Biology subjects

Sawyer, K. S.

Publications and source records attributed to Sawyer, K. S..

3 recordsLinked to original sources

bioRxiv2018

Components of Executive Function Predict Regional Prefrontal Volumes

Objective: Designed to measure a diversity of executive functioning (EF) through classical neuropsychological tests, the Delis-Kaplan Executive Function Scale (D-KEFS) allows for the investigation of the neural architecture of EF. We examined how the D-KEFS Tower, Verbal Fluency, Design Fluency, Color-Word Interference, and Trail Making Test tasks related to regional frontal lobe volumes, quantifying how components of EF were represented in disparate neural networks. Method: Adults from the Nathan Kline Institute - Rockland Sample (NKI-RS), an open-access community study of brain development, with complete MRI (3T scanner) and D-KEFS data were selected for analysis (N = 478; ages 20-85). In a mixed-effects model predicting volume, D-KEFS task, D-KEFS score, region of interest (ROI; 13 frontal, 1 occipital control), were entered as fixed effects with intercepts for participants as random effects. Results: Unitary EF (average of D-KEFS scores) was positively associated with superior frontal, rostral middle frontal, and lateral orbitofrontal volumes; a negative association was observed with frontal pole volume (| z-score slope | range = 0.040 to 0.051). Diverse EF skills (individual D-KEFS task scores) were differentially associated with two or three ROIs, respectively, but to a stronger extent (| z-score slope | range = 0.053 to 0.103). Conclusions: The neural correlates found for the D-KEFS support the prefrontal modularity of EF at both the unitary (aspects of EF ability common to all tasks) and task (diverse EF skills) levels. The separation of task-general variance in neurocognition from task-specific variance can further evaluate neuropsychological tests as indices of brain integrity.

neuroscience↗

bioRxiv2017

Cerebral White Matter Sex Dimorphism in Alcoholism: A Diffusion Tensor Imaging Study

Background: Excessive alcohol consumption is associated with widespread brain damage, including abnormalities in frontal and limbic brain regions. In a prior study of neuronal circuitry connecting the frontal lobes and limbic system structures in abstinent alcoholic men, we demonstrated decreases in white matter fractional anisotropy (FA) on diffusion tensor magnetic resonance imaging (dMRI). In the present study, we examined sex differences in alcoholism-related abnormalities of white matter connectivity. Methods: dMRI scans were acquired from 49 abstinent alcoholic individuals (26 women) and 41 nonalcoholic controls (22 women). Tract-based spatial statistical tools were used to estimate regional FA of white matter tracts and to determine sex differences and their relation to measures of alcoholism history. Results: Sex-related differences in white matter connectivity were observed in association with alcoholism: Compared to nonalcoholic men, alcoholic men had diminished FA in portions of the corpus callosum, the superior longitudinal fasciculi II and III, and the arcuate fasciculus and extreme capsule. In contrast, alcoholic women had higher FA in these regions. Sex differences also were observed for correlations between corpus callosum FA and length of sobriety. Conclusions: Sexual dimorphism in white matter microstructure in abstinent alcoholics may implicate underlying differences in the neurobehavioral liabilities for developing alcohol abuse disorders, or for sequelae following abuse.

neuroscience↗

bioRxiv2017

On the Impact of Interhemispheric White Matter: Age, Executive Functioning, and Dedifferentiation in the Frontal Lobes

IntroductionIn middle age, declines in executive functioning (EF) are associated with decrements in the quality and/or quantity of white and grey matter. Recruitment of homologous regions has been identified as a compensatory mechanism for cognitive decline in later middle age, however research into neural substrates of EF has yet to be guided by dedifferentiation models. We hypothesized that frontal-parietal grey matter volume, interhemispheric white matter and intrahemispheric white matter fractional anisotropy (FA) will be predictive of EF. Further, we hypothesized that the comparative association between interhemispheric white matter and EF will increase with age, because of compensatory recruitment.\n\nMethodsNeurocognitive test data, DTI, and T1 MPRAGE scans (n = 444) were obtained from the NKI-Rockland Sample. Structural equation modeling was used to examine the relationship between age, EF, interhemispheric white matter (forceps minor; FM), intrahemispheric white matter (superior longitudinal fasciculus; SLF), and a frontal-parietal grey matter network. EF and grey matter were modelled as latent variables, with EF examined as the criterion. Additionally, a subsample of participants aged 55-85 (n = 168) was analyzed to examine the influence of age related compensatory mechanisms.\n\nResultsThere was a significant relationship between FM, grey matter, and EF, which was fully mediated by age. There was a significant relationship between SLF and EF, which was not mediated by age. For older adults, only the age-mediated pathway from FM to EF was significant.\n\nDiscussionUsing structural imaging data, support was found for age-related interhemispheric mechanisms of compensation, but not intrahemispheric mechanisms.\n\nKey points(1) Neural substrates of executive functioning are not static across the lifespan. (2) In older adults, white matter becomes more salient as a structural correlate of executive functioning, as recruitment needs increase. (3) While the importance of interhemispheric white matter is mediated by age, intrahemispheric recruitment remains consistent across the lifespan, and is not the primary mechanism of age-based compensation in community dwelling older adults.

neuroscience↗