Neuroanatomical substrates of executive functions: Beyond prefrontal structures

Cognitive dysfunction and white matter hyperintensities in Fabry disease

Fabry disease (FD) is an X-linked lysosomal storage disorder with multi-system involvement including cerebrovascular disease. Patients with FD also have a high risk of ischaemic stroke and TIA. White matter hyperintensities are common, but their clinical impact on cognition remains uncertain. Previous studies have examined the neuropsychological profile of FD, but have been inconclusive in part due to methodological limitations including small sample sizes. We sought to address these limitations in a case-control study of 26 patients with Fabry disease with mild to moderate disease symptoms matched with 18 healthy controls for age and premorbid intellectual level. We obtained detailed neuropsychological data and MRI neuroimaging data on the severity of white matter changes. Mood was accounted for as a possible confounder. Our results showed significant compromise of executive functions and information processing speed for the FD group. Error analyses suggested that the compromise of executive functions could not be entirely accounted for by slowed information processing speed. We demonstrated significant correlations between cognitive decline and the overall volume of white matter hyperintensities in the FD group. Our results point to significant compromise of cognition in FD even without stroke or mood difficulties. This suggests that neuropsychological assessment and rehabilitation should be routinely offered to patients with FD.

Lower White Matter Volume and Worse Executive Functioning Reflected in Higher Levels of Plasma GFAP among Older Adults with and Without Cognitive Impairment

OBJECTIVE

There are minimal data directly comparing plasma neurofilament light (NfL) and glial fibrillary acidic protein (GFAP) in aging and neurodegenerative disease research. We evaluated associations of plasma NfL and plasma GFAP with brain volume and cognition in two independent cohorts of older adults diagnosed as clinically normal (CN), mild cognitive impairment (MCI), or Alzheimer's dementia.

METHODS

We studied 121 total participants (Cohort 1: n = 50, age 71.6 ± 6.9 years, 78% CN, 22% MCI; Cohort 2: n = 71, age 72.2 ± 9.2 years, 45% CN, 25% MCI, 30% dementia). Gray and white matter volumes were obtained for total brain and broad subregions of interest (ROIs). Neuropsychological testing evaluated memory, executive functioning, language, and visuospatial abilities. Plasma samples were analyzed in duplicate for NfL and GFAP using single molecule array assays (Quanterix Simoa). Linear regression models with structural MRI and cognitive outcomes included plasma NfL and GFAP simultaneously along with relevant covariates.

RESULTS

Higher plasma GFAP was associated with lower white matter volume in both cohorts for temporal (Cohort 1: β = -0.33, p = .002; Cohort 2: β = -0.36, p = .03) and parietal ROIs (Cohort 1: β = -0.31, p = .01; Cohort 2: β = -0.35, p = .04). No consistent findings emerged for gray matter volumes. Higher plasma GFAP was associated with lower executive function scores (Cohort 1: β = -0.38, p = .01; Cohort 2: β = -0.36, p = .007). Plasma NfL was not associated with gray or white matter volumes, or cognition after adjusting for plasma GFAP.

CONCLUSIONS

Plasma GFAP may be more sensitive to white matter and cognitive changes than plasma NfL. Biomarkers reflecting astroglial pathophysiology may capture complex dynamics of aging and neurodegenerative disease.

Neurological Music Therapy Rebuilds Structural Connectome after Traumatic Brain Injury: Secondary Analysis from a Randomized Controlled Trial

Background: Traumatic brain injury (TBI) is a common and devastating neurological condition, associated often with poor functional outcome and deficits in executive function. Due to the neuropathology of TBI, neuroimaging plays a crucial role in its assessment, and while diffusion MRI has been proposed as a sensitive biomarker, longitudinal studies evaluating treatment-related diffusion MRI changes are scarce. Recent evidence suggests that neurological music therapy can improve executive functions in patients with TBI and that these effects are underpinned by neuroplasticity changes in the brain. However, studies evaluating music therapy induced structural connectome changes in patients with TBI are lacking. Design: Single-blind crossover (AB/BA) randomized controlled trial (NCT01956136). Objective: Here, we report secondary outcomes of the trial and set out to assess the effect of neurological music therapy on structural white matter connectome changes and their association with improved execute function in patients with TBI. Methods: Using an AB/BA design, 25 patients with moderate or severe TBI were randomized to receive a 3-month neurological music therapy intervention either during the first (AB, n = 16) or second (BA, n = 9) half of a 6-month follow-up period. Neuropsychological testing and diffusion MRI scans were performed at baseline and at the 3-month and 6-month stage. Findings: Compared to the control group, the music therapy group increased quantitative anisotropy (QA) in the right dorsal pathways (arcuate fasciculus, superior longitudinal fasciculus) and in the corpus callosum and the right frontal aslant tract, thalamic radiation and corticostriatal tracts. The mean increased QA in this network of results correlated with improved executive function. Conclusions: This study shows that music therapy can induce structural white matter neuroplasticity in the post-TBI brain that underpins improved executive function.

The Effect of Deep Micro Vibrotactile Stimulation on Cognitive Function of Mild Cognitive Impairment and Mild Dementia

Background: The purpose of this study was to clarify the effect of Deep Micro Vibrotactile (DMV) stimulation on the cognitive functions in elderly people with mild cognitive impairment or mild dementia. Methods: A total of 35 participants with dementia from three nursing homes, who had completed treatment with DMV stimulation at 15−40 Hz (hereinafter, 15−40 Hz DMV stimulation) for a month were recruited for this study. The subjects had received continuous 15−40 Hz DMV stimulation for 24 h a day for 1 month. We assessed the effect of the treatment on the cognitive functions (by the word list memory (WM) test, trail making test-part A (TMT-A) and part B (TMT-B), and symbol digit substitution task (SDST)) and physical functions (grip strength (GS) and usual walking speed (UWS)), by comparing the results at the baseline and after the 1-month intervention (DMV stimulation). Results: The results revealed that the performances in the WM test (p < 0.05), TMT-B (p < 0.05), and SDST (p < 0.01) improved significantly after the intervention. Conclusion: Our findings suggest that 15−40 Hz DMV stimulation is might be effective for improving the cognitive functions in elderly people with dementia. Furthermore, our novel findings showed the different effectiveness of the treatment depending on the stage of cognitive impairments.

Age-related differences in white matter microstructure measured by advanced diffusion MRI in healthy older adults at risk for Alzheimer's disease

Neurite orientation dispersion and density imaging (NODDI) is an advanced diffusion imaging technique, which can detect more distinct microstructural features compared to conventional Diffusion Tensor Imaging (DTI). NODDI allows the signal to be divided into multiple water compartments and derive measures for orientation dispersion index (ODI), neurite density index (NDI) and volume fraction of isotropic diffusion compartment (FISO). This study aimed to investigate which diffusion metric-fractional anisotropy (FA), mean diffusivity (MD), NDI, ODI, or FISO-is most influenced by aging and reflects cognitive function in a population of healthy older adults at risk for Alzheimer's disease (AD). Age was significantly associated with all but one diffusion parameters and regions of interest. NDI and MD in the cingulate region adjacent to the cingulate cortex showed a significant association with a composite measure of Executive Function and was proven to partially mediate the relationship between aging and Executive Function decline. These results suggest that both DTI and NODDI parameters are sensitive to age-related differences in white matter regions vulnerable to aging, particularly among older adults at risk for AD.

