Mareen Weber

Physical Exercise Habits Correlate with Gray Matter Volume of the Hippocampus in Healthy Adult Humans

Physical activity facilitates neurogenesis of dentate cells in the rodent hippocampus, a brain region critical for memory formation and spatial representation. Recent findings in humans also suggest that aerobic exercise can lead to increased hippocampal volume and enhanced cognitive functioning in children and elderly adults. However, the association between physical activity and hippocampal volume during the period from early adulthood through middle age has not been effectively explored. Here, we correlated the number of minutes of self-reported exercise per week with gray matter volume of the hippocampus using voxel-based morphometry (VBM) in 61 healthy adults ranging from 18 to 45 years of age. After controlling for age, gender, and total brain volume, total minutes of weekly exercise correlated significantly with volume of the right hippocampus. Findings highlight the relationship between regular physical exercise and brain structure during early to middle adulthood.

Voxel-based morphometric gray matter correlates of daytime sleepiness.

Sleep disorders such as narcolepsy, obstructive sleep apnea, and chronic insomnia have been associated with reduced gray matter volume of the ventromedial prefrontal cortex (VMPFC). Functional neuroimaging and behavioral data also implicate this region as important in sleep-related problems and the ability to resist the impairing effects of sleep loss on cognition. However, no study has linked gray matter volume within this region to normal self-reported levels of daytime sleepiness. We therefore hypothesized that reduced gray matter volume within the VMPFC would be related to greater self-reported levels of general daytime sleepiness, as assessed by the Epworth Sleepiness Scale (ESS) in a sample of 36 healthy non-clinical participants. Using voxel-based morphometry, scores of the ESS were correlated with gray matter volume, after controlling for age, gender, and whole brain volume. Daytime sleepiness correlated negatively with gray matter volume in a cluster of voxels within the left gyrus rectus and medial orbitofrontal cortex. Findings converge with prior evidence to suggest that the VMPFC and medial orbitofrontal cortex may play a particularly important role in sleep-wake related phenomena including sleep disorders and trait-like individual differences in vulnerability to the impairing effects of sleep deprivation on neurobehavioral performance, and also in normal variations in self-reported daytime sleepiness.

Insomnia-related complaints correlate with functional connectivity between sensory-motor regions.

According to the hyperarousal theory of insomnia, difficulty in initiating or maintaining sleep occurs as a result of increased cognitive and physiological arousal caused by acute stressors and associated cognitive rumination, placing the individual in a perpetual cycle of hyperarousal and increased sensitivity to sensory stimulation. We tested the hypothesis that difficulty in initiating or maintaining sleep would be associated with increased functional connectivity between primary sensory processing and motor planning regions. Fifty-eight healthy adults (29 men, 29 women) completed a self-report inventory about sleep onset and maintenance problems and underwent a 6-min resting-state functional MRI scan. Bilateral regions of interest (ROIs) were placed in primary visual cortex, auditory cortex, olfactory cortex, and the supplementary motor cortex, and the mean processed signal time course was extracted and correlated with each of the other ROIs. Difficulty in falling asleep was associated with increased functional connectivity between the primary visual cortex and other sensory regions such as the primary auditory cortex, olfactory cortex, and the supplementary motor cortex. The primary auditory cortex also showed greater connectivity with the supplementary motor cortex in those with sleep initiation problems. Problems with sleep maintenance were associated with greater connectivity between the primary visual cortex and the olfactory cortex. Consistent with the predictions of the hyperarousal model, difficulty in falling asleep was associated with greater functional connectivity between primary sensory and supplementary motor regions. Such augmented functional connectivity may contribute to the sustained sensory processing of environmental stimuli, potentially prolonging the latency to sleep.

