Interaction between striatal volume and DAT1 polymorphism predicts working memory development during adolescence.

There is considerable inter-individual variability in the rate at which working memory (WM) develops during childhood and adolescence, but the neural and genetic basis for these differences are poorly understood. Dopamine-related genes, striatal activation and morphology have been associated with increased WM capacity after training. Here we tested the hypothesis that these factors would also explain some of the inter-individual differences in the rate of WM development. We measured WM performance in 487 healthy subjects twice: at age 14 and 19. At age 14 subjects underwent a structural MRI scan, and genotyping of five single nucleotide polymorphisms (SNPs) in or close to the dopamine genes DRD2, DAT-1 and COMT, which have previously been associated with gains in WM after WM training. We then analyzed which biological factors predicted the rate of increase in WM between ages 14 and 19. We found a significant interaction between putamen size and DAT1/SLC6A3 rs40184 polymorphism, such that TC heterozygotes with a larger putamen at age 14 showed greater WM improvement at age 19. The effect of the DAT1 polymorphism on WM development was exerted in interaction with striatal morphology. These results suggest that development of WM partially share neuro-physiological mechanism with training-induced plasticity.

EFhd2/Swiprosin-1 is a common genetic determinator for sensation-seeking/low anxiety and alcohol addiction.

In many societies, the majority of adults regularly consume alcohol. However, only a small proportion develops alcohol addiction. Individuals at risk often show a high sensation-seeking/low-anxiety behavioural phenotype. Here we asked which role EF hand domain containing 2 (EFhd2; Swiprosin-1) plays in the control of alcohol addiction-associated behaviours. EFhd2 knockout (KO) mice drink more alcohol than controls and spontaneously escalate their consumption. This coincided with a sensation-seeking and low-anxiety phenotype. A reversal of the behavioural phenotype with ß-carboline, an anxiogenic inverse benzodiazepine receptor agonist, normalized alcohol preference in EFhd2 KO mice, demonstrating an EFhd2-driven relationship between personality traits and alcohol preference. These findings were confirmed in a human sample where we observed a positive association of the EFhd2 single-nucleotide polymorphism rs112146896 with lifetime drinking and a negative association with anxiety in healthy adolescents. The lack of EFhd2 reduced extracellular dopamine levels in the brain, but enhanced responses to alcohol. In confirmation, gene expression analysis revealed reduced tyrosine hydroxylase expression and the regulation of genes involved in cortex development, Eomes and Pax6, in EFhd2 KO cortices. These findings were corroborated in Xenopus tadpoles by EFhd2 knockdown. Magnetic resonance imaging (MRI) in mice showed that a lack of EFhd2 reduces cortical volume in adults. Moreover, human MRI confirmed the negative association between lifetime alcohol drinking and superior frontal gyrus volume. We propose that EFhd2 is a conserved resilience factor against alcohol consumption and its escalation, working through Pax6/Eomes. Reduced EFhd2 function induces high-risk personality traits of sensation-seeking/low anxiety associated with enhanced alcohol consumption, which may be related to cortex function.

The Arf6 activator Efa6/PSD3 confers regional specificity and modulates ethanol consumption in Drosophila and humans.

Ubiquitously expressed genes have been implicated in a variety of specific behaviors, including responses to ethanol. However, the mechanisms that confer this behavioral specificity have remained elusive. Previously, we showed that the ubiquitously expressed small GTPase Arf6 is required for normal ethanol-induced sedation in adult Drosophila. Here, we show that this behavioral response also requires Efa6, one of (at least) three Drosophila Arf6 guanine exchange factors. Ethanol-naive Arf6 and Efa6 mutants were sensitive to ethanol-induced sedation and lacked rapid tolerance upon re-exposure to ethanol, when compared with wild-type flies. In contrast to wild-type flies, both Arf6 and Efa6 mutants preferred alcohol-containing food without prior ethanol experience. An analysis of the human ortholog of Arf6 and orthologs of Efa6 (PSD1-4) revealed that the minor G allele of single nucleotide polymorphism (SNP) rs13265422 in PSD3, as well as a haplotype containing rs13265422, was associated with an increased frequency of drinking and binge drinking episodes in adolescents. The same haplotype was also associated with increased alcohol dependence in an independent European cohort. Unlike the ubiquitously expressed human Arf6 GTPase, PSD3 localization is restricted to the brain, particularly the prefrontal cortex (PFC). Functional magnetic resonance imaging revealed that the same PSD3 haplotype was also associated with a differential functional magnetic resonance imaging signal in the PFC during a Go/No-Go task, which engages PFC-mediated executive control. Our translational analysis, therefore, suggests that PSD3 confers regional specificity to ubiquitous Arf6 in the PFC to modulate human alcohol-drinking behaviors.