Episodic Memory Impairment Mediates the Loss of Awareness in Mild Cognitive Impairment

INTRODUCTION

Loss of awareness is a common symptom in Alzheimer's Disease (AD) and responsible for a significant loss of functional abilities. The mechanisms underlying loss of awareness in AD is unknown, although previous findings have implicated dysfunction of primary executive functioning (EF) or episodic memory (EM) to be the cause. Therefore, our main study objective was to explore the involvement of EF and EM dysfunction in amyloid-related loss of awareness across the clinical spectrum of AD.

METHODS

A total of 895 participants (362 clinically normal [CN], 422 people with mild cognitive impairment [MCI] and 111 with dementia) from the Alzheimer's Disease Neuroimaging Initiative were used for the analyses. A sub-analysis was performed in 202 participants who progressed in their clinical diagnosis from CN to MCI or MCI to dementia as well as dementia patients. Mediation models were used in each clinical group with awareness (assessed with the Everyday Cognitive function questionnaire) as a dependent variable to determine whether EF and/or EM would mediate the effect of amyloid on awareness. We also ran these analyses with subjective and informant complaints as dependent variables. Direct correlations between all variables were also performed.

RESULTS

We found evidence for a decline in awareness across the groups, with increased awareness observed in the CN group and decreased awareness observed in the MCI and dementia groups. Our results showed that EM, and not EF, partially mediated the relationship between amyloid and awareness such that greater amyloid and lower EM performance was associated with lower awareness. When analyzing each group separately, this finding was only observed in the MCI group and in the group containing progressors and dementia patients. When repeating the analyses for subjective and informant complaints separately, the results were replicated only for the informant's complaints.

DISCUSSION

Our results demonstrate that decline in EM and, to a lesser degree, EF, mediate the effect of amyloid on awareness. In line with previous studies demonstrating the development of anosognosia in the prodromal stage, our findings suggest that decreased awareness is the result of an inability for the participant to update his/her insight into his/her cognitive performance (i.e., demonstrating a petrified self).

Normative Data for Verbal Fluency, Trail Making, and Rey-Osterrieth Complex Figure Tests on Monolingual Spanish-Speaking Older Adults

OBJECTIVE

This study aimed to generate updated normative data for commonly used tests in neuropsychological assessment applied to older monolingual Spanish-speaking adults: Verbal fluency tests, the Trail Making Test (TMT), and the Rey-Osterrieth complex figure test (ROCF).

METHOD

To obtain normative data, 382 cognitively healthy 60- to 90-year-old Spanish monolingual participants from the Autonomous Community of Madrid (Spain) with 0-22 years education were assessed using an overlapping interval strategy that involved cell and midpoint techniques, and that assessed the influence of age, education, and sex.

RESULTS

Age and education were associated with the scores in the verbal fluency tests, TMT, and ROCF, whereas sex only significantly affected the TMT results. Age-adjusted scaled scores (SSA) based on percentile ranks were also converted into age-education scaled scores (SSAE) using a linear regression model. In addition, tables with the relevant adjustments for sex are provided for TMT-A and TMT-B.

CONCLUSIONS

Thus, this study provides updated, uniform normative data for widely used neuropsychological tests on older Spanish adults. The normative procedure followed helps to make consistent comparisons when using these neuropsychological tests, which will improve the interpretation of the data obtained when these tools are employed, reducing the risk of misdiagnosing cognitive impairment in older adults.

White Matter Characteristics of Cognitive Impairment in Tap-Test Positive Idiopathic Normal Pressure Hydrocephalus: A Diffusion Tensor Tract-Based Spatial Study

The present study was designed to systemically evaluate changes in the diffusion tensor imaging (DTI)-derived parameters of iNPH (idiopathic normal pressure hydrocephalus) patients with different responses to the tap test (TT), and to correlate cognitive impairment with white matter (WM) degeneration. This study included 22 iNPH patients and 14 healthy controls with structural magnetic resonance imaging (MRI) and DTI scanning. DTI was used to explore the differences in fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) for all participants. DTI parameters were evaluated using an ROI (region of interest)-based and tract-based spatial statistics (TBSS) approach. Neuropsychological assessments and the idiopathic normal pressure hydrocephalus grading scoring scale (iNPHGS) were performed. Compared to the TT non-responders, the TT responders group had significantly lower FA values in the corpus callosum, cingulum cingulate gyrus, superior longitudinal fasciculus, and lower AD values in the right cingulum cingulate gyrus and the left posterior thalamic radiation. Besides, the MD values were significantly increased in the corpus callosum, left anterior corona radiata, and the RD values in the corpus callosum and cingulum cingulate gyrus. In addition, the cognitive improvement was negatively correlated with FA of the corpus callosum, cingulum cingulate gyrus, and MD values of the genu of corpus callosum. While, the cognitive improvement was positively related to the AD of the cingulum cingulate gyrus, superior longitudinal, and RD values of the corpus callosum, cingulum cingulate gyrus and uncinate fasciculus. The ROI specific WM lesions in iNPH patients are the underlying basis for cognitive impairment.

Factor structure of the BRIEF-P teacher version in a sample of Bosnian preschool children with intellectual disability

Executive functions (EF) play a key role in child's development as they are necessary prerequisites for everyday functioning and later academic success. Much research has been directed at examining whether EF are unidimensional or multidimensional construct. In this study, we tested two theoretically driven models and one mathematically driven EF model based on the Behavior Rating Inventory of Executive Functions - Preschool Edition (BRIEF-P). The sample for this study consisted of 102 children with intellectual disability (77 boys, 25 girls), aged 40-71 months (mean age- 62.1 months, SD- 7.6 months). Early childhood special education teachers completed the BRIEF-P Teacher Version. Confirmatory Factor Analysis was used to assess the validity of different EF models. The original BRIEF-P, with a second-order, three-factor model and one-factor model were not a good fit to the data. Mathematically driven one-factor model, with the addition of correlated errors between the scales of working memory and shift, and working memory and plan/organize was a good model fit. The current study indicates that EF differentiation begins to emerge at preschool age in children with intellectual disabilities. Understanding EF structure in children with intellectual disability will help create better intervention programs for this population.

Topographical functional correlates of interindividual differences in executive functions in young healthy twins

Executive functions (EF) are a set of higher-order cognitive abilities that enable goal-directed behavior by controlling lower-level operations. In the brain, those functions have been traditionally associated with activity in the Frontoparietal Network, but recent neuroimaging studies have challenged this view in favor of more widespread cortical involvement. In the present study, we aimed to explore whether the network that serves as critical hubs at rest, which we term network reliance, differentiate individuals as a function of their level of EF. Furthermore, we investigated whether such differences are driven by genetic as compared to environmental factors. For this purpose, resting-state functional magnetic resonance imaging data and the behavioral testing of 453 twins from the Colorado Longitudinal Twins Study were analyzed. Separate indices of EF performance were obtained according to a bifactor unity/diversity model, distinguishing between three independent components representing: Common EF, Shifting-specific and Updating-specific abilities. Through an approach of step-wise in silico network lesioning of the individual functional connectome, we show that interindividual differences in EF are associated with different dependencies on neural networks at rest. Furthermore, these patterns show evidence of mild heritability. Such findings add knowledge to the understanding of brain states at rest and their connection with human behavior, and how they might be shaped by genetic influences.

