Gender differences in attention-deficit/hyperactivity disorder

Cross-species approaches to pathological gambling: a review targeting sex differences, adolescent vulnerability and ecological validity of research tools

Decision-making plays a pivotal role in daily life as impairments in processes underlying decision-making often lead to an inability to make profitable long-term decisions. As a case in point, pathological gamblers continue gambling despite the fact that this disrupts their personal, professional or financial life. The prevalence of pathological gambling will likely increase in the coming years due to expanding possibilities of on-line gambling through the Internet and increasing liberal attitudes towards gambling. It therefore represents a growing concern for society. Both human and animal studies rapidly advance our knowledge on brain-behaviour processes relevant for understanding normal and pathological gambling behaviour. Here, we review in humans and animals three features of pathological gambling which hitherto have received relatively little attention: (1) sex differences in (the development of) pathological gambling, (2) adolescence as a (putative) sensitive period for (developing) pathological gambling and (3) avenues for improving ecological validity of research tools. Based on these issues we also discuss how research in humans and animals may be brought in line to maximize translational research opportunities.

Multiple deficits in ADHD: executive dysfunction, delay aversion, reaction time variability, and emotional deficits

BACKGROUND

The notion that ADHD constitutes a heterogeneous disorder is well accepted. However, this study contributes with new important knowledge by examining independent effects of a large range of neuropsychological deficits. In addition, the study investigated whether deficits in emotional functioning constitute a dissociable component of ADHD.

METHOD

The study included children with ADHD (n = 102; 7-13 years) and a control sample individually matched with regard to age and gender. The administered tasks were designed to tap into three different neuropsychological domains: executive functions (i.e., working memory, inhibition, and shifting), delay aversion, and reaction time variability. Parent ratings of emotion regulation and a test of emotion recognition were also included.

RESULTS

Children with ADHD differed significantly from controls on all measures, except for delay aversion and recognition of disgust. No main effects of gender or interaction effects of gender and group were found. More importantly, executive functioning, reaction time variability, and emotional functioning all contributed independently to distinguishing between children with ADHD and controls.

CONCLUSIONS

 The current study supports the view of ADHD as a heterogeneous disorder related to multiple neuropsychological deficits. In addition, emotional functioning appears to be an area of importance for ADHD that needs to be incorporated into future theoretical models.

Sexual dimorphism in expression of insulin and insulin-like growth factor-I receptors in developing rat cerebellum

The insulin and insulin-like growth factor-1 (IGF-1) are considered to play important roles in brain development; and their cognate receptors -InsR and IGF-1R- localized within distinct brain regions including cerebellum. Using Real-Time PCR and western blot analysis, we compared the expression of InsR and IGF-1R in male and female developing rat cerebellum at P0, P7, and P14. At all time points studied, the cerebellar expression of IGF-1R, both at mRNA and protein levels was higher than that of InsR. The lowest InsR and IGF-1R mRNA and protein levels were measured in the neonate cerebellum, independent of gender. In males, the highest InsR and IGF-1R mRNA and protein expression were found at P7. InsR and IGF-1R expression increased significantly between P0 and P7, followed by a marked downregulation at P14. In contrast, in females, mRNA and protein levels of InsR and IGF-1R remain unchanged between P0 and P7, and are upregulated at P14. Therefore, peaked InsR and IGF-1R expression in female cerebelli occurred at P14. Interestingly, changes in mRNA expression and in protein levels followed the same developmental pattern, indicating that InsR and IGF-1R transcription is not subject to modulatory effects during the first 2 weeks of development. These findings indicate that there are prominent sexual differences in InsR and IGF-1R expression in the developing rat cerebellum, suggesting a probable mechanism for the control of gender differences in development and function of the cerebellum.

DSM-IV ADHD symptoms self-ratings by adolescents: test of invariance across gender

OBJECTIVE

Measurement invariance deals with whether the expected scores on a measure are the same or different across different groups when the groups have the same level of the underlying latent trait scores. The study used multiple-group confirmatory factor analysis (CFA) to examine measurement invariance across male and female adolescent self-ratings of the ADHD symptoms (recoded as binary scores).

METHOD

To accomplish this, 178 male and 185 female adolescents, between 12 and 17 years of age, completed an ADHD rating scale.

