Eileen Luders

The impact of aging on subregions of the hippocampal complex in healthy adults

&NA; The hippocampal complex, an anatomical composite of several subregions, is known to decrease in size with increasing age. However, studies investigating which subregions are particularly prone to age‐related tissue loss revealed conflicting findings. Possible reasons for such inconsistencies may reflect differences between studies in terms of the cohorts examined or techniques applied to define and measure hippocampal subregions. In the present study, we enhanced conventional MR‐based information with microscopically defined cytoarchitectonic probabilities to investigate aging effects on the hippocampal complex in a carefully selected sample of 96 healthy subjects (48 males/48 females) aged 18–69 years. We observed significant negative correlations between age and volumes of the cornu ammonis, fascia dentata, subiculum, and hippocampal‐amygdaloid transition area, but not the entorhinal cortex. The estimated age‐related annual atrophy rates were most pronounced in the left and right subiculum with −0.23% and −0.22%, respectively. These findings suggest age‐related atrophy of the hippocampal complex overall, but with differential effects in its subregions. If confirmed in future studies, such region‐specific information may prove useful for the assessment of diseases and disorders known to modulate age‐related hippocampal volume loss. HighlightsAge‐related hippocampal atrophy in healthy adults is low (≤ 0.2% per year).All subregions of the hippocampal complex lose volume with increasing age.The highest age‐related volume loss was observed in the subiculum.The lowest age‐related volume loss was observed in the entorhinal cortex.

Promising Links between Meditation and Reduced (Brain) Aging: An Attempt to Bridge Some Gaps between the Alleged Fountain of Youth and the Youth of the Field

Over the last decade, an increasing number of studies has reported a positive impact of meditation on cerebral aging. However, the underlying mechanisms for these seemingly brain-protecting effects are not well-understood. This may be due to the fact, at least partly, that systematic empirical meditation research has emerged only recently as a field of scientific scrutiny. Thus, on the one hand, critical questions remain largely unanswered; and on the other hand, outcomes of existing research require better integration to build a more comprehensive and holistic picture. In this article, we first review theories and mechanisms pertaining to normal (brain) aging, specifically focusing on telomeres, inflammation, stress regulation, and macroscopic brain anatomy. Then, we summarize existing research integrating the developing evidence suggesting that meditation exerts positive effects on (brain) aging, while carefully discussing possible mechanisms through which these effects may be mediated.

Associations between corpus callosum size and ADHD symptoms in older adults: The PATH through life study

Neuroimaging studies of attention-deficit/hyperactivity disorder (ADHD) have revealed deviations of the corpus callosum in children and adolescents. However, little is known about the link between callosal morphology and symptoms of inattention or hyperactivity in adulthood, especially later in life. Here, we investigated in a large population-based sample of 280 adults (150 males, 130 females) in their late sixties and early seventies whether ADHD symptoms correlate with callosal thickness. In addition, we tested for significant sex interactions, which were followed by correlation analyses stratified by sex. Within males, there were significant negative correlations with respect to inattention and hyperactivity in various callosal regions, including the anterior third, anterior and posterior midbody, isthmus, and splenium. A thinner corpus callosum may be associated with fewer fibers or less myelination of fibers. Thus, the observed negative correlations suggest impaired inter-hemispheric communication channels necessary to sustain motor control and attention, which may contribute to symptoms of hyperactivity, impulsivity and/or inattention. Interestingly, within females, callosal thickness was positively related to hyperactivity in a small area within the rostral body, suggesting a sexually dimorphic neurobiology of ADHD symptoms. Altogether, the present results may reflect a lasting relationship between callosal morphology and ADHD symptoms throughout life.

Investigating the differential contributions of sex and brain size to gray matter asymmetry

Scientific reports of sex differences in brain asymmetry - the difference between the two hemispheres - are rather inconsistent. Some studies report no sex differences whatsoever, others reveal striking sex effects, with large discrepancies across studies in the magnitude, direction, and location of the observed effects. One reason for the lack of consistency in findings may be the confounding effects of brain size as male brains are usually larger than female brains. Thus, the goal of this study was to investigate the differential contributions of sex and brain size to asymmetry with a particular focus on gray matter. For this purpose, we applied a well-validated workflow for voxel-wise gray matter asymmetry analyses in a sample of 96 participants (48 males/48 females), in which a subsample of brains (24 males/24 females) were matched for size. By comparing outcomes based on three different contrasts - all males versus all females; all large brains versus all small brains; matched males versus matched females - we were able to disentangle the contributing effects of sex and brain size, to reveal true (size-independent) sex differences in gray matter asymmetry: Males show a significantly stronger rightward asymmetry than females within the cerebellum, specifically in lobules VII, VIII, and IX. This finding agrees closely with prior research suggesting sex differences in sensorimotor, cognitive and emotional function, which are all moderated by the respective cerebellar sections. No other significant sex effects on gray matter were detected across the remainder of the brain.