Neurocognitive factorial structure of executive functions: Evidence from neurotypicals and frontotemporal dementia

The latent structure of executive functions (EFs) remains controversial. Confirmatory factorial analysis (CFA) has provided support for both multidimensional (assumes EFs to be functionally separable but related components) and bifactor (proposes all components are nested within a common factor) models. However, these CFA models have never been compared in patient samples, nor regarding their neuroanatomical correlates. Here, we systematically contrast both approaches in neurotypicals and in a neurodegenerative lesion model (patients with the behavioral variant frontotemporal dementia, bvFTD), characterized by executive deficits associated with frontal neurodegeneration. First, CFA was used to test the models' fit in a sample of 341 neurotypicals and 29 bvFTD patients based on performance in an executive frontal screening battery which assesses working memory, motor inhibition, verbal inhibition, and abstraction capacity. Second, we compared EFs factor and observed scores between patients and matched controls. Finally, we used voxel-based morphometry (VBM) to compare the grey matter correlates of factor and observed scores. CFA results showed that both models fit the data well. The multidimensional model, however, was more sensitive than the bifactor model and the observed scores to detect EFs impairments in bvFTD patients. VBM results for the multidimensional model revealed common and unique grey matter correlates for EFs components across prefrontal-insular, posterior, and temporal cortices. Regarding the bifactor model, only the common factor was associated with prefrontal-insular hubs. Observed scores presented scant, non-frontal grey matter associations. Converging behavioral and neuroanatomical evidence from healthy populations and a neurodegenerative model of EFs supports an underlying multidimensional structure.

Functional Integrity of Executive Control Network Contributed to Retained Executive Abilities in Mild Cognitive Impairment

Background: Mild cognitive impairment (MCI) is considered to be a transitional state between normal aging and Alzheimer's dementia (AD). Recent studies have indicated that executive function (EF) declines during MCI. However, only a limited number of studies have investigated the neural basis of EF deficits in MCI. Herein, we investigate the changes of regional brain spontaneous activity and functional connectivity (FC) of the executive control network (ECN) between high EF and low EF groups. Methods: According to EF composite score (ADNI-EF) from the Alzheimer's Disease Neuroimaging Initiative (ADNI), we divided MCI into two groups, including the MCI-highEF group and MCI-lowEF group. Resting-state functional MRI was utilized to investigate the fractional amplitude of low-frequency fluctuation (fALFF) and ECN functional connectivity across 23 healthy controls (HC), 11 MCI-highEF, and 14 MCI-lowEF participants. Moreover, a partial correlation analysis was carried out to examine the relationship between altered fALFF or connectivity of the ECN and the ADNI-EF. Results: Compared to HC, the MCI-highEF participants demonstrated increased fALFF in the left superior temporal gyrus (STG), as well as decreased fALFF in the right precentral gyrus, right postcentral gyrus, and left middle frontal gyrus (MFG). The MCI-lowEF participants demonstrated increased fALFF in the cerebellar vermis and decreased fALFF in the left MFG. Additionally, compared to HC, the MCI-highEF participants indicated no significant difference in connectivity of the ECN. Furthermore, the MCI-lowEF participants showed increased ECN FC in the left cuneus and left MFG, as well as decreased ECN functional connectivity in the right parahippocampal gyrus (PHG). Notably, the altered fALFF in the left MFG was positively correlated to ADNI-EF, while the altered fALFF in cerebellar vermis is negatively correlated with ADNI-EF across the two MCI groups and the HC group. Altered ECN functional connectivity in the right PHG is negatively correlated to ADNI-EF, while altered ECN functional connectivity in the left cuneus is negatively correlated to ADNI-EF across the three groups. Conclusions: Our current study demonstrates the presence of different patterns of regional brain spontaneous activity and ECN FC in the MCI-highEF group and MCI-lowEF group. Furthermore, the ECN FC of the MCI-highEF group was not disrupted, which may contribute to retained EF in MCI.

Whole-brain white matter network reorganization in HIV

The human immunodeficiency virus (HIV) causes an infectious disease with a high viral tropism toward CD4 T-lymphocytes and macrophage. Since the advent of combined antiretroviral therapy (CART), the number of opportunistic infectious disease has diminished, turning HIV into a chronic condition. Nevertheless, HIV-infected patients suffer from several life-long symptoms, including the HIV-associated neurocognitive disorder (HAND), whose biological substrates remain unclear. HAND includes a range of cognitive impairments which have a huge impact on daily patient life. The aim of this study was to examine putative structural brain network changes in HIV-infected patient to test whether diffusion-imaging-related biomarkers could be used to discover and characterize subtle neurological alterations in HIV infection. To this end, we employed multi-shell, multi-tissue constrained spherical deconvolution in conjunction with probabilistic tractography and graph-theoretical analyses. We found several statistically significant effects in both local (right postcentral gyrus, right precuneus, right inferior parietal lobule, right transverse temporal gyrus, right inferior temporal gyrus, right putamen and right pallidum) and global graph-theoretical measures (global clustering coefficient, global efficiency and transitivity). Our study highlights a global and local reorganization of the structural connectome which support the possible application of graph theory to detect subtle alteration of brain regions in HIV patients.Clinical Relevance-Brain measures able to detect subtle alteration in HIV patients could also be used in e.g. evaluating therapeutic responses, hence empowering clinical trials.

A Systematic Review of Cognition-Brain Morphology Relationships on the Schizophrenia-Bipolar Disorder Spectrum

The nature of the relationship between cognition and brain morphology in schizophrenia-spectrum disorders (SSD) and bipolar disorder (BD) is uncertain. This review aimed to address this, by providing a comprehensive systematic investigation of links between several cognitive domains and brain volume, cortical thickness, and cortical surface area in SSD and BD patients across early and established illness stages. An initial search of PubMed and Scopus databases resulted in 1486 articles, of which 124 met inclusion criteria and were reviewed in detail. The majority of studies focused on SSD, while those of BD were scarce. Replicated evidence for specific regions associated with indices of cognition was minimal, however for several cognitive domains, the frontal and temporal regions were broadly implicated across both recent-onset and established SSD, and to a lesser extent BD. Collectively, the findings of this review emphasize the significance of both frontal and temporal regions for some domains of cognition in SSD, while highlighting the need for future BD-related studies on this topic.

The Relations Between Physical Activity Level, Executive Function, and White Matter Microstructure in Older Adults

The population of older adults is increasing, indicating a need to examine factors that may prevent or mitigate age-related cognitive decline. The current study examined whether microstructural white matter characteristics mediated the relation between physical activity and executive function in older adults without any self-reported psychiatric and neurological disorders or cognitive impairment (N = 43, mean age = 73 y). Physical activity was measured by average intensity and number of steps via accelerometry. Diffusion tensor imaging was used to examine microstructural white matter characteristics, and neuropsychological testing was used to examine executive functioning. Parallel mediation models were analyzed using microstructural white matter regions of interest as mediators of the association between physical activity and executive function. Results indicated that average steps was significantly related to executive function (β = 0.0003, t = 2.829, P = .007), while moderate to vigorous physical activity was not (β = 0.0007, t = 1.772, P = .08). White matter metrics did not mediate any associations. This suggests that microstructural white matter characteristics alone may not be the mechanism by which physical activity impacts executive function in aging.

