Principles of organisation within the pathways in the brainstem and thalamus

Abstract

There are few detailed studies on the pathways through the human brainstem and even fewer on those through the pons. This thesis aims to address this lack of fine detail, and used ultra-high-field magnetic resonance imaging (MRI) of human and macaque brains to identify and characterise fibre tracts connecting cortical and spinal areas as they traverse through brainstem and thalamic structures. The material in this thesis is based on a unique dataset of ultra-high-field (7 Tesla – Duke and 11, 7 Tesla – Johns Hopkins) MRI scans on postmortem specimens, on which deterministic tractography has been applied based on high-angular-resolution diffusion imaging (HARDI) and subsequently higher order tensor glyph models.

The first results section of the thesis (Chapter 3) maps the descending fibre bundles associated with movement. From the motor cortical areas, the fibres of the internal capsule are traced through the crus cerebri, basilar pons and pyramids in three dimensions to reveal their organisation into functional and topographic subdivisions. While human cortico-pontine, -bulbar and -spinal tracts were traditionally considered to be dispersed, or a “melange”, I show here a much more discrete and defined organisation of these descending fibre bundles.

Nine descending fibre bundles are identified and their anatomical location and terminations are described. A hitherto unknown pathway at the midline of the pons has been discovered and named herein as the Stria Pontis which connects the neocortex to the pontine tegmentum. Ten transverse fibre bundles connecting the pontine nuclei to the cerebellum are also identified.

The second results section (Chapter 4) analyses the sensory pathways; the dorsal column - medial lemniscus pathway, the spinothalamic tract, the spinal trigeminal tract and the trigeminothalamic tracts.

The third results section (Chapter 5) analyses the dentato-rubro-thalamic tract. The mapping identifies the superior cerebellar peduncle, the patterning of the fibres within the superior cerebellar decussation, the patterning of the fibres within the red nucleus and finally the projection of the dentato-rubro-thalamic tract from the red nucleus to the ventral lateral nucleus of the thalamus. Finally, I characterised 117 already known anatomical parts, areas and structures of the brainstem and thalamus in 3D.