Interactive effects of APOE and CHRNA4 on attention and white matter volume in healthy middle-aged and older adults

The Contribution of Genetic Factors to Cognitive Impairment and Dementia: Apolipoprotein E Gene, Gene Interactions, and Polygenic Risk

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Although it has been studied for years, the pathogenesis of AD is still controversial. Genetic factors may play an important role in pathogenesis, with the apolipoprotein E (APOE) gene among the greatest risk factors for AD. In this review, we focus on the influence of genetic factors, including the APOE gene, the interaction between APOE and other genes, and the polygenic risk factors for cognitive function and dementia. The presence of the APOE ε4 allele is associated with increased AD risk and reduced age of AD onset. Accelerated cognitive decline and abnormal internal environment, structure, and function of the brain were also found in ε4 carriers. The effect of the APOE promoter on cognition and the brain was confirmed by some studies, but further investigation is still needed. We also describe the effects of the associations between APOE and other genetic risk factors on cognition and the brain that exhibit a complex gene⁻gene interaction, and we consider the importance of using a polygenic risk score to investigate the association between genetic variance and phenotype.

Healthy Aging and Dementia: Two Roads Diverging in Midlife?

Dementia, particularly Alzheimer’s disease (AD), is a growing pandemic that presents profound challenges to healthcare systems, families, and societies throughout the world. By 2050, the number of people living with dementia worldwide could almost triple, from 47 to 132 million, with associated costs rising to $3 trillion. To reduce the future incidence of dementia, there is an immediate need for interventions that target the disease process from its earliest stages. Research programs are increasingly starting to focus on midlife as a critical period for the beginning of AD-related pathology, yet the indicators of the incipient disease process in asymptomatic individuals remain poorly understood. We address this important knowledge gap by examining evidence for cognitive and structural brain changes that may differentiate, from midlife, healthy aging and pathological AD-related processes. This review crystallizes emerging trends for divergence between the two and highlights current limitations and opportunities for future research in this area.

RT Slowing to Valid Cues on a Reflexive Attention Task in Children and Young Adults

Peripheral cueing tasks can be used to measure reflexive (automatic) attention. In these tasks, increases in response time or RT (costs) typically follow contralateral (invalid) cues as attention must move from the location of the cue to the target. Reductions in RT (benefits) to a target typically follow ipsilateral (valid) cues because the cue draws attention to where the target will appear. Two exceptions to RT benefits are inhibition of return (IOR) and masking. IOR is the tendency to respond slower to targets that appear in locations attended within the last 200–2000 ms. Masking occurs when the visibility of a target is blocked by another stimulus (e.g., the cue). Herein, we describe two experiments, both using a modified Posner task with “earth rockets” as cues and “alien spaceships” as targets. Cues were equally likely to appear on the left or right side of a display following targets. Participants were instructed to press a left or right key corresponding to a left or right target. In Experiment 1, we obtained data from 203 children (10.58–16.55 years old). We discovered unexpected costs following cues that typically provide RT benefits. In Experiment 2, we explored IOR, masking, and age differences in the occurrence of these costs. We manipulated the cue-target temporal distance (“stimulus onset asynchrony” or SOA) to explore IOR and the cue-target spatial distance to explore masking. We also considered a wider age range. Sixty-three children and 41 young adults participated. Experiment 2 revealed a three-way interaction between SOA, spatial distance, and age. At the shorter SOA (100 ms) and moderate spatial distance, unexpected costs followed valid cues for younger children (7.07–10.15 years old). These costs also occurred in young adults (18.00–23.02 years old) following far distance cues at this SOA. At the longer SOA (200 ms), these costs followed moderate and far cues for younger children and near cues for young adults. Older children (10.31–14.92 years) did not have unexpected costs. We explain the findings in terms of masking, IOR, and possible developmental mechanisms.

Putting attention in the spotlight: The influence of APOE genotype on visual search in mid adulthood

The Apolipoprotein E e4 allele is associated with greater cognitive decline with age, yet effects of this gene are also observed earlier in the lifespan. This research explores genotype differences (e2, e3, e4) in the allocation of visuospatial attention in mid-adulthood. Sixty-six volunteers, aged 45-55 years, completed two paradigms probing the active selection of information at the focus of attention (a dynamic scaling task) and perceptual capacity differences. Two methods of statistical comparison (parametric statistics, Bayesian inference) found no significant difference between e4 carriers and the homozygous e3 group on either the dynamic scaling or perceptual load task. E2 carriers, however, demonstrated less efficient visual search performance on the dynamic scaling task. The lack of an e4 difference in visuospatial attention, despite previous suggestion in the literature of genotype effects, indicates that select attentional processes are intact in e4 carriers in mid-adulthood. The association of e2 genotype with slower visual search performance complicates the premised protective effects of this allele in cognitive ageing.

The influence of CHRNA4, COMT, and maternal sensitivity on orienting and executive attention in 6-month-old infants

Despite claims concerning biological mechanisms sub-serving infant attention, little experimental work examines its underpinnings. This study examines how candidate polymorphisms from the cholinergic (CHRNA4 rs1044396) and dopaminergic (COMT rs4680) systems, respectively indicative of parietal and prefrontal/anterior cingulate involvement, are related to 6-month-olds' (n=217) performance during a visual expectation eye-tracking paradigm. As previous studies suggest that both cholinergic and dopaminergic genes may influence susceptibility to the influence of other genetic and environmental factors, we further examined whether these candidate genes interact with one another and/or with early caregiving experience in predicting infants' visual attention. We detected an interaction between CHRNA4 genotype and observed maternal sensitivity upon infants' orienting to random stimuli and a CHRNA4-COMT interaction effect upon infants' orienting to patterned stimuli. Consistent with adult research, we observed a direct effect of COMT genotype on anticipatory looking to patterned stimuli. Findings suggest that CHRNA4 genotype may influence susceptibility to other attention-related factors in infancy. These interactions may account for the inability to establish a link between CHRNA4 and orienting in infant research to date, despite developmental theorizing suggesting otherwise. Moreover, findings suggest that by 6months, dopamine, and relatedly, the prefrontal cortex/anterior cingulate, may be important to infant attention.

