Gender differences in the functional organization of the brain for working memory

Gender differences in healthy aging and Alzheimer's Dementia: A 18 F-FDG-PET study of brain and cognitive reserve

Cognitive reserve (CR) and brain reserve (BR) are protective factors against age-associated cognitive decline and neurodegenerative disorders. Very limited evidence exists about gender effects on brain aging and on the effect of CR on brain modulation in healthy aging and Alzheimer's Dementia (AD). We investigated gender differences in brain metabolic activity and resting-state network connectivity, as measured by ¹⁸ F-FDG-PET, in healthy aging and AD, also considering the effects of education and occupation. The clinical and imaging data were retrieved from large datasets of healthy elderly subjects (HE) (225) and AD patients (282). In HE, males showed more extended age-related reduction of brain metabolism than females in frontal medial cortex. We also found differences in brain modulation as metabolic increases induced by education and occupation, namely in posterior associative cortices in HE males and in the anterior limbic-affective and executive networks in HE females. In AD patients, the correlations between education and occupation levels and brain hypometabolism showed gender differences, namely a posterior temporo-parietal association in males and a frontal and limbic association in females, indicating the involvement of different networks. Finally, the metabolic connectivity in both HE and AD aligned with these results, suggesting greater efficiency in the posterior default mode network for males, and in the anterior frontal executive network for females. The basis of these brain gender differences in both aging and AD, obtained exploring cerebral metabolism, metabolic connectivity and the effects of education and occupation, is likely at the intersection between biological and sociodemographic factors. Hum Brain Mapp 38:4212-4227, 2017. © 2017 Wiley Periodicals, Inc.

Sex-specific cognitive abnormalities in early-onset psychosis

Objectives:

Brain maturation differs depending on the area of the brain and sex. Girls show an earlier peak in maturation of the prefrontal cortex. Although differences between adult females and males with schizophrenia have been widely studied, there has been less research in girls and boys with psychosis. The purpose of this study was to examine differences in verbal and visual memory, verbal working memory, auditory attention, processing speed, and cognitive flexibility between boys and girls.

Methods:

We compared a group of 80 boys and girls with first-episode psychosis to a group of controls.

Results:

We found interactions between group and sex in verbal working memory (p = 0.04) and auditory attention (p = 0.01). The female controls showed better working memory (p = 0.01) and auditory attention (p = 0.001) than males. However, we did not find any sex differences in working memory (p = 0.91) or auditory attention (p = 0.93) in the psychosis group.

Conclusions:

These results are consistent with the presence of sex-modulated cognitive profiles at first presentation of early-onset psychosis.

Sex differences in verbal working memory performance emerge at very high loads of common neuroimaging tasks

Working memory (WM) supports a broad range of intelligent cognition and has been the subject of rich cognitive and neural characterization. However, the highest ranges of WM have not been fully characterized, especially for verbal information. Tasks developed to test multiple levels of WM demand (load) currently predominate brain-based WM research. These tasks are typically used at loads that allow most healthy participants to perform well, which facilitates neuroimaging data collection. Critically, however, high performance at lower loads may obscure differences that emerge at higher loads. A key question not yet addressed at high loads concerns the effect of sex. Thoroughgoing investigation of high-load verbal WM is thus timely to test for potential hidden effects, and to provide behavioral context for effects of sex observed in WM-related brain structure and function. We tested 111 young adults, matched on genotype for the WM-associated COMT-Val^108/158Met polymorphism, on three classic WM tasks using verbal information. Each task was tested at four WM loads, including higher loads than those used in previous studies of sex differences. All tasks loaded on a single factor, enabling comparison of verbal WM ability at a construct level. Results indicated sex effects at high loads across tasks and within each task, such that males had higher accuracy, even among groups that were matched for performance at lower loads.

Sex differences in verbal and nonverbal learning before and after temporal lobe epilepsy surgery

Women outperform men in a host of episodic memory tasks, yet the neuroanatomical basis for this effect is unclear. It has been suggested that the anterior temporal lobe might be especially relevant for sex differences in memory. In the current study, we investigated whether temporal lobe epilepsy (TLE) has an influence on sex effects in learning and memory and whether women and men with TLE differ in their risk for memory deficits after epilepsy surgery. 177 patients (53 women and 41 men with left TLE, 42 women and 41 men with right TLE) were neuropsychologically tested before and one year after temporal lobe resection. We found that women with TLE had better verbal, but not figural, memory than men with TLE. The female advantage in verbal memory was not affected by temporal lobe resection. The same pattern of results was found in a more homogeneous subsample of 84 patients with only hippocampal sclerosis who were seizure-free after surgery. Our findings challenge the concept that the anterior temporal lobe plays a central role in the verbal memory advantage for women.

Gender Differences in Verbal and Visuospatial Working Memory Performance and Networks

BACKGROUND

Working memory (WM) has been a matter of intensive basic and clinical research for some decades now. The investigation of WM function and dysfunction may facilitate the understanding of both physiological and pathological processes in the human brain. Though WM paradigms are widely used in neuroscientific and psychiatric research, conclusive knowledge about potential moderating variables such as gender is still missing.

METHODS

We used functional magnetic resonance imaging to investigate the effects of gender on verbal and visuospatial WM maintenance tasks in a large and homogeneous sample of young healthy subjects.

RESULTS

We found significant gender effects on both the behavioral and neurofunctional level. Females exhibited disadvantages with a small effect size in both WM domains accompanied by stronger activations in a set of brain regions (including bilateral substantia nigra/ventral tegmental area and right Broca's area) independent of WM modality. As load and task difficulty effects have been shown for some of these regions, the stronger activations may reflect a slightly lower capacity of both WM domains in females. Males showed stronger bilateral intraparietal activations next to the precuneus which were specific for the visuospatial WM task. Activity in this specific region may be associated with visuospatial short-term memory capacity.

CONCLUSION

These findings provide evidence for a slightly lower capacity in both WM modalities in females.

Ecological momentary assessment of working memory under conditions of simultaneous marijuana and tobacco use

BACKGROUND AND AIMS

The neuropsychological correlates of simultaneous marijuana and tobacco use are largely unknown, which is surprising as both substances have similar neural substrates and have opposing influences on working memory (WM). This study examined the effects of marijuana alone, tobacco alone and simultaneous marijuana and tobacco use on WM.

DESIGN

Primary aims were tested using a within-subject design, controlling for multiple subject- and momentary-level confounds via ecological momentary assessment (EMA).

