Spend time outdoors for your brain - an in-depth longitudinal MRI study.

OBJECTIVES: The effects of nature on physical and mental health are an emerging topic in empirical research with increasing influence on practical health recommendations. Here we set out to investigate the association between spending time outdoors and brain structural plasticity in conjunctions with self-reported affect. METHODS: We established the Day2day study, which includes an unprecedented in-depth assessment of variability of brain structure in a serial sequence of 40-50 structural magnetic resonance imaging (MRI) acquisitions of each of six young healthy participants for 6-8 months (n = 281 MRI scans in total). RESULTS: A whole-brain analysis revealed that time spent outdoors was positively associated with grey matter volume in the right dorsolateral prefrontal cortex and positive affect, also after controlling for physical activity, fluid intake, free time, and hours of sunshine. CONCLUSIONS: Results indicate remarkable and potentially behaviorally relevant plasticity of cerebral structure within a short time frame driven by the daily time spent outdoors. This is compatible with anecdotal evidence of the health and mood-promoting effects of going for a walk. The study may provide the first evidence for underlying cerebral mechanisms of so-called green prescriptions with possible consequences for future interventions in mental disorders.

Hierarchical associations of alcohol use disorder symptoms in late adolescence with markers during early adolescence.

High adolescent alcohol consumption is predictive for alcohol problems later in life. To tailor interventions, early identification of risk groups for adolescent alcohol consumption is important. The IMAGEN dataset was utilized to investigate predictors for problematic alcohol consumption at age 18-20 years as a function self and parental personality and drug-related measures as well as life-events and cognitive variables all assessed at age 14 years (N = 1404). For this purpose the binary partitioning algorithm ctree was used in an explorative analysis. The algorithm recursively selects significant input variables and splits the outcome variable based on these, yielding a conditional inference tree. Four significant split variables, namely Place of residence, the Disorganization subscale of the Temperament and Character Inventory, Sex, and the Sexuality subscale of the life-events questionnaire were found to distinguish between adolescents scoring high or low on the Alcohol Use Disorders Identification Test about five years later (all p < 0.001). The analyis adds to the literature on predictors of adolescent drinking problems using a large European sample. The identified split variables could easily be collected in community samples. If their validity is proven in independent samples, they could facilitate intervention studies in the field of adolescent alcohol prevention.

Identifying predictors of within-person variance in MRI-based brain volume estimates.

Adequate reliability of measurement is a precondition for investigating individual differences and age-related changes in brain structure. One approach to improve reliability is to identify and control for variables that are predictive of within-person variance. To this end, we applied both classical statistical methods and machine-learning-inspired approaches to structural magnetic resonance imaging (sMRI) data of six participants aged 24-31 years gathered at 40-50 occasions distributed over 6-8 months from the Day2day study. We explored the within-person associations between 21 variables covering physiological, affective, social, and environmental factors and global measures of brain volume estimated by VBM8 and FreeSurfer. Time since the first scan was reliably associated with Freesurfer estimates of grey matter volume and total cortex volume, in line with a rate of annual brain volume shrinkage of about 1 percent. For the same two structural measures, time of day also emerged as a reliable predictor with an estimated diurnal volume decrease of, again, about 1 percent. Furthermore, we found weak predictive evidence for the number of steps taken on the previous day and testosterone levels. The results suggest a need to control for time-of-day effects in sMRI research. In particular, we recommend that researchers interested in assessing longitudinal change in the context of intervention studies or longitudinal panels make sure that, at each measurement occasion, (a) a given participant is measured at the same time of day; (b) all participants are measured at about the same time of day. Furthermore, the potential effects of physical activity, including moderate amounts of aerobic exercise, and testosterone levels on MRI-based measures of brain structure deserve further investigation.

Postpartal Neural Plasticity of the Maternal Brain: Early Renormalization of Pregnancy-Related Decreases?

