worse than male athletes on visual memory (mean, 65.1% and 70.1%, respectively; P = .049) and reported more symptoms (mean, 14.4 and 10.1, respectively) after concussion (P = .035). High school athletes performed worse than college athletes on verbal (mean, 78.8% and 82.7%, respectively; P = .001) and visual (mean, 65.8% and 69.4%, respectively; P = .01) memory. High school athletes were still impaired on verbal memory 7 days after concussion compared with collegiate athletes (P = .001). High school male athletes scored worse on the BESS than college male athletes (mean, 18.8 and 13.0, respectively; P = .001). College female athletes scored worse on the BESS than high school female athletes (mean, 21.1 and 16.9, respectively; P = .001).

CONCLUSION

The results of the current study supported age differences in memory and sex differences in memory and symptoms and an interaction between age and sex on postural stability after concussion that warrant consideration from clinicians and researchers when interpreting symptoms, specific components of NCT, and postural stability tests. Future research should develop and assess interventions tailored to age and sex differences and include younger (<14 years) participants.

Prefrontal cortex and drug abuse vulnerability: translation to prevention and treatment interventions

Vulnerability to drug abuse is related to both reward seeking and impulsivity, two constructs thought to have a biological basis in the prefrontal cortex (PFC). This review addresses similarities and differences in neuroanatomy, neurochemistry and behavior associated with PFC function in rodents and humans. Emphasis is placed on monoamine and amino acid neurotransmitter systems located in anatomically distinct subregions: medial prefrontal cortex (mPFC); lateral prefrontal cortex (lPFC); anterior cingulate cortex (ACC); and orbitofrontal cortex (OFC). While there are complex interconnections and overlapping functions among these regions, each is thought to be involved in various functions related to health-related risk behaviors and drug abuse vulnerability. Among the various functions implicated, evidence suggests that mPFC is involved in reward processing, attention and drug reinstatement; lPFC is involved in decision-making, behavioral inhibition and attentional gating; ACC is involved in attention, emotional processing and self-monitoring; and OFC is involved in behavioral inhibition, signaling of expected outcomes and reward/punishment sensitivity. Individual differences (e.g., age and sex) influence functioning of these regions, which, in turn, impacts drug abuse vulnerability. Implications for the development of drug abuse prevention and treatment strategies aimed at engaging PFC inhibitory processes that may reduce risk-related behaviors are discussed, including the design of effective public service announcements, cognitive exercises, physical activity, direct current stimulation, feedback control training and pharmacotherapies. A major challenge in drug abuse prevention and treatment rests with improving intervention strategies aimed at strengthening PFC inhibitory systems among at-risk individuals.

Construction of a (18)F-FDG PET normative database of Japanese healthy elderly subjects and its application to demented and mild cognitive impairment patients

OBJECTIVE

To construct a (18)F-FDG PET normative database of Japanese healthy elderly subjects and to apply it to demented and mild cognitive impairment (MCI) patients.

METHODS

Seventy-seven Japanese normal volunteers from 41 to 84 years of age (36 males and 41 females) who underwent clinical, neuropsychological, and MRI examinations were selected. In these subjects, (18)F-FDG PET/CT scans were performed, (18)F-FDG PET images were analyzed using the 3D-SSP program, and a normative database for cerebral glucose metabolism was constructed. Then, (18)F-FDG PET images from 14 demented and MCI patients were evaluated based on the normative database.

RESULTS

The 77 healthy elderly subjects were divided into three groups according to their age. In these subjects, the difference in glucose metabolism between males and females was minimal in contrast, glucose metabolism showed a weak reciprocal correlation with aging in several cerebral regions. The 3D-SSP images of 14 demented and MCI patients based on the age-matched (18)F-FDG PET normative database showed decreased patterns of glucose metabolism similar to those of previous studies on dementia diseases and MCI.

CONCLUSIONS

An age-matched normative database can be applied to the evaluation of single subjects, and the application of a mixed database of males and females is viable. Normative databases are useful for detecting dementia diseases and their MCI.

Sex differences in the functional neuroanatomy of working memory in adults with ADHD

OBJECTIVE

Although attention deficit hyperactivity disorder (ADHD) in adults is associated with significant morbidity and dysfunction and afflicts both sexes, relatively few imaging studies have examined female subjects and none have had sufficient power to adequately examine sex differences. The authors examined sex differences in the neural functioning of adults with ADHD during performance of a verbal working memory task.

METHOD

The participants were 44 adults with ADHD matched on age, sex, and estimated IQ to 49 comparison subjects. Accuracy and reaction time on an N-back task were measured to assess working memory. The blood-oxygen-level-dependent functional MRI response was used as a measure of neural activity.

