Microstructural white matter connectivity underlying the attentional networks system

Bridging Reduced Grip Strength and Altered Executive Function: Specific Brain White Matter Structural Changes in Patients with Alzheimer's Disease

Objective

To investigate the correlation between specific fiber tracts and grip strength and cognitive function in patients with Alzheimer's disease (AD) by fixel-based analysis (FBA).

Methods

AD patients were divided into AD with low grip strength (AD-LGS, n=29) and AD without low grip strength (AD-nLGS, n=25), along with 31 normal controls (NC). General data, neuropsychological tests, grip strength and cranial magnetic resonance imaging (MRI) scans were collected. FBA evaluated white matter (WM) fiber metrics, including fiber density (FD), fiber cross-sectional (FC), and fiber density and cross-sectional area (FDC). The mean fiber indicators of the fiber tracts of interest (TOI) were extracted in cerebral region of significant statistical differences in FBA to further compare the differences between groups and analyze the correlation between fiber properties and neuropsychological test scores.

Results

Compared to AD-nLGS group, AD-LGS group showed significant reductions in FDC in several cerebral regions. In AD patients, FDC values of bilateral uncinate fasciculus and left superior longitudinal fasciculus were positively correlated with Clock Drawing Test scores, while FDC of splenium of corpus callosum, bilateral anterior cingulate tracts, forceps major, and bilateral inferior longitudinal fasciculus were positively correlated with the Executive Factor Score of Memory and Executive Screening scale scores.

Conclusion

Reduced grip strength in AD patients is associated with extensive impairment of WM structural integrity. Changes in FDC of specific WM fiber tracts related to executive function play a significant mediating role in the reduction of grip strength in AD patients.

Altered lateralization of the cingulum in deployment-related traumatic brain injury: An ENIGMA military-relevant brain injury study

Traumatic brain injury (TBI) in military populations can cause disruptions in brain structure and function, along with cognitive and psychological dysfunction. Diffusion magnetic resonance imaging (dMRI) can detect alterations in white matter (WM) microstructure, but few studies have examined brain asymmetry. Examining asymmetry in large samples may increase sensitivity to detect heterogeneous areas of WM alteration in mild TBI. Through the Enhancing Neuroimaging Genetics Through Meta-Analysis Military-Relevant Brain Injury working group, we conducted a mega-analysis of neuroimaging and clinical data from 16 cohorts of Active Duty Service Members and Veterans (n = 2598). dMRI data were processed together along with harmonized demographic, injury, psychiatric, and cognitive measures. Fractional anisotropy in the cingulum showed greater asymmetry in individuals with deployment-related TBI, driven by greater left lateralization in TBI. Results remained significant after accounting for potentially confounding variables including posttraumatic stress disorder, depression, and handedness, and were driven primarily by individuals whose worst TBI occurred before age 40. Alterations in the cingulum were also associated with slower processing speed and poorer set shifting. The results indicate an enhancement of the natural left laterality of the cingulum, possibly due to vulnerability of the nondominant hemisphere or compensatory mechanisms in the dominant hemisphere. The cingulum is one of the last WM tracts to mature, reaching peak FA around 42 years old. This effect was primarily detected in individuals whose worst injury occurred before age 40, suggesting that the protracted development of the cingulum may lead to increased vulnerability to insults, such as TBI.

White matter and sustained attention in children with attention/deficit-hyperactivity disorder: A longitudinal fixel-based analysis

Sustained attention is a cognitive function with known links to academic success and mental health disorders such as attention/deficit-hyperactivity disorder (ADHD). Several functional networks are critical to sustained attention, however the association between white matter maturation in tracts linking functional nodes and sustained attention in typical and atypical development is unknown. 309 diffusion-weighted imaging scans were acquired from 161 children and adolescents (80 ADHD, 81 control) at up to three timepoints over ages 9-14. A fixel-based analysis approach was used to calculate mean fiber density and fiber-bundle cross section in tracts of interest. Sustained attention was measured using omission errors and response time variability on the out-of-scanner sustained attention to response task. Linear mixed effects models examined associations of age, group and white matter metrics with sustained attention. Greater fiber density in the bilateral superior longitudinal fasciculus (SLF) I and right SLF II was associated with fewer attention errors in the control group only. In ADHD and control groups, greater fiber density in the left ILF and right thalamo-premotor pathway, as well as greater fiber cross-section in the left SLF I and II and right SLF III, was associated with better sustained attention. Relationships were consistent across the age span. Results suggest that greater axon diameter or number in the dorsal and middle SLF may facilitate sustained attention in neurotypical children but does not assist those with ADHD potentially due to disorder-related alterations in this region. Greater capacity for information transfer across the SLF was associated with attention maintenance in 9-14-year-olds regardless of diagnostic status, suggesting white matter macrostructure may also be important for attention maintenance. White matter and sustained attention associations were consistent across the longitudinal study, according with the stability of structural organization over this time. Future studies can investigate modifiability of white matter properties through ADHD medications.

