The brain should integrate related but not unrelated information from different senses. Temporal patterning of inputs to different modalities may provide critical information about whether those inputs are related or not. We studied effects of temporal correspondence between auditory and visual streams on human brain activity with functional magnetic resonance imaging (fMRI). Streams of visual flashes with irregularly jittered, arrhythmic timing could appear on right or left, with or without a stream of auditory tones that coincided perfectly when present (highly unlikely by chance), were noncoincident with vision (different erratic, arrhythmic pattern with same temporal statistics), or an auditory stream appeared alone. fMRI revealed blood oxygenation level-dependent (BOLD) increases in multisensory superior temporal sulcus (mSTS), contralateral to a visual stream when coincident with an auditory stream, and BOLD decreases for noncoincidence relative to unisensory baselines. Contralateral primary visual cortex and auditory cortex were also affected by audiovisual temporal correspondence or noncorrespondence, as confirmed in individuals. Connectivity analyses indicated enhanced influence from mSTS on primary sensory areas, rather than vice versa, during audiovisual correspondence. Temporal correspondence between auditory and visual streams affects a network of both multisensory (mSTS) and sensory-specific areas in humans, including even primary visual and auditory cortex, with stronger responses for corresponding and thus related audiovisual inputs.

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The locus coeruleus (LC), a major origin of noradrenergic projections in the central nervous system (CNS), may serve a critical role in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). As such, there is considerable interest to develop magnetic resonance imaging (MRI) techniques to assess the integrity of the LC in vivo. The high neuromelanin content of the LC serves as an endogenous contrast for MRI but existing protocols suffer from low spatial resolution along the rostrocaudal axis of the LC rendering it difficult to differentiate its integrity in caudal and rostral portions. This study presents a novel approach to investigate the human LC in vivo using T-weighted Fast Low Angle Shot (FLASH) MRI at 3 T (T). Using high-resolution isotropic imaging to minimise the effect of low spatial resolution in the slice direction, this study aimed to characterise the rostrocaudal distribution of LC signal intensity attributed to neuromelanin from 25 young (22-30) and 57 older (61-80) adults. We found a significant age-related increase in maximum but not median signal intensity, indicating age-related differences were not homogenous. Instead, they were confined to the rostral third of the LC with relative sparing of the caudal portion. The findings presented demonstrate in vivo T-weighted FLASH imaging may be used to characterise signal intensity changes across the entire rostrocaudal length of the LC (a corresponding standardised LC map is available for download), which may help to identify how the human LC is differentially affected in aging and neurodegenerative disease.

In echo-planar-based diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI), the evaluation of diffusion parameters such as apparent diffusion coefficients and anisotropy indices is affected by image distortions that arise from residual eddy currents produced by the diffusion-sensitizing gradients. Correction methods that coregister diffusion-weighted and non-diffusion-weighted images suffer from the different contrast properties inherent in these image types. Here, a postprocessing correction scheme is introduced that makes use of the inverse characteristics of distortions generated by gradients with reversed polarity. In this approach, only diffusion-weighted images with identical contrast are included for correction. That is, non-diffusion-weighted images are not needed as a reference for registration. Furthermore, the acquisition of an additional dataset with moderate diffusion-weighting as suggested In diffusion-weighted echo-planar imaging (EPI), eddycurrent-related distortions add to the susceptibility-induced distortions that are generally seen on images measured by EPI. The magnitude and shape of these particular artifacts change with the chosen direction and strength of the applied diffusion-sensitizing gradients. Both diffusionweighted and non-diffusion-weighted images are necessary for the subsequent calculation of diffusion parameters such as apparent diffusion coefficients (ADCs) or anisotropy indices. Thus, significant miscalculations of maps depicting such parameters would occur if the acquired underlying images are warped against each other. Large errors are especially prominent in regions with high local contrast. While computational methods based on MR diffusion imaging, such as fiber tracking algorithms (1,2) or the mathematical modeling of high angular resolved diffusion data (3,4), become more and more sophisticated, attention must be paid to the reliability of the input data.Hence, an optimal distortion correction scheme for diffusion-weighted images still remains a goal.The high impact of eddy currents on diffusion-weighted imaging (DWI) is caused by strong diffusion-sensitizing magnetic field gradients flanked by short ramp times. Because in EPI the bandwidth in the phase-encoding direction is inevitably low, this direction is primarily prone to substantial eddy-current-generated distortions. Until now, several methods have been introduced to mitigate the problems caused by eddy-current-related distortions. Preemphasis settings may facilitate the generation of stabilized and, therefore, eddy-current-neutralizing gradient waveforms (5). Unfortunately, the application of a preemphasis technique does not fully eliminate eddy-currentrelated distortions. For this reason, other methods have been proposed in recent years that either reduce the eddy currents by modifications of the pulse sequence design or correct for the distortions during data postprocessing. Procedures using phantom scans as a reference have been suggested as well (6). Eddy-current-minimizing modifications of the...

