Abnormal Brain Connectivity in the Primary Visual Pathway in Human Albinism

In albinism, the ipsilateral projection of retinal axons is significantly reduced, and most fibres project contralaterally. The retina and optic chiasm have been proposed as sites for misrouting. The number of lateral geniculate nucleus (LGN) relay neurons has been linked to LGN volume, suggesting a correlation between LGN size and the number of tracts traveling through the optic radiation (OR) to the primary visual cortex (V1). Using diffusion data and both deterministic and probabilistic tractography, we studied differences in OR between albinism and controls. Statistical analyses measured white matter integrity in areas corresponding to the OR, as well as LGN to V1 connectivity. Results revealed reduced white matter integrity and connectivity in the OR region in albinism compared to controls, suggesting altered structural development. Previous reports of smaller LGN and the altered thalamo-cortical connectivity reported here demonstrate the effect of misrouting on structural organization of the visual pathway in albinism

Attention alters certainty but not appearance

We measured subjects’ decision confidence to determine whether paying attention to a stimulus altered its appearance or merely influenced the response decision mechanism. In three separate experiments, subjects judged the relative appearance of two Gabor patches, one of which was cued, that differed in contrast and reported whether they were certain of each response. In Experiments 1 and 2, subjects performed a comparative judgment, reporting which stimulus had the higher contrast, and in Experiment 3, subjects performed an equality judgment, reporting whether the two stimuli had the same or different contrast. Experiments 1 and 3 employed an exogenous attentional pre-cue, and Experiment 2 used a non-attentional post-cue, with explicit instructions to choose the cued target when uncertain. We modeled the subjects’ confidence as the totality of the information present in each trial, which included the contrast of each target stimulus, the decision function based on the difference between their contrasts, and the boost in information caused by attention. In Experiments 1 and 2, the cues caused subjects to more likely report that the cued stimulus had higher contrast. In Experiment 1, attention shifted the subjects’ confidence distribution, while the post-cue in Experiment 2 did not. In Experiment 3, attention did not affect the contrast judgment but did shift the confidence distribution. We thus report interesting disconnects between confidence and decisions, which were predicted by our model. We conclude that attention acts early in the decision process, but without overwriting the veridical contrast appearance, which is still available to subjects.</p

Measuring Connectivity in the Primary Visual Pathway in Human Albinism Using Diffusion Tensor Imaging and Tractography

In albinism, the number of ipsilaterally projecting retinal ganglion cells (RGCs) is significantly reduced. The retina and optic chiasm have been proposed as candidate sites for misrouting. Since a correlation between the number of lateral geniculate nucleus (LGN) relay neurons and LGN size has been shown, and based on previously reported reductions in LGN volumes in human albinism, we suggest that fiber projections from LGN to the primary visual cortex (V1) are also reduced. Studying structural differences in the visual system of albinism can improve the understanding of the mechanism of misrouting and subsequent clinical applications. Diffusion data and tractography are useful for mapping the OR (optic radiation). This manuscript describes two algorithms for OR reconstruction in order to compare brain connectivity in albinism and controls.An MRI scanner with a 32-channel head coil was used to acquire structural scans. A T1-weighted 3D-MPRAGE sequence with 1 mm(3 )isotropic voxel size was used to generate high-resolution images for V1 segmentation. Multiple proton density (PD) weighted images were acquired coronally for right and left LGN localization. Diffusion tensor imaging (DTI) scans were acquired with 64 diffusion directions. Both deterministic and probabilistic tracking methods were run and compared, with LGN as the seed mask and V1 as the target mask. Though DTI provides relatively poor spatial resolution, and accurate delineation of OR may be challenging due to its low fiber density, tractography has been shown to be advantageous both in research and clinically. Tract based spatial statistics (TBSS) revealed areas of significantly reduced white matter integrity within the OR in patients with albinism compared to controls. Pairwise comparisons revealed a significant reduction in LGN to V1 connectivity in albinism compared to controls. Comparing both tracking algorithms revealed common findings, strengthening the reliability of the technique

Elevated C-reactive protein among symptomatic youth with bipolar disorder

Rationale and Objectives: Increased levels of high-sensitivity C-reactive protein (CRP) are associated with mood symptoms in adults with bipolar disorder (BD). The few studies on this topic in youth with BD have not included controls. We, therefore, examined CRP levels in relation to symptomatic status in youth with and without BD. Methods: Participants included 154 youth (mean age 17 years; 48 asymptomatic BD, 39 symptomatic BD, 67 healthy controls (HC)). Rank analysis of covariance test examined group differences in CRP, controlling for age and sex. Correlation between CRP and mood symptom severity was examined using Spearman’s correlation within the BD group. Results: There were significant group differences in CRP levels ( F(2,151) = 5.06, p = 0.007, [Formula: see text]); post hoc analyses showed higher CRP levels in the symptomatic BD group compared with HC ( p = 0.01). In sensitivity analyses, this finding was no longer significant after controlling for body mass index (BMI). CRP was not significantly associated with symptomatic severity. Conclusions: CRP levels are elevated among symptomatic youth with BD, partly related to BMI. As elevated BMI is associated with mood symptom burden, prospective studies are warranted to parse the associations among mood symptoms, BMI, and inflammation. Given the proportion of time that youth with BD are symptomatic, present findings raise concern about the long-term impact of elevated CRP on blood vessels, brain, and related clinical outcomes. </jats:sec