Age-Related Variations in Regional White Matter Volumetry and Microstructure During the Post-adolescence Period: A Cross-Sectional Study of a Cohort of 1,713 University Students

Human brain white matter undergoes a protracted maturation that continues well into adulthood. Recent advances in diffusion-weighted imaging (DWI) methods allow detailed characterizations of the microstructural architecture of white matter, and they are increasingly utilized to study white matter changes during development and aging. However, relatively little is known about the late maturational changes in the microstructural architecture of white matter during post-adolescence. Here we report on regional changes in white matter volume and microstructure in young adults undergoing university-level education. As part of the MRi-Share multi-modal brain MRI database, multi-shell, high angular resolution DWI data were acquired in a unique sample of 1,713 university students aged 18-26. We assessed the age and sex dependence of diffusion metrics derived from diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) in the white matter regions as defined in the John Hopkins University (JHU) white matter labels atlas. We demonstrate that while regional white matter volume is relatively stable over the age range of our sample, the white matter microstructural properties show clear age-related variations. Globally, it is characterized by a robust increase in neurite density index (NDI), and to a lesser extent, orientation dispersion index (ODI). These changes are accompanied by a decrease in diffusivity. In contrast, there is minimal age-related variation in fractional anisotropy. There are regional variations in these microstructural changes: some tracts, most notably cingulum bundles, show a strong age-related increase in NDI coupled with decreases in radial and mean diffusivity, while others, mainly cortico-spinal projection tracts, primarily show an ODI increase and axial diffusivity decrease. These age-related variations are not different between males and females, but males show higher NDI and ODI and lower diffusivity than females across many tracts. These findings emphasize the complexity of changes in white matter structure occurring in this critical period of late maturation in early adulthood.

The effect of vascular health factors on white matter microstructure mediates age-related differences in executive function performance

Even within healthy aging, vascular risk factors can detrimentally influence cognition, with executive functions (EF) particularly vulnerable. Fronto-parietal white matter (WM) connectivity in part, supports EF and may be particularly sensitive to vascular risk. Here, we utilized structural equation modeling in 184 healthy adults (aged 20-94 years of age) to test the hypotheses that: 1) fronto-parietal WM microstructure mediates age effects on EF; 2) higher blood pressure (BP) and white matter hyperintensity (WMH) burden influences this association. All participants underwent comprehensive cognitive and neuropsychological testing including tests of processing speed, executive function (with a focus on tasks that require switching and inhibition) and completed an MRI scanning session that included FLAIR imaging for semi-automated quantification of white matter hyperintensity burden and diffusion-weighted imaging for tractography. Structural equation models were specified with age (as a continuous variable) and blood pressure predicting within-tract WMH burden and fractional anisotropy predicting executive function and processing speed. Results indicated that fronto-parietal white matter of the genu of the corpus collosum, superior longitudinal fasciculus, and the inferior frontal occipital fasciculus (but not cortico-spinal tract) mediated the association between age and EF. Additionally, increased systolic blood pressure and white matter hyperintensity burden within these white matter tracts contribute to worsening white matter health and are important factors underlying age-brain-behavior associations. These findings suggest that aging brings about increases in both BP and WMH burden, which may be involved in the degradation of white matter connectivity and in turn, negatively impact executive functions as we age.

Cerebral White Matter Myelination and Relations to Age, Gender, and Cognition: A Selective Review

White matter makes up about fifty percent of the human brain. Maturation of white matter accompanies biological development and undergoes the most dramatic changes during childhood and adolescence. Despite the advances in neuroimaging techniques, controversy concerning spatial, and temporal patterns of myelination, as well as the degree to which the microstructural characteristics of white matter can vary in a healthy brain as a function of age, gender and cognitive abilities still exists. In a selective review we describe methods of assessing myelination and evaluate effects of age and gender in nine major fiber tracts, highlighting their role in higher-order cognitive functions. Our findings suggests that myelination indices vary by age, fiber tract, and hemisphere. Effects of gender were also identified, although some attribute differences to methodological factors or social and learning opportunities. Findings point to further directions of research that will improve our understanding of the complex myelination-behavior relation across development that may have implications for educational and clinical practice.

Assessing combinatorial effects of HIV infection and former cocaine dependence on cognitive control processes: A high-density electrical mapping study of response inhibition

Stimulant drug use in HIV + patients is associated with poor personal and public health outcomes, including high-risk sexual behavior and faster progression from HIV to AIDS. Inhibitory control--the ability to withhold a thought, feeling, or action--is a central construct involved in the minimization of risk-taking behaviors. Recent neuroimaging and behavioral evidence indicate normalization of inhibitory control processes in former cocaine users as a function of the duration of drug abstinence, but it is unknown whether this recovery trajectory persists in former users with comorbid HIV. Here, we investigate the neural correlates of inhibitory control in 103 human subjects using high-density EEG recording as participants performed a Go/NoGo response inhibition task. Four groups of participants were recruited, varying on HIV and cocaine-dependence status. Electrophysiological responses to successful inhibitions and behavioral task performance were compared among groups. Results indicate persistent behavioral and neurophysiological impairment in HIV+ patients' response inhibition despite current abstinence from cocaine. Analysis of task performance showed that HIV+ abstinent cocaine-dependent participants demonstrate the lowest performance of all groups across all metrics of task accuracy. Planned comparisons of electrophysiological components revealed a main effect of scalp site and an interaction between HIV-status and scalp site on N2 amplitudes during successful inhibitions. Analysis of the P3 time region showed a main effect of scalp site and an interaction between HIV-status and cocaine dependence. These results suggest synergistic alterations in the neurophysiology of response inhibition and indicate that abstinence-related recovery of inhibitory control may be attenuated in patients with HIV.

Development and validation of the Uniform Data Set (v3.0) executive function composite score (UDS3-EF)

INTRODUCTION

Cognitive composite scores offer a means of precisely measuring executive functioning (EF).

METHODS

We developed the Uniform Data Set v3.0 EF composite score (UDS3-EF) in 3507 controls from the National Alzheimer's Coordinating Center dataset using item-response theory and applied nonlinear and linear demographic adjustments. The UDS3-EF was validated with other neuropsychological tests and brain magnetic resonance imaging from independent research cohorts using linear models.

RESULTS

Final model fit was good-to-excellent: comparative fit index = 0.99; root mean squared error of approximation = 0.057. UDS3-EF scores differed across validation cohorts (controls > mild cognitive impairment > Alzheimer's disease-dementia ≈ behavioral variant frontotemporal dementia; P < 0.001). The UDS3-EF correlated most strongly with other EF tests (βs = 0.50 to 0.85, Ps < 0.001) and more with frontal, parietal, and temporal lobe gray matter volumes (βs = 0.18 to 0.33, Ps ≤ 0.004) than occipital gray matter (β = 0.12, P = 0.04). The total sample needed to detect a 40% reduction in UDS3-EF change (n = 286) was ≈40% of the next best measure (F-words; n = 714).

CONCLUSIONS

The UDS3-EF is well suited to quantify EF in research and clinical trials and offers psychometric and practical advantages over its component tests.

The Oxford digital multiple errands test (OxMET): Validation of a simplified computer tablet based multiple errands test

Impairments in executive functioning are common following Acquired Brain Injury, though there are few screening tools which present a time efficient and ecologically valid approach to assessing the consequences of executive impairments. We present the Oxford Digital Multiple Errands Test (OxMET), a novel and simplified computer-tablet version of a Multiple Errands Test. We recruited 124 neurologically healthy controls and 105 stroke survivors to complete the OxMET task. Normative data and internal consistency were established from the healthy control data. Convergent and divergent validation was assessed in a mixed subset of 158 participants who completed the OxMET and OCS-Plus. Test-retest reliability was examined across a mixed subset of 39 participants. Finally, we investigated the known-group discriminability of the OxMET. The OxMET demonstrated very high internal consistency, and stable group level test-retest performance as well as good convergent and divergent validity. The OxMET demonstrated high sensitivity and good specificity in overall differentiation of stroke survivors from controls. The Oxford Digital Multiple Errands Test is a brief, easy to administer tool, designed to quickly screen for potential consequences of executive impairments in a virtual environment shopping task on a computer tablet. Initial normative data and validation within a chronic stroke cohort is presented.