Structural and resting-state MRI detects regional brain differences in young and mid-age healthy APOE-e4 carriers compared with non-APOE-e4 carriers

The presence of the e4 allele of the apolipoprotein E (APOE) gene is the best-known genetic risk factor for Alzheimer's disease. In this study, we investigated the link between functional and behavioural differences and regional brain volume and cortical thickness differences in those who carry the e4 allele (e4+) and those who only carry the e3 allele (e3/e3). We studied these genotype populations in two age groups: a young group (average age, 21 years) and a mid-age group (average age, 50 years). High-resolution T1 -weighted MRI scans were analysed with Freesurfer to measure regional white matter brain volume and cortical thickness differences between genotype groups at each age. These data were correlated with behavioural findings in the same cohort. Resting-state MRI was also conducted to identify differences in underlying brain functional connectivity. We found that there was a positive correlation between the thickness of the parahippocampal cortex in young e4+ individuals and performance on an episodic memory task. Young e4+ individuals also showed a positive correlation between white matter volume in the left anterior cingulate and performance on a covert attention task. At mid-age, e4+ individuals had structural differences relative to e3/e3 individuals in these areas: the parahippocampal cortex was thicker and white matter volume in the left anterior cingulate was greater than in e3/e3 individuals. We discuss the possibility that an over-engagement with these regions by e4+ individuals in youth may have a neurogenic effect that is observable later in life. The cuneus appears to be an important region for APOE-driven differences in the brain, with greater functional connectivity among young e3/e3 individuals and greater white matter volume in young e4+ individuals.

Genetic contributions to attentional response time slopes across repeated trials

Background

Attention provides vital contribution to everyday functioning, and deficits in attention feature in many psychological disorders. Improved understanding of attention may eventually be critical to early identification and treatment of attentional deficits. One step in that direction is to acquire a better understanding of genetic associations with performance on a task measuring reflexive (exogenous) visual attention. Reflexive attention is an important component of overall attention because (along with voluntary selective attention) it participates in determining where attention is allocated and how susceptible to distractors the subject might be. The task that we used involves the presentation of a target that is preceded by one of several different types of cues (none, double, or single, either ipsilateral or contralateral to where the target subsequently appears). We used several different outcome measures depending on the cue presented. We have previously studied the relationship between selected genes and mean response time (RT). Here we report on the contributions of genetic markers to RT increases or decreases over the course of the task (linear trend in RT slope).

Results

Specifically, we find that RT slope for a variety of reflexive attention outcome measures is dependent on DAT1 genotype. DRD4 was near significant for one outcome measure in the final (best) model. APOE, COMT, and DBH were not significant in any models.

Conclusions

It is especially interesting that genotype predicts linear changes in RT across trials (and not just mean differences or moment-to-moment variability). DAT1 is a gene that produces a protein involved in the transport of dopamine from the synapse. To our knowledge, this is the first study that has associated neurotransmitter genotypes with RT slope on a reflexive attention experiment. The direction of these effects is consistent with genetic risk for attention deficit hyperactivity disorder (ADHD). That is, those with two risk alleles for ADHD (6R/6R on the DAT1 intron 8 VNTR) either got slower as the task progressed or had the least improvement. Those with no risk alleles (5R/5R) had the most improvement in RT as the task progressed.

Longitudinal change in working memory as a function of APOE genotype in midlife and old age

Previous investigations into whether the APOE-ε4 allele exerts cognitive effects at midlife have been inconclusive. We have advanced a "cognitive phenotype" hypothesis arguing that the ε4 allele of the apolipoprotein E gene (APOE) is associated with lower efficiency of neuronal plasticity thereby resulting in poorer cognitive performance independently of the pathology of Alzheimer's disease (Greenwood et al., ). This hypothesis is best tested at midlife, prior to the neuron loss associated with AD diagnosis. This hypothesis predicts that the ε4 allele would alter cognition regardless of age through plasticity mechanisms, but would not induce longitudinal decline in midlife. The alternative "prodrome" hypothesis predicts that the APOE-ε4 allele would be associated with longitudinal cognitive decline as early as midlife due to prodromal effects of AD. We tested these hypotheses with a working memory task in a large cross-sectional sample of cognitively screened APOE-ε4 carriers and non-carriers and also in a small longitudinal sample over 3 years. The sample was divided into middle-aged (mean age 50, range 40-59) and older (mean age 69, range 60-84) individuals. Cross-sectionally, we observed that older, but not middle-aged, APOE-ε4 carriers had lower accuracy than ε4 non-carriers, mainly under the hardest discrimination condition. Longitudinally, we observed increases in accuracy in middle-aged APOE-ε4 carriers, suggesting a cognitive phenotype that includes ability to benefit from experience. We observed a longitudinal decrease in older APOE-ε4 carriers, suggesting an AD prodrome.

A draft network of ligand-receptor-mediated multicellular signalling in human

Cell-to-cell communication across multiple cell types and tissues strictly governs proper functioning of metazoans and extensively relies on interactions between secreted ligands and cell-surface receptors. Herein, we present the first large-scale map of cell-to-cell communication between 144 human primary cell types. We reveal that most cells express tens to hundreds of ligands and receptors to create a highly connected signalling network through multiple ligand-receptor paths. We also observe extensive autocrine signalling with approximately two-thirds of partners possibly interacting on the same cell type. We find that plasma membrane and secreted proteins have the highest cell-type specificity, they are evolutionarily younger than intracellular proteins, and that most receptors had evolved before their ligands. We provide an online tool to interactively query and visualize our networks and demonstrate how this tool can reveal novel cell-to-cell interactions with the prediction that mast cells signal to monoblastic lineages via the CSF1-CSF1R interacting pair.

Subtle visuomotor difficulties in preclinical Alzheimer's disease

BACKGROUND

Individuals with preclinical Alzheimer's disease (Pre-AD) present nonimpaired cognition, as measured by standard neuropsychological tests. However, detecting subtle difficulties in cognitive functions may be necessary for an early diagnosis and intervention.

OBJECTIVES

A new computer-based visuomotor coordination task (VMC) was developed to investigate the possible presence of early visuomotor difficulties in Pre-AD individuals. Associations between VMC task performance and AD biomarkers were studied. The influence of ApoE status on participants' performance was addressed, as well as the relationship between performance and subjective cognitive decline (SCD).

METHODS

Sixty-six cognitively normal (CN) elders (19 Pre-AD and 47 control participants [CTR]) and 15 patients with AD performed the VMC task, which consisted in executing visually guided goal-directed movements that required the coordination of the visual and motor systems. All participants underwent ApoE analysis and lumbar puncture. CN participants also completed an extensive standard neuropsychological battery.

RESULTS

Despite presenting normal cognition in standard tests, Pre-AD participants exhibited higher response times (RTs) to complete the VMC task than CTR (p < .01). Besides, patients with AD showed higher RTs than CTR (p < .001) and Pre-AD (p < .05), and more errors than CTR (p < .005). RTs in ApoE4 carriers were higher than that observed in ApoE4 noncarriers (p < .01). In CN individuals, RTs were related to amyloid β-protein 42 (AB42) biomarker (p < .01) and informant-rated SCD (p < .01).

CONCLUSIONS

The VMC task is able to discriminate Pre-AD from CTR individuals. Moreover, VMC results are associated with AB42 levels in CN individuals, suggesting that visuomotor dysfunction may be a sensitive marker of Pre-AD.

