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.

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.

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.

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.

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

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.

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.

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.

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.