RESULTS

A group-by-sex analysis of variance showed no between-group differences in either reaction time or percent correct for the working memory task. For both sexes combined, the adults with ADHD showed less activity than comparison subjects in prefrontal regions. However, sex-by-group analyses revealed an interaction, such that male ADHD subjects showed significantly less activity in right frontal, temporal, and subcortical regions and left occipital and cerebellar regions relative to male comparison subjects, whereas female ADHD subjects showed no differences from female comparison subjects. Exploratory correlation analyses revealed negative associations between working-memory-related activation and number of hyperactive symptoms for men and number of inattentive symptoms for women.

CONCLUSIONS

Male but not female adults with ADHD showed significantly altered patterns of neural activity during a verbal working memory task. Men and women showed different associations between neural activity and ADHD symptoms.

Effects of sex and normal aging on regional brain activation during verbal memory performance

This study examined the main and interactive effects of age and sex on relative glucose metabolic rate (rGMR) within gray matter of 39 cortical Brodmann areas (BAs) and the cingulate gyrus using (18)FDG-PET during a verbal memory task in 70 healthy normal adults, aged 20-87 years. Women showed significantly greater age-related rGMR decline in left cingulate gyrus than men (BAs 25, 24, 23, 31, 29). Both groups showed a decline in the anterior cingulate--a neuroanatomical structure that mediates effective cognitive-emotional interactions (BAs 32, 24, 25), while the other frontal regions did not show substantial decline. No sex differences in rGMR were identified within temporal, parietal and occipital lobes. Sex differences were observed for rGMR within subcomponents of the cingulate gyrus with men higher in BA25 and BA29, but lower in BA24 and BA 23 compared to women. For men, better memory performance was associated with greater rGMR in BA24, whereas in women better performance was associated with orbitofrontal-BA12. These results suggest that both age-related metabolic decline and sex differences within frontal regions are more marked in medial frontal and cingulate areas, consistent with some age-related patterns of affective and cognitive change.

Changes in glucose metabolism due to aging and gender-related differences in the healthy human brain

Using [(18)F]fluoro-deoxy-glucose-PET, we studied relative metabolic changes due to age- and gender-related differences in the brain of 126 healthy subjects from their twenties to seventies. We used a data-extraction technique, the three-dimensional stereotactic surface projections (3D-SSP) method, to measure metabolic changes with fewer effects of regional anatomic variances. Simple regression analysis revealed significant age-related increases in relative metabolic values in the parahippocampal and amygdala regions in both sexes in their twenties to forties, and significant age-related decreases in both sexes in their fifties to seventies. Relative values in the frontal lobe showed significant age-related decreases in both sexes in their twenties to forties, but these effects were not seen in subjects in their fifties to seventies. Significant gender differences in correlation coefficients of relative values with age were shown in the parahippocampal, primary sensorimotor, temporal, thalamus and vermis regions in subjects in their 20s to 40s, but disappeared in subjects in their twenties to forties, but were not apparent in subjects in their fifties to seventies except in the vermis. Males in their twenties to sixties and females in their fifties showed significant laterality in relative values in the temporal lobes. Our study demonstrated age- and gender-related differences in glucose metabolism in healthy subjects.

Resting brain glucose uptake in headache-free migraineurs

BACKGROUND AND OBJECTIVE

To compare metabolism in the brains of migraineurs during headache-free periods with those obtained from healthy volunteers.

METHODS

Eleven migraineurs (defined by the International Headache Society's criteria) presented during spontaneous headache-free intervals to undergo (18)FDG PET brain imaging of glucose metabolism. The control group consisted of 14 healthy volunteers. Comparison of images was done using Statistical Parametric Mapping to detect significant (P < .05) differences in brain glucose metabolism between the 2 groups.

RESULTS

Two regions of significant increase in glucose uptake were identified in migraineurs relative to the control population. The 2 regions were mapped predominantly to the posterior white matter of the cerebrum and cerebellum.

CONCLUSIONS

Our study demonstrates the presence of what may be a primary metabolic disturbance in the posterior white matter of the brain in migraineurs.