Disentangling the autism-anxiety overlap: fMRI of reward processing in a community-based longitudinal study.

Up to 40% of youth with autism spectrum disorder (ASD) also suffer from anxiety, and this comorbidity is linked with significant functional impairment. However, the mechanisms of this overlap are poorly understood. We investigated the interplay between ASD traits and anxiety during reward processing, known to be affected in ASD, in a community sample of 1472 adolescents (mean age=14.4 years) who performed a modified monetary incentive delay task as part of the Imagen project. Blood-oxygen-level dependent (BOLD) responses to reward anticipation and feedback were compared using a 2x2 analysis of variance test (ASD traits: low/high; anxiety symptoms: low/high), controlling for plausible covariates. In addition, we used a longitudinal design to assess whether neural responses during reward processing predicted anxiety at 2-year follow-up. High ASD traits were associated with reduced BOLD responses in dorsal prefrontal regions during reward anticipation and negative feedback. Participants with high anxiety symptoms showed increased lateral prefrontal responses during anticipation, but decreased responses following feedback. Interaction effects revealed that youth with combined ASD traits and anxiety, relative to other youth, showed high right insula activation when anticipating reward, and low right-sided caudate, putamen, medial and lateral prefrontal activations during negative feedback (all clusters PFWE<0.05). BOLD activation patterns in the right dorsal cingulate and right medial frontal gyrus predicted new-onset anxiety in participants with high but not low ASD traits. Our results reveal both quantitatively enhanced and qualitatively distinct neural correlates underlying the comorbidity between ASD traits and anxiety. Specific neural responses during reward processing may represent a risk factor for developing anxiety in ASD youth.

The use of neuroimaging in dementia by Irish general practitioners.

BACKGROUND: More than 48,000 people in Ireland are living with dementia, and the number is likely to rise to 130,000 by 2041. Dementia frequently remains undiagnosed, depriving many of early interventions and the opportunity to plan for the future. Neuroimaging is helpful in the diagnosis of dementia, yet it is often insufficiently utilised. General practitioners (GPs) often decide which patients should be referred on for specialist assessment and as such play a crucial role in dementia diagnosis. AIMS: To establish the accessibility of neuroimaging in dementia by GPs, current referral patterns, confidence in referral and opinions on radiology reports. METHODS: The research design was a postal survey among GPs in single and group practices in urban, rural and semi-rural areas in the east and southeast of Ireland. GPs were identified from the Irish Medical Directory and posted individual anonymous questionnaires. RESULTS: A third of participants reported that they had no direct access to neuroimaging. Access differed between public and private patients. GPs primarily referred to computed tomography and magnetic resonance imaging, but only 14.6 % based these referrals on published guidelines. A total of 47.8 % of participants were not very confident in their ability to choose the most appropriate modality. CONCLUSION: Access to neuroimaging investigations for suspected cases of dementia varies between locations and public and private systems. To improve diagnostic rates and ensure appropriate utilisation of imaging resources, GPs require access to clinical and referral guidelines to ensure appropriate use of neuroimaging and the best possible patient outcomes.

Resilience and corpus callosum microstructure in adolescence.

