The inside-out technique: tailoring fiber dissection for the study of the superficial white matter

2195 

Abstract Submission 

Guillaume Dannhoff^1,2, Alex Morichon¹, Mykyta Smirnov^1,3, Laurent Barantin¹, Christophe Destrieux^1,4, Igor Lima Maldonado^1,4

¹UMR 1253, iBrain, Université de Tours, Inserm, Tours, France, ²CHRU de Strasbourg, Strasbourg, France, ³BAOBAB, NeuroSpin, Paris-Saclay University, CNRS, CEA, Gif-Sur-Yvette, France, ⁴CHRU de Tours, Tours, France

Guillaume Dannhoff  
UMR 1253, iBrain, Université de Tours, Inserm|CHRU de Strasbourg
Tours, France|Strasbourg, France

Alex Morichon  
UMR 1253, iBrain, Université de Tours, Inserm
Tours, France

Mykyta Smirnov  
UMR 1253, iBrain, Université de Tours, Inserm|BAOBAB, NeuroSpin, Paris-Saclay University, CNRS, CEA
Tours, France|Gif-Sur-Yvette, France

Laurent Barantin  
UMR 1253, iBrain, Université de Tours, Inserm
Tours, France

Christophe Destrieux  
UMR 1253, iBrain, Université de Tours, Inserm|CHRU de Tours
Tours, France|Tours, France

Igor Lima Maldonado  
UMR 1253, iBrain, Université de Tours, Inserm|CHRU de Tours
Tours, France|Tours, France

Despite major methodological advances in the exploration of the cerebral white matter (Axer et al., 2011; Beaujoin et al., 2019) and growing interest in short association fibers (SAF) (Guevara et al., 2020), the latter remain underexplored. The examination of these connections through the classical fiber dissection (Ludwig and Klingler, 1956) is significantly impeded by the fact that the procedure involves the removal of the cerebral cortex, leading to a smooth surface where the bundles are scarcely visible, and causing the loss of a substantial portion of the sulco-gyral anatomy. To address the methodological renewal necessary for the accurate analysis of these delicate and superficial structures, we present the novel technique for inside-out fiber dissection of the post-mortem human brain that approaches subcortical fibers from their deep aspect with the preservation of the cortex.

Six cerebral hemispheres were obtained from a body donation program and fixed in 10% formalin. After two cycles of freezing and thawing (Klingler, 1935), a standardized fiber dissection protocol was carried out, consisting of peeling fibers from deep structures towards the cortex. In the end, it allowed the isolation of intergyral fibers in the subcortical white matter. The following elements were assessed: quality of the dissection plane containing the deeper fasciculi; visibility of fiber crossings, as well as neighboring, intergyral, and intragyral association fibers; and capability of the method to enable the evaluation of thickness of an isolated layer of the subcortical white matter.

Inside-out fiber dissection enabled the selective isolation of the outermost layer of the superficial white matter in the lateral and medial aspects of the human telencephalon. SAF were easily cleaved from deeper fibers, as their deeper aspect was less adherent to underlying fibers than their outer aspect was to the cortex. Characterization of the SAF layer thickness and fiber orientation was performed without significant difficulty. The increased contrast between gray and white matter caused by the tissue preparation enabled the assessment of SAF layer thickness through direct observation and T2-weighted ex vivo MRI.

The inside-out fiber dissection technique effectively demonstrates intergyral association fibers in the post-mortem human brain. This technique completes the neuroscientist's armamentarium, circumventing a severe methodological obstacle and providing the anatomical substrate necessary for modeling neural circuits and validating diffusion imaging of the superficial white matter.

Other Methods ²

Anatomy and Functional Systems

White Matter Anatomy, Fiber Pathways and Connectivity ¹

White Matter

Other - dissection; short association fibers; post-mortem