RESULTS

For the measurement model, the results support the invariance for the configural model (same factor structure and the same items associated with the latent factors), metric invariance (same strength of the associations of items with the factors) for the factor loadings of 17 of the 18 symptoms, and all the error variances. For the construct model, there was invariance for the inattention (IA) and hyperactivity/impulsivity (HI) latent factor variances, covariances, and mean scores. Thus, there was good support for gender equivalency for the ADHD symptoms.

CONCLUSION

These findings extend existing gender invariance data for the ADHD symptoms. The theoretical and clinical implications of the findings as well as the revision implications for Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-V) are discussed.

Prospective follow-up of girls with attention-deficit/hyperactivity disorder into early adulthood: continuing impairment includes elevated risk for suicide attempts and self-injury

OBJECTIVE

We performed a 10-year prospective follow-up of a childhood-ascertained (6-12 years), ethnically and socioeconomically diverse sample of girls with attention-deficit/hyperactivity disorder (ADHD; N = 140: combined type [ADHD-C] n = 93; inattentive type [ADHD-I] n = 47) plus a matched comparison group (N = 88). Girls were recruited from schools, mental health centers, pediatric practices, and via advertisements; extensive evaluations confirmed ADHD versus comparison status.

METHOD

Ten-year outcomes (age range 17-24 years; retention rate = 95%) included symptoms (ADHD, externalizing, internalizing), substance use, eating pathology, self-perceptions, functional impairment (global, academic, service utilization), self-harm (suicide attempts, self-injury), and driving behavior.

RESULTS

Participants with childhood-diagnosed ADHD continued to display higher rates of ADHD and comorbid symptoms, showed more serious impairment (both global and specific), and had higher rates of suicide attempts and self-injury than the comparison sample, with effect sizes from medium to very large; yet the groups did not differ significantly in terms of eating pathology, substance use, or driving behavior. ADHD-C and ADHD-I types rarely differed significantly, except for suicide attempts and self-injury, which were highly concentrated in ADHD-C. Domains of externalizing behavior, global impairment, service utilization, and self-harm (self-injury and suicide attempts) survived stringent control of crucial childhood covariates (age, demographics, comorbidities, IQ).

CONCLUSIONS

Girls with childhood ADHD maintain marked impairment by early adulthood, spreading from symptoms to risk for serious self-harm. Our future research addresses the viability of different diagnostic conceptions of adult ADHD and their linkages with core life impairments.

Sex and dose-related differences in methylphenidate adolescent locomotor sensitization and effects on brain-derived neurotrophic factor

This study analyzed repeated methylphenidate (MPH) administration and its effects on brain-derived neurotrophic factor (BDNF) in the dorsal striatum and nucleus accumbens of male and female adolescent rats. In Experiment 1, rats were administered intraperitoneal (ip) saline, 1, 3, or 5 mg/kg dose of MPH every second day from postnatal day (P)33-P49. Locomotor activity was analyzed for 10 min after each administration. Results revealed that the 1 mg/kg dose of MPH produced locomotor suppression, however, the 5 mg/kg dose of MPH produced locomotor sensitization and robust behavioral activation in females as compared to males. In Experiment 2, animals were administered ip saline or the 5 mg/kg dose of MPH using an identical regimen but a 30 min behavioral test was employed. Dorsal striatum and nucleus accumbens tissue was assayed for BDNF at P50. Females demonstrated sensitization to MPH and increased locomotor activation compared to males. Interestingly, females given MPH demonstrated a significant 42% decrease of striatal BDNF whereas males administered MPH demonstrated a significant 50.4% increase of striatal BDNF compared to controls. There were no effects on accumbal BDNF. This report demonstrates robust sex differences in the behavioral response, but sex-dependent changes in striatal BDNF in response to MPH in adolescence.

Distinguishing comorbidity and successful management of adult ADHD

OBJECTIVE

Given high rates of comorbidity, lack of awareness and global acceptance, and varying guidelines for its management, adult ADHD may be an especially difficult condition to diagnose and treat. The objective of this review was to explore and characterize similarities and differences among comorbidities associated with adult ADHD.

METHOD

A review of the literature over the past 10 years was performed using Ovid.