BACKGROUND: Resilience is the capacity of individuals to resist mental disorders despite exposure to stress. Little is known about its neural underpinnings. The putative variation of white-matter microstructure with resilience in adolescence, a critical period for brain maturation and onset of high-prevalence mental disorders, has not been assessed by diffusion tensor imaging (DTI). Lower fractional anisotropy (FA) though, has been reported in the corpus callosum (CC), the brain's largest white-matter structure, in psychiatric and stress-related conditions. We hypothesized that higher FA in the CC would characterize stress-resilient adolescents. METHOD: Three groups of adolescents recruited from the community were compared: resilient with low risk of mental disorder despite high exposure to lifetime stress (n = 55), at-risk of mental disorder exposed to the same level of stress (n = 68), and controls (n = 123). Personality was assessed by the NEO-Five Factor Inventory (NEO-FFI). Voxelwise statistics of DTI values in CC were obtained using tract-based spatial statistics. Regional projections were identified by probabilistic tractography. RESULTS: Higher FA values were detected in the anterior CC of resilient compared to both non-resilient and control adolescents. FA values varied according to resilience capacity. Seed regional changes in anterior CC projected onto anterior cingulate and frontal cortex. Neuroticism and three other NEO-FFI factor scores differentiated non-resilient participants from the other two groups. CONCLUSION: High FA was detected in resilient adolescents in an anterior CC region projecting to frontal areas subserving cognitive resources. Psychiatric risk was associated with personality characteristics. Resilience in adolescence may be related to white-matter microstructure.

BDNF Val66Met and reward-related brain function in adolescents: role for early alcohol consumption.

Changes in reward processing have been identified as one important pathogenetic mechanism in alcohol addiction. The nonsynonymous single nucleotide polymorphism in the brain-derived neurotrophic factor (BDNF) gene (rs6265/Val66Met) modulates the central nervous system activity of neurotransmitters involved in reward processing such as serotonin, dopamine, and glutamate. It was identified as crucial for alcohol consumption in healthy adults and, in rats, specifically related to the function in the striatum, a region that is commonly involved in reward processing. However, studies in humans on the association of BDNF Val66Met and reward-related brain functions and its role for alcohol consumption, a significant predictor of later alcohol addiction, are missing. Based on an intermediate phenotype approach, we assessed the early orientation toward alcohol and alcohol consumption in 530 healthy adolescents that underwent a monetary incentive delay task during functional magnetic resonance imaging. We found a significantly lower response in the putamen to reward anticipation in adolescent Met carriers with high versus low levels of alcohol consumption. During reward feedback, Met carriers with low putamen reactivity were significantly more likely to orient toward alcohol and to drink alcohol 2 years later. This study indicates a possible effect of BDNF Val66Met on alcohol addiction-related phenotypes in adolescence.

Genomic architecture of human neuroanatomical diversity.

Human brain anatomy is strikingly diverse and highly inheritable: genetic factors may explain up to 80% of its variability. Prior studies have tried to detect genetic variants with a large effect on neuroanatomical diversity, but those currently identified account for <5% of the variance. Here, based on our analyses of neuroimaging and whole-genome genotyping data from 1765 subjects, we show that up to 54% of this heritability is captured by large numbers of single-nucleotide polymorphisms of small-effect spread throughout the genome, especially within genes and close regulatory regions. The genetic bases of neuroanatomical diversity appear to be relatively independent of those of body size (height), but shared with those of verbal intelligence scores. The study of this genomic architecture should help us better understand brain evolution and disease.

Single nucleotide polymorphism in the neuroplastin locus associates with cortical thickness and intellectual ability in adolescents.

Despite the recognition that cortical thickness is heritable and correlates with intellectual ability in children and adolescents, the genes contributing to individual differences in these traits remain unknown. We conducted a large-scale association study in 1583 adolescents to identify genes affecting cortical thickness. Single-nucleotide polymorphisms (SNPs; n=54,837) within genes whose expression changed between stages of growth and differentiation of a human neural stem cell line were selected for association analyses with average cortical thickness. We identified a variant, rs7171755, associating with thinner cortex in the left hemisphere (P=1.12 × 10(-)(7)), particularly in the frontal and temporal lobes. Localized effects of this SNP on cortical thickness differently affected verbal and nonverbal intellectual abilities. The rs7171755 polymorphism acted in cis to affect expression in the human brain of the synaptic cell adhesion glycoprotein-encoding gene NPTN. We also found that cortical thickness and NPTN expression were on average higher in the right hemisphere, suggesting that asymmetric NPTN expression may render the left hemisphere more sensitive to the effects of NPTN mutations, accounting for the lateralized effect of rs7171755 found in our study. Altogether, our findings support a potential role for regional synaptic dysfunctions in forms of intellectual deficits.