SETTING

Data collection occurred in the Chicago, USA area in participants' natural environments.

PARTICIPANTS

Participants were 287 community young adults from a larger natural history study, oversampled for ever smoking, all of whom event-recorded at least one substance use occasion during the study week.

MEASUREMENTS

Momentary tobacco, marijuana and alcohol use were recorded during multiple EMA across 1 week of data capture. WM was assessed at the end of each EMA assessment. Contextual variables that may influence WM were recorded via EMA.

FINDINGS

There were main effects for marijuana and tobacco: WM was poorer with marijuana [odds ratio (OR) = 0.91, 95% confidence interval (CI) = 0.84-0.99] and better with tobacco (OR = 1.11, 95% CI = 1.04-1.18). These effects were not qualified by an interaction (OR = 1.03, 95% CI = 0.84-1.26). Alcohol also reduced WM (OR = 0.87, 95% CI = 0.79-0.95), and the tobacco × alcohol interaction was significant (OR = 0.81, 95% CI = 0.66-0.99), indicating that the facilitative effect of tobacco disappeared with concurrent alcohol use.

CONCLUSIONS

Relative to when individuals did not use these substances, working memory decreased with acute marijuana and alcohol use and increased with acute tobacco use. However, the putative effect of marijuana on working memory and the facilitative effect of tobacco on working memory were no longer present when used simultaneously with tobacco and alcohol, respectively. Data suggest that tobacco use may compensate for working memory decrements from marijuana among young adults and highlight the importance of investigating further the negative impact of alcohol use on cognition.

Motor Subtype as a Predictor of Future Working Memory Performance in Idiopathic Parkinson's Disease

Parkinson's disease is a progressive neurodegenerative disorder associated with reduced spatial and verbal working memory ability. There are two established motor subtypes of PD, tremor dominant (TD) and postural instability and gait difficulty (PIGD). This study used structural equation modelling to explore the longitudinal relationship between the two subtypes and working memory assessed at a 2-year follow-up. The study comprised 84 males and 30 females (N = 114), aged between 39 and 85 (M = 64.82, SD = 9.23) with confirmed PD. There was no significant relationship between motor subtype at Time 1 and working memory at Time 2. Postural symptom severity at Time 1 predicted Time 2 spatial working memory for the PIGD subtype (p = .011) but not the TD subtype. Tremor symptoms were not associated with Time 2 working memory in either subtype. Predictive significance of Time 1 postural symptoms only in the PIGD subtype suggests an interaction between symptom dominance (subtype) and symptom severity that future subtyping should consider. This study demonstrates a predictive relationship between postural difficulties and working memory performance assessed at a 2-year follow-up. Establishing physical symptoms as predictors of cognitive change could have significant clinical importance.

Modeling distinct imaging hemodynamics early after TBI: the relationship between signal amplitude and connectivity

Over the past decade, fMRI studies of cognitive change following traumatic brain injury (TBI) have investigated blood oxygen level dependent (BOLD) activity during working memory (WM) performance in individuals in early and chronic phases of recovery. Recently, BOLD fMRI work has largely shifted to focus on WM and resting functional connectivity following TBI. However, fundamental questions in WM remain. Specifically, the effects of injury on the basic relationships between local and interregional functional neuroimaging signals during WM processing early following moderate to severe TBI have not been examined. This study employs a mixed effects model to examine prefrontal cortex and parietal lobe signal change during a WM task, the n-back, and whether there is covariance between regions of high amplitude signal change, (synchrony of elicited activity (SEA) very early following TBI. We also examined whether signal change and SEA differentially predict performance during WM. Overall, percent signal change in the right prefrontal cortex (rPFC) was and important predictor of both reaction time (RT) and SEA in early TBI and matched controls. Right prefrontal cortex (rPFC) percent signal change positively predicted SEA within and between persons regardless of injury status, suggesting that the link between these neurodynamic processes in WM-activated regions remains unaffected even very early after TBI. Additionally, rPFC activity was positively related to RT within and between persons in both groups. Right parietal (rPAR) activity was negatively related to RT within subjects in both groups. Thus, the local signal intensity of the rPFC in TBI appears to be a critical property of network functioning and performance in WM processing and may be a precursor to recruitment observed in chronic samples. The present results suggest that as much research moves toward large scale functional connectivity modeling, it will be essential to develop integrated models of how local and distant neurodynamics promote WM performance after TBI.

Normative data on the n-back task for children and young adolescents

The n-back task is a frequently used measure of working memory (WM) in cognitive neuroscience research contexts, and it has become widely adopted in other areas over the last decade. This study aimed to obtain normative data for the n-back task from a large sample of children and adolescents. To this end, a computerized verbal n-back task with three levels of WM load (1-back, 2-back, and 3-back) was administered to 3722 Spanish school children aged 7–13 years. Results showed an overall age-related increase in performance for the different levels of difficulty. This trend was less pronounced at 1-back than at 2-back when hits were considered. Gender differences were also observed, with girls outperforming boys although taking more time to respond. The theoretical implications of these results are discussed. Normative data stratified by age and gender for the three WM load levels are provided.

Neural correlates of visuospatial working memory in attention-deficit/hyperactivity disorder and healthy controls

Impaired visuospatial working memory (VSWM) is suggested to be a core neurocognitive deficit in attention-deficit/hyperactivity disorder (ADHD), yet the underlying neural activation patterns are poorly understood. Furthermore, it is unclear to what extent age and gender effects may play a role in VSWM-related brain abnormalities in ADHD. Functional magnetic resonance imaging (fMRI) data were collected from 109 individuals with ADHD (60% male) and 103 controls (53% male), aged 8-25 years, during a spatial span working memory task. VSWM-related brain activation was found in a widespread network, which was more widespread compared with N-back tasks used in the previous literature. Higher brain activation was associated with higher age and male gender. In comparison with controls, individuals with ADHD showed greater activation in the left inferior frontal gyrus (IFG) and the lateral frontal pole during memory load increase, effects explained by reduced activation on the low memory load in the IFG pars triangularis and increased activation during high load in the IFG pars opercularis. Age and gender effects did not differ between controls and individuals with ADHD. Results indicate that individuals with ADHD have difficulty in efficiently and sufficiently recruiting left inferior frontal brain regions with increasing task difficulty.