Cortical thickness mediates the relationship between DRD2 C957T polymorphism and executive function across the adult lifespan

Dopamine (DA) signaling is critical for optimal cognitive performance. Aging is accompanied by a change in the strength of this signaling, with a loss of striatal and extrastriatal D2 binding potential. The reduction in dopamine modulation with age negatively influences various aspects of cognition. DRD2 C957T (rs6277) impacts DA D2 receptor density and availability, with C homozygotes linked to lower striatal DA availability and reduced executive functioning (EF), but also high extrastriatal binding potential. Here, we investigated in 176 participants aged 20-94 years whether: (1) DRD2 C carriers differ from T carriers in cortical thickness or subcortical volume in areas of high concentrations of D2 receptors that receive projections from mesocortical or nigrostriatal dopaminergic pathways; (2) whether the DRD2*COMT relationship has any synergistic effects on cortical thickness; (3) whether the effect of DRD2 on brain structure depends upon age; and (4) whether DRD2-related regional thinning affects executive function performance. We show that DRD2 impacts cortical thickness in the superior parietal lobule, precuneus, and anterior cingulate (marginal after FDR correction), while statistically controlling sex, age, and COMT genotype. Specifically, C homozygotes demonstrated thinner cortices than both heterozygotes and/or T homozygotes in an age-invariant manner. Additionally, DRD2 predicted executive function performance via cortical thickness. The results highlight that genetic influences on dopamine availability impact cognitive performance via the contribution of brain structure in cortical regions influenced by DRD2.

Neuropsychology of executive functions in patients with focal lesion in the prefrontal cortex: A systematic review

Executive functions are conceptualized as a set of cognitive processes that coordinate more basic processes for the resolution of complex behaviors. This neuronal substrate is believed to reside in the most anterior part of the brain. A systematic review of the high-impact literature was carried out to investigate what were the main deficits in executive functions after brain injury. It was found that the literature is fundamentally oriented towards the investigation of the ventromedial cortex and its deficits in decision-making and moral reasoning. Research on the dorsolateral cortex and more cognitive functions such as working memory is relegated to a second choice. This review proposes that a correct functioning of the ventromedial cortex is necessary in order to integrate emotional, cognitive and sensory information for an adequate choice in decision making and moral reasoning. It has also been found that the main deficits of working memory in the dorsolateral cortex are more associated with complex and visuospatial tasks. However, an increase in research synthesizing this type of study is necessary to reach more definitive conclusions.

Free water: A marker of age-related modifications of the cingulum white matter and its association with cognitive decline

Diffusion MRI is extensively used to investigate changes in white matter microstructure. However, diffusion measures within white matter tissue can be affected by partial volume effects due to cerebrospinal fluid and white matter hyperintensities, especially in the aging brain. In previous aging studies, the cingulum bundle that plays a central role in the architecture of the brain networks supporting cognitive functions has been associated with cognitive deficits. However, most of these studies did not consider the partial volume effects on diffusion measures. The aim of this study was to evaluate the effect of free water elimination on diffusion measures of the cingulum in a group of 68 healthy elderly individuals. We first determined the effect of free water elimination on conventional DTI measures and then examined the effect of free water elimination on verbal fluency performance over 12 years. The cingulum bundle was reconstructed with a tractography pipeline including a white matter hyperintensities mask to limit the negative impact of hyperintensities on fiber tracking algorithms. We observed that free water elimination increased the ability of conventional DTI measures to detect associations between tissue diffusion measures of the cingulum and changes in verbal fluency in older individuals. Moreover, free water content and mean diffusivity measured along the cingulum were independently associated with changes in verbal fluency. This suggests that both tissue modifications and an increase in interstitial isotropic water would contribute to cognitive decline. These observations reinforce the importance of using free water elimination when studying brain aging and indicate that free water itself could be a relevant marker for age-related cingulum white matter modifications and cognitive decline.

Differences between young and older adults in unity and diversity of executive functions

Miyake and colleagues (2000) identified three independent but correlated components of executive function in young adults - set shifting, inhibition, and updating. The present study compared the factor structure in young adults to two groups of older adults (ages 60-73 and 74-98). A three-factor model of shifting, inhibition and updating was confirmed in young adults, but the factors were weakly or uncorrelated. In both older groups, a two-factor solution was indicated, updating/inhibition and shifting, which were moderately correlated in young-older adults, and strongly correlated in the old-older group. A nested factors model in the oldest group revealed a common factor, which loaded on all but one of the tests, and a shifting-specific factor. We concluded that in young adulthood, shifting, updating and inhibition may operate relatively independently. As people age and processing becomes less efficient, they may rely increasingly on general executive control processes, reallocating their limited resources to optimize performance.

The effect of cardiorespiratory fitness and physical activity levels on cognitive functions in survivors of childhood acute lymphoblastic leukemia

Introduction. Most childhood acute lymphoblastic leukemia (ALL) survivors develop chronic treatment-related adverse effects several years after the end of the treatment. Regular physical activity and a good cardiorespiratory fitness can decrease the risks of neurological disturbances and increase cognitive function scores. The aim of this study was to examine the effect of good cardiorespiratory fitness and physical activity levels on cognitive functions.Methods. We enrolled 219 survivors of childhood ALL. The participants underwent a cardiopulmonary exercise test, neuropsychological tests of executive functions (i.e. verbal fluency, cognitive flexibility, working memory, processing speed) and completed a physical activity questionnaire. We calculated the odds ratio to obtain the preventive fraction of physical activity and cardiorespiratory fitness levels on cognitive functions.Results. The cohort is 52% male and 48% female. A total of 182 survivors (83%) have a cardiorespiratory fitness below their predicted (<100%). Our analyses show that there is an association between good cardiorespiratory fitness and processing speed (preventive fraction of 70% for dominant hand (p < 0.01) and 65% for non-dominant hand (p < 0.01)) and with cognitive flexibility identified as the category switching measure of the D-KEFS verbal fluency (preventive fraction of 61%; p < 0.05).Conclusion. Good cardiorespiratory fitness and good levels of physical activity were associated to a preventive fraction for most cognitive function parameters measured. Good cardiorespiratory fitness levels were significantly associated with a lower prevalence of deficits in processing speed (i.e., dominant hand and non-dominant hand) and in cognitive flexibility (i.e., category switching) in childhood acute lymphoblastic leukemia survivors.

