Mapping Human Brain Pathways: Challenges and Opportunities in the Integration of Scales

Abstract

The human brain is composed of a complex web of pathways. Diffusion magnetic resonance (MR) tractography relies on the principle of diffusion to reconstruct brain pathways. Its tractography is broadly applicable to a range of problems as it is amenable to being studied in individuals of any age and from any species. However, it is well-known that this technique can generate biologically implausible pathways, especially in regions of the brain where multiple fibers cross. This review highlights potential mis-connections in two cortico-cortical association pathways with a focus on the aslant tract and inferior frontal occipital fasciculus. There is a lack of alternative methods to validate observations from diffusion MR tractography, which emphasize the need to develop new integrative approaches to trace human brain pathways. This review discusses integrative approaches in neuroimaging, anatomical, and transcriptional variation as having much potential to trace pathways and map modifications in the evolution of human brain pathways.

The time-evolving epileptic brain network: concepts, definitions, accomplishments, perspectives

“…In order to identify such network constituents, a large number of approaches is employed to parcellate the brain ( Eickhoff et al, 2018 ; Amunts et al, 2020 ; Bijsterbosch et al, 2020 ; Royer et al, 2022b ) and to identify and characterize white matter fibers ( Mori and Van Zijl, 2002 ; Jeurissen et al, 2019 ). The variety of techniques requires appropriate approaches to verify and increase the reproducibility of results ( Bonilha et al, 2015 ; Welton et al, 2015 ; Zalesky et al, 2016 ; Roine et al, 2019 ; Lawrence et al, 2021 ; Alemán-Gómez et al, 2022 ; Borrelli et al, 2022 ; Seider et al, 2022 ; Charvet, 2023 ; Madole et al, 2023 ).…”

Polarimetric Images of Biological Tissues Based on the Arrow Decomposition of Mueller Matrices

“…Therefore, with this channel, we are capable of detecting information about the directionality of the fibers by means of macroscopic and nondestructive measures of the sample. Brain connectivity and its functional expression is probably the present frontier of applied neuroscience, as there is no gold-standard technique for pathway mapping apart from peri-mortem tract-tracing injections that are not ethically suitable for the study of human connectivity [77]. Histology or ultrastructure-based methods can distinguish fiber orientation but are not useful for tracing long range tracts, which are only revealed by specific techniques of microdissection [78] where resolution in smaller areas is lost.…”

“…In vivo diffusion magnetic resonance tractography is a widely used method that, however, lacks (by design) histological counterchecks and is unable to resolve crossing tracts, as well as providing amputated images in areas such as the corticospinal tract where terminations are unambiguous (see Ref. [77] for a review on the matter). There are two methodological studies that provide acceptable anatomical resolution after the ex vivo analysis of the directionality of white matter tracts in large specimens: optical coherence tomography [79] and Mueller matrix polarimetry [80].…”