Individual response speed is modulated by variants of the gene encoding the alpha 4 sub-unit of the nicotinic acetylcholine receptor (CHRNA4)

Acetylcholine (ACh) is a known modulator of several domains of cognition, among them attention, memory and learning. The neurotransmitter also influences the speed of information processing, particularly the detection of targets and the selection of suitable responses. We examined the effect of the rs1044396 (C/T) polymorphism of the gene encoding the nicotinic acetylcholine receptor α4-subunit (CHRNA4) on response speed and selective visual attention. To this end, we administered a Stroop task, a Negative priming task and an exogenous Posner-Cuing task to healthy participants (n = 157). We found that the CHRNA4 rs1044396 polymorphism modulated the average reaction times (RTs) across all three tasks. Dependent on the C allele dosage, the RTs linearly increased. Homozygous T allele carriers were always fastest, while homozygous C allele carriers were always slowest. We did not observe effects of this polymorphism on selective attention. In sum, we conclude that naturally occurring variations within the cholinergic system influence an important factor of information processing. This effect might possibly be produced by the neuromodulator system rather than the deterministic system of cortical ACh.

TVA-based assessment of attentional capacities-associations with age and indices of brain white matter microstructure

In this study the primary aims were to characterize the effects of age on basic components of visual attention derived from assessments based on a theory of visual attention (TVA) in 325 healthy volunteers covering the adult lifespan (19-81 years). Furthermore, we aimed to investigate how age-related differences on TVA parameters are associated with white matter (WM) microstructure as indexed by diffusion tensor imaging (DTI). Finally, we explored how TVA parameter estimates were associated with complex, or multicomponent indices of processing speed (Digit-symbol substitution, DSS) and fluid intelligence (gF). The results indicated that the TVA parameters for visual short-term memory capacity, K, and for attentional selectivity, α, were most strongly associated with age before the age of 50. However, in this age range, it was the parameter for processing speed, C, that was most clearly associated with DTI indices, in this case fractional anisotropy (FA), particularly in the genu and body of the corpus callosum. Furthermore, differences in the C parameter partially mediated differences in DSS within this age range. After the age of 50, the TVA parameter for the perceptual threshold, t 0, as well as K, were most strongly related to participant age. Both parameters, but t 0 more strongly so than K, were associated WM diffusivity, particularly in projection fibers such as the internal capsule, the sagittal stratum, and the corona radiata. Within this age range, t 0 partially mediated age-related differences in gF. The results are consistent with, and provide novel empirical support for the neuroanatomical localization of TVA computations as outlined in the neuronal interpretation of TVA (NTVA). Furthermore, the results indicate that to understand the biological sources of age-related changes in processing speed and fluid cognition, it may be useful to employ methods that allow for computational fractionation of these multicomponent measures.

Cognitive decline and brain pathology in aging--need for a dimensional, lifespan and systems vulnerability view

Changes in brain structure and activity as well as cognitive function are commonly seen in aging. However, it is not known when aging of brain and cognition starts, and how much of the changes observed in seemingly healthy older adults that can be ascribed to incipient neurodegenerative disease. Recent research has yielded evidence that the borders between development and aging sometimes can be fuzzy, as can the borders between dementing disease and normal age changes. In this review, we argue that many factors affecting cognitive decline and dementia represents quantitative rather than qualitative differences in characteristics that commonly exist in the population. Further, factors known to affect brain and cognition in aging will often do so through a life-long accumulation of impact, and does not need to be specific to aging. And finally, a host of environmental and genetic factors and their interplay determine optimal aging, leaving room for potential for environmental interventions to affect the outcome of the aging process. Together, we argue that these factors call for a dimensional rather than categorical, lifespan rather than aging, and multidimensional systems-vulnerability rather than simple "hypothetical biomarker" model of age-associated cognitive decline and dementia. This has implications for how we should view lifespan trajectories of change in brain and cognitive function, and how we can study, prevent, diagnose and treat age-associated cognitive deficits.

Synergy effects of HbA1c and variants of APOE and BDNFVal66Met explains individual differences in memory performance

We aimed at exploring if synergy effects of Brain-Derived Neurotrophic Factor (BDNF) Val(66)Met, Apolipoprotein E (APOE) and HbA1c (glycated haemoglobin) could explain individual differences in memory performance over 10 years in a population based sample of nondemented adults (N=888, 35-85 years at baseline). Episodic memory was affected by such agents, wheras semantic memory was spared. Both age and HbA1c were associated with episodic memory decline. BDNF(66)Met carriers with higher HbA1c levels evidenced slope decline in episodic recall. We found support for joint effects of BDNFVal(66)Met×APOE×HbA1c and BDNFVal(66)Met×APOE×age on rates of episodic memory change over ten years, after controlling for age, sex, education and cardiovascular diseases. We conclude that variants of genetic polymorphisms act in synergy with long-term blood glucose control in shaping patterns of cognitive aging.

General fluid-type intelligence is related to indices of white matter structure in middle-aged and old adults

General fluid-type intelligence (gF) reflects abstract reasoning and problem solving abilities, and is an important predictor for lifetime trajectories of cognition, and physical and mental health. Structural and functional neuroimaging studies have demonstrated the role of parieto-frontal gray matter, but the white matter (WM) underpinnings of gF and the contribution of individual gF components to gF-WM relationship still need to be explored. The aim of this study was to characterize, in a sample of 100 healthy middle-aged and old subjects (mean=63.8 years), the relationship between gF and indices of WM structure obtained from diffusion tensor magnetic resonance imaging (DT-MRI) (fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD)). gF was estimated by principal component analysis including measures of episodic memory, reasoning, and processing speed. Tract-based spatial statistics and permutation-based inference statistics were used to test the association between gF and WM indices, while controlling for the effect of age and sex. We hypothesized a positive relationship between gF and WM structure. Based on previous studies, we further hypothesized that this relationship was heavily influenced by the processing speed component of gF. We found a robust relationship between gF and DT-MRI measures of FA, RD and MD in all major WM tracts. Higher gF score was related to higher degree of WM integrity, in middle-aged as well as old individuals. Thus, the distributed relationship between gF and indices of WM microstructure is consistent with the notion that gF reflects efficient signaling between cortical areas. Furthermore, analysis of relationships between WM measures and gF components revealed an association with information processing speed and reasoning ability, but not with episodic memory. Thus, although all subcomponents loaded high on gF factor, the speed-related components were most strongly associated with DT-MRI-derived measures. These results suggest that DT-MRI can be used to parse gF.