Reduced gray matter volume in the anterior cingulate, orbitofrontal cortex and thalamus as a function of mild depressive symptoms: a voxel-based morphometric analysis

BACKGROUND Studies investigating structural brain abnormalities in depression have typically employed a categorical rather than dimensional approach to depression [i.e., comparing subjects with Diagnostic and Statistical Manual of Mental Disorders (DSM)-defined major depressive disorder (MDD) v. healthy controls]. The National Institute of Mental Health, through their Research Domain Criteria initiative, has encouraged a dimensional approach to the study of psychopathology as opposed to an over-reliance on categorical (e.g., DSM-based) diagnostic approaches. Moreover, subthreshold levels of depressive symptoms (i.e., severity levels below DSM criteria) have been found to be associated with a range of negative outcomes, yet have been relatively neglected in neuroimaging research. METHOD To examine the extent to which depressive symptoms--even at subclinical levels--are linearly related to gray matter volume reductions in theoretically important brain regions, we employed whole-brain voxel-based morphometry in a sample of 54 participants. RESULTS The severity of mild depressive symptoms, even in a subclinical population, was associated with reduced gray matter volume in the orbitofrontal cortex, anterior cingulate, thalamus, superior temporal gyrus/temporal pole and superior frontal gyrus. A conjunction analysis revealed concordance across two separate measures of depression. CONCLUSIONS Reduced gray matter volume in theoretically important brain regions can be observed even in a sample that does not meet DSM criteria for MDD, but who nevertheless report relatively elevated levels of depressive symptoms. Overall, these findings highlight the need for additional research using dimensional conceptual and analytic approaches, as well as further investigation of subclinical populations.

Gray matter correlates of Trait and Ability models of emotional intelligence

Research suggests that emotional intelligence capacities may be related to the functional integrity of the corticolimbic regions including the ventromedial prefrontal cortex, insula, and amygdala. No study has yet examined regional brain volumes in relation to the two dominant models of emotional intelligence: the Ability model, which posits a set of specific demonstrable capabilities for solving emotional problems, and the Trait model, which proposes a set of stable emotional competencies that can be assessed through subjectively rated self-report scales. In 36 healthy participants, we correlated scores on the Mayer–Salovey–Caruso Emotional Intelligence Test (an Ability measure) and the Bar-On Emotional Quotient Inventory (a Trait measure) with regional brain volumes using voxel-based morphometry. Total Mayer–Salovey–Caruso Emotional Intelligence Test scores were positively correlated with the left insula grey matter volume. The Strategic emotional intelligence subscale correlated positively with the left ventromedial prefrontal cortex and insular volume. In contrast, for the Bar-On Emotional Quotient Inventory, Stress Management scores correlated positively with the bilateral ventromedial prefrontal cortex volume. Amygdala volumes were unrelated to emotional intelligence measures. Findings support the role of the ventromedial prefrontal cortex and insula as key nodes in the emotional intelligence circuitry.

Habitual ‘sleep credit’ is associated with greater grey matter volume of the medial prefrontal cortex, higher emotional intelligence and better mental health

In modern society, people often fail to obtain the amount of sleep that experts recommend for good health and performance. Insufficient sleep can lead to degraded cognitive performance and alterations in emotional functioning. However, most people also acknowledge that on a regular basis they obtain more sleep than they subjectively perceive they need at a minimum to stave off performance decrements, a construct we describe as subjective ‘sleep credit’. Few people would contest the notion that getting more sleep is better, but data on both behavioural and neuroanatomical correlates of ‘sleep credit’ are surprisingly limited. We conducted a voxel‐based morphometric study to assess cerebral grey matter correlates of habitually sleeping more than ones subjective requirements. We further tested whether these structural correlates are associated with perceived emotional intelligence and indices of psychopathology while controlling for age, gender, and total intracranial volume. In a sample of 55 healthy adults aged 18–45 years (28 males, 27 females), whole‐brain multiple regression showed that habitual subjective ‘sleep credit’ was correlated positively with grey matter volume within regions of the left medial prefrontal cortex and right orbitofrontal gyrus. Volumes were extracted and regressed against self‐report emotion and psychopathology indices. Only grey matter volume of the medial prefrontal cortex cluster correlated with greater emotional intelligence and lower scores on several indices of psychopathology. Findings converge with previous evidence of the role of the medial prefrontal cortex in the relationship between sleep and emotional functioning, and suggest that behaviour and brain structure vary with habitual ‘sleep credit’.