BACKGROUND/AIMS: Human pregnancy goes along with decreasing gray matter volume in the brain of the mother. Whether these reductions remain for years or renormalize shortly after delivery is unclear. The present study used a longitudinal control group design to investigate postpartal neural plasticity. METHODS: 24 healthy young women were assessed with cognitive and hormonal measures in late pregnancy and underwent a brain scan within the first two months after delivery (TP1). They were compared to 24 naturally cycling women. A follow-up cognitive and imaging measurement was performed three months after the first scan in both groups (TP2, 4-5 months postpartally in the mothers). RESULTS: Compared to the control group, widespread gray matter volume increases from the first to second scan were observed in the new mothers (TP2 > TP1, whole-brain analysis). These were especially pronounced in frontal and cerebellar regions. The time by group interaction pattern of gray matter indicated a postpartal renormalization process, most likely following pregnancy-related decreases. Age was negatively correlated to postpartal gray matter increase in most of the regions. Despite pronounced changes in brain structure, the two groups did not reliably differ in cognitive performance. CONCLUSION: The results reveal the potential for plasticity in the adult female brain following pregnancy. They support the assumption that the volume reductions during pregnancy renormalize at least partly in the early postpartal phase. The course of renormalization seems to differ between participants of different ages. Future studies are needed to further investigate inter-individual variability and the time course of postpartal neural change.

Reliable local dynamics in the brain across sessions are revealed by whole-brain modeling of resting state activity.

Resting state fMRI is a tool for studying the functional organization of the human brain. Ongoing brain activity at "rest" is highly dynamic, but procedures such as correlation or independent component analysis treat functional connectivity (FC) as if, theoretically, it is stationary and therefore the fluctuations observed in FC are thought as noise. Consequently, FC is not usually used as a single-subject level marker and it is limited to group studies. Here we develop an imaging-based technique capable of reliably portraying information of local dynamics at a single-subject level by using a whole-brain model of ongoing dynamics that estimates a local parameter, which reflects if each brain region presents stable, asynchronous or transitory oscillations. Using 50 longitudinal resting-state sessions of one single subject and single resting-state sessions from a group of 50 participants we demonstrate that brain dynamics can be quantified consistently with respect to group dynamics using a scanning time of 20 min. We show that brain hubs are closer to a transition point between synchronous and asynchronous oscillatory dynamics and that dynamics in frontal areas have larger heterogeneity in its values compared to other lobules. Nevertheless, frontal regions and hubs showed higher consistency within the same subject while the inter-session variability found in primary visual and motor areas was only as high as the one found across subjects. The framework presented here can be used to study functional brain dynamics at group and, more importantly, at individual level, opening new avenues for possible clinical applications.

Day2day: investigating daily variability of magnetic resonance imaging measures over half a year.

BACKGROUND: Most studies of brain structure and function, and their relationships to cognitive ability, have relied on inter-individual variability in magnetic resonance (MR) images. Intra-individual variability is often ignored or implicitly assumed to be equivalent to the former. Testing this assumption empirically by collecting enough data on single individuals is cumbersome and costly. We collected a dataset of multiple MR sequences and behavioural covariates to quantify and characterize intra-individual variability in MR images for multiple individuals. METHODS AND DESIGN: Eight participants volunteered to undergo brain scanning 40-50 times over the course of 6 months. Six participants completed the full set of sessions. T1-weighted, T2*-weighted during rest, T2-weighted high-resolution hippocampus, diffusion-tensor imaging (DTI), and proton magnetic resonance spectroscopy sequences were collected, along with a rich set of stable and time-varying physical, behavioural and physiological variables. Participants did not change their lifestyle or participated in any training programs during the period of data collection. CONCLUSION: This imaging dataset provides a large number of MRI scans in different modalities for six participants. It enables the analysis of the time course and correlates of intra-individual variability in structural, chemical, and functional aspects of the human brain.

Resting-state fMRI correlations: From link-wise unreliability to whole brain stability.

The functional architecture of spontaneous BOLD fluctuations has been characterized in detail by numerous studies, demonstrating its potential relevance as a biomarker. However, the systematic investigation of its consistency is still in its infancy. Here, we analyze within- and between-subject variability and test-retest reliability of resting-state functional connectivity (FC) in a unique data set comprising multiple fMRI scans (42) from 5 subjects, and 50 single scans from 50 subjects. We adopt a statistical framework that enables us to identify different sources of variability in FC. We show that the low reliability of single links can be significantly improved by using multiple scans per subject. Moreover, in contrast to earlier studies, we show that spatial heterogeneity in FC reliability is not significant. Finally, we demonstrate that despite the low reliability of individual links, the information carried by the whole-brain FC matrix is robust and can be used as a functional fingerprint to identify individual subjects from the population.