Intra-individual reaction time variability in mild cognitive impairment and Alzheimer's disease: gender, processing load and speed factors

Compared to cognitively healthy ageing (CH), intra-individual variability in reaction time (IIV_RT), a behavioural marker of neurological integrity, is commonly reported to increase in both Alzheimer’s disease (AD) and mild cognitive impairment (MCI). It varies in MCI with respect to whether it represents the pro-dromal stages of dementia or not; being greatest in those most likely to convert. Abnormal IIV_RT in MCI therefore represents a potential measure of underlying functional integrity that may serve to differentiate MCI from CH and to help identify those patients for whom MCI is the result of a progressive pathological process. As the clinical approach to MCI is increasingly stratified with respect to gender, we investigated whether this factor could influence study outcome. The influence of RT_SPEED and processing load upon IIV_RT was also examined. Under low processing load conditions, IIV_RT was significantly increased in both MCI and AD compared to CH. However, correcting for an individual’s processing speed abolished this effect in MCI but not in AD, indicating that the increased IIV_RT in MCI and AD may result from different factors. In MCI but not in CH, IIV_RT was significantly greater for females. Increasing task processing load by adding distracting information, although increasing overall IIV_RT, failed to improve the differentiation between CH and both MCI and AD, and in MCI resulted in a reduction in the influence of gender upon study outcome. The outcome of studies investigating IIV_RT in MCI and AD compared to CH therefore appear influenced by the gender of the participants, by task-related processing load and processing speed.

Polymorphism in the CHRNA4 gene is associated with rapid scene categorization performance

The CHRNA4 gene is known to be associated with individual differences in attention. However, its associations with other cognitive functions remain to be elucidated. In the present study, we investigated the effects of genetic variations in CHRNA4 on rapid scene categorization by 100 healthy human participants. In Experiment 1, we also conducted the Attention Network Test (ANT) in order to examine whether the genetic effects could be accounted for by attention. CHRNA4 was genotyped as carrying the TT, CT, or CC allele. The scene categorization task required participants to judge whether the category of a scene image (natural or man-made) was consistent with a cue word displayed at the response phase. The target-mask stimulus onset asynchrony (SOA) ranged from 13 to 93 ms. In comparison with CC-allele carriers, CT- and TT-allele carriers responded more accurately at the long SOA (93 ms) only during natural-scene categorization. In contrast, we observed no consistent association between CHRNA4 and the ANT, and no intertask correlation between scene categorization and the ANT. To validate our natural-scene categorization results, Experiment 2, carried out with an independent sample of 100 participants and a different stimulus set, successfully replicated the association between CHRNA4 genotypes and natural-scene categorization accuracy at long SOAs (67 and 93 ms). Our findings demonstrate, for the first time, that genetic variations in CHRNA4 can moderately contribute to individual differences in natural-scene categorization performance.

Subthreshold Depressive Symptoms have a Negative Impact on Cognitive Functioning in Middle-Aged and Older Males

INTRODUCTION

Cognitive aging is associated with a decline on measures of fluid intelligence (gF), whereas crystallized intelligence (gC) tends to remain stable. In the present study we asked if depressive symptoms might contribute to explain the decline on gF in a sample of healthy middle-aged and older adults.

METHOD

The Norwegian sample included 83 females and 42 males (M = 60, SD = 7.9 years). gF was calculated from factor-analysis, including tests of matrix reasoning (WASI), memory function (CVLT-II), processing speed and executive function (CDT; CWIT). gC was derived from a Vocabulary subtest (WASI). Depressive symptoms were assessed by self-reports on Beck's Depression Index (BDI) and ranged from 0 to 21 (M = 6, SD = 4.5).

RESULTS

Increased age was correlated with a decline on gF (r = -0.436, p  < 0.001), but not gC (r=-0.103, p = ns.). The BDI score in the whole sample was correlated with gF (r = -0.313, p < 0.001). A more detailed analysis showed that the BDI score correlated with measures of both gF and gC in males. The correlations were non-significant for females on all measures, with the exception of a measure of processing speed/executive function. A regression analysis including age and sex in the first step, showed that symptoms of depression significantly contributed to explain decline on gF, F(3, 124) = 16.653, p < 0.001, R? = 0.292, ΔR? = 0.054.

DISCUSSION

The results showed that symptoms of depression were negatively correlated with cognitive functioning in males even when the symptom-level was below clinical threshold. This indicates that minimal symptoms of depression in older men are clinically relevant to address.

Does variability in cognitive performance correlate with frontal brain volume?

Little is known about the neural correlates of within-person variability in cognitive performance. We investigated associations between regional brain volumes and trial-to-trial, block-to-block, and day-to-day variability in choice-reaction time, and episodic and working memory accuracy. Healthy younger (n=25) and older (n=18) adults underwent 101 daily assessments of cognitive performance, and their regional brain volumes were measured manually on magnetic resonance images. Results showed that smaller prefrontal white matter volumes were associated with higher block-to-block variability in choice-reaction time performance, with a stronger association observed among older adults. Smaller volumes of the dorsolateral prefrontal cortex covaried with higher block-to-block variability in episodic memory (number-word pair) performance. This association was stronger for younger adults. The observed associations between variability and brain volume were not due to individual differences in mean performance. Trial-to-trial and day-to-day variability in cognitive performance were unrelated to regional brain volume. We thus report novel findings demonstrating that block-by-block variability in cognitive performance is associated with integrity of the prefrontal regions and that between-person differences in different measures of variability of cognitive performance reflect different age-related constellations of behavioral and neural antecedents.

Imaging and Cognitive Genetics: The Norwegian Cognitive NeuroGenetics Sample

Data collection for the Norwegian Cognitive NeuroGenetics sample (NCNG) was initiated in 2003 with a research grant (to Ivar Reinvang) to study cognitive aging, brain function, and genetic risk factors. The original focus was on the effects of aging (from middle age and up) and candidate genes (e.g., APOE, CHRNA4) in cross-sectional and longitudinal designs, with the cognitive and MRI-based data primarily being used for this purpose. However, as the main topic of the project broadened from cognitive aging to imaging and cognitive genetics more generally, the sample size, age range of the participants, and scope of available phenotypes and genotypes, have developed beyond the initial project. In 2009, a genome-wide association (GWA) study was undertaken, and the NCNG proper was established to study the genetics of cognitive and brain function more comprehensively. The NCNG is now controlled by the NCNG Study Group, which consists of the present authors. Prominent features of the NCNG are the adult life-span coverage of healthy participants with high-dimensional imaging, and cognitive data from a genetically homogenous sample. Another unique property is the large-scale (sample size 300–700) use of experimental cognitive tasks focusing on attention and working memory. The NCNG data is now used in numerous ongoing GWA-based studies and has contributed to several international consortia on imaging and cognitive genetics. The objective of the following presentation is to give other researchers the information necessary to evaluate possible contributions from the NCNG to various multi-sample data analyses.

Executive Dysfunction in MCI: Subtype or Early Symptom

Mild cognitive impairment (MCI) may take several forms, and amnestic MCI (aMCI) has been recognized as an early stage of Alzheimer's Disease (AD). Impairment in executive functions including attention (eMCI) may be indicative of several neurodegenerative conditions. Executive impairment is frequently found in aMCI, it is significant for prognosis, and patients with eMCI may go on to develop AD. Recent studies have found changes in white matter integrity in patients with eMCI to be more sensitive than measures of cortical atrophy. Studies of genetic high-risk groups using sensitive cognitive neuroscience paradigms indicate that changes in executive function may be a cognitive marker useful for tracking development in an AD pathophysiological process.