The Road Ahead to Cure Alzheimer's Disease: Development of Biological Markers and Neuroimaging Methods for Prevention Trials Across all Stages and Target Populations.

Alzheimer's disease (AD) is a slowly progressing non-linear dynamic brain disease in which pathophysiological abnormalities, detectable in vivo by biological markers, precede overt clinical symptoms by many years to decades. Use of these biomarkers for the detection of early and preclinical AD has become of central importance following publication of two international expert working group's revised criteria for the diagnosis of AD dementia, mild cognitive impairment (MCI) due to AD, prodromal AD and preclinical AD. As a consequence of matured research evidence six AD biomarkers are sufficiently validated and partly qualified to be incorporated into operationalized clinical diagnostic criteria and use in primary and secondary prevention trials. These biomarkers fall into two molecular categories: biomarkers of amyloid-beta (Aß) deposition and plaque formation as well as of tau-protein related hyperphosphorylation and neurodegeneration. Three of the six gold-standard ("core feasible) biomarkers are neuroimaging measures and three are cerebrospinal fluid (CSF) analytes. CSF Aß1-42 (Aß1-42), also expressed as Aß1-42 : Aß1-40 ratio, T-tau, and P-tau Thr181 & Thr231 proteins have proven diagnostic accuracy and risk enhancement in prodromal MCI and AD dementia. Conversely, having all three biomarkers in the normal range rules out AD. Intermediate conditions require further patient follow-up. Magnetic resonance imaging (MRI) at increasing field strength and resolution allows detecting the evolution of distinct types of structural and functional abnormality pattern throughout early to late AD stages. Anatomical or volumetric MRI is the most widely used technique and provides local and global measures of atrophy. The revised diagnostic criteria for "prodromal AD" and "mild cognitive impairment due to AD" include hippocampal atrophy (as the fourth validated biomarker), which is considered an indicator of regional neuronal injury. Advanced image analysis techniques generate automatic and reproducible measures both in regions of interest, such as the hippocampus and in an exploratory fashion, observer and hypothesis-indedendent, throughout the entire brain. Evolving modalities such as diffusion-tensor imaging (DTI) and advanced tractography as well as resting-state functional MRI provide useful additionally useful measures indicating the degree of fiber tract and neural network disintegration (structural, effective and functional connectivity) that may substantially contribute to early detection and the mapping of progression. These modalities require further standardization and validation. The use of molecular in vivo amyloid imaging agents (the fifth validated biomarker), such as the Pittsburgh Compound-B and markers of neurodegeneration, such as fluoro-2-deoxy-D-glucose (FDG) (as the sixth validated biomarker) support the detection of early AD pathological processes and associated neurodegeneration. How to use, interpret, and disclose biomarker results drives the need for optimized standardization. Multimodal AD biomarkers do not evolve in an identical manner but rather in a sequential but temporally overlapping fashion. Models of the temporal evolution of AD biomarkers can take the form of plots of biomarker severity (degree of abnormality) versus time. AD biomarkers can be combined to increase accuracy or risk. A list of genetic risk factors is increasingly included in secondary prevention trials to stratify and select individuals at genetic risk of AD. Although most of these biomarker candidates are not yet qualified and approved by regulatory authorities for their intended use in drug trials, they are nonetheless applied in ongoing clinical studies for the following functions: (i) inclusion/exclusion criteria, (ii) patient stratification, (iii) evaluation of treatment effect, (iv) drug target engagement, and (v) safety. Moreover, novel promising hypothesis-driven, as well as exploratory biochemical, genetic, electrophysiological, and neuroimaging markers for use in clinical trials are being developed. The current state-of-the-art and future perspectives on both biological and neuroimaging derived biomarker discovery and development as well as the intended application in prevention trials is outlined in the present publication.