The effects of gender differences on the use of annotatable multimedia e-readers

Purpose

– This paper aims to examine how gender differences influence students’ reactions to the use of the annotatable multimedia e-reader (AME). To reach this aim, we develop an AME where various annotation tools are provided to help students learn English in-class and after-class.

Design/methodology/approach

– An empirical study was conducted with 63 fifth-grade students from an elementary school. A pre-test and post-test were used to identify their prior knowledge and learning achievement, respectively. A questionnaire was applied to identify participants’ perceptions towards the AME.

Findings

– The results show that students’ post-test scores are significantly related to after-class behaviour, instead of in-class behaviour. Females prefer to use the text annotation and teachers’ voice, but it is voice annotation that is beneficial to improve their learning achievement. Conversely, males prefer to use the text-to-speech only, but it is text annotation that is helpful to improve their learning achievement. Additionally, the ease of use affects males’ intention to use the AME to learn English after-class while it has no effects on females.

Originality/value

– This study not only shows the importance of gender differences but also demonstrates the essence of after-class learning behaviour. More importantly, a framework is proposed to support designers to develop e-readers that can accommodate the preferences of females and males.

Genetic influences on brain developmental trajectories on neuroimaging studies: from infancy to young adulthood

Human brain development has been studied intensively with neuroimaging. However, little is known about how genes influence developmental brain trajectories, even though a significant number of genes (about 10,000, or approximately one-third) in the human genome are expressed primarily in the brain and during brain development. Interestingly, in addition to showing differential expression among tissues, many genes are differentially expressed across the ages (e.g., antagonistic pleiotropy). Age-specific gene expression plays an important role in several critical events in brain development, including neuronal cell migration, synaptogenesis and neurotransmitter receptor specificity, as well as in aging and neurodegenerative disorders (e.g., Alzheimer disease or amyotrophic lateral sclerosis). In addition, the majority of psychiatric and mental disorders are polygenic, and many have onsets during childhood and adolescence. In this review, we summarize the major findings from neuroimaging studies that link genetics with brain development, from infancy to young adulthood. Specifically, we focus on the heritability of brain structures across the ages, age-related genetic influences on brain development and sex-specific developmental trajectories.

The Importance of Visual Experience, Gender, and Emotion in the Assessment of an Assistive Tactile Mouse

Tactile maps are efficient tools to improve spatial understanding and mobility skills of visually impaired people. Their limited adaptability can be compensated with haptic devices which display graphical information, but their assessment is frequently limited to performance-based metrics only which can hide potential spatial abilities in O&M protocols. We assess a low-tech tactile mouse able to deliver three-dimensional content considering how performance, mental workload, behavior, and anxiety status vary with task difficulty and gender in congenitally blind, late blind, and sighted subjects. Results show that task difficulty coherently modulates the efficiency and difficulty to build mental maps, regardless of visual experience. Although exhibiting attitudes that were similar and gender-independent, the females had lower performance and higher cognitive load, especially when congenitally blind. All groups showed a significant decrease in anxiety after using the device. Tactile graphics with our device seems therefore to be applicable with different visual experiences, with no negative emotional consequences of mentally demanding spatial tasks. Going beyond performance-based assessment, our methodology can help with better targeting technological solutions in orientation and mobility protocols.

Examining network dynamics after traumatic brain injury using the extended unified SEM approach

The current study uses effective connectivity modeling to examine how individuals with traumatic brain injury (TBI) learn a new task. We make use of recent advancements in connectivity modeling (extended unified structural equation modeling, euSEM) and a novel iterative grouping procedure (Group Iterative Multiple Model Estimation, GIMME) in order to examine network flexibility after injury. The study enrolled 12 individuals sustaining moderate and severe TBI to examine the influence of task practice on connections between 8 network nodes (bilateral prefrontal cortex, anterior cingulate, inferior parietal lobule, and Crus I in the cerebellum). The data demonstrate alterations in networks from pre to post practice and differences in the models based upon distinct learning trajectories observed within the TBI sample. For example, better learning in the TBI sample was associated with diminished connectivity within frontal systems and increased frontal to parietal connectivity. These findings reveal the potential for using connectivity modeling and the euSEM to examine dynamic networks during task engagement and may ultimately be informative regarding when networks are moving in and out of periods of neural efficiency.

Sex Differences in Working Memory after Mild Traumatic Brain Injury: A Functional MR Imaging Study

PURPOSE

To evaluate sex differences in mild traumatic brain injury (MTBI) with working memory functional magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Research ethics committee approval and patient written informed consent were obtained. Working memory brain activation patterns were assessed with functional MR imaging in 30 patients (15 consecutive men and 15 consecutive women) with MTBI and 30 control subjects (15 consecutive men and 15 consecutive women). Two imaging studies were performed in patients: the initial study, which was performed within 1 month after the injury, and a follow-up study, which was performed 6 weeks after the first study. For each participant, digit span and continuous performance testing were performed before functional MR imaging. Clinical data were analyzed by using Kruskal-Wallis, Mann-Whitney U, Wilcoxon signed rank, and Fisher exact tests. Within- and between-group differences of functional MR imaging data were analyzed with one- and two-sample t tests, respectively.

RESULTS

Among female participants, the total digit span score was lower in the MTBI group than in the control group (P = .044). In initial working memory functional MR imaging studies, hyperactivation was found in the male MTBI group and hypoactivation was found in the female MTBI group compared with control male and female groups, respectively. At the 6-week follow-up study, the female MTBI group showed persistent hypoactivation, whereas the male MTBI group showed a regression of hyperactivation at visual comparison of activation maps. The male MTBI group was also found to have a higher initial ß value than the male control group (P = .040), and there was no significant difference between the male MTBI group and the male control group (P = .221) at follow-up evaluation, which was comparable to findings on activation maps. In the female MTBI group, average ß values at both initial and follow-up studies were lower compared with those in the female control group but were not statistically significant (P = .663 and P = .191, respectively).

CONCLUSION

Female patients with MTBI had lower digit span scores than did female control subjects, and functional MR imaging depicted sex differences in working memory functional activation; hypoactivation with nonrecovery of activation change at follow-up studies may suggest a worse working memory outcome in female patients with MTBI.