Integrating Cytoarchitectonic Probabilities with MRI-Based Signal Intensities to Calculate Regional Volumes of Interest

Hypotheses on specific brain structures are frequently assessed using anatomically defined regions of interest (ROIs) in structural T1-weighted images. The definition of these ROIs is often based on macroscopic landmarks (sulci, gyri, etc.) that do not necessarily coincide with the functional architecture of the brain. Microscopic labeling, on the other hand, enables a precise localization of anatomical boundaries. Thus, defining ROIs using cytoarchitectonic information might be a suitable alternative to the traditional landmark-based approach. In this chapter, we describe in detail how to perform such cytoarchitectonic ROI analyses by integrating voxel-wise cytoarchitectonic probabilities (using freely available maps created post mortem) with MR-based signal intensities (using standard T1-weighted data obtained in vivo). After elucidating common techniques to create ROIs (see Sect. 1), detailed information is provided with respect to the cytoarchitectonically defined probabilistic maps, i.e., the foundation for the proposed cytoarchitectonic ROI approach (see Sect. 2). The methodological aspects pertaining to this approach constitute the heart of the chapter and comprise three main steps: probability map selection, preprocessing, and integration (see Sect. 3). The chapter concludes with practical tips and helpful pointers for conducting a cytoarchitectonic ROI analysis (see Sect. 4).

Potential Brain Age Reversal after Pregnancy: Younger Brains at 4–6 Weeks Postpartum

Pregnancy is accompanied by complex biological adaptations, including extreme hormonal fluctuations. Moreover, changes on the endocrine level are accompanied by changes in cerebral anatomy, such as reductions in brain or gray matter volume. Since declining brain and tissue volumes are characteristic for normal aging, the question arises of whether such pregnancy-induced anatomical effects are permanent or transient. To answer this question, we acquired high-resolution brain image data of 14 healthy women in their mid-twenties to late thirties at two time points: within 1-2u202fdays of childbirth (early postpartum) and at 4-6u202fweeks after childbirth (late postpartum). At both time points, we estimated the brain ages for each woman using a well-validated machine learning approach based on pattern recognition. Ultimately, this algorithm - designed to identify anatomical correlates of age across the entire brain - reveals a single score for each individual: the BrainAGE index. Comparing the BrainAGE indices between both time points, female brains at late postpartum were estimated to be considerably younger than at early postpartum. On average, that difference was about five years (meanu202f±u202fSD: 5.4u202f±u202f2.4u202fyears). These findings suggest a substantial restoration/rejuvenation effect after giving birth, which is evident already within the first couple of months.

Atypical Callosal Morphology in Children with Speech Sound Disorder

Speech sound disorder (SSD) is common, yet its neurobiology is poorly understood. Recent studies indicate atypical structural and functional anomalies either in one hemisphere or both hemispheres, which might be accompanied by alterations in inter-hemispheric connectivity. Indeed, abnormalities of the corpus callosum - the main fiber tract connecting the two hemispheres - have been linked to speech and language deficits in associated disorders, such as stuttering, dyslexia, aphasia, etc. However, there is a dearth of studies examining the corpus callosum in SSD. Here, we investigated whether a sample of 18 children with SSD differed in callosal morphology from 18 typically developing children carefully matched for age. Significantly reduced dimensions of the corpus callosum, particularly in the callosal anterior third, were observed in children with SSD. These findings indicating pronounced callosal aberrations in SSD make an important contribution to an understudied field of research and may suggest that SSD is accompanied by atypical lateralization of speech and language function.

Sex differences in associations between spatial ability and corpus callosum morphology

Rotating mental representations of objects is accompanied by widespread bilateral brain activations. Thus, interhemispheric communication channels may play a relevant part when engaging in mental rotation tasks. Indeed, links between mental rotation and dimensions of the corpus callosum—the brains main commissure system—have been reported. However, existing findings are sparse and inconsistent across studies. Here we set out to further characterize the nature of any such links, including their exact location across the corpus callosum. For this purpose, we applied an advanced image analysis approach assessing callosal thickness at 100 equidistant points in a sample of 38 healthy adults (19 men, 19 women), aged between 22 and 45 years. We detected a sex interaction, with significant structure–performance relationships in women, but not in men. Specifically, better mental rotation performance was linked to a thicker female corpus callosum within regions of the callosal splenium, posterior midbody, and anterior third. These findings may suggest sex differences in problem solving strategies where in women, more than in men, stronger interhemispheric connectivity—especially between occipitoparietal, frontal, and prefrontal regions—is associated with improved task performance.

Altered Gray Matter Volumes in Language-Associated Regions in Children with Developmental Language Disorder and Speech Sound Disorder

Developmental language disorder (DLD) and speech sound disorder (SSD) are common, and although scientific evidence for structural and functional alterations in DLD/SSD is accumulating, current neuroimaging studies provide an incongruent picture. Here, we hypothesized that children affected by DLD and SSD present with gray matter (or gray matter asymmetry) aberrations in brain areas associated with language processing compared to typically developing (TD) children. To assess this hypothesis, we enhanced MRI-based information with microscopically defined cytoarchitectonic probabilities of Brocas area (BA 45, BA 44) as well as an auditory area (TE 3.0). We detected a larger rightward gray matter asymmetry in BA 45 in children with DLD (nxa0=xa013) and with SSD (nxa0=xa018) compared to TD children (nxa0=xa018), albeit only on a trend level. Interestingly though, we observed significantly larger gray matter volumes in right BA 45 in DLD compared to SSD children (and also compared to TD children).