Organisation of cingulum bundle fibres connecting the anterior thalamic nuclei with the rodent anterior cingulate and retrosplenial cortices

Despite considerable interest in the properties of the cingulum bundle, descriptions of the composition of this major pathway in the rodent brain have not kept pace with advances in tract tracing. Using complementary approaches in rats and mice, this study examined the dense, reciprocal connections the anterior thalamic nuclei have with the cingulate and retrosplenial cortices, connections thought to be major contributors to the rodent cingulum bundle. The rat data came from a mixture of fluorescent and viral tracers, some injected directly into the bundle. The mouse data were collated from the Allen Mouse Brain Atlas. The projections from the three major anterior thalamic nuclei occupied much of the external medullary stratum of the cingulum bundle, where they were concentrated in its more medial portions. These anterior thalamic projections formed a rostral-reaching basket of efferents prior to joining the cingulum bundle, with anteromedial efferents taking the most rostral routes, often reaching the genu of the corpus callosum, while anterodorsal efferents took the least rostral route. In contrast, the return cortico-anterior thalamic projections frequently crossed directly through the bundle or briefly joined the internal stratum of the cingulum bundle, often entering the internal capsule before reaching the anterior thalamus. These analyses confirm that anterior thalamic connections comprise an important component of the rodent cingulum bundle, while also demonstrating the very different routes used by thalamo-cortical and cortico-thalamic projections. This information reveals how the composition of the cingulum bundle alters along its length.

Network-behavior mapping of lasting executive impairments after low-grade glioma surgery

Executive functions (EF) may be significantly impaired following low-grade glioma (LGG) surgery, especially in the event of white matter (WM) disruption. The aim of this study was to identify the connective tracts associated with EF impairments after LGG surgery, and to provide new insights into the WM network architecture of EF. EF measurements were collected in 270 patients at the chronic postoperative phase. This comprised cognitive flexibility, verbal inhibition and fluency abilities (phonological and categorical). The scores were z-corrected for age and educational level, and further submitted to a principal component analysis (PCA). Tracwise and disconnectome-behavior analyses were then performed using EF measures independently but also the extracted components from PCA. For the first analyses, 15 tracts of interest were selected. Two principal components were extracted from the behavioral data, interpreted as 'EF' and 'language' components. Robust, bonferroni-corrected correlations were established between the EF component and Layers II and III of the left superior longitudinal fasciculus, and between phonological fluency/inhibition and the same tracts. Less powerful but still significant correlations were also observed with the left frontal aslant and fronto-striatal tracts. These results were confirmed by disconnectome-behavior analyses. Our results indicate that surgically-related disruption of the fronto-parietal and the frontal cortico-subcortical connectivity, and of the frontal aslant tract, is related to long-lasting EF impairments. In addition to providing new insights into the WM pathways supporting EF, these findings are especially useful for both surgical planning and the predictive approach of neuropsychological disorders in the context of LGG surgery.

Impact of cognitive reserve on clinical and neuropsychological measures in patients with mild cognitive impairment

OBJECTIVE

Cognitive reserve influences age of onset, speed of progression, and clinical manifestations of Alzheimer's disease. We investigated whether cognitive reserve interacts with clinical and neuropsychological parameters in mild cognitive impairment (MCI).

METHODS

In this cross-sectional study, we recruited 273 people (70.6 ± 10.1 years, 54.6% women) suffering from subjective memory complaints (n = 65), MCI (n = 121), or dementia (n = 87). Patients underwent neuropsychological evaluation, laboratory testing, and brain imaging. Additionally, we obtained information on years of education and help-seeking motivation.

RESULTS

MCI patients with a university degree were significantly older than those without (71.6 ± 9.6 vs. 66.9 ± 10.3, p = 0.02). University-educated MCI patients demonstrated superior performance in verbal fluency. Intrinsic help-seeking motivation (self-referral) was associated with higher cognitive reserve. Female MCI patients presented with greater intrinsic motivation.

CONCLUSION

Cognitive reserve modulates clinical and neuropsychological measures in patients with MCI.

Executive functioning and spatial processing in anorexia nervosa: an experimental study and its significance for the allocentric lock theory

PURPOSE

The allocentric lock theory (ALT) suggests that people with eating disorders have difficulties in multisensory integration in two reference frames-egocentric and allocentric, whereby the egocentric, but not allocentric, is impaired. This leads to a distorted body image that contributes to the development and maintenance of the disorder. The current study aimed to explore a facet of the ALT, namely, the visuo-spatial aspect, and its relation to cognitive flexibility in patients with anorexia nervosa (AN).

METHODS

Fifty-five participants took part in the study: 20 AN patients and 35 controls, matched by age and education. The object perspective taking test (OPTT) and the mental rotation test (MRT), tapping egocentric and allocentric representations, respectively, and a set-shifting task were administered. The brief symptom inventory was used to measure overall levels of distress.

RESULTS

AN patients showed higher level of distress. They performed poorer on the OPTT and set-shifting task but not on the MRT. The OPTT and MRT were correlated for controls but not for AN patients, while the set-shifting task and body mass index were associated with the OPTT but not with the MRT for the AN patients.

CONCLUSIONS

The findings support the ALT by demonstrating impaired visual egocentric representations and intact allocentric visual functions in AN patients, with cognitive flexibility associated only with the egocentric frame. Therefore, egocentric frame impairment in AN patients may be influenced by visual perception and cognitive flexibility deficiency.

LEVEL OF EVIDENCE

Level III: case-control analytic study.

White matter injury and neurodevelopmental disabilities: A cross-disease (dis)connection

White matter (WM) injury, once known primarily in preterm newborns, is emerging in its non-focal (diffused), non-necrotic form as a critical component of subtle brain injuries in many early-life diseases like prematurity, intrauterine growth restriction, congenital heart defects, and hypoxic-ischemic encephalopathy. While advances in medical techniques have reduced the number of severe outcomes, the incidence of tardive impairments in complex cognitive functions or psychopathology remains high, with lifelong detrimental effects. The importance of WM in coordinating neuronal assemblies firing and neural groups synchronizing within multiple frequency bands through myelination, even mild alterations in WM structure, may interfere with the cognitive performance that increasing social and learning demands would exploit tardively during children growth. This phenomenon may contribute to explaining longitudinally the high incidence of late-appearing impairments that affect children with a history of perinatal insults. Furthermore, WM abnormalities have been highlighted in several neuropsychiatric disorders, such as autism and schizophrenia. In this review, we gather and organize evidence on how diffused WM injuries contribute to neurodevelopmental disorders through different perinatal diseases and insults. An insight into a possible common, cross-disease, mechanism, neuroimaging and monitoring, biomarkers, and neuroprotective strategies will also be presented.

The human cingulum: From the limbic tract to the connectionist paradigm

The cingulum is a core component of the limbic lobe and part of the circuit that was described by Papez where environmental experiences become endowed with emotional awareness. Recent techniques for the study of cerebral connectivity have updated this fasciculus' morphology and led to the acknowledgment that its involvement in superior functions goes far beyond emotion processing. Long and robust, the cingulum is a long association fasciculus with terminations in all cerebral lobes. These observations plead for a pivotal rethinking of its role in the human brain and lead to the conclusion that to merely consider it as the main fasciculus of the limbic system was actually a reductionism. This paper summarizes the key facts regarding why the cingulum is now perceived as a primary interconnecting apparatus in the medial aspect of the cerebral hemisphere.