Computerized spatial delayed recognition span task: a specific tool to assess visuospatial working memory

A new tablet device version (IOS platform) of the Spatial Delayed Recognition Span Task (SDRST) was developed with the aim of investigating visuospatial Working Memory (WM) abilities based on touchscreen technology. This new WM testing application will be available to download for free in Apple Store app (“SDRST app”). In order to verify the feasibility of this computer-based task, we conducted three experiments with different manipulations and groups of participants. We were interested in investigating if (1) the SDRST is sensitive enough to tap into cognitive differences brought by aging and dementia; (2) different experimental manipulations work successfully; (3) cortical brain activations seen in other WM tasks are also demonstrated here; and (4) non-human primates are able to answer the task. Performance (scores and response time) was better for young than older adults and higher for the latter when compared to Alzheimer’s disease (AD) patients. All groups performed better with facial stimuli than with images of scenes and with emotional than with neutral stimuli. Electrophysiology data showed activation on prefrontal and frontal areas of scalp, theta band activity on the midline area, and gamma activity in left temporal area. There are all scalp regions known to be related to attention and WM. Besides those data, our sample of adult captive capuchin monkeys (Sapajus libidinosus) answered the task above chance level. Taken together, these results corroborate the reliability of this new computer-based SDRST as a measure of visuospatial WM in clinical and non-clinical populations as well as in non-human primates. Its tablet app allows the task to be administered in a wide range of settings, including hospitals, homes, schools, laboratories, universities, and research institutions.

Electrophysiological measures of resting state functional connectivity and their relationship with working memory capacity in childhood

Functional connectivity is the statistical association of neuronal activity time courses across distinct brain regions, supporting specific cognitive processes. This coordination of activity is likely to be highly important for complex aspects of cognition, such as the communication of fluctuating task goals from higher-order control regions to lower-order, functionally specific regions. Some of these functional connections are identifiable even when relevant cognitive tasks are not being performed (i.e. at rest). We used magnetoencephalographic recordings projected into source space to demonstrate that resting state networks in childhood have electrophysiological underpinnings that are evident in the spontaneous fluctuations of oscillatory brain activity. Using the temporal structure of these oscillatory patterns we were able to identify a number of functional resting state networks analogous to those reported in the adult literature. In a second analysis we fused this dynamic temporal information with the spatial information from a functional magnetic resonance imaging analysis of functional connectivity, to demonstrate that inter-subject variability in these electrophysiological measures of functional connectivity is correlated with individual differences in cognitive ability: the strength of connectivity between a fronto-parietal network and lower-level processing areas in inferior temporal cortex was associated with spatial working memory capacity, as measured outside the scanner with educationally relevant standardized assessments. This study represents the first exploration of the electrophysiological mechanisms underpinning resting state functional connectivity in source space in childhood, and the extent to which the strength of particular connections is associated with cognitive ability.

Assessing the impact of typeface design in a text-rich automotive user interface

Text-rich driver-vehicle interfaces are increasingly common in new vehicles, yet the effects of different typeface characteristics on task performance in this brief off-road based glance context remains sparsely examined. Subjects completed menu selection tasks while in a driving simulator. Menu text was set either in a 'humanist' or 'square grotesque' typeface. Among men, use of the humanist typeface resulted in a 10.6% reduction in total glance time as compared to the square grotesque typeface. Total response time and number of glances showed similar reductions. The impact of typeface was either more modest or not apparent for women. Error rates for both males and females were 3.1% lower for the humanist typeface. This research suggests that optimised typefaces may mitigate some interface demands. Future work will need to assess whether other typeface characteristics can be optimised to further reduce demand, improve legibility, increase usability and help meet new governmental distraction guidelines. Practitioner Summary: Text-rich in-vehicle interfaces are increasingly common, but the effects of typeface on task performance remain sparsely studied. We show that among male drivers, menu selection tasks are completed with 10.6% less visual glance time when text is displayed in a 'humanist' typeface, as compared to a 'square grotesque'.

Does consumption of LC omega-3 PUFA enhance cognitive performance in healthy school-aged children and throughout adulthood? Evidence from clinical trials

Long-chain (LC) omega-3 PUFA derived from marine sources may play an important role in cognitive performance throughout all life stages. Docosahexaenoic acid (DHA), the dominant omega-3 in the brain, is a major component of neuronal cell membranes and affects various neurological pathways and processess. Despite its critical role in brain function, human’s capacity to synthesize DHA de novo is limited and its consumption through the diet is important. However, many individuals do not or rarely consume seafood. The aim of this review is to critically evaluate the current evidence from randomised controlled trials (RCT) in healthy school-aged children, younger and older adults to determine whether consumption of LC omega-3 PUFA improves cognitive performance and to make recommendations for future research. Current evidence suggests that consumption of LC omega-3 PUFA, particularly DHA, may enhance cognitive performance relating to learning, cognitive development, memory and speed of performing cognitive tasks. Those who habitually consume diets low in DHA, children with low literacy ability and malnourished and older adults with age-related cognitive decline and mild cognitive impairment seem to benefit most. However, study design limitations in many RCTs hamper firm conclusions. The measurement of a uniform biomarker, e.g., % DHA in red blood cells, is essential to establish baseline DHA-status, to determine targets for cognitive performance and to facilitate dosage recommendations. It is recommended that future studies be at least 16 weeks in duration, account for potential interaction effects of gender, age and apolipoprotein E genotype, include vegan/vegetarian populations, include measures of speed of cognitive performance and include brain imaging technologies as supportive information on working mechanisms of LC omega-3 PUFA.

Gender differences in working memory networks: a BrainMap meta-analysis

Gender differences in psychological processes have been of great interest in a variety of fields. While the majority of research in this area has focused on specific differences in relation to test performance, this study sought to determine the underlying neurofunctional differences observed during working memory, a pivotal cognitive process shown to be predictive of academic achievement and intelligence. Using the BrainMap database, we performed a meta-analysis and applied activation likelihood estimation to our search set. Our results demonstrate consistent working memory networks across genders, but also provide evidence for gender-specific networks whereby females consistently activate more limbic (e.g., amygdala and hippocampus) and prefrontal structures (e.g., right inferior frontal gyrus), and males activate a distributed network inclusive of more parietal regions. These data provide a framework for future investigations using functional or effective connectivity methods to elucidate the underpinnings of gender differences in neural network recruitment during working memory tasks.

