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Title: Virtual dissection of subcortical non-image forming visual pathways in the human brain with DTI tractography
Author: Koller, Kristin
ISNI:       0000 0004 6352 3685
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2016
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This thesis presents novel evidence in support of a functional role for the anatomy of subcortical non-image forming white matter connections in the human brain. Observations of preserved ability to process threat in the absence of visual awareness in cortically blind patients suggest the existence of an older, primitive and phylogenetically conserved visual circuit that processes orientation to threat. Three pathways including the retinotectal tract, the stria terminalis and a putative pathway for processing visual threat connecting the superior colliculus and the amygdala via the pulvinar were virtually dissected with DTI tractography in healthy participants in vivo. Additionally, connectivity strength of dissected pathways were tested as predictors of performance on behavioural eye-tracking paradigms designed to optimise reflexive orienting responses to salient peripheral visual stimuli including abrupt onsets and threat. Behavioural findings demonstrated a temporal hemifield advantage for short latency reflexive saccades performed within a ‘gap’ paradigm, supporting the prediction that the superior colliculus receives retinal afferents via the retinotectal pathway that summon reflexive saccades. Saccadic bias to orient to threatening stimuli on a temporal order saccade decision task also demonstrated an advantage in the temporal hemifield, consistent with predictions that retinal afferents to the superior colliculus contribute to a subcortical threat mediating circuit connecting the superior colliculus, pulvinar and amygdala. Connectivity strength of anatomical demonstrations of a putative threat mediating connection between the superior colliculus, pulvinar and amygdala predicted a bias to orient to visual threat, thereby validating anatomical dissections presented here with functional evidence. Topography of the SC-amygdala pathway demonstrated a trajectory from the pulvinar to the lateral amygdala. The anatomy of the outflow of the amygdala connecting to the bed nucleus of the stria terminalis was also considered, demonstrating anatomically distinct trajectories of the two pathways despite occupying topographies in close proximity. Stria terminalis connectivity strength also predicted a bias to threat, providing novel evidence for a functional role in selective orienting to threat, potentially driven by superior-colliculus afferents to amygdala nuclei.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available