RESULTS

A myriad of comorbid conditions such as impulse-control/personality, anxiety, mood, substance use, learning, and sleep disorders overlap with adult ADHD. Furthermore, a number of such conditions have symptoms that can mimic those of ADHD, including hyperactivity, impulsivity, inattention, and disruption of circadian rhythms, adding to the complexity of recognition and diagnosis of ADHD in adults. Extensive research shows that adults with ADHD appear to benefit from treatment with stimulant medications in similar ways as children, including significant improvements on driving performance. However, fear surrounding the abuse of stimulants is an important issue. Nevertheless, evidence suggests that children with ADHD who are treated with stimulant medication are less likely to develop a substance use disorder in adolescence and adulthood.

CONCLUSION

There are a wide range of comorbidities with adult ADHD with many having overlapping symptoms. The benefits observed with ADHD treatment, however, emphasize the importance of recognition and treatment of adult ADHD.

Executive functions in girls with ADHD followed prospectively into young adulthood

OBJECTIVE

We prospectively followed an ethnically and socioeconomically diverse sample of girls with ADHD (n = 140) and a matched comparison group (n = 88) into young adulthood (Mage = 19.6), 10 years after childhood initial assessments, to evaluate neuropsychological functioning. We hypothesized that neuropsychological deficits would persist through young adulthood for those with ADHD, and that those with continuing ADHD symptomatology in young adulthood would show the largest impairments.

METHOD

Neuropsychological measures at follow-up emphasized executive functions (EF) including planning, organization, inhibitory control, sustained attention, working memory, and set shifting.

RESULTS

Parallel to findings from childhood and adolescence, the girls with childhood-diagnosed ADHD displayed medium to large deficits in EF relative to comparisons at follow-up, even with statistical control of baseline demographic and comorbidity variables. The addition of IQ as a covariate attenuated differences but several remained significant. Comparisons between the inattentive and combined subtypes of ADHD yielded nonsignificant results with small effect sizes. EF impairments were evident in both participants whose ADHD diagnoses persisted and in those whose ADHD symptoms had remitted to a nondiagnosable level; both subgroups had more EF deficits than those who did not meet criteria for ADHD in either childhood or young adulthood.

CONCLUSIONS

Those in both the persistent and remitted ADHD groups showed impairments in EF relative to comparisons and generally did not differ from each other. Overall, childhood ADHD in girls portends neuropsychological/EF deficits that persist for at least 10 years.

Management of attention-deficit/hyperactivity disorder: the importance of psychosocial and medication treatments

Attention-deficit/hyperactivity disorder (ADHD) assessment and treatment in children and adolescents is complex. Key biological and psychosocial risk factors need to be identified and treated because of their potential mediating interaction that affect the onset, progression, and psychosocial and medication treatment response of core ADHD symptoms and common associated co-morbid conditions. Both psychosocial and medication treatments, alone and in combination, have been shown to reduce the core ADHD symptoms and those of its key co-morbid disorders. Yet, to date, the potential synergism between targeted and specific medication and psychosocial treatments remains poorly understood and under-researched. Interestingly, recent positron emission tomography findings emphasise the importance of contextual salience and positive reinforcement strategies for stimulant medication, the primary medication treatment for ADHD, to have its effect. This is not surprising, given recent epigenetic models of gene-environment interaction that are revolutionising our understanding of developmental disorders like ADHD. This annotation briefly outlines the emerging evidence that supports the role of psychosocial treatment alongside medication treatment in the management of ADHD. Future significant clinical directions are noted.

Sexual differentiation of the brain and ADHD: what is a sex difference in prevalence telling us?

Sexual differentiation of the brain is a function of various processes that prepare the organism for successful reproduction in adulthood. Release of gonadal steroids during both the perinatal and the pubertal stages of development organizes many sex differences, producing changes in brain excitability and morphology that endure across the lifespan. To achieve these sexual dimorphisms, gonadal steroids capitalize on a number of distinct mechanisms across brain regions. Comparison of the developing male and female brain provides insight into the mechanisms through which synaptic connections are made, and circuits are organized that mediate sexually dimorphic behaviors. The prevalence of most psychiatric and neurological disorders differ in males versus females, including disorders of attention, activity and impulse control. While there is a strong male bias in incidence of attention deficit and hyperactivity disorders, the source of that bias remains controversial. By elucidating the biological underpinnings of male versus female brain development, we gain a greater understanding of how hormones and genes do and do not contribute to the differential vulnerability in one sex versus the other.