Neuropsychological performance in older insomniacs

The purpose of this study was to examine daytime performance in older adults fulfilling the diagnostic criteria for DSM-IV Insomnia, using a comprehensive battery of neuropsychological tests, and to compare these objective findings with measures of self-reported cognitive functioning. A total of 121 participants (69% women) with a mean age of 64.0 were part of a thorough neuropsychological examination at a University-based neuropsychological clinic in Western Norway. Twenty-five percent of the participants fulfilled the diagnostic criteria for insomnia. In sum, the insomnia patients were not different from the good sleepers on any neuropsychological test measure, and none of the results on the performance measures were associated with the sleep-related daytime complaints. However, the insomniacs did rate their subjective memory performance as significantly worse than the good sleepers, and they also reported more depressive symptoms. We conclude that DSM-IV defined insomnia was not associated with any performance based measure; only with self-reported symptoms.

Age-related differences in memory and executive functions in healthy APOE ɛ4 carriers: the contribution of individual differences in prefrontal volumes and systolic blood pressure

Advanced age and vascular risk are associated with declines in the volumes of multiple brain regions, especially the prefrontal cortex, and the hippocampus. Older adults, even unencumbered by declining health, perform less well than their younger counterparts in multiple cognitive domains, such as episodic memory, executive functions, and speed of perceptual processing. Presence of a known genetic risk factor for cognitive decline and vascular disease, the ɛ4 allele of the apolipoprotein E (APOE) gene, accounts for some share of those declines; however, the extent of the joint contribution of genetic and physiological vascular risk factors on the aging brain and cognition is unclear. In a sample of healthy adults (age 19-77), we examined the effects of a vascular risk indicator (systolic blood pressure, SBP) and volumes of hippocampus (HC), lateral prefrontal cortex (lPFC), and prefrontal white matter (pFWM) on processing speed, working memory (WM), and recognition memory. Using path analyses, we modeled indirect effects of age, SBP, and brain volumes on processing speed, WM, and memory and compared the patterns of structural relations among those variables in APOE ɛ4 carriers and ɛ3 homozygotes. Among ɛ4 carriers, age differences in WM were explained by increase in SBP, reduced FWM volume, and slower processing. In contrast, lPFC and FWM volumes, but not BP, explained a share of age differences in WM among ɛ3 homozygotes. Thus, even in healthy older carriers of the APOE ɛ4 allele, clinically unremarkable increase in vascular risk may be associated with reduced frontal volumes and impaired cognitive functions.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Gene-based analysis of regionally enriched cortical genes in GWAS data sets of cognitive traits and psychiatric disorders

BACKGROUND

Despite its estimated high heritability, the genetic architecture leading to differences in cognitive performance remains poorly understood. Different cortical regions play important roles in normal cognitive functioning and impairment. Recently, we reported on sets of regionally enriched genes in three different cortical areas (frontomedial, temporal and occipital cortices) of the adult rat brain. It has been suggested that genes preferentially, or specifically, expressed in one region or organ reflect functional specialisation. Employing a gene-based approach to the analysis, we used the regionally enriched cortical genes to mine a genome-wide association study (GWAS) of the Norwegian Cognitive NeuroGenetics (NCNG) sample of healthy adults for association to nine psychometric tests measures. In addition, we explored GWAS data sets for the serious psychiatric disorders schizophrenia (SCZ) (n = 3 samples) and bipolar affective disorder (BP) (n = 3 samples), to which cognitive impairment is linked.

PRINCIPAL FINDINGS

At the single gene level, the temporal cortex enriched gene RAR-related orphan receptor B (RORB) showed the strongest overall association, namely to a test of verbal intelligence (Vocabulary, P = 7.7E-04). We also applied gene set enrichment analysis (GSEA) to test the candidate genes, as gene sets, for enrichment of association signal in the NCNG GWAS and in GWASs of BP and of SCZ. We found that genes differentially expressed in the temporal cortex showed a significant enrichment of association signal in a test measure of non-verbal intelligence (Reasoning) in the NCNG sample.

CONCLUSION

Our gene-based approach suggests that RORB could be involved in verbal intelligence differences, while the genes enriched in the temporal cortex might be important to intellectual functions as measured by a test of reasoning in the healthy population. These findings warrant further replication in independent samples on cognitive traits.

A cognitive phenotype for a polymorphism in the nicotinic receptor gene CHRNA4

Drawing on converging behavioral, electrophysiological, and imaging evidence, we advance an hypothesis for a cognitive phenotype of a SNP in the CHRNA4 gene encoding the α(4) subunit of α(4)β(2) nicotinic receptors. First, we review evidence that visuospatial attention can be decomposed into several component processes. Secondly, we consider evidence that one component, redirection of attention, is modulated by the nicotinic cholinergic system. Third, we review evidence that nicotinic stimulation exerts effects at the network level. Fourth, we consider evidence that normal variation in this SNP exerts nicotine-like modulatory effects on visuospatial attention. Fifth, we hypothesize that the cognitive phenotype of the CHRNA4 rs1044396 SNP is characterized by greater ability of T allele carriers to preferentially process events in the attentional focus compared to events outside the attentional focus. Finally, we consider effects of the CHNRA4 rs1044396 SNP on brain activity and cognition in light of our hypothesized cognitive phenotype. This hypothesis makes an important contribution to the development of cognitive phenomics by arguing for a cognitive phenotype of CHRNA4.

Exogenous visual orienting is associated with specific neurotransmitter genetic markers: a population-based genetic association study

Background

Currently, there is a sense that the spatial orienting of attention is related to genotypic variations in cholinergic genes but not to variations in dopaminergic genes. However, reexamination of associations with both cholinergic and dopaminergic genes is warranted because previous studies used endogenous rather than exogenous cues and costs and benefits were not analyzed separately. Examining costs (increases in response time following an invalid pre-cue) and benefits (decreases in response time following a valid pre-cue) separately could be important if dopaminergic genes (implicated in disorders such as attention deficit disorder) independently influence the different processes of orienting (e.g., disengage, move, engage).

Methodology/Principal Findings

We tested normal subjects (N = 161) between 18 and 61 years. Participants completed a computer task in which pre-cues preceded the presence of a target. Subjects responded (with a key press) to the location of the target (right versus left of fixation). The cues could be valid (i.e., appear where the target would appear) or invalid (appear contralateral to where the target would appear). DNA sequencing assays were performed on buccal cells to genotype known genetic markers and these were examined for association with task scores. Here we show significant associations between visual orienting and genetic markers (on COMT, DAT1, and APOE; R²s from 4% to 9%).