Evolving knowledge of sex differences in brain structure, function, and chemistry

Clinical and epidemiologic evidence demonstrates sex differences in the prevalence and course of various psychiatric disorders. Understanding sex-specific brain differences in healthy individuals is a critical first step toward understanding sex-specific expression of psychiatric disorders. Here, we evaluate evidence on sex differences in brain structure, chemistry, and function using imaging methodologies, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), and structural magnetic resonance imaging (MRI) in mentally healthy individuals. MEDLINE searches of English-language literature (1980-November 2006) using the terms sex, gender, PET, SPECT, MRI, fMRI, morphometry, neurochemistry, and neurotransmission were performed to extract relevant sources. The literature suggests that while there are many similarities in brain structure, function, and neurotransmission in healthy men and women, there are important differences that distinguish the male from the female brain. Overall, brain volume is greater in men than women; yet, when controlling for total volume, women have a higher percentage of gray matter and men a higher percentage of white matter. Regional volume differences are less consistent. Global cerebral blood flow is higher in women than in men. Sex-specific differences in dopaminergic, serotonergic, and gamma-aminobutyric acid (GABA)ergic markers indicate that male and female brains are neurochemically distinct. Insight into the etiology of sex differences in the normal living human brain provides an important foundation to delineate the pathophysiological mechanisms underlying sex differences in neuropsychiatric disorders and to guide the development of sex-specific treatments for these devastating brain disorders.

The Science of Sex Differences in Science and Mathematics

Amid ongoing public speculation about the reasons for sex differences in careers in science and mathematics, we present a consensus statement that is based on the best available scientific evidence. Sex differences in science and math achievement and ability are smaller for the mid-range of the abilities distribution than they are for those with the highest levels of achievement and ability. Males are more variable on most measures of quantitative and visuospatial ability, which necessarily results in more males at both high- and low-ability extremes; the reasons why males are often more variable remain elusive. Successful careers in math and science require many types of cognitive abilities. Females tend to excel in verbal abilities, with large differences between females and males found when assessments include writing samples. High-level achievement in science and math requires the ability to communicate effectively and comprehend abstract ideas, so the female advantage in writing should be helpful in all academic domains. Males outperform females on most measures of visuospatial abilities, which have been implicated as contributing to sex differences on standardized exams in mathematics and science. An evolutionary account of sex differences in mathematics and science supports the conclusion that, although sex differences in math and science performance have not directly evolved, they could be indirectly related to differences in interests and specific brain and cognitive systems. We review the brain basis for sex differences in science and mathematics, describe consistent effects, and identify numerous possible correlates. Experience alters brain structures and functioning, so causal statements about brain differences and success in math and science are circular. A wide range of sociocultural forces contribute to sex differences in mathematics and science achievement and ability-including the effects of family, neighborhood, peer, and school influences; training and experience; and cultural practices. We conclude that early experience, biological factors, educational policy, and cultural context affect the number of women and men who pursue advanced study in science and math and that these effects add and interact in complex ways. There are no single or simple answers to the complex questions about sex differences in science and mathematics.

Sex differences in medial and lateral orbitofrontal cortex hypoperfusion in cocaine-dependent men and women

BACKGROUND

The different clinical trajectories of cocaine-dependent men and women may be a consequence of distinct neurobiological substrates. Hypoperfusion of the orbitofrontal cortex (OFC) has previously been reported in individuals addicted to cocaine and has been posited as a biological mediator of relapse due to impulsivity or impaired decision making.

OBJECTIVE

This study assessed regional cerebral blood flow (rCBF) between abstinent cocaine-dependent men and women and sex-matched healthy controls.

METHODS

Cocaine-dependent subjects were abstinent from cocaine for 11 to 28 days and had no other major mental health or substance use disorders. rCBF was assessed with single photon emission computed tomography after administration of a placebo saline infusion. A resting scan was also obtained in a subset of cocaine-dependent and control men.

RESULTS

In the 35 cocaine-dependent and 37 healthy control subjects examined, a sex-by-group effect was observed for the left lateral (P=0.001), right lateral (P=0.002), and medial (P<0.02) OFC. Cocaine-dependent men demonstrated significantly lower right and left lateral, but not medial, OFC rCBF compared with sex-matched healthy controls after placebo infusion (P<or=0.001). Similar bilateral OFC decreases were observed in male cocaine-dependent subjects at rest. In contrast, cocaine-dependent women showed lower rCBF in the medial, but not lateral, OFC relative to sex-matched healthy controls after placebo infusion (P<0.01). Male cocaine-dependent subjects also showed decreased rCBF (P<0.01) in the bilateral anterolateral temporal cortex and anterior cingulate, whereas decreased rCBF was observed in female cocaine-dependent subjects in the bilateral superior frontal gyri. Large and diffuse areas of increased rCBF were observed after placebo infusion in cocaine-dependent men, but not in women, relative to sex-matched healthy controls.

CONCLUSIONS

rCBF appears to be reduced in the bilateral OFC in cocaine-dependent men and in the medial OFC in cocaine-dependent women. Sex differences in the medial and lateral OFC rCBF may be relevant to understanding relapse characteristics differentiating men and women addicted to cocaine.