The influence of sex-linked genetic mechanisms on attention and impulsivity

It is now generally agreed that there are inherent sex differences in healthy individuals across a number of neurobiological domains (including brain structure, neurochemistry, and cognition). Moreover, there is a burgeoning body of evidence highlighting sex differences within neuropsychiatric populations (in terms of the rates of incidence, clinical features/progression, neurobiology and pathology). Here, we consider the extent to which attention and impulsivity are sexually dimorphic in healthy populations and the extent to which sex might modulate the expression of disorders characterised by abnormalities in attention and/or impulsivity such as attention deficit hyperactivity disorder (ADHD), autism and addiction. We then discuss general genetic mechanisms that might underlie sex differences in attention and impulsivity before focussing on specific positional and functional candidate sex-linked genes that are likely to influence these cognitive processes. Identifying novel sex-modulated molecular targets should ultimately enable us to develop more effective therapies in disorders associated with attentional/impulsive dysfunction.

Gender differences in symptoms of comorbidity in toddlers with ASD using the BISCUIT-Part 2

OBJECTIVE

Examine if gender differences exist with respect to comorbid symptoms in young children with Autistic Disorder (AD), Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS) and atypical controls.

DESIGN

A factorial MANOVA was conducted for the main analysis and follow-up post-hocs were conducted where significant differences were found.

METHODS

The Baby and Infant Screen for Children with aUtIsm Traits, Part 2 was administered to caregivers of 438 young children.

RESULTS

The MANOVA was significant, F(10, 858) = 19.38, p < 0.001, Pillai's Trace = 0.37. No gender differences were found; however, diagnostic groups differed significantly on symptoms with AD exhibiting more symptoms than PDD-NOS, followed by atypical controls. No interaction between gender and diagnosis was found.

CONCLUSIONS

Those with AD exhibited greater comorbid symptoms which is consistent with previous research. Current finding also support previous literature which state that gender differences are evident only during certain periods in the lifespan.

The influence of television and video game use on attention and school problems: a multivariate analysis with other risk factors controlled

BACKGROUND

Research on youth mental health has increasingly indicated the importance of multivariate analyses of multiple risk factors for negative outcomes. Television and video game use have often been posited as potential contributors to attention problems, but previous studies have not always been well-controlled or used well-validated outcome measures. The current study examines the multivariate nature of risk factors for attention problems symptomatic of attention deficit hyperactivity disorder and poor school performance.

METHOD

A predominantly Hispanic population of 603 children (ages 10-14) and their parents/guardians responded to multiple behavioral measures. Outcome measures included parent and child reported attention problem behaviors on the Child Behavior Checklist (CBCL) as well as poor school performance as measured by grade point average (GPA).

RESULTS

Results found that internal factors such as male gender, antisocial traits, family environment and anxiety best predicted attention problems. School performance was best predicted by family income. Television and video game use, whether total time spent using, or exposure to violent content specifically, did not predict attention problems or GPA.

INTERPRETATION

Television and video game use do not appear to be significant predictors of childhood attention problems. Intervention and prevention efforts may be better spent on other risk factors.

A staged approach for identifying children with developmental coordination disorder from the population

The purpose of this study was to describe the motor, attention and intellectual characteristics of a population-based sample of children first screened for motor impairment and to discuss the recruitment and identification methods employed. A two stage cross-sectional, school-based survey was conducted to screen for children with motor coordination difficulties and to identify children with an existing diagnosis of attention deficit hyperactivity disorder/attention deficit disorder (ADHD/ADD). The identified children, and a random sample of typically developing children, were assessed to confirm or rule out the presence of developmental coordination disorder (DCD). Six thousand four hundred and seventy five children were invited to participate; 2943 children, with parental consent, completed the initial screening process. Two hundred eighty four children with possible motor impairment were identified. The parents of 113 children consented to a full assessment. Sixty eight children of the 113 children met diagnostic criteria for DCD, and 26 also had ADHD. Twenty eight of the 55 children who screened in with a diagnosis of ADHD were subsequently found to have DCD. The total number of children with confirmed characteristics of DCD was reduced after application of DCD diagnostic criteria. This study differs from others with regard to the additional screening for children with ADHD/ADD. The second stage assessment notably increased the number of children identified with both ADHD and DCD.