Subjective memory complaints in community dwelling healthy older people: the influence of brain and psychopathology.

OBJECTIVES: Subjective memory complaints (SMC) are common. We aimed to characterize the relationship between psychiatric illness and white matter disease to SMC in a sample of healthy older people. MEASUREMENTS: Cognitively normal subjects between 55 and 90 years had age-adjusted and education-adjusted Consortium to Establish a Registry for Alzheimer's disease (CERAD) scores ≤1.5 SD from standard mean. ApoE genotyping was performed using polymerase chain reaction. Sixty subjects (30 SMC, 30 controls) underwent 3T MRI, which was rated by two raters blinded to the diagnosis, for periventricular (PVH) and deep white matter hyperintensities (DWMH) using the Fazekas scale. Subjective memory was assessed by asking the participant, Do you feel like your memory or thinking is becoming worse? RESULTS: Two hundred and fifteen volunteers were assessed. Ninety-six were cognitively normal (mean age 62.5 years). SMC were reported by 52/96 subjects (54%). These were compared with subjects who denied SMC. Participants with a history of depression or anxiety were more likely to have SMC (p = 0.02). The frequency distribution of ApoE4 allele and CERAD scores were similar. White matter load was similar (p ≤ 0.47), with a high prevalence of PVH and DWMH seen (100% and 88% of scans, respectively). CONCLUSION: Both SMC and white matter disease were common. SMC were associated with a history of depression or anxiety but not with white matter disease. Evaluation for a history of depression and anxiety in people with SMC is supported by these findings.

[Structural and functional neuronal connectivity in Alzheimer's disease: a combined DTI and fMRI study]. / Strukturelle und funktionelle neuronale Konnektivität bei der Alzheimer-Krankheit : Eine kombinierte DTI- und fMRT-Studie.

BACKGROUND: Cognitive performance depends on intact cortical connectivity. Important for memory processing in the human brain is the connection between posterior cingulate cortex and hippocampus, directly as well as indirectly via the parahippocampal gyrus. These brain areas are involved early in Alzheimer's disease (AD). At the same time, they belong to the default mode network (DMN), a functional network showing high functional connectivity under resting state conditions. In AD, this connectivity in specifically compromised, offering the possibility to investigate the structural basis of functional brain connectivity. METHODS: We studied 18 patients with mild to moderate AD, 16 patients with mild cognitive impairment (MCI) and 20 healthy control subjects using diffusion tensor imaging (DTI) and resting state fMRI at 3.0 Tesla. We determined the effect of structural integrity in the posterior cingulate as assessed by DTI on the functional connectivity between posterior cingulate, hippocampus and parahippocampus during resting state in these three groups. RESULTS: Structural integrity was reduced in posterior cingulate fibre tracts in patients with AD in the left hemisphere; however, this effect was partly accounted for by age differences. All three groups showed high functional connectivity between posterior cingulate cortex and hippocampus, via both the direct and the indirect pathways. Determination of effective connectivity yielded a negative fractional anisotropy (FA)-moderated correlation on the direct pathway in AD and MCI for both hemispheres, and in healthy controls for the right hemisphere. The indirect pathway showed a negative FA-moderated correlation in AD for the right hemisphere and in MCI for both hemispheres. Healthy controls showed a positive correlation on the indirect pathway for the left hemisphere. CONCLUSION: Our data suggest that under healthy conditions, effective connectivity in the DMN between posterior cingulate cortex and hippocampus is mainly maintained by the indirect pathway via the parahippocampal gyrus. Patients with AD and patients with MCI show changes in this connectivity with a partial allocation to the direct pathway, most likely reflecting early parahippocampal lesions. The combination of DTI and fMRI broadens our understanding of human brain connectivity and its pathological changes with AD.

On the development of markers for pathological TDP-43 in amyotrophic lateral sclerosis with and without dementia.