Cingulum and abnormal psychological stress response in schizophrenia

Stress is implicated in many aspects of schizophrenia, including heightened distress intolerance. We examined how affect and microstructure of major brain tracts involved in regulating affect may contribute to distress intolerance in schizophrenia. Patients with schizophrenia spectrum disorders (n = 78) and community controls (n = 95) completed diffusion weighted imaging and performed psychological stress tasks. Subjective affect was collected pre and post stressors. Individuals who did not persist during one or both stress tasks were considered distress intolerant (DI), and otherwise distress tolerant (DT). Fractional anisotropy (FA) of the dorsal cingulum showed a significant diagnosis x DT/DI phenotype interaction (p = 0.003). Post-hoc tests showed dorsal cingulum FA was significantly lower in DI patients compared with DI controls (p < 0.001), but not different between DT groups (p = 0.27). Regarding affect responses to stress, irritability showed the largest stress-related change (p < 0.001), but irritability changes were significantly reduced in DI patients compared to DI controls (p = 0.006). The relationship between irritability change and performance errors also differed among patients (ρ = -0.29, p = 0.011) and controls (ρ = 0.21, p = 0.042). Further modeling highlighted the explanatory power of dorsal cingulum for predicting DI even after performance and irritability were taken into account. Distress intolerance during psychological stress exposure is related to microstructural properties of the dorsal cingulum, a key structure for cognitive control and emotion regulation. In schizophrenia, the affective response to psychological stressors is abnormal, and distress intolerant patients had significantly reduced dorsal cingulum FA compared to distress intolerant controls. The findings provide new insight regarding distress intolerance in schizophrenia.

Conscientiousness mediates the link between brain structure and consideration of future consequence

The individual difference in valuing immediate and future outcomes is referred to as consideration of future consequences (CFC, including CFC-Future [CFC-F] and CFC-Immediate [CFC-I]), which significantly influences daily behaviour. Although CFC is believed to be affected by brain features and personalities, the relational model of brain correlates, personalities and CFC has yet to be determined. This study was designed to explore the brain structure related to CFC-F and CFC-I and the mediating role of conscientiousness. We adopted a voxel-based morphometry study and used grey matter density (GMD) as an indication of brain structure. The results showed that GMD in the ventromedial prefrontal cortex (VMPFC) was positively associated with CFC-F; however, we did not find relevant regions affecting CFC-I. Furthermore, conscientiousness was found to mediate the relationship between GMD in the VMPFC and CFC-F. This study provides initial evidence concerning the neural basis of CFC-F and argues that the features of brain structure could be associated with CFC-F through related high-order personality traits. Additionally, the distinction between CFC-F and CFC-I may be based on differences in brain structure.

Potential Benefits of Physical Activity in MCI and Dementia

Physical activity improves overall health and reduces the risk of many negative health outcomes and may be effective in improving cognition, independent functioning, and psychological health in older adults. Given the evidence linking physical activity with improvements in various aspects of health and functioning, interventions exploring pathways for decreasing risk of dementia in those with mild cognitive impairment (MCI) and improving outcomes for those with dementia are of critical importance. The present review highlights the work examining physical activity interventions in order to achieve a comprehensive understanding of the potential benefits of physical activity for individuals experiencing cognitive decline. The primary focus is on aerobic exercise as this is the main intervention in the literature. Our review supports the thesis that physical activity can promote healthy aging in terms of cognition, independent functioning, and psychological health for individuals experiencing cognitive decline. Specifically, physical activity improves cognition, especially executive functioning and memory in MCI, independent functioning in MCI and dementia, and psychological health in dementia. Given that benefits of physical activity have been observed across these domains, such interventions provide an avenue for preventing decline and/or mitigating impairment across several domains of functioning in older adults with MCI or dementia and may be recommended (and adjusted) for patients across a range of settings, including medical and mental health settings. Further implications for clinical intervention and future directions for research are discussed.

Maternal reading and fluency abilities are associated with diffusion properties of ventral and dorsal white matter tracts in their preschool-age children

Early language exposure and shared parent-child reading, as assessed by maternal reading ability and fluency, affect the child's future language and cognitive abilities. The aim of the current study was to explore the association between maternal reading ability and fluency and diffusion properties of language- and cognition-related white matter tracts in their pre-school age children using diffusion tensor imaging (DTI). DTI data were acquired from fifteen girls (mean age: 3.83 ± 0.49 years). Reading ability and fluency were assessed in their mothers. Effects of hemisphere and node on diffusion properties were measured at 100 points along white matter tracts related to language and cognitive abilities. Significant positive correlations were found between maternal reading ability and fractional anisotropy in left and right dorsal and ventral language and executive functions-related tracts, while maternal reading fluency was associated with higher fractional anisotropy in ventral tracts, mainly in the left hemisphere. Fractional Anisotropy was significantly higher in the left compared to the right arcuate, cingulum cingulate, and inferior longitudinal fasciculus and higher in the right compared to the left superior longitudinal fasciculus. Our results signify the importance of maternal reading as a facilitator of the child's future language and cognitive abilities.

Fluency and rule breaking behaviour in the frontal cortex

Design (DF) and phonemic fluency tests (FAS; D-KEFS, 2001) are commonly used to investigate voluntary generation. Despite this, several important issues remain poorly investigated. In a sizeable sample of patients with focal left or right frontal lesion we established that voluntary generation performance cannot be accounted for by fluid intelligence. For DF we found patients performed significantly worse than healthy controls (HC) only on the switch condition. However, no significant difference between left and right frontal patients was found. In contrast, left frontal patients were significantly impaired when compared with HC and right frontal patients on FAS. These lateralization findings were complemented, for the first time, by three neuroimaging; investigations. A traditional frontal subgrouping method found significant differences on FAS between patients with or without Left Inferior Frontal Gyrus lesions involving BA 44 and/or 45. Parcel Based Lesion Symptom Mapping (PLSM) found lower scores on FAS were significantly associated with damage to posterior Left Middle Frontal Gyrus. An increase in rule break errors, so far only anecdotally reported, was associated with damage to the left dorsal anterior cingulate and left body of the corpus callosum, supporting the idea that conflict resolution and monitoring impairments may play a role. Tractwise statistical analysis (TSA) revealed that patients with disconnection; in the left anterior thalamic projections, frontal aslant tract, frontal; orbitopolar tract, pons, superior longitudinal fasciculus I and II performed significantly worse than patients without disconnection in these tracts on FAS. In contrast, PLSM and TSA analyses did not reveal any significant relationship between lesion location and performance on the DF switch condition. Overall, these findings suggest DF may have limited utility as a tool in detecting lateralized frontal executive dysfunction, whereas FAS and rule break behavior appears to be linked to a set of well localized left frontal grey matter regions and white matter tracts.

Reinforcer Pathology: Implications for Substance Abuse Intervention

The rate at which individuals discount future rewards (i.e., discounting rate) is strongly associated with their propensity for substance abuse as well as myriad other negative health behaviors. An excessive preference for immediately available rewards suggests a shortened time horizon in which immediate rewards are overvalued and future, potentially negative consequences are undervalued. This review outlines Reinforcer Pathology Theory (i.e., the interaction between excessive preference for immediately available rewards and the overvaluation of a particular commodity that offers brief, intense reinforcement), its neurobiological/behavioral underpinnings, and its implications for treating substance use disorders. In doing so, the current review provides an overview of a variety of ways in which interventions have been used to manipulate aspects of reinforcer pathology in an individual, including narrative theory, framing manipulations, and neuromodulation (e.g., working memory training, TMS) which may serve as promising avenues for the modulation of the temporal window and/or valuation of reinforcers.