Increased symptoms of attention deficit hyperactivity disorder and major depressive disorder symptoms in Nail-patella syndrome: potential association with LMX1B loss-of-function

Nail-Patella syndrome (NPS) is an autosomal dominant disorder that is the result of heterozygous loss-of-function mutations in LMX1B, coding for a LIM homeobox (LIM-HD) transcription factor. Analyses of lmx1b mutant mice have revealed the role of Lmx1b in the development of mesencephalic dopaminergic neurons and the serotonergic system; these areas have been linked with symptoms of attention deficit hyperactivity disorder (ADHD) and major depressive disorder (MDD). Fifty adults (38 females, 12 males) with NPS completed the Conners' Adult ADHD Rating Scales-Self-report: Long Version (CAARS) and Beck Depression Inventory-II (BDI-II). The objective was to describe the neurobehavioral phenotype of these subjects and examine possible relationships between neurobehavioral symptoms and NPS. Elevated levels of DSM-IV-TR ADHD Inattentive symptoms were reported on the CAARS by 22% of the NPS sample. The BDI-II Total score was elevated for 40% of the NPS sample. There was a significant increase in the odds of an elevated BDI-II Total score when any of the three CAARS scales were elevated (odds ratios ranging from 11.455 to 15.615). The CAARS and BDI-II did not significantly differ with gender, age, or education level. There was no significant association between genetic mutation-predicted protein status and elevations on CAARS or BDI-II. Individuals with NPS reported co-occurring symptoms of ADHD and MDD, with higher levels of co-occurrence than reported in the literature for the general population. The co-occurrence of these symptoms may be related to mesencephalic dopaminergic neurologic pathway abnormalities that are a consequence of LMX1B loss of function.

Treatment stabilization in children and adolescents with attention-deficit/hyperactivity disorder: data from the Netherlands

OBJECTIVE

To evaluate the number of patients reaching stable treatment with a stimulant (methylphenidate or dexamphetamine) or non-stimulant (atomoxetine) attention-deficit/hyperactivity disorder (ADHD) medication approved for use in the Netherlands, and the time to treatment stabilization among children and adolescents aged 6-17 years.

RESEARCH DESIGN AND METHODS

Prescription data from the PHARMO medical record linkage system from 48 geo-demographic areas in the Netherlands (2003-2006) were analyzed from newly treated patients with ADHD aged 6-17 years. Only patients with ≥ 5 dispensings for any ADHD drug during follow-up (at least 12 months) and no missing information on type of drug, strength, and number of pills per day were included.

MAIN OUTCOME MEASURES

Attainment of a stable dosing regimen was defined as no change in type of drug (including a switch from an immediate release (IR) to a long-acting (LA) formulation), strength, and number of pills per day for five consecutive dispensings. Time to stable dosing regimen was defined as the number of days between the first dispensing for an ADHD drug and the first of five unchanged dispensings.

RESULTS

Of 4909 children or adolescents initiating treatment, 3099 met selection criteria. More patients starting therapy with LA methylphenidate (82.4%) achieved treatment stabilization during follow-up than with IR methylphenidate (74.8%; p < 0.01) or atomoxetine (69.8%; p < 0.05). More patients initiated on LA methylphenidate patients (43.9%) achieved treatment stabilization without changing their index medication or dose compared to those initiated on IR methylphenidate (25.3%) or atomoxetine (8.1%; p < 0.0001 for both comparisons). Among patients achieving treatment stabilization, those initiating treatment with LA methylphenidate had a significantly shorter time to treatment stabilization (14 days) than patients initially treated with IR methylphenidate (56 days; p < 0.001) or atomoxetine (31 days; p < 0.05). Mean number of pills per day varied between 1.0 and 1.8 at initial treatment and 1.1 and 1.9 at treatment stabilization. Potential limitations of the study include the use of ADHD-medication dispensing as a proxy for an ADHD diagnosis and the impact of different titration schedules for the various ADHD medications.

CONCLUSION

Overall, 2316 of the 3066 eligible patients (75.5%) achieved treatment stabilization during follow-up. Among children and adolescents with ADHD in the Netherlands, the time to treatment stabilization varied according to choice of initial treatment and was shortest for LA methylphenidate.