Pathological 43-kDa transactive response sequence DNA-binding protein (TDP-43) has been recognized as the major disease protein in amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration with ubiquitin positive, tau and α-synuclein negative inclusions (FTLD-U) and the transitional forms between these multisystem conditions. In order to develop TDP-43 into a successful ALS biomarker, the natural history of TDP-43 pathology needs to be characterized and the underlying pathophysiology established. Here we propose a spatial and temporal "two-axes" model of central nervous system vulnerability for TDP-43 linked degeneration and review recent studies on potential biomarkers related to pathological TDP-43 in the cerebrospinal fluid (CSF), blood, and skeletal muscle. The model includes the following two arms: Firstly, a "motor neuron disease" or "spinal cord/brainstem to motor cortex" axis (with degeneration possibly ascending from the lower motor neurons to the upper motor neurons); and secondly, a "dementia" or "corticoid/allocortex to neocortex" axis (with a probable spread of TDP-43 linked degeneration from the mediotemporal lobe to wider mesocortical and neocortical brain areas). At the cellular level, there is a gradual disappearance of normal TDP-43 in the nucleus in combination with the formation of pathological aggregates in the cell body and cellular processes, which can also be used to identify the stage of the disease process. Moreover, TDP-43 lesions in subpial/subependymal or perivascular localizations have been noted, and this might account for increased CSF and blood TDP-43 levels through mechanisms that remain to be elucidated.

Effects of aging on default mode network activity in resting state fMRI: does the method of analysis matter?

UNLABELLED: Functional MRI (fMRI) of default mode network (DMN) brain activity during resting state is gaining attention as a potential non-invasive biomarker to diagnose incipient Alzheimer's disease. The aim of this study was to identify effects of normal aging on the DMN using different methods of fMRI processing and evaluation. METHODS: fMRI was acquired in 17 young and 21 old healthy subjects and the data were analyzed with (a) volumes of interest (VOI)-based signal time course and (b) independent component analyses (ICA). In the first approach, the strength of DMN region inter-connectivity (as expressed with correlation coefficients) was of primary interest, the second method provided a measure of the magnitude of DMN co-activation. RESULTS: The older subjects exhibited significantly lower DMN activity in the posterior cingulate (PCC, t-test P<.001) as well as a tendency to lower activity in all other DMN regions in comparison to the younger subjects. We found no significant effect of age on DMN inter-connectivity. CONCLUSION: Effects of normal aging such as loss of PCC co-activity could be detected by ICA, but not by signal time course correlation analyses of DMN inter-connectivity. This either indicates lower sensitivity of inter-connectivity measures to detect subtle DMN changes or indicate that ICA and time course analyses determine different properties of DMN co-activation. Our results, therefore, provide fundamental knowledge for a potential future use of functional MRI as biomarker for neurodegenerative dementias where diminished DMN activity needs to be reliably differentiated from that observed in health aging.

Age-dependent differences in human brain activity using a face- and location-matching task: an FMRI study.

PURPOSE: To evaluate the differences of cortical activation patterns in young and elderly healthy subjects for object and spatial visual processing using a face- and location-matching task. MATERIALS AND METHODS: We performed a face- and a location-matching task in 15 young (mean age: 28 +/- 9 years) and 19 elderly (mean age: 71 +/- 6 years) subjects. Each experiment consisted of 7 blocks alternating between activation and control condition. For face matching, the subjects had to indicate whether two displayed faces were identical or different. For location matching, the subjects had to press a button whenever two objects had an identical position. For control condition, we used a perception task with abstract images. Functional imaging was performed on a 1.5-tesla scanner using an EPI sequence. RESULTS: In the face-matching task, the young subjects showed bilateral (right > left) activation in the occipito-temporal pathway (occipital gyrus, inferior and middle temporal gyrus). Predominantly right hemispheric activations were found in the fusiform gyrus, the right dorsolateral prefrontal cortex (inferior and middle frontal gyrus) and the superior parietal gyrus. In the elderly subjects, the activated areas in the right fronto-lateral cortex increased. An additional activated area could be found in the medial frontal gyrus (right > left). In the location-matching task, young subjects presented increased bilateral (right > left) activation in the superior parietal lobe and precuneus compared with face matching. The activations in the occipito-temporal pathway, in the right fronto-lateral cortex and the fusiform gyrus were similar to the activations found in the face-matching task. In the elderly subjects, we detected similar activation patterns compared to the young subjects with additional activations in the medial frontal gyrus. CONCLUSION: Activation patterns for object-based and spatial visual processing were established in the young and elderly healthy subjects. Differences between the elderly and young subjects could be evaluated, especially by using a face-matching task.