Sex dependence of cognitive functions in bipolar disorder

The objective of the present study was to assess the performance of lithium treated euthymic bipolar patients in tests measuring spatial working memory (SWM), planning, and verbal fluency and to delineate the influence of gender on cognitive functioning. Fifty-nine euthymic bipolar patients, treated with lithium carbonate for at least 5 yr, were studied. Patients and controls underwent a neuropsychological assessment. Bipolar patients had significantly worse results than the healthy controls in the spatial memory and planning as well as verbal fluency tests. We detected a gender-related imbalance in the SWM results. Deficits in SWM were observed in male-only comparisons but not in female-only comparisons. The SWM scores were significantly poorer in male patients than in male controls. In female-only comparisons, female patients did not have significantly poorer SWM results in any category than their controls. Bipolar women scored worse in some other tests. The present study points to the different patterns of neuropsychological disturbances in female and male patients and suggests that sex-dependent differences should be taken into account in order to tailor the therapeutic intervention aimed at the improvement of cognitive functions.

The decline of verbal and visuospatial working memory across the adult life span

It has been well established that working memory abilities decrease with advancing age; however, the specific time point in the adult life span at which this deficit begins and the rate at which it advances are still controversial. There is no agreement on whether working memory declines equally for visuospatial and verbal information, and the literature disagrees on how task difficulty may influence this decay. We addressed these questions in a lifespan sample of 1,500 participants between 21 and 80 years old. The n-back task was used, with letters and circles presented at different positions around an imaginary circle, to evaluate working memory in the verbal and visuospatial domains, respectively. The participants' task was to judge whether the current stimulus matched a stimulus that was shown n trials prior. Both domains were evaluated in two levels of difficulty: 1-back and 2-back. The comparison across decades showed that discrimination in the visuospatial and 1-back tasks started to decline earlier in women than in men; however, discrimination was equal between the sexes in the verbal and 2-back tasks. Performance on tasks in the visuospatial domain exhibited more pronounced decline than in those in the verbal domain. The rate of decline in working memory accuracy was superior in 2-back tasks than in 1-back tasks, independent of the domain. These results revealed that the effects of aging on working memory are less dependent on the type of information and more reliant on the resources demanded by the task.

Effects of working memory load, a history of conduct disorder, and sex on decision making in substance dependent individuals

BACKGROUND

Substance dependence and antisocial psychopathology, such as a history of childhood conduct disorder (HCCD), are associated with impulsive or disadvantageous decision making and reduced working memory capacity (WMC). Reducing WMC via a working memory load increases disadvantageous decision making in healthy adults, but no previous studies have examined this effect in young adults with substance dependence and HCCD.

METHOD

Young adults with substance dependence (SubDep; n=158, 71 female), substance dependence and HCCD (SubDep+HCCD; n=72, 24 female), and control participants (n=152, 84 female) completed a test of decision making (the Iowa Gambling Task; IGT) with or without a concurrent working memory load intended to tax WMC. Outcomes were (i) net advantageous decisions on the IGT, and (ii) preferences for infrequent- versus frequent-punishment decks.

RESULTS

SubDep+HCCD men made fewer advantageous decisions on the IGT than control men without a load, but there were no group differences among women in that condition. Load was associated with fewer advantageous decisions for SubDep+HCCD women and control men, but not for men or women in the other groups. Participants showed greater preference for infrequent-punishment, advantageous decks under load as well.

CONCLUSIONS

There are gender differences in the effects of substance dependence, HCCD, and working memory load on decision making on the IGT. Decision making by control men and SubDep+HCCD women suffered the most under load. Load increases preferences for less-frequent punishments, similar to a delay discounting effect. Future research should clarify the cognitive and neural mechanisms underlying these effects.

Neural correlates of cognitive remediation in patients with mood disorders

Little is known about the brain changes that mediate improvement following cognitive remediation. We used neuropsychological tests and functional magnetic resonance imaging to study working memory and recollection memory in patients with mood disorders, before (PRE) and after (POST) 10 weeks of cognitive remediation. Thirty-eight patients completed a recollection memory task at PRE (28 had complete PRE and POST scans) and 35 patients completed an n-back working memory task at PRE (23 had complete PRE and POST scans). We also compared patients at PRE with two groups of healthy controls subjects (n=18 for the recollection memory task and n=15 for the working memory task). At PRE, compared to controls, patients had (i) poorer backward digit span scores, (ii) lower accuracy scores and weaker frontopolar activation during the 2-back condition, and (iii) poorer recollection scores and altered medial temporal activation on the recollection memory task. Following remediation, patients (i) improved on the backward digit span, (ii) activation increased in lateral and medial prefrontal, superior temporal, and lateral parietal regions in the 2-back condition, and (iii) recollection-related activation increased in the bilateral hippocampus. Improvements in 2-back accuracy correlated with activation increases in lateral and medial prefrontal and lateral parietal regions, and improved recollection scores correlated with activation increases in the left hippocampus. PRE-POST improvements on the backward digit span correlated with PRE-POST improvements in 2-back task accuracy; however, there was no direct association between improvement on the backward digit span following training and change in functional activation. These findings suggest that cognitive remediation may lead to behavioural improvements on tests of working memory. The relation between behavioural change and changes in functional activation following remediation requires further study.

Effects of peripubertal gonadotropin-releasing hormone agonist on brain development in sheep--a magnetic resonance imaging study

In many species sexual dimorphisms in brain structures and functions have been documented. In ovine model, we have previously demonstrated that peri-pubertal pharmacological blockade of gonadotropin releasing hormone (GnRH) action increased sex-differences of executive emotional behavior. The structural substrate of this behavioral alteration however is unknown. In this magnetic resonance image (MRI) study on the same animals, we investigated the effects of GnRH agonist (GnRHa) treatment on the volume of total brain, hippocampus and amygdala. In total 41 brains (17 treated; 10 females and 7 males, and 24 controls; 11 females and 13 males) were included in the MRI study. Image acquisition was performed with 3-T MRI scanner. Segmentation of the amygdala and the hippocampus was done by manual tracing and total gray and white matter volumes were estimated by means of automated brain volume segmentation of the individual T2-weighted MRI volumes. Statistical comparisons were performed with general linear models. Highly significant GnRHa treatment effects were found on the volume of left and right amygdala, indicating larger amygdalae in treated animals. Significant sex differences were found for total gray matter and right amygdala, indicating larger volumes in male compared to female animals. Additionally, we observed a significant interaction between sex and treatment on left amygdala volume, indicating stronger effects of treatment in female compared to male animals. The effects of GnRHa treatment on amygdala volumes indicate that increasing GnRH concentration during puberty may have an important impact on normal brain development in mammals. These novel findings substantiate the need for further studies investigating potential neurobiological side effects of GnRHa treatment on the brains of young animals and humans.