Emotional intelligence correlates with functional responses to dynamic changes in facial trustworthiness

Emotional intelligence (EI) refers to a constellation of traits, competencies, or abilities that allow individuals to understand emotional information and successfully navigate and solve social/emotional problems. While little is known about the neurobiological substrates that underlie EI, some evidence suggests that these capacities may involve a core neurocircuitry involved in emotional decision-making that includes the ventromedial prefrontal cortex (vmPFC), anterior cingulate cortex (ACC), insula, and amygdala. In a sample of 39 healthy volunteers (22 men; 17 women), scores on the Bar-On EQ-i (a trait/mixed model of EI) and Mayer–Salovey–Caruso Emotional Intelligence Test (MSCEIT; an ability model of EI) were correlated with functional magnetic resonance imaging responses during brief presentations of moving facial expressions that changed in the level of perceived trustworthiness. Core emotion neurocircuitry was responsive to dynamic changes in facial features, regardless of whether they reflected increases or decreases in apparent trustworthiness. In response to facial movements indicating decreasing trustworthiness, MSCEIT correlated positively with functional responses of the vmPFC and rostral ACC, whereas the EQ-i was unrelated to regional activation. Systematic differences in EI ability appear to be significantly related to the responsiveness of the vmPFC and rostral ACC to facial movements suggesting potential trustworthiness.

Voxel-based morphometric gray matter correlates of posttraumatic stress disorder.

Posttraumatic stress disorder (PTSD) is associated with functional abnormalities within a neurocircuitry that includes the hippocampus, amygdala, and medial prefrontal cortex. Evidence of structural abnormalities within these regions, and their association with PTSD severity and symptom burden is, however, sparse. The present study evaluated the relation between indices of gray matter volume and PTSD symptom severity using voxel-based morphometry. Fifteen individuals meeting DSM-IV criteria for PTSD completed the Clinician Administered PTSD Scale and underwent structural magnetic resonance imaging. Greater PTSD severity and avoidance/numbing were correlated with increased gray matter volume of the right amygdala-hippocampal complex. Greater hyper-arousal was associated with reduced gray matter volume in the left superior medial frontal gyrus. Findings are consistent with current neurocircuitry models of PTSD, which posit that the disorder is associated with structural and functional variance within this distributed network.

Cortico-limbic responsiveness to high-calorie food images predicts weight status among women

Objectives:Excessive weight gain and obesity are currently among the world’s major threats to health. Women show significantly higher rates of obesity and eating disorders relative to men, but the factors contributing to these gender differences remain uncertain. We examined the correlations between regional brain responses to images of high-calorie versus low-calorie foods and self-reported motivational status, including ratings of general appetite, overeating propensity, state hunger and desire for specific foods.Subjects:Thirty-eight healthy right-handed adults (22 male; 16 female) ages 18–45 participated. There were no differences between males and females with regard to age or body mass index (BMI).Results:Overall, motivational status correlated significantly with activation within the amygdala, insula and orbitofrontal cortex. Regional activation was then used to predict BMI, an indicator of long-term food consumption and energy expenditure. The combined model was significant, accounting for 76% of the variance in BMI for women, whereas the same regions were not predictive of weight status among men.Conclusions:Findings suggest that long-term weight status is related to visual responsiveness to calorie-dense food imagery among women.

Microstructure of frontoparietal connections predicts individual resistance to sleep deprivation

Sleep deprivation (SD) can degrade cognitive functioning, but growing evidence suggests that there are large individual differences in the vulnerability to this effect. Some evidence suggests that baseline differences in the responsiveness of a fronto-parietal attention system that is activated during working memory (WM) tasks may be associated with the ability to sustain vigilance during sleep deprivation. However, the neurocircuitry underlying this network remains virtually unexplored. In this study, we employed diffusion tensor imaging (DTI) to investigate the association between the microstructure of the axonal pathway connecting the frontal and parietal regions--i.e., the superior longitudinal fasciculus (SLF)--and individual resistance to SD. Thirty healthy participants (15 males) aged 20-43 years underwent functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) at rested wakefulness prior to a 28-hour period of SD. Task-related fronto-parietal fMRI activation clusters during a Sternberg WM Task were localized and used as seed regions for probabilistic fiber tractography. DTI metrics, including fractional anisotropy, mean diffusivity, axial and radial diffusivity were measured in the SLF. The psychomotor vigilance test (PVT) was used to evaluate resistance to SD. We found that activation in the left inferior parietal lobule (IPL) and dorsolateral prefrontal cortex (DLPFC) positively correlated with resistance. Higher fractional anisotropy of the left SLF comprising the primary axons connecting IPL and DLPFC was also associated with better resistance. These findings suggest that individual differences in resistance to SD are associated with the functional responsiveness of a fronto-parietal attention system and the microstructural properties of the axonal interconnections.