Differences in navigation performance and postpartal striatal volume associated with pregnancy in humans.

Pregnancy is accompanied by prolonged exposure to high estrogen levels. Animal studies have shown that estrogen influences navigation strategies and, hence, affects navigation performance. High estrogen levels are related to increased use of hippocampal-based allocentric strategies and decreased use of striatal-based egocentric strategies. In humans, associations between hormonal shifts and navigation strategies are less well studied. This study compared 30 peripartal women (mean age 28years) to an age-matched control group on allocentric versus egocentric navigation performance (measured in the last month of pregnancy) and gray matter volume (measured within two months after delivery). None of the women had a previous pregnancy before study participation. Relative to controls, pregnant women performed less well in the egocentric condition of the navigation task, but not the allocentric condition. A whole-brain group comparison revealed smaller left striatal volume (putamen) in the peripartal women. Across the two groups, left striatal volume was associated with superior egocentric over allocentric performance. Limited by the cross-sectional study design, the findings are a first indication that human pregnancy might be accompanied by structural brain changes in navigation-related neural systems and concomitant changes in navigation strategy.

Hormonal contraceptive use is associated with neural and affective changes in healthy young women.

Previous neuroimaging research has demonstrated that female gonadal hormones can alter the structure and function of adult women's brains. So far, we do not know how hormonal contraceptives affect female brain structure, in part because within-person longitudinal observations are lacking. Here, we compared 28 young women before and after three months of regular contraceptive intake with 28 naturally cycling women of comparable age. The goal was to explore within-person neural change in women using contraceptives. Neuroimaging, hormonal, cognitive, and affect data were collected at two time points for each participant. A voxel-wise whole-brain comparison of both groups revealed decreased gray matter volume in the left amygdala/anterior parahippocampal gyrus in women using contraceptives as compared to the control group. Resting-state functional connectivity of this region with the dorsolateral prefrontal cortex changed from positive to negative connectivity following contraceptive intake whereas the opposite held for the control group. An exploratory analysis revealed that gray matter volume in the left amygdala/anterior parahippocampal gyrus was associated with positive affect at the second time point. There were no systematic differences in cognitive performance change between the groups. These findings provide initial insights into effects of hormonal contraceptives on the human brain and expand previous findings on hormone-related amygdala/hippocampal complex plasticity. The affected brain regions may be related to psychological wellbeing, underlining the importance of future studies on contraceptive-induced brain changes.

Normal aging increases postural preparation errors: Evidence from a two-choice response task with balance constraints.

Correlational studies indicate an association between age-related decline in balance and cognitive control, but these functions are rarely addressed within a single task. In this study, we investigate adult age differences in a two-choice response task with balance constraints under three levels of response conflict. Sixteen healthy young (20-30 years) and 16 healthy older adult participants (59-74 years) were cued symbolically (letter L vs. R) to lift either the left or the right foot from the floor in a standing position. Response conflict was manipulated by task-irrelevant visual stimuli showing congruent, incongruent, or no foot lift movement. Preparatory weight shifts (PWS) and foot lift movements were recorded using force plates and optical motion capture. Older adults showed longer response times (foot lift) and more PWS errors than younger adults. Incongruent distractors interfered with performance (greater response time and PWS errors), but this compatibility effect did not reliably differ between age groups. Response time effects of age and compatibility were strongly reduced or absent in trials without PWS errors, and for the onset of the first (erroneous) PWS in trials with preparation error. In addition, in older adults only, compatibility effects in the foot lift task correlated significantly with compatibility effects in the Flanker task. The present results strongly suggest that adult age differences in response latencies in a task with balance constraints are related to age-associated increases in postural preparation errors rather than being an epiphenomenon of general slowing.

Hippocampal volume and functional connectivity changes during the female menstrual cycle.