Conclusions/Significance

One measure in particular – the response time cost of a single dim, invalid cue – was associated with dopaminergic markers on COMT and DAT1. Additionally, variations of APOE genotypes based on the ε2/ε3/ε4 alleles were also associated with response time differences produced by simultaneous cues with unequal luminances. We conclude that individual differences in visual orienting are related to several dopaminergic markers as well as to a cholinergic marker. These results challenge the view that orienting is not associated with genotypic variation in dopaminergic genes.

Individual differences in cognition, affect, and performance: behavioral, neuroimaging, and molecular genetic approaches

We describe the use of behavioral, neuroimaging, and genetic methods to examine individual differences in cognition and affect, guided by three criteria: (1) relevance to human performance in work and everyday settings; (2) interactions between working memory, decision-making, and affective processing; and (3) examination of individual differences. The results of behavioral, functional MRI (fMRI), event-related potential (ERP), and molecular genetic studies show that analyses at the group level often mask important findings associated with sub-groups of individuals. Dopaminergic/noradrenergic genes influencing prefrontal cortex activity contribute to inter-individual variation in working memory and decision behavior, including performance in complex simulations of military decision-making. The interactive influences of individual differences in anxiety, sensation seeking, and boredom susceptibility on evaluative decision-making can be systematically described using ERP and fMRI methods. We conclude that a multi-modal neuroergonomic approach to examining brain function (using both neuroimaging and molecular genetics) can be usefully applied to understanding individual differences in cognition and affect and has implications for human performance at work.

Genetic variation in nicotinic receptors affects brain networks involved in reorienting attention

Prior evidence suggests that a genetic variation in nicotinic receptors modulates visuospatial attention in humans. Brain areas contributing to this modulation are largely unknown. Here we investigate the influence of the nicotinic receptor gene CHRNA4 (rs 1044396) on brain networks involved in detecting unattended events. Subjects were genotyped and studied with functional magnetic resonance imaging while performing a cued target detection task with valid, neutral and invalid trials. Two brain areas within a core region of the attention network, the right temporoparietal junction, showed a genotype dependent modulation. CHRNA4 C/C homozygotes showed differentially higher neural activity in the right middle temporal gyrus when reorienting attention was required in invalid trials. In contrast, T/T homozygotes had stronger activations within the right superior temporal gyrus. An analysis of functional connectivity further revealed that these temporoparietal regions have a distinct connectivity pattern. The superior temporal gyrus recruited by T/T homozygotes shows stronger connections to temporal and parietal brain regions, which are primarily involved in shifting attention, independent of stimulus frequency. In contrast, the middle temporal gyrus exhibits stronger connections to the caudate nucleus, which is involved in detecting violations of expectations. These findings suggest that, depending on genotype, detection of stimuli outside the focus of attention is more driven by reorienting or by expectation signals.

Risk gene variants for nicotine dependence in the CHRNA5-CHRNA3-CHRNB4 cluster are associated with cognitive performance

Recent studies strongly support an association of the nicotinic acetylcholine receptor gene cluster CHRNA5-CHRNA3-CHRNB4 with nicotine dependence (ND). However, the precise genotype-phenotype relationship is still unknown. Clinical and epidemiological data on smoking behavior raise the possibility that the relevant gene variants may indirectly contribute to the development of ND by affecting cognitive performance in some smokers who consume nicotine for reasons of "cognition enhancement." Here, we tested seven single nucleotide polymorphisms (SNPs) rs684513, rs637137, rs16969968, rs578776, rs1051730, rs3743078, rs3813567 from the CHRNA5-CHRNA3-CHRNB4 gene cluster for association with ND, measures of cognitive performance and gene expression. As expected, we found all SNPs being associated with ND in three independent cohorts (KORA, NCOOP, ESTHER) comprising 5,561 individuals. In an overlapping sample of 2,186 subjects we found three SNPs (rs16969968, rs1051730, rs3743078) being associated with cognitive domains from the Wechsler-Adult-Intelligence Scale (WAIS-R)-most notably in the performance subtest "object assembly" and the verbal subtest "similarities." In a refined analysis of a subsample of 485 subjects, two of these three SNPs (rs16969968, rs1051730) were associated with n-back task performance/Continuous Performance Test. Furthermore, two CHRNA5 risk alleles (rs684513, rs637137) were associated with CHRNA5 mRNA expression levels in whole blood in a subgroup of 190 subjects. We here report for the first time an association of CHRNA5-CHRNA3-CHRNB4 gene variants with cognition possibly mediating in part risk for developing ND. The observed phenotype-genotype associations may depend on altered levels of gene expression. © 2010 Wiley-Liss, Inc.

Neurogenetic effects on cognition in aging brains: a window of opportunity for intervention?

Knowledge of genetic influences on cognitive aging can constrain and guide interventions aimed at limiting age-related cognitive decline in older adults. Progress in understanding the neural basis of cognitive aging also requires a better understanding of the neurogenetics of cognition. This selective review article describes studies aimed at deriving specific neurogenetic information from three parallel and interrelated phenotype-based approaches: psychometric constructs, cognitive neuroscience-based processing measures, and brain imaging morphometric data. Developments in newer genetic analysis tools, including genome wide association, are also described. In particular, we focus on models for establishing genotype-phenotype associations within an explanatory framework linking molecular, brain, and cognitive levels of analysis. Such multiple-phenotype approaches indicate that individual variation in genes central to maintaining synaptic integrity, neurotransmitter function, and synaptic plasticity are important in affecting age-related changes in brain structure and cognition. Investigating phenotypes at multiple levels is recommended as a means to advance understanding of the neural impact of genetic variants relevant to cognitive aging. Further knowledge regarding the mechanisms of interaction between genetic and preventative procedures will in turn help in understanding the ameliorative effect of various experiential and lifestyle factors on age-related cognitive decline.

Genetic variation of CHRNA4 does not modulate attention in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder, characterised by cognitive decline and attentional impairment. Recently, variation in CHRNA4 (rs1044396) has been shown to affect visual and auditory function, affecting speed and attention, in healthy adults. An association between CHRNA4 variation and PD has not been shown. To determine the link between CHRNA4 variation and attentional deficit in PD. A genotype-phenotype correlation between the common CHRNA4:rs1044396 variant and several baseline parameters of attention was carried out in a large cohort of PD cases (n=222) and controls (n=159). We identified significant associations to measures of attention in PD patients compared to controls. However, we found no significant link to CHRNA4:rs1044396 genotypes to baseline attention variables in PD or in controls. We conclude that CHRNA4:rs1044396 genotypes do not significantly influence the attentional deficit found in PD patients. Contrary to previous studies, we also found no significant influence in healthy age-matched controls.