Funcionamiento de las redes atencionales en la adultez joven y el nivel de educación

El objetivo del presente estudio fue observar el efecto de las variables nivel de estudios y adultez joven en la tarea de redes atencionales. Para ello, participaron 58 personas de población general separados en grupos de estudiantes y no estudiantes, y en adultez emergente y temprana, con los cuales se llevó a cabo un diseño experimental, utilizando como paradigma principal la tarea de redes atencionales. Los resultados mostraron que los grupos de estudiantes y no estudiantes no difirieron en rendimiento en ninguna de las condiciones de las redes, pero que, en cuanto a la variable adultez joven, hubo un efecto de interacción entre el tipo de adultez y la red de orientación, siendo el grupo adulto emergente más rápido que el grupo adulto temprano. Además, un análisis correlacional demostró que la edad correlacionó moderada y positivamente con el tiempo de reacción de todas las condiciones de la tarea atencional. Al final se discute la importancia del nivel de educación superior y la adultez joven sobre el funcionamiento de las redes atencionales en el campo de la psicología diferencial, y se mencionan las implicaciones de estos resultados en el ámbito clínico.

Predicting Attentional Vulnerability to Sleep Deprivation: A Multivariate Pattern Analysis of DTI Data

BACKGROUND

Large individual differences exist in sleep deprivation (SD) induced sustained attention deterioration. Several brain imaging studies have suggested that the activities within frontal-parietal network, cortico-thalamic connections, and inter-hemispheric connectivity might underlie the neural correlates of vulnerability/resistance to SD. However, those traditional approaches are based on average estimates of differences at the group level. Currently, a neuroimaging marker that can reliably predict this vulnerability at the individual level is lacking.

METHODS

Efficient transfer of information relies on the integrity of white matter (WM) tracts in the human brain, we therefore applied machine learning approach to investigate whether the WM diffusion metrics can predict vulnerability to SD. Forty-nine participants completed the psychomotor vigilance task (PVT) both after resting wakefulness (RW) and after 24 h of sleep deprivation (SD). The number of PVT lapse (reaction time > 500 ms) was calculated for both RW condition and SD condition and participants were categorized as vulnerable (24 participants) or resistant (25 participants) to SD according to the change in the number of PVT lapses between the two conditions. Diffusion tensor imaging were acquired to extract four multitype WM features at a regional level: fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity. A linear support vector machine (LSVM) learning approach using leave-one-out cross-validation (LOOCV) was performed to assess the discriminative power of WM features in SD-vulnerable and SD-resistant participants.

RESULTS

LSVM analysis achieved a correct classification rate of 83.67% (sensitivity: 87.50%; specificity: 80.00%; and area under the receiver operating characteristic curve: 0.85) for differentiating SD-vulnerable from SD-resistant participants. WM fiber tracts that contributed most to the classification model were primarily commissural pathways (superior longitudinal fasciculus), projection pathways (posterior corona radiata, anterior limb of internal capsule) and association pathways (body and genu of corpus callosum). Furthermore, we found a significantly negative correlation between changes in PVT lapses and the LSVM decision value.

CONCLUSION

These findings suggest that WM fibers connecting (1) regions within frontal-parietal attention network, (2) the thalamus to the prefrontal cortex, and (3) the left and right hemispheres contributed the most to classification accuracy.

Measuring attention and vigilance in the laboratory vs. online: The split-half reliability of the ANTI-Vea

Over the past few years, there has been growing interest in using online methods for collecting data from large samples. However, only a few studies have administered online behavioral tasks to assess attention outside the lab. In the present study, we assessed the classic attentional functions and two vigilance components using two versions of the Attentional Networks Test for Interactions and Vigilance-executive and arousal vigilance components (ANTI-Vea): (1) a standard version, performed under typical experimental conditions (n = 314), and (2) an online version, completed outside the lab (n = 303). Both versions were equally effective in assessing (1) the main effects and interactions of phasic alertness, orienting, and executive control, and (2) the executive (i.e., a decline in the ability to detect infrequent critical signals) and the arousal (i.e., a progressive slowness and variability in responses to stimuli from the environment) vigilance decrement across time on task. Responses were generally slower in the online than in the standard version. Importantly, the split-half reliability observed for both tasks was (1) higher for executive control (~.67) than for phasic alertness and orienting (< .40), as observed in previous versions of the task, and (2) between .71 and .99 for the executive and arousal vigilance measures. We expect the present study will be of interest to researchers aiming to assess attentional functions with a valid and reliable method that, importantly, is publicly available on an open website ( https://www.ugr.es/~neurocog/ANTI/ ) and is easy to use in applied contexts.