Age-related differences in cortical activity during a visuo-spatial working memory task with facial stimuli

Emotion, importantly displayed by facial expressions, is one of the most significant memory modulators. The interaction between memory and the different emotional valences change across lifespan, while young adults (YA) are expected to better recall negative events (Negativity Bias Hypothesis), older adults (OA) tend to focus on positive stimuli (Positivity Effect Hypothesis). This research work aims at verifying whether cortical electrical activity of these two age groups would also be differently influenced by emotional valences in a visuo-spatial working memory task. 27 YA (13 males) and 25 OA (14 males), all healthy volunteers, underwent electroencephalographic recordings (21 scalp electrodes montage), while performing the Spatial Delayed Recognition Span Task using a touch screen with different stimuli categories: neutral, positive and negative faces and geometric pictures. YA obtained higher scores than OA, and showed higher activation of theta and alpha bands in the frontal and midline regions, besides a more evident right-hemispheric asymmetry on alpha band when compared to OA. For both age groups, performance in the task was worse for positive faces than to negative and to neutral faces. Facial stimuli induced a better performance and higher alpha activation on the pre-frontal region for YA, and on the midline, occipital and left temporal regions for OA when compared to geometric figures. The superior performance of YA was expected due to the natural cognitive deficits connected to ageing, as was a better performance with facial stimuli due to the evolutionary importance of faces. These results were related to cortical activity on areas of importance for action-planning, decision making and sustained attention. Taken together, they are in accordance with the Negativity Bias but do not support the Positivity Effect. The methodology used was able to identify age-related differences in cortical activity during emotional mnemonic processing and may be interesting to future investigations.

Timing and gender determine if acute pain impairs working memory performance

The effects of pain on memory are complex, and little is known about the vulnerability of working memory (WM) performance when individuals complete a WM test while concurrently experiencing pain. Here, we subjected 78 healthy nonsmoking participants to either acute pain or a control condition while we administered a WM test. In this context, we also tested WM 20 minutes after pain in order to determine if timing of pain affected WM performance, and assessed objective and subjective measures of pain. We hypothesized that pain would impair WM performance during pain. Further, women's WM performance would be impaired more than men. Importantly, there was an interaction between gender and condition, with women exposed to pain experiencing impairments during but not after the cold pressor task. Our data imply that timing and gender are critically important in whether acute pain is costly to WM performance. Our findings have interesting clinical, professional, and educational implications, and understanding the influence of pain could help to improve the interpretation of WM tests in these diverse settings.

PERSPECTIVE

Results of this study support the growing body of work that attests to the detrimental effect of pain on WM performance. Further, this study provides new evidence that concurrently experiencing cold pressor pain impairs WM in regularly menstruating women and women taking a contraceptive.

Effects of age and gender on neural networks of motor response inhibition: from adolescence to mid-adulthood

Functional inhibitory neural networks mature progressively with age. However, nothing is known about the impact of gender on their development. This study employed functional magnetic resonance imaging (fMRI) to investigate the effects of age, sex, and sex by age interactions on the brain activation of 63 healthy males and females, between 13 and 38 years, performing a Stop task. Increasing age was associated with progressively increased activation in typical response inhibition areas of right inferior and dorsolateral prefrontal and temporo-parietal regions. Females showed significantly enhanced activation in left inferior and superior frontal and striatal regions relative to males, while males showed increased activation relative to females in right inferior and superior parietal areas. Importantly, left frontal and striatal areas that showed increased activation in females, also showed significantly increased functional maturation in females relative to males, while the right inferior parietal activation that was increased in males showed significantly increased functional maturation relative to females. The findings demonstrate for the first time that sex-dimorphic activation patterns of enhanced left fronto-striatal activation in females and enhanced right parietal activation in males during motor inhibition appear to be the result of underlying gender differences in the functional maturation of these brain regions.

DHA supplementation improved both memory and reaction time in healthy young adults: a randomized controlled trial

BACKGROUND

Docosahexaenoic acid (DHA) is important for brain function, and its status is dependent on dietary intakes. Therefore, individuals who consume diets low in omega-3 (n-3) polyunsaturated fatty acids may cognitively benefit from DHA supplementation. Sex and apolipoprotein E genotype (APOE) affect cognition and may modulate the response to DHA supplementation.

OBJECTIVES

We investigated whether a DHA supplement improves cognitive performance in healthy young adults and whether sex and APOE modulate the response.

DESIGN

Healthy adults (n = 176; age range: 18-45 y; nonsmoking and with a low intake of DHA) completed a 6-mo randomized, placebo-controlled, double-blind intervention in which they consumed 1.16 g DHA/d or a placebo. Cognitive performance was assessed by using a computerized cognitive test battery. For all tests, z scores were calculated and clustered into cognitive domains as follows: episodic and working memory, attention, reaction time (RT) of episodic and working memory, and attention and processing speed. ANCOVA was conducted with sex and APOE as independent variables.

RESULTS

RTs of episodic and working memory improved with DHA compared with placebo [mean difference (95% CI): -0.18 SD (-0.33, -0.03 SD) (P = 0.02) and -0.36 SD (-0.58, -0.14 SD) (P = 0.002), respectively]. Sex × treatment interactions occurred for episodic memory (P = 0.006) and the RT of working memory (P = 0.03). Compared with the placebo, DHA improved episodic memory in women [0.28 SD (0.08, 0.48 SD); P = 0.006] and RTs of working memory in men [-0.60 SD (-0.95, -0.25 SD); P = 0.001]. APOE did not affect cognitive function, but there were some indications of APOE × sex × treatment interactions.

CONCLUSIONS

DHA supplementation improved memory and the RT of memory in healthy, young adults whose habitual diets were low in DHA. The response was modulated by sex. This trial was registered at the New Zealand Clinical Trials Registry (http://www.anzctr.org.au/default.aspx) as ACTRN12610000212055.