Promoting successful cognitive aging: a comprehensive review

Promoting successful cognitive aging is a topic of major importance to individuals and the field of public health. This review presents a coherent framework not only for evaluating factors, protective activities, and enhancing agents that have already been proposed, but also ones that will be put forward in the future. The promotion of successful cognitive aging involves the dual goals of preventing loss of information processing capacity and cognitive reserve, and enhancing brain capacity and cognitive reserve. Four major lines of evidence are available for evaluating whether a proposed factor promotes successful cognitive aging: 1) epidemiologic/cohort studies; 2) animal/basic science studies; 3) human "proof-of-concept" studies; and 4) human intervention studies. Each line of evidence has advantages and limitations that will be discussed. Through illustrative examples, we trace the ways in which each method informs us about the potential value of several proposed factors. Currently, lines of converging evidence allow the strongest case to be made for physical and cognitively stimulating activities. Although epidemiological data seem to favor the use of statins to lower the risk of dementia, more definitive recommendations await further randomized controlled studies. There is presently no clear evidence that antioxidants or Ginkgo biloba promote successful cognitive aging. The impact of resveratrol, fish oil, and a long list of other proposed agents needs to be determined. Clinicians remain well-positioned to identify and aggressively treat vascular risk factors, diabetes, sleep disorders, and other conditions that may reduce brain capacity, and to encourage activities that can build cognitive reserve.

Epistasis between APOE and nicotinic receptor gene CHRNA4 in age related cognitive function and decline

Healthy participants (n = 237) aged 45-79 were tested neuropsychologically with tests of memory, speed, and cognitive control and followed up for 3-5 years (mean, 3.4 years). The sample was genotyped for apolipoprotein E (APOE) and CHolinergic Receptor for Nicotine Alpha 4 (CHRNA4), and genetic effects on cognitive function at initial testing and on cognitive decline was studied. We predicted relatively stronger effects of APOE on memory, and of CHRNA4 on speeded tasks. The predictions were partially confirmed, but we found interactive effects of APOE and CHRNA4 in several cognitive domains. Being an APOE epsilon4/CHRNA4 TT carrier was associated with slower and less efficient performance, and with steeper decline in speed tasks and in delayed recall. Age dependent genetic effects were found for both APOE and CHRNA4, where old participants (60-79 years) showed a negative influence of TT carrier status on initial memory performance, but a tendency for steeper memory decline in epsilon4 carriers. Inconsistent and small effects of APOE reported in previous studies of healthy groups may be caused by failure to consider epistasis of APOE with nicotinic receptor and other genes.

Apolipoprotein E ε4-related thickening of the cerebral cortex modulates selective attention

APOE ε4 carriers have thicker cortex in several neocortical areas than ε4 noncarriers (Espeseth T., Westlye L.T., Fjell A.M., Walhovd K.B., Rootwelt H., Reinvang I., 2008. Accelerated age-related cortical thinning in healthy carriers of apolipoprotein E ε4. Neurobiol. Aging 29, 329-340). To investigate potential physiological and cognitive correlates of these anatomical effects structural magnetic resonance imaging (MRI) data were obtained from 20 APOE ε3 homozygotes and 20 ε4 hetero- and homozygotes, and event-related potentials (ERPs) were recorded during a selective attention task (i.e. three-stimulus oddball). Several areas in both hemispheres were thicker in ε4 carriers than in noncarriers. ε4 carriers also had lower amplitudes to distractors (P3a) and lower target detection accuracy than noncarriers. Mean thickness in cortical areas were correlated with P3a amplitudes, which in turn correlated with accuracy. Path analyses showed that APOE-related difference in accuracy was mediated by APOE-related differences in cortical thickness and P3a amplitudes. The results suggest that APOE ε4 modulates the structural integrity of critical nodes in brain attentional networks.

Why do young women smoke? VI. A controlled study of nicotine effects on attention: pharmacogenetic interactions

In prior studies we found that young, female smokers manifest poorer performance than non-smokers on attention-related tasks and that these findings can be moderated by variation in nicotinic acetylcholine receptor (nAChR) genes. We predicted that under controlled conditions (1) nicotine would improve functioning on attentional tasks in smokers who previously manifested relatively poor performance, and that (2) smokers who carry genetic variations associated with poorer attention performance would derive greater benefit from nicotine. To test these hypotheses, 31 young female smokers, who participated in our previous study, performed the Matching Familiar Figures Test (MFFT), Tower of London Test and Continuous Performance Task (CPT) in a double-blind, within-between subject design, placebo or nicotine (4 mg as gum) serving as the within factor and genetic profile as the between factor. Repeated measures ANCOVA controlling for attention deficit symptomatology, substance abuse and nicotine dependence showed better performance under nicotine among participants with higher levels of attention deficit symptoms (MFFT errors: P=0.04; CPT commissions: P=0.01) and nicotine dependence (CPT stability of response: P=0.04) and greater consumption of caffeine (CPT stability of response: P=0.04). An interactive effect of genetic profile was demonstrated for SNP rs2337980 in CHRNA7. These findings suggest that nicotine may have stronger short-term facilitating effects on attention in women who have more attention deficit symptoms and consume more nicotine and caffeine. This effect may be modified by a specific genetic make-up. Such individuals may be at increased risk for nicotine addiction and for greater difficulties in smoking cessation.

Both a nicotinic single nucleotide polymorphism (SNP) and a noradrenergic SNP modulate working memory performance when attention is manipulated

We investigated the relation between the two systems of visuospatial attention and working memory by examining the effect of normal variation in cholinergic and noradrenergic genes on working memory performance under attentional manipulation. We previously reported that working memory for location was impaired following large location precues, indicating the scale of visuospatial attention has a role in forming the mental representation of the target. In one of the first studies to compare effects of two single nucleotide polymorphisms (SNPs) on the same cognitive task, we investigated the neurotransmission systems underlying interactions between attention and memory. Based on our previous report that the CHRNA4 rs#1044396 C/T nicotinic receptor SNP affected visuospatial attention, but not working memory, and the DBH rs#1108580 G/A noradrenergic enzyme SNP affected working memory, but not attention, we predicted that both SNPs would modulate performance when the two systems interacted and working memory was manipulated by attention. We found the scale of visuospatial attention deployed around a target affected memory for location of that target. Memory performance was modulated by the two SNPs. CHRNA4 C/C homozygotes and DBH G allele carriers showed the best memory performance but also the greatest benefit of visuospatial attention on memory. Overall, however, the CHRNA4 SNP exerted a stronger effect than the DBH SNP on memory performance when visuospatial attention was manipulated. This evidence of an integrated cholinergic influence on working memory performance under attentional manipulation is consistent with the view that working memory and visuospatial attention are separate systems which can interact.