Hippocampal volume has been shown to be sensitive to variations in estrogen and progesterone levels across rodents' estrous cycle. However, little is known about the covariation of hormone levels and brain structure in the course of the human menstrual cycle. Here, we examine this covariation with a multi-method approach that includes several brain imaging methods and hormonal assessments. We acquired structural and functional scans from 21 naturally cycling women on four time points during their cycles (early follicular phase, late follicular phase, ovulation and luteal phase). Hormone blood concentrations and cognitive performance in different domains were assessed on each of the measurement occasions. Structural MRI images were processed by means of whole-brain voxel-based morphometry and FreeSurfer. With either method, bilateral increases in hippocampal volume were found in the late follicular phase relative to the early follicular phase. The gray matter probability in regions of hippocampal volume increase was associated with lower mean diffusivity in the same region. In addition, we observed higher functional connectivity between the hippocampi and the bilateral superior parietal lobe in the late follicular phase. We did not find any reliable cycle-related performance variations on the cognitive tasks. The present results show that hormonal fluctuations covary with hippocampal structure and function in the course of the human menstrual cycle.

Amygdala/hippocampal activation during the menstrual cycle: evidence for lateralization of effects across different tasks.

Variations in hormonal levels between the follicular and the luteal phase of the female menstrual cycle are associated with variations in emotional and cognitive aspects of behavior. The functional neural correlates of these cycle-related variations have been explored in previous neuroimaging studies. We summarize the existing findings of functional magnetic resonance imaging (fMRI) studies to identify regions of increased brain activation in the follicular or luteal phases of the cycle that are concordant across studies. Eleven fMRI studies reporting coordinates of higher brain activation in one of the two main cycle phases were included in the analysis. Activation likelihood estimation was used to determine concordance. We found higher left amygdala/hippocampal activation during the luteal phase and higher right amygdala/hippocampal activation during the follicular phase. Additionally, the anterior cingulate cortex and temporal pole showed increased activation during the luteal phase and the superior temporal gyrus during the follicular phase. The observed pattern of cycle-dependent functional lateralization of the amygdala/hippocampal complex is consistent with findings on cycle-related behavioral variations and on sex differences in lateralization of activity in amygdala and hippocampus.

Investigating socio-cognitive processes in deception: a quantitative meta-analysis of neuroimaging studies.

Recent neuroimaging studies have found a broad network of brain regions involved in deception, including the prefrontal cortex, insula, anterior cingulate cortex (ACC), and inferior parietal lobule (IPL). Although deception can be conceptualized as the attempt to deliberately cause another person to accept a false belief, research to date has mainly focused on executive control processes when participants are instructed to lie under certain conditions. Recently, more ecologically valid and interactive experimental paradigms have been used in which subjects were also requested to take the perspective of another person, read his or her intentions, and make a self-determined decision to deceive that person and break a moral rule. To investigate the influence of these socio-cognitive processes on the neural network of deception, we performed a quantitative meta-analysis combining the data from 416 participants across 22 fMRI and two PET studies. Based on the description of the experimental paradigm, studies were divided in social interactive and non-interactive deception studies. Increased activation in the dorsal ACC, the right temporo-parietal junction (TPJ)/angular gyrus, and the bilateral temporal pole (TP) was found to be greater in social interactive than in non-interactive deception. These results demonstrate the important role of perspective taking, theory of mind, and moral reasoning processes in deception as well as conflict processing. In addition to the role of executive control processes determined by previous meta-analyses, our findings show the importance of these socio-cognitive processes in deception and give new insight into the function and interpretation of the brain regions involved.

Balancing cognitive control: how observed movements influence motor performance in a task with balance constraints.

We investigated the influence of observed movements on executed movements in a task requiring lifting one foot from the floor while maintaining whole-body balance. Sixteen young participants (20-30 years) performed foot lift movements, which were either cued symbolically by a letter (L/R, indicating to lift the left/right foot) or by a short movie showing a foot lift movement. In the symbol cue condition, stimuli from the movie cue condition were used as distractors, and vice versa. Anticipatory postural adjustments (APAs) and actual foot lifts were recorded using force plates and optical motion capture. Foot lift responses were generally faster in response to the movie compared to the symbol cue condition. Moreover, incongruent movement distractors interfered with performance in the symbol cue condition, as shown by longer response times and increased number of APAs. Latencies of the first (potentially wrong) APA in a trial were shorter for movie compared to symbol cues but were not affected by cue-distractor congruency. Amplitude of the first APA was smaller when it was followed by additional APAs compared to trials with a single APA. Our results show that automatic imitation tendencies are integrated with postural control in a task with balance constraints. Analysis of the number, timing and amplitude of APAs indicates that conflicts between intended and observed movements are not resolved at a purely cognitive level but directly influence overt motor performance, emphasizing the intimate link between perception, cognition and action.