Neuropsychological profile of executive function in girls with attention-deficit/hyperactivity disorder

The majority of research on neurobehavioral functioning among children with Attention-Deficit/Hyperactivity Disorder (ADHD) is based on samples comprised primarily (or exclusively) of boys. Although functional impairment is well established, available research has yet to specify a neuropsychological profile distinct to girls with ADHD. The purpose of this study was to examine performance within four components of executive function (EF) in contemporaneously recruited samples of girls and boys with ADHD. Fifty-six children with ADHD (26 girls) and 90 controls (42 girls), ages 8-13, were administered neuropsychological tests emphasizing response inhibition, response preparation, working memory, and planning/shifting. There were no significant differences in age or SES between boys or girls with ADHD or their sex-matched controls; ADHD subtype distribution did not differ by sex. Compared with controls, children with ADHD showed significant deficits on all four EF components. Girls and boys with ADHD showed similar patterns of deficit on tasks involving response preparation and working memory; however, they manifested different patterns of executive dysfunction on tasks related to response inhibition and planning. Girls with ADHD showed elevated motor overflow, while boys with ADHD showed greater impairment during conscious, effortful response inhibition. Girls, but not boys with ADHD, showed impairment in planning. There were no differences between ADHD subtypes on any EF component. These findings highlight the importance of studying boys and girls separately (as well as together) when considering manifestations of executive dysfunction in ADHD.

Executive functions and selective attention are favored in middle-aged healthy women carriers of the Val/Val genotype of the catechol-o-methyltransferase gene: a behavioral genetic study

BACKGROUND

Cognitive deficits such as poor memory, the inability to concentrate, deficits in abstract reasoning, attention and set-shifting flexibility have been reported in middle-aged women. It has been suggested that cognitive decline may be due to several factors which include hormonal changes, individual differences, normal processes of aging and age-related changes in dopaminergic neurotransmission. Catechol-O-methyltransferase (COMT), a common functional polymorphism, has been related to executive performance in young healthy volunteers, old subjects and schizophrenia patients. The effect of this polymorphism on cognitive function in middle-aged healthy women is not well known. The aim of the current study was to investigate whether measures of executive function, sustained attention, selective attention and verbal fluency would be different depending on the COMT genotype and task demand.

METHOD

We genotyped 74 middle-aged healthy women (48 to 65 years old) for the COMT Val158Met polymorphism. We analyzed the effects of this polymorphism on executive functions (Wisconsin Card Sorting Test), selective attention (Stroop test), sustained attention (Continuous Performance Test) and word generation (Verbal Fluency test), which are cognitive functions that involve the frontal lobe.

RESULTS

There were 27 women with the Val/Val COMT genotype, 15 with the Met/Met genotype, and 32 with the Val/Met genotype. Women carriers of the Val/Val genotype performed better in executive functions, as indicated by a lower number of errors committed in comparison with the Met/Met or Val/Met groups. The correct responses on selective attention were higher in the Val/Val group, and the number of errors committed was higher in the Met/Met group during the incongruence trial in comparison with the Val/Val group. Performance on sustained attention and the number of words generated did not show significant differences between the three genotypes.

CONCLUSION

These findings indicate that middle-aged women carriers of the Val158 allele, associated with high-activity COMT, showed significant advantage over Met allele in executive processes and cognitive flexibility. These results may help to explain, at least in part, individual differences in cognitive decline in middle-aged women with dopamine-related genes.

Same sex, no sex, and unaware sex in neurotoxicology

Males and females of virtually all species differ in how they respond to their environment. Because such differences exist in almost all biological realms, including disease patterns and therapeutic outcomes, they have evoked calls by various bodies to incorporate their assessment in research. Neurobehavioral indices pose special questions because, unlike outwardly visible markers, they are described by complex functional outcomes or subtle alterations in brain structure. These divergent responses arise because they are inscribed in the genome itself and then by endocrine mechanisms that govern sexual differentiation of the brain during development and operate throughout life. Other organ systems that exhibit sex differences include the liver, an important consideration for neurotoxicology because it may process many toxic chemicals differentially in males and females. Despite the scope and pervasiveness of sex differences, however, they are disregarded by much of neurotoxicology research. Males predominate in behavioral experiments, few such experiments study both sexes, some investigators fail to even describe the sex of their subjects, and in vitro studies tend to wholly ignore sex, even for model systems aimed at neurological disorders that display marked sex differences. The public is acutely aware of sex differences in behavior, as attested by its appetite for books on the topic. It closely follows debates about the proportion of women in professions that feature science and mathematics. Neurotoxicology, especially in the domain of laboratory research, will be hindered in its ability to translate its findings into human health measures if it assigns sex differences to a minor role. It must also be sensitive to how such debates are framed. Often, the differences evoking the most discussion are subtle in scope. They do not lend themselves to the typical analyses conducted by experimenters; that is, reliance on mean differences and null hypothesis testing.