Older adults are known to gain more than younger adults from the simultaneous presentation of semantically congruent sensory stimuli. Although these findings are quite exciting, they may not solely be due to age-related differences in multisensory processing. Rather, enhanced integration may be explained by alterations associated with general cognitive slowing. This study utilized a task that eliminated most high-order cognitive processing. As such, no significant differences in unisensory response times were seen; however, older adults actually showed faster multisensory responses than younger adults. Older adults continued to show significantly greater multisensory enhancement than younger adults. Data support the conclusion that differences in multisensory processing for older adults cannot be explained solely by the effects of general cognitive slowing.

BackgroundArachidonic acid (AA) is a long-chain omega-6 polyunsaturated fatty acid (PUFA) synthesized from the precursor dihomo-gamma-linolenic acid (DGLA) that plays a vital role in immunity and inflammation. Variants in the Fatty Acid Desaturase (FADS) family of genes on chromosome 11q have been shown to play a role in PUFA metabolism in populations of European and Asian ancestry; no work has been done in populations of African ancestry to date.ResultsIn this study, we report that African Americans have significantly higher circulating levels of plasma AA (p = 1.35 × 10-48) and lower DGLA levels (p = 9.80 × 10-11) than European Americans. Tests for association in N = 329 individuals across 80 nucleotide polymorphisms (SNPs) in the Fatty Acid Desaturase (FADS) locus revealed significant association with AA, DGLA and the AA/DGLA ratio, a measure of enzymatic efficiency, in both racial groups (peak signal p = 2.85 × 10-16 in African Americans, 2.68 × 10-23 in European Americans). Ancestry-related differences were observed at an upstream marker previously associated with AA levels (rs174537), wherein, 79-82% of African Americans carry two copies of the G allele compared to only 42-45% of European Americans. Importantly, the allelic effect of the G allele, which is associated with enhanced conversion of DGLA to AA, on enzymatic efficiency was similar in both groups.ConclusionsWe conclude that the impact of FADS genetic variants on PUFA metabolism, specifically AA levels, is likely more pronounced in African Americans due to the larger proportion of individuals carrying the genotype associated with increased FADS1 enzymatic conversion of DGLA to AA.

Over the past 50 years, increases in dietary n-6 polyunsaturated fatty acids (PUFAs), such as linoleic acid, have been hypothesized to cause or exacerbate chronic inflammatory diseases. This study examines an individual’s innate capacity to synthesize n-6-long chain PUFAs (LC-PUFAs), with respect to the fatty acid desaturase (FADS) locus in Americans of African and European descent with diabetes/metabolic syndrome. Compared to European Americans (EAm), African Americans (AfAm) exhibited markedly higher serum levels of arachidonic acid (AA) (EAm 7.9±2.1; AfAm 9.8±1.9 % of total fatty acids, mean ± sd; p<2.29×10−9) and the AA to n-6-precursor fatty acid ratio, which estimates FADS1 activity (EAm 5.4±2.2, AfAm 6.9±2.2; p=1.44×10−5). Seven single nucleotide polymorphisms (SNP) mapping to the FADS locus revealed strong association with AA, eicosapentaenoic acid (EPA) and dihomogamma-linolenic acid (DGLA) in the EAm. Importantly, EAm homozygous for the minor allele (T) had significantly lower AA levels (TT: 6.3±1.0; GG: 8.5±2.1; p=3.0×10−5) and AA/DGLA ratios (TT: 3.4±0.8; GG: 6.5±2.3; p=2.2×10−7) but higher DGLA levels (TT: 1.9±0.4; GG: 1.4±0.4; p=3.3×10−7) compared to those homozygous for the major allele (GG). Allele frequency patterns suggest that the GG genotype at rs174537 (associated with higher circulating levels of AA) is much higher in AfAm (0.81) compared to EAm (0.46). Similarly, marked differences in rs174537 genotypic frequencies were observed in HapMap populations. These data suggest that there are likely important differences in the capacity of different populations to synthesize LC-PUFAs. These differences may provide a genetic mechanism contributing to health disparities between populations of African and European descent.

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Age-related alterations in white matter have the potential to profoundly affect cognitive functioning. In fact, magnetic resonance imaging (MRI) studies using fractional anisotropy (FA) to measure white matter integrity reveal a positive correlation between FA and behavioral performance in older adults. Confounding these results are imaging studies demonstrating age-related white matter atrophy in some areas displaying altered FA, suggesting changes in diffusion may be simply an epiphenomenon of tissue loss. In the current study, structural MRI techniques were used to identify the relationship between white matter integrity and decreased volume in healthy aging adults. The data demonstrated that white matter atrophy did in fact account for differences in some areas, but significant FA decreases remained across much of the white matter after adjusting for atrophy. Results suggest a complex relationship between changes in white matter integrity and volume. FA appears to be more sensitive than volume loss to changes in normal appearing tissue, and these FA changes may actually precede white matter atrophy in some brain areas. As such, the ability to detect early white matter alterations may facilitate development of targeted treatments that prevent or slow age-related white matter degradation and associated cognitive sequelae.

Stimuli occurring in multiple sensory modalities that are temporally synchronous or spatially coincident can be integrated together to enhance perception. Additionally, the semantic content or meaning of a stimulus can influence cross-modal interactions, improving task performance when these stimuli convey semantically congruent or matching information, but impairing performance when they contain non-matching or distracting information. Attention is one mechanism that is known to alter processing of sensory stimuli by enhancing perception of task-relevant information and suppressing perception of task-irrelevant stimuli. It is not known, however, to what extent attention to a single sensory modality can minimize the impact of stimuli in the unattended sensory modality and reduce the integration of stimuli across multiple sensory modalities. Our hypothesis was that modality-specific selective attention would limit processing of stimuli in the unattended sensory modality, resulting in a reduction of performance enhancements produced by semantically matching multisensory stimuli, and a reduction in performance decrements produced by semantically non-matching multisensory stimuli. The results from two experiments utilizing a cued discrimination task demonstrate that selective attention to a single sensory modality prevents the integration of matching multisensory stimuli that is normally observed when attention is divided between sensory modalities. Attention did not reliably alter the amount of distraction caused by non-matching multisensory stimuli on this task; however, these findings highlight a critical role for modality-specific selective attention in modulating multisensory integration.

Previous research demonstrates that modality-specific selective attention attenuates multisensory integration in healthy young adults. Additionally, older adults evidence enhanced multisensory integration compared to younger adults. We hypothesized that these increases were due to changes in top-down suppression, and therefore older adults would demonstrate multisensory integration while selectively attending. Performance of older and younger adults was compared on a cued discrimination task. Older adults had greater multisensory integration than younger adults in all conditions, yet were still able to reduce integration using selective attention. This suggests that attentional processes are intact in older adults, but are unable to compensate for an overall increase in the amount of sensory processing during divided attention.

Determining power and sample size in neuroimaging studies is a challenging task because of the massive multiple comparisons among tens of thousands of correlated voxels. To facilitate this task, we propose a power analysis method based on random field theory (RFT) by modeling signal areas within images as non-central random field. With this framework, power can be calculated for specific areas of anticipated signals within the brain while accounting for the 3D nature of signals. This framework can also be extended to visualize local variability in sensitivity as a power map and a sample size map. We validated our non-central RFT framework based on Monte-Carlo simulations. Moreover, we applied our method to a blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) data set with a small sample size in order to demonstrate its use in study planning. From the simulations, we found that our method was able to estimate power quite accurately. In the fMRI data analysis, despite the small sample size, we were able to determine power and the number of subjects required to detect signals.