The arcuate fasciculi are white‐matter pathways that connect frontal and temporal lobes in each hemisphere. The arcuate plays a key role in the language network and is believed to be left‐lateralized, in line with left hemisphere dominance for language. Measuring the arcuate in vivo requires diffusion magnetic resonance imaging–based tractography, but asymmetry of the in vivo arcuate is not always reliably detected in previous studies. It is unknown how the choice of tractography algorithm, with each method's freedoms, constraints, and vulnerabilities to false‐positive and ‐negative errors, impacts findings of arcuate asymmetry. Here, we identify the arcuate in two independent datasets using a number of tractography strategies and methodological constraints, and assess their impact on estimates of arcuate laterality. We test three tractography methods: a deterministic, a probabilistic, and a tractography‐evaluation (LiFE) algorithm. We extract the arcuate from the whole‐brain tractogram, and compare it to an arcuate bundle constrained even further by selecting only those streamlines that connect to anatomically relevant cortical regions. We test arcuate macrostructure laterality, and also evaluate microstructure profiles for properties such as fractional anisotropy and quantitative R1. We find that both tractography choice and implementing the cortical constraints substantially impact estimates of all indices of arcuate laterality. Together, these results emphasize the effect of the tractography pipeline on estimates of arcuate laterality in both macrostructure and microstructure.

No abstract

How to quantify local axonal orientations Mapping the axonal trajectories of the brain’s white matter at cellular resolution is a long-standing goal of neuroscience. However, existing methods for mapping the axons are either limited to animal studies or require highly specialized equipment for data acquisition and processing. Nissl staining identifies cell nuclei and has been used extensively to investigate parcellations of the cortical gray matter, but the white matter has largely been neglected with this technique. Schurr and Mezer now show that Nissl staining, together with structure tensor analysis, can be used to study white matter architecture and the organization of the glial cell framework around axons over the whole brain. This technique greatly advances our knowledge regarding the organization of glial cells and the fine-grained organization of axonal projections in the brain. —PRS

No abstract

No abstract