Functional connectivity of the fusiform gyrus during a face-matching task in subjects with mild cognitive impairment.

Cognitive function requires a high level of functional interaction between regions of a network supporting cognition. Assuming that brain activation changes denote an advanced state of disease progression, changes in functional connectivity may precede changes in brain activation. The objective of this study was to investigate changes in functional connectivity of the right middle fusiform gyrus (FG) in subjects with mild cognitive impairment (MCI) during performance of a face-matching task. The right middle FG is a key area for processing face stimuli. Brain activity was measured using functional MRI. There were 16 MCI subjects and 19 age-matched healthy controls. The linear correlation coefficient was utilized as a measure of functional connectivity between the right middle FG and all other voxels in the brain. There were no statistical differences found in task performance or activation between groups. The right middle FG of the healthy control and MCI groups showed strong bilateral positive linear correlation with the visual cortex, inferior and superior parietal lobules, dorsolateral prefrontal cortex (DLPFC) and anterior cingulate. The healthy controls showed higher positive linear correlation of the right middle FG to the visual cortex, parietal lobes and right DLPFC than the MCI group, whereas the latter had higher positive linear correlation in the left cuneus. In the healthy controls, the right middle FG had negative linear correlation with right medial frontal gyrus and superior temporal gyrus and with left inferior parietal lobule (IPL), angular gyrus, superior frontal gyrus and anterior cingulate gyrus, but the MCI group had negative linear correlation with the left IPL, angular gyrus, precuneus, anterior cingulate, and to right middle temporal gyrus and posterior cingulate gyrus. In the negatively linearly correlated regions, the MCI group had reduced functional connectivity to the frontal areas, right superior temporal gyrus and left IPL. Different regions of the cuneus and IPL had increased functional connectivity in either group. The putative presence of Alzheimer's disease neuropathology in MCI affects functional connectivity from the right middle FG to the visual areas and medial frontal areas. In addition, higher linear correlation in the MCI group in the parietal lobe may indicate the initial appearance of compensatory processes. The results demonstrate that functional connectivity can be an effective marker for the detection of changes in brain function in MCI subjects.

Task difficulty in a simultaneous face matching task modulates activity in face fusiform area.

The level of difficulty of a task can alter the neural network that activates for performance of the task. Previous studies have shown increased activation with task difficulty in the frontal lobes while the effects in the extrastriate visual areas have been unclear. We hypothesized that the face fusiform area (FFA), an area specialized for face processing, would increase activation as task difficulty increased in a face matching task. The difficulty level was increased by degrading the quality of the images. The degradation levels were 10%, 20%, 40% and 60%. Based on the correct response rate, the data were divided into a baseline level (composed of non-degraded and 10% degraded images) and a difficult level (composed of the 20%, 40% and 60% degraded images). Brain activation was measured using functional magnetic resonance imaging. The baseline face matching task activated a wide network of regions that included bilaterally the occipital, temporal and parietal lobes and the right frontal lobe. A novel behavioral finding was that task difficulty did not linearly increase with image degradation. The novel brain imaging finding was that the FFA is modulated by task difficulty and performance in the task was linearly correlated to activation in FFA. In addition, we found that activation in the dorsolateral prefrontal cortex (DLPFC) had increased activation as task difficulty increased. When adding the response time as a covariate, the differences in the DLPFC did not remain statistically significant. Increased task difficulty also led to a decrease in activation of visual areas in the extrastriate cortex. Task difficulty increased activation in the FFA to enhance the face processing and suppressed activation in visual extrastriate areas that processed low level properties of the stimuli. Task difficulty led to enhanced response in the FFA and suppressed response in other visual areas.