Working memory deficits in healthy APOE epsilon 4 carriers

Studies on the cognitive effects of APOE allele variation in healthy persons have mainly focused on episodic memory performance as most sensitive to genetic effects. The present study focuses on working memory performance, measured both in an experimental paradigm, the AX-Continuous Performance Task (AX-CPT), and in neuropsychological test paradigms of span capacity and interference control. In a highly functioning healthy group (N=186) of mean age 64.5 years we found evidence of reduced working memory performance in APOE epsilon4 carriers, with sex and epsilon4 dose as modifying variables. Several aspects of capacity and control in working memory were affected, while genetic effects were not present for measures of episodic memory. The pattern of results suggests that response inhibition is sensitive to genetic effects. In healthy individuals the broad range of neurobiological mechanisms associated with APOE is consistent with effects on non-memory cognitive subsystems, and gender effects may be modulated by interaction of APOE with myelination, androgen mechanisms, or broad patterns of age-related changes in gene expression.

Variants in doublecortin- and calmodulin kinase like 1, a gene up-regulated by BDNF, are associated with memory and general cognitive abilities

BACKGROUND

Human memory and general cognitive abilities are complex functions of high heritability and wide variability in the population. The brain-derived neurotrophic factor (BDNF) plays an important role in mammalian memory formation.

METHODOLOGY / PRINCIPAL FINDING

Based on the identification of genes markedly up-regulated during BDNF-induced synaptic consolidation in the hippocampus, we selected genetic variants that were tested in three independent samples, from Norway and Scotland, of adult individuals examined for cognitive abilities. In all samples, we show that markers in the doublecortin- and calmodulin kinase like 1 (DCLK1) gene, are significantly associated with general cognition (IQ scores) and verbal memory function, resisting multiple testing. DCLK1 is a complex gene with multiple transcripts which vary in expression and function. We show that the short variants are all up-regulated after BDNF treatment in the rat hippocampus, and that they are expressed in the adult human brain (mostly in cortices and hippocampus). We demonstrate that several of the associated variants are located in potential alternative promoter- and cis-regulatory elements of the gene and that they affect BDNF-mediated expression of short DCLK1 transcripts in a reporter system.

CONCLUSION

These data present DCLK1 as a functionally pertinent gene involved in human memory and cognitive functions.

Hippocampal volumes are important predictors for memory function in elderly women

Background

Normal aging involves a decline in cognitive function that has been shown to correlate with volumetric change in the hippocampus, and with genetic variability in the APOE-gene. In the present study we utilize 3D MR imaging, genetic analysis and assessment of verbal memory function to investigate relationships between these factors in a sample of 170 healthy volunteers (age range 46–77 years).

Methods

Brain morphometric analysis was performed with the automated segmentation work-flow implemented in FreeSurfer. Genetic analysis of the APOE genotype was determined with polymerase chain reaction (PCR) on DNA from whole-blood. All individuals were subjected to extensive neuropsychological testing, including the California Verbal Learning Test-II (CVLT). To obtain robust and easily interpretable relationships between explanatory variables and verbal memory function we applied the recent method of conditional inference trees in addition to scatterplot matrices and simple pairwise linear least-squares regression analysis.

Results

APOE genotype had no significant impact on the CVLT results (scores on long delay free recall, CVLT-LD) or the ICV-normalized hippocampal volumes. Hippocampal volumes were found to decrease with age and a right-larger-than-left hippocampal asymmetry was also found. These findings are in accordance with previous studies. CVLT-LD score was shown to correlate with hippocampal volume. Multivariate conditional inference analysis showed that gender and left hippocampal volume largely dominated predictive values for CVLT-LD scores in our sample. Left hippocampal volume dominated predictive values for females but not for males. APOE genotype did not alter the model significantly, and age was only partly influencing the results.

Conclusion

Gender and left hippocampal volumes are main predictors for verbal memory function in normal aging. APOE genotype did not affect the results in any part of our analysis.

123I-5-IA-85380 SPECT imaging of nicotinic receptors in Alzheimer disease and mild cognitive impairment

Postmortem binding studies have established that the concentration of alpha(4)beta(2)-nicotinic acetylcholine receptors (alpha(4)beta(2)-nAChR) is reduced in advanced Alzheimer disease (AD). However, the status of this receptor in mild or prodromal AD has remained the subject of controversy.

METHODS

We compared alpha(4)beta(2)-nAChR availability in 8 brain regions of living human subjects who had AD and mild cognitive impairment (MCI) with that in age-matched healthy control subjects by using the ligand (123)I-5-IA-85380 ((123)I-5-IA) and SPECT. All subjects (n = 32) were nonsmokers; they were administered (123)I-5-IA as a bolus plus a constant infusion and imaged 6-8 h later under equilibrium conditions. The effect of diagnosis on regional alpha(4)beta(2)-nAChR availability (regional brain activity/total parent concentration in plasma, proportional to the binding potential) was analyzed using multivariate analysis of covariance, controlling for the effects of age and sex.

RESULTS

Despite a significant overall effect of diagnostic group on mean alpha(4)beta(2)-nAChR availability, univariate analyses revealed no group differences for any brain region analyzed. An exploratory analysis of the relationship between regional alpha(4)beta(2)-nAChR availability and neuropsychologic variables yielded several plausible correlations. However, after Bonferroni adjustment, only the correlation between the anterior cingulate and the Trail Making Test, Part B, in the healthy control subjects remained significant.

CONCLUSION

These results are consistent with several postmortem and in vivo studies suggesting the preservation of nAChRs during the prodromal and early stages of AD. They support the interpretation that nAChR and other cholinergic reductions in AD are late-stage phenomena.

Increased sensitivity to effects of normal aging and Alzheimer's disease on cortical thickness by adjustment for local variability in gray/white contrast: a multi-sample MRI study

MRI-based estimates of cerebral morphometric properties, e.g. cortical thickness, are pivotal to studies of normal and pathological brain changes. These measures are based on automated or manual segmentation procedures, which utilize the tissue contrast between gray and white matter on T(1)-weighted MR images. Tissue contrast is unlikely to remain a constant property across groups of different age and health. An important question is therefore how the sensitivity of cortical thickness estimates is influenced by variability in WM/GM contrast. The effect of adjusting for variability in WM/GM contrast on age sensitivity of cortical thickness was tested in 1189 healthy subjects from six different samples, enabling evaluation of consistency of effects within and between sites and scanners. Further, the influence of Alzheimer's disease (AD) diagnosis on cortical thickness with and without correction for contrast was tested in an additional sample of 96 patients. In healthy controls, regional increases in the sensitivity of the cortical thickness measure to age were found after correcting for contrast. Across samples, the strongest effects were observed in frontal, lateral temporal and parietal areas. Controlling for contrast variability also increased the cortical thickness estimates' sensitivity to AD, thus replicating the finding in an independent clinical sample. The results showed increased sensitivity of cortical estimates to AD in areas earlier reported to be compromised in AD, including medial temporal, inferior and superior parietal regions. In sum, the findings indicate that adjusting for contrast can increase the sensitivity of MR morphometry to variables of interest.