LCModel and AMARES, two widely used quantitation tools for magnetic resonance spectroscopy (MRS) data, were employed to analyze simulated spectra similar to those typically obtained at short echo times (TEs) in the human brain at 1.5 T. The study focused mainly on the influence of signal-to-noise ratios (SNRs) and different linewidths on the accuracy and precision of the quantification results, and their effectiveness in accounting for the broad signal contribution of macromolecules and lipids (often called the baseline in in vivo MRS). When applied in their standard configuration (i.e., fitting a spline as a baseline for LCModel, and weighting the first data points for AMARES), both methods performed comparably but with their own characteristics. LCModel and AMARES quantitation benefited considerably from the incorporation of baseline information into the prior knowledge. However, the more accurate quantitation of the sum of glutamate and glutamine (Glx) favored the use of LCModel. Metabolite-to-creatine ratios estimated by LCModel with extended prior knowledge are more accurate than absolute concentrations, and are nearly independent of SNR and line broadening. In clinical magnetic resonance spectroscopy (MRS) of the brain, short echo times (TEs) are employed to optimize the signal-to-noise ratio (SNR), reduce signal attenuation due to transverse relaxation and scalar coupling, and enable the quantification of more than the three dominant singlet resonances (i.e., N-acetylaspartate (NAA), creatine (Cr), and choline (Cho)). Generally, it is difficult to quantify short-TE spectra because of the overlapping metabolite signals and the contribution of macromolecule and lipid components. In addition to software of MR tomographs and various in-house developments at research sites (1-3), two sophisticated and well documented software packages are widely used: LCModel (4) and Magnetic Resonance User Interface (MRUI) (5). These software packages are used worldwide by many groups not only because of their availability and performance, but also because they provide results with a broader basis of comparability. The commercially available software package LCModel (6) fits spectra in the frequency domain using a basis set of spectra of in vitro metabolite solutions acquired under conditions identical to those under which in vivo data are acquired. AMARES (7), which is part of the MRUI package (5), has the advantage of being free of charge to nonprofit organizations. This advanced quantitation toolbox analyzes spectra in the time domain utilizing a priori information that can be introduced flexibly. LCModel employs a "black box" approach, and thus requires less user interaction than AMARES.For application purposes, however, it is important to determine how quantitation depends on linewidth and SNR, and how the two methods handle the broad macromolecular and lipid signal contributions. Of course, the best way to account for macromolecular signal contribution is to acquire the macromolecular spectrum by inversion recovery (8) ...

SignificanceLocus coeruleus (LC) integrity in cognitively normal older adults is a potentially important preclinical marker in dementia. Our study establishes a link between variability in LC integrity and cognitive decline related to noradrenergic modulation in old age. We find that in older adults, reduced LC integrity explains lower memory performance. This effect was more pronounced for memory related to negative events, and accompanied by increased pupil diameter size in response to negative events. The study provides a strong motivation for future research investigating the role of LC integrity in healthy, as well as in pathological, aging.

Summary The absence of the optic chiasm is an extraordinary and extreme abnormality in the nervous system. The abnormality produces highly atypical functional responses in the cortex, including overlapping hemifield representations and bilateral population receptive fields in both striate and extrastriate visual cortex. Even in the presence of these large functional abnormalities, the effect on visual perception and daily life is not easily detected. Here we demonstrate that in two achiasmic humans the gross topography of the geniculo-striate and occipital callosal connections remains largely unaltered. We conclude that visual function is preserved by reorganization of intra-cortical connections instead of large-scale reorganizations of the visual cortex. Thus developmental mechanisms of local wiring within cortical maps compensate for the improper gross wiring to preserve function in human achiasma.

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