Association between cognitive performance and cortical glucose metabolism in patients with mild Alzheimer's disease.

BACKGROUND: Neuronal and synaptic function in Alzheimer's disease (AD) is measured in vivo by glucose metabolism using positron emission tomography (PET). OBJECTIVE: We hypothesized that neuronal activation as measured by PET is a more sensitive index of neuronal dysfunction than activity during rest. We investigated if the correlations between dementia severity as measured with the Mini Mental State Examination (MMSE) and glucose metabolism are an artifact of brain atrophy. METHOD: Glucose metabolism was measured using [18F]fluorodeoxyglucose PET during rest and activation due to audiovisual stimulation in 13 mild to moderate AD patients (MMSE score > or = 17). PET data were corrected for brain atrophy. RESULTS: In the rest condition, glucose metabolism was correlated with the MMSE score primarily within the posterior cingulate and parietal lobes. For the activation condition, additional correlations were within the primary and association audiovisual areas. Most local maxima remained significant after correcting for brain atrophy. CONCLUSION: PET activity measured during audiovisual stimulation was more sensitive to functional alterations in glucose metabolism in AD patients compared to the resting PET. The association between glucose metabolism and MMSE score was not dependent on brain atrophy.

Regional pattern of hippocampus and corpus callosum atrophy in Alzheimer's disease in relation to dementia severity: evidence for early neocortical degeneration.

We used volumetric MRI and analysis of areas under receiver operating characteristic (ROC) curves to directly compare the extent of hippocampus-amygdala formation (HAF) and corpus callosum atrophy in patients with Alzheimer's disease (AD) in different clinical stages of dementia. Based on neuropathological studies, we hypothesized that HAF atrophy, representing allocortical neuronal degeneration, would precede atrophy of corpus callosum, representing loss of neocortical association neurons, in early AD. HAF and corpus callosum sizes were significantly reduced in 27 AD patients (37% and 16%, respectively) compared to 28 healthy controls. In mildly- and moderately-demented AD patients, the ROC derived index of atrophy was greater for HAF volume than for total corpus callosum area. The index of atrophy of posterior corpus callosum was not significantly different from HAF at mild, moderate or severe stages of dementia. In conclusion, these findings suggest a characteristic regional pattern of allocortical and neocortical neurodegeneraton in AD. Our data indicate that neuronal loss in parietotemporal cortex (represented by atrophy of corpus callosum splenium) may occur simultaneously with allocortical neurodegeneration in mild AD. Moreover, ROC analysis may provide a statistical framework to determine atrophy patterns of different brain structures in neurodegenerative diseases in vivo.

A new rapid landmark-based regional MRI segmentation method of the brain.

BACKGROUND: Neurodegenerative and cerebrovascular diseases show a distinct distribution of regional atrophy and subcortical lesions. OBJECTIVE: To develop an easily applicable landmark-based method for segmentation of the brain into the four cerebral lobes from MRI images. METHOD: The segmentation method relies on a combination of anatomical landmarks and geometrical definitions. It is applied on the surface reconstruction of the MRI volume. The internal borders between the lobes are defined on the axial slices of the brain. The reliability of this method was determined from MRI scans of 10 subjects. To illustrate the use of the method, it was applied to MRI scans of an independent group of 10 healthy elderly subjects and 10 patients with vascular dementia to determine the regional distribution of white matter hyperintensities (WMH). RESULTS: The intra-rater relative error (and intra-class correlation coefficient) of the lobe segmentation ranged from 1.6% to 6.9% (from 0.91 to 0.99). The inter-rater relative error (and intra-class correlation coefficient) ranged from 1.4% to 5.2% (from 0.96 to 0.99). Density of WMH was significantly higher in all four lobes in VD patients compared to controls (p<0.05). Within each group, WMH density was significantly higher in frontal and parietal than in temporal and occipital lobes (p<0.05). CONCLUSION: This landmark based method can accommodate age and disease-related changes in brain morphology. It may be particularly useful for the study of neurodegenerative and cerebrovascular disease and for the validation of template-based automated techniques.