Structural core of the executive control network: A high angular resolution diffusion MRI study

Executive function (EF) is a set of cognitive capabilities considered essential for successful daily living, and is negatively affected by ageing and neurodegenerative conditions. Underpinning EF performance are functional nodes in the executive control network (ECN), while the structural connectivity underlying this network is not well understood. In this paper, we evaluated the structural white matter tracts that interconnect the ECN and investigated their relationship to the EF performance. Using high‐angular resolution diffusion MRI data, we performed tractography analysis of structural connectivity in a cognitively normal cohort (n = 140), specifically targeting the connectivity between ECN nodes. Our data revealed the presence of a strongly‐connected “structural core” of the ECN comprising three components: interhemispheric frontal connections, a fronto‐parietal subnetwork and fronto‐striatal connections between right dorsolateral prefrontal cortex and right caudate. These pathways were strongly correlated with EF performance (p = .003). Post‐hoc analysis of subregions within the significant ECN connections showed that these effects were driven by a highly specific subset of interconnected cortical regions. The structural core subnetwork of the functional ECN may be an important feature crucial to a better future understanding of human cognition and behaviour.

Developing and Validating a Big-Store Multiple Errands Test

The Multiple Errands Test (MET) is an ecologically valid assessment that characterizes how executive dysfunction manifests in everyday activities. Due to the naturalistic nature of this assessment, clinicians and researchers have had to develop site-specific versions resulting in numerous published versions and making it difficult to establish standard psychometric properties. The aim of this study was to develop a standardized, community version of the MET designed to be used in large department stores meeting set criteria that would not require site specific modifications. This paper reports on the development, content validity, feasibility, and inter-rater reliability of a Big-Store MET, and the performance of healthy participants on this test. Items were selected to match previously published versions in relation to quantity and complexity. Content validity was established by having experts (n = 4) on the MET review the proposed Big-Store version and evaluate the task consistency with previously published versions. To assess feasibility of administration, and inter-rater reliability, a convenience sample of 14 community dwelling adults, self-reporting as healthy, were assessed by two trained raters. We found the Big-Store MET to be feasible to deliver (completed within 30 min, scores show variability, acceptable to participants in community environment) and inter-rater reliability to be very high (ICCs = 0.92-0.99) with the exception of frequency of strategy use. This study introduces the Big-Store MET to the literature, establishes its preliminary validity and reliability thus laying the foundation for a standardized, community-based version of the MET.

Inhibition impairment in frontotemporal dementia, amyotrophic lateral sclerosis, and Alzheimer's disease: clinical assessment and metabolic correlates

The ability to reject an automatic tendency, i.e. inhibition, has been linked to the prefrontal cortex, but its neural underpinnings are still controversial. Neurodegenerative diseases represent an interesting model to explore this issue, given its frequent impairment in these disorders. We investigated the inhibitory impairment and its neural basis using four different tests, which evaluate the presence of inhibitory dysfunction (Stroop test, Hayling test, and two graphical perseveration tests), and assessed their correlation with brain metabolism using ¹⁸F-fluorodeoxyglucose positron emission tomography in a group of 76 participants with behavioral variant frontotemporal dementia (bvFTD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS) and healthy controls (HC). Inhibition impairment was more frequent in bvFTD and AD, than ALS and HC. AD and bvFTD only differed in the strategy used in Hayling test, and the frequency of impairment in graphical perseveration tests. Correlation between inhibition tests was moderate. The Stroop test correlated with several regions of the frontal and parietal lobes, mainly on the left side. Hayling test correlated with almost all regions of the frontal lobe and, especially, with the orbitofrontal cortex. Some differences in the impaired regions in each disease were found. Inhibition ability was mainly impaired in bvFTD and AD, and it correlated with the bilateral frontal lobe metabolism. There were certain particularities according to the specific task and patients evaluated. These dissimilarities may support the concept of inhibition as a multidimensional construct, with the involvement of common and divergent neural mechanisms.

Cognitive correlates of α4β2 nicotinic acetylcholine receptors in mild Alzheimer's dementia

In early Alzheimer's dementia, there is a need for PET biomarkers of disease progression with close associations to cognitive dysfunction that may aid to predict further cognitive decline and neurodegeneration. Amyloid biomarkers are not suitable for that purpose. The α4β2 nicotinic acetylcholine receptors (α4β2-nAChRs) are widely abundant in the human brain. As neuromodulators they play an important role in cognitive functions such as attention, learning and memory. Post-mortem studies reported lower expression of α4β2-nAChRs in more advanced Alzheimer's dementia. However, there is ongoing controversy whether α4β2-nAChRs are reduced in early Alzheimer's dementia. Therefore, using the recently developed α4β2-nAChR-specific radioligand (-)-18F-flubatine and PET, we aimed to quantify the α4β2-nAChR availability and its relationship to specific cognitive dysfunction in mild Alzheimer's dementia. Fourteen non-smoking patients with mild Alzheimer's dementia, drug-naïve for cholinesterase therapy, were compared with 15 non-smoking healthy controls matched for age, sex and education by applying (-)-18F-flubatine PET together with a neuropsychological test battery. The one-tissue compartment model and Logan plot method with arterial input function were used for kinetic analysis to obtain the total distribution volume (VT) as the primary, and the specific binding part of the distribution volume (VS) as the secondary quantitative outcome measure of α4β2-nAChR availability. VS was determined by using a pseudo-reference region. Correlations between VT within relevant brain regions and Z-scores of five cognitive functions (episodic memory, executive function/working memory, attention, language, visuospatial function) were calculated. VT (and VS) were applied for between-group comparisons. Volume of interest and statistical parametric mapping analyses were carried out. Analyses revealed that in patients with mild Alzheimer's dementia compared to healthy controls, there was significantly lower VT, especially within the hippocampus, fronto-temporal cortices, and basal forebrain, which was similar to comparisons of VS. VT decline in Alzheimer's dementia was associated with distinct domains of impaired cognitive functioning, especially episodic memory and executive function/working memory. Using (-)-18F-flubatine PET in patients with mild Alzheimer's dementia, we show for the first time a cholinergic α4β2-nAChR deficiency mainly present within the basal forebrain-cortical and septohippocampal cholinergic projections and a relationship between lower α4β2-nAChR availability and impairment of distinct cognitive domains, notably episodic memory and executive function/working memory. This shows the potential of (-)-18F-flubatine as PET biomarker of cholinergic α4β2-nAChR dysfunction and specific cognitive decline. Thus, if validated by longitudinal PET studies, (-)-18F-flubatine might become a PET biomarker of progression of neurodegeneration in Alzheimer's dementia.

Age-related differences in the structural and effective connectivity of cognitive control: a combined fMRI and DTI study of mental arithmetic

Cognitive changes with aging are highly variable across individuals. This study investigated whether cognitive control performance might depend on preservation of structural and effective connectivity in older individuals. Specifically, we tested inhibition following working memory (WM) updating and maintenance. We analyzed diffusion tensor imaging and functional magnetic resonance imaging data in thirty-four young adults and thirty-four older adults, who performed an arithmetic verification task during functional magnetic resonance imaging. Results revealed larger arithmetic interference in older adults relative to young adults after WM updating, whereas both groups showed similar interference after WM maintenance. In both groups, arithmetic interference was associated with larger activations and stronger effective connectivity among bilateral anterior cingulate, bilateral inferior frontal gyrus, and left angular gyrus, with larger activations of frontal regions in older adults than in younger adults. In older adults, preservation of frontoparietal structural microstructure, especially involving the inferior frontaloccipital fasciculus, was associated with reduced interference, and stronger task-related effective connectivity. These results highlight how both structural and functional changes in the cognitive control network contribute to individual variability in performance during aging.