Subregions of the human superior frontal gyrus and their connections

The superior frontal gyrus (SFG) is located at the superior part of the prefrontal cortex and is involved in a variety of functions, suggesting the existence of functional subregions. However, parcellation schemes of the human SFG and the connection patterns of each subregion remain unclear. We firstly parcellated the human SFG into the anteromedial (SFGam), dorsolateral (SFGdl), and posterior (SFGp) subregions based on diffusion tensor tractography. The SFGam was anatomically connected with the anterior and mid-cingulate cortices, which are critical nodes of the cognitive control network and the default mode network (DMN). The SFGdl was connected with the middle and inferior frontal gyri, which are involved in the cognitive execution network. The SFGp was connected with the precentral gyrus, caudate, thalamus, and frontal operculum, which are nodes of the motor control network. Resting-state functional connectivity analysis further revealed that the SFGam was mainly correlated with the cognitive control network and the DMN; the SFGdl was correlated with the cognitive execution network and the DMN; and the SFGp was correlated with the sensorimotor-related brain regions. The SFGam and SFGdl were further parcellated into three and two subclusters that are well corresponding to Brodmann areas. These findings suggest that the human SFG consists of multiple dissociable subregions that have distinct connection patterns and that these subregions are involved in different functional networks and serve different functions. These results may improve our understanding on the functional complexity of the SFG and provide us an approach to investigate the SFG at the subregional level.

The role of executive function in posttraumatic stress disorder: a systematic review

BACKGROUND

Although posttraumatic stress disorder (PTSD) has been associated with disturbances in verbal memory, studies examining executive functioning in PTSD show mixed results.

METHODS

A systematic review and meta-analysis were performed to compare executive functioning in patients with current PTSD and controls without any psychiatric disorder. Standard mean differences (SMD) in executive functioning scores were calculated using random-effects models. Covariates were added to examine whether differences exist between subgroups.

RESULTS

Across 18 studies, 1080 subjects were included. In comparison with 431 exposed controls and 227 healthy controls, 422 people with PTSD showed significantly impaired executive functioning. Subgroup analyses revealed more pronounced differences between PTSD patients and exposed controls than healthy controls. Male gender, higher age, war trauma, and higher severity of co-morbid depressive symptoms were related to poorer executive functioning in PTSD patients compared to exposed controls.

LIMITATIONS

Due to insufficient data and heterogeneity, not all subgroup differences or characteristics could be taken into account.

CONCLUSIONS

Overall, PTSD patients were found to show impaired executive functioning. Future research should further elucidate the subgroup effects and focus on clinical implications with regard to daily functioning and treatment outcome.

The influence of cerebral small vessel disease on default mode network deactivation in mild cognitive impairment

Introduction

Cerebral small vessel disease (CSVD) is thought to contribute to cognitive dysfunction in patients with mild cognitive impairment (MCI). The underlying mechanisms, and more specifically, the effects of CSVD on brain functioning in MCI are incompletely understood. The objective of the present study was to examine the effects of CSVD on brain functioning, activation and deactivation, in patients with MCI using task-related functional MRI (fMRI).

Methods

We included 16 MCI patients with CSVD, 26 MCI patients without CSVD and 25 controls. All participants underwent a physical and neurological examination, neuropsychological testing, structural MRI, and fMRI during a graded working memory paradigm.

Results

MCI patients with and without CSVD had a similar neuropsychological profile and task performance during fMRI, but differed with respect to underlying (de)activation patterns. MCI patients with CSVD showed impaired deactivation in the precuneus/posterior cingulate cortex, a region known to be involved in the default mode network. In MCI patients without CSVD, brain activation depended on working memory load, as they showed relative ‘hyperactivation’ during vigilance, and ‘hypoactivation’ at a high working memory load condition in working memory related brain regions.

Conclusions

We present evidence that the potential underlying mechanism of CSVD affecting cognition in MCI is through network interference. The observed differences in brain activation and deactivation between MCI patients with and without CSVD, who had a similar ‘clinical phenotype’, support the view that, in patients with MCI, different types of pathology can contribute to cognitive impairment through different pathways.

Lower cognitive reserve in the aging human immunodeficiency virus-infected brain

More HIV-infected individuals are living longer; however, how their brain function is affected by aging is not well understood. One hundred twenty-two men (56 seronegative control [SN] subjects, 37 HIV subjects with normal cognition [HIV+NC], 29 with HIV-associated neurocognitive disorder [HAND]) performed neuropsychological tests and had acceptable functional magnetic resonance imaging scans at 3 Tesla during tasks with increasing attentional load. With older age, SN and HIV+NC subjects showed increased activation in the left posterior (reserve, "bottom-up") attention network for low attentional-load tasks, and further increased activation in the left posterior and anterior ("top-down") attention network on intermediate (HIV+NC only) and high attentional-load tasks. HAND subjects had only age-dependent decreases in activation. Age-dependent changes in brain activation differed between the 3 groups, primarily in the left frontal regions (despite similar brain atrophy). HIV and aging act synergistically or interactively to exacerbate brain activation abnormalities in different brain regions, suggestive of a neuroadaptive mechanism in the attention network to compensate for declined neural efficiency. While the SN and HIV+NC subjects compensated for their declining attention with age by using reserve and "top-down" attentional networks, older HAND subjects were unable to compensate which resulted in cognitive decline.

Sex, lies and fMRI--gender differences in neural basis of deception

Deception has always been a part of human communication as it helps to promote self-presentation. Although both men and women are equally prone to try to manage their appearance, their strategies, motivation and eagerness may be different. Here, we asked if lying could be influenced by gender on both the behavioral and neural levels. To test whether the hypothesized gender differences in brain activity related to deceptive responses were caused by differential socialization in men and women, we administered the Gender Identity Inventory probing the participants’ subjective social sex role. In an fMRI session, participants were instructed either to lie or to tell the truth while answering a questionnaire focusing on general and personal information. Only for personal information, we found differences in neural responses during instructed deception in men and women. The women vs. men direct contrast revealed no significant differences in areas of activation, but men showed higher BOLD signal compared to women in the left middle frontal gyrus (MFG). Moreover, this effect remained unchanged when self-reported psychological gender was controlled for. Thus, our study showed that gender differences in the neural processes engaged during falsifying personal information might be independent from socialization.

Gender differences in brain regional homogeneity of healthy subjects after normal sleep and after sleep deprivation: a resting-state fMRI study

OBJECTIVE

To explore the gender differences of brain regional homogeneity (ReHo) in healthy subjects during the resting-state, after normal sleep, and after sleep deprivation (SD) using functional magnetic resonance imaging (fMRI) and the ReHo method.

METHODS

Sixteen healthy subjects (eight males and eight females) each underwent the resting-state fMRI exams twice, i.e., once after normal sleep and again after 24h's SD. According to the gender and sleep, 16 subjects were all measured twice and divided into four groups: the male control group (MC), female control group (FC), male SD group (MSD), and female SD group (FSD). The ReHo method was used to calculate and analyze the data, SPM5 software was used to perform a two-sample T-test and a two-pair T-test with a P value <0.001, and cluster volume ≥ 270 mm(3) was used to determine statistical significance.

RESULTS

Compared with the MC, the MSD showed significantly higher ReHo in the right paracentral lobule (BA3/6), but in no obviously lower regions. Compared with the FC, the FSD showed significantly higher ReHo in bilateral parietal lobes (BA2/3), bilateral vision-related regions of occipital lobes (BA17/18/19), right frontal lobe (BA4/6), and lower ReHo in the right frontal lobe. Compared with the FC, the MC showed significantly higher ReHo in the left occipital lobe (BA18/19), and left temporal lobe (BA21), left frontal lobe, and lower ReHo in the right insula and in the left parietal lobe. Compared with the FSD, the MSD showed significantly higher ReHo in the left cerebellum posterior lobe (uvula/declive of vermis), left parietal lobe, and bilateral frontal lobes, and lower ReHo in the right occipital lobe (BA17) and right frontal lobe (BA4).

CONCLUSIONS

The differences of brain activity in the resting state can be widely found not only between the control and SD group in a same gender group, but also between the male group and female group. Thus, we should take the gender differences into consideration in future fMRI studies, especially the treatment of brain-related diseases (e.g., depression).

Learning in the fast lane: new insights into neuroplasticity

The timescale of structural remodeling that accompanies functional neuroplasticity is largely unknown. Although structural remodeling of human brain tissue is known to occur following long-term (weeks) acquisition of a new skill, little is known as to what happens structurally when the brain needs to adopt new sequences of procedural rules or memorize a cascade of events within minutes or hours. Using diffusion tensor imaging (DTI), an MRI-based framework, we examined subjects before and after a spatial learning and memory task. Microstructural changes (as reflected by DTI measures) of limbic system structures (hippocampus and parahippocampus) were significant after only 2 hr of training. This observation was also found in a supporting rat study. We conclude that cellular rearrangement of neural tissue can be detected by DTI, and that this modality may allow neuroplasticity to be localized over short timescales.

Sexual dimorphism and laterality in the evolution of the primate prefrontal cortex

Social selective pressures are commonly considered as the main driving force of primate brain evolution. Primate social behaviour is, however, known to be sexually dimorphic, and no previous study has made a direct comparison between male and female brain structures across species. We quantify sex-specific evolutionary trends in the prefrontal cortex of anthropoid primates (including humans) to investigate how sexual selection has shaped brain evolution in primates. The prefrontal cortex is of particular importance to the investigation of sexual dimorphism in primate brain evolution because of its association to those cognitive capacities central to primate (and human) evolution: sociality and higher-order cognitive processing. Our results demonstrate sex-by-hemisphere differences in the evolution of the prefrontal cortex in humans and non-human anthropoid primates congruent with the principal selective pressures considered to underlie anthropoid behavioural evolution. Our findings further show how sexual selection can shape brain adaptation in primates and provide an evolutionary framework for interpreting sex and sex-by-hemisphere differences in cortical organization in humans and non-human primates.

Altered brain activation during visuomotor integration in chronic active cannabis users: relationship to cortisol levels

Cannabis is the most abused illegal substance in the United States. Alterations in brain function and motor behavior have been reported in chronic cannabis users, but the results have been variable. The current study aimed to determine whether chronic active cannabis use in humans may alter psychomotor function, brain activation, and hypothalamic-pituitary-axis (HPA) function in men and women. Thirty cannabis users (16 men, 14 women, 18-45 years old) and 30 nondrug user controls (16 men, 14 women, 19-44 years old) were evaluated with neuropsychological tests designed to assess motor behavior and with fMRI using a 3 Tesla scanner during a visually paced finger-sequencing task, cued by a flashing checkerboard (at 2 or 4 Hz). Salivary cortisol was measured to assess HPA function. Male, but not female, cannabis users had significantly slower performance on psychomotor speed tests. As a group, cannabis users had greater activation in BA 6 than controls, while controls had greater activation in the visual area BA 17 than cannabis users. Cannabis users also had higher salivary cortisol levels than controls (p = 0.002). Chronic active cannabis use is associated with slower and less efficient psychomotor function, especially in male users, as indicated by a shift from regions involved with automated visually guided responses to more executive or attentional control areas. The greater but altered brain activities may be mediated by the higher cortisol levels in the cannabis users, which in turn may lead to less efficient visual-motor function.

Influence of estradiol on functional brain organization for working memory

Working memory is a cognitive function that is affected by aging and disease. To better understand the neural substrates for working memory, the present study examined the influence of estradiol on working memory using functional magnetic resonance imaging. Pre-menopausal women were tested on a verbal n-back task during the early (EF) and late follicular (LF) phases of the menstrual cycle. Although brain activation patterns were similar across the two phases, the most striking pattern that emerged was that estradiol had different associations with the two hemispheres. Increased activation in left frontal circuitry in the LF phase was associated with increased estradiol levels and decrements in working memory performance. In contrast, increased activation in right hemisphere regions in the LF phase was associated with improved task performance. The present study showed that better performance in the LF than the EF phase was associated with a pattern of reduced recruitment of the left-hemisphere and increased recruitment of the right-hemisphere in the LF compared to EF phase. We speculate that estradiol interferes with left-hemisphere working-memory processing in the LF phase, but that recruitment of the right hemisphere can compensate for left-hemisphere interference. This may be related to the proposal that estradiol can reduce cerebral asymmetries by modulating transcallosal communication (Hausmann, 2005).

Gender and drug effects on neuroimaging in epilepsy

Men are different from women, and patients with epilepsy are different in many aspects from healthy control subjects. Quantitative or semiquantitative analysis of neuroimaging data depends on the comparison between either a single patient against a group of healthy or unaffected controls, or comparisons between groups of patients and controls. Matching for gender is desired, but is sometimes not possible, for example, in the case of nuclear medicine with women in childbearing age usually not being recruited as healthy controls. Antiepileptic drug treatment is the other major confounder for comparisons of cognitive functioning between patients and healthy control subjects. Whether these two covariates, gender and drug effects, are of interest or nuisance variables depends on the question and design of the neuroimaging study.