Objective: To examine the relationship between structural organization, functional processing and task performance of the visual system in a cohort of Huntington’s disease (HD) gene-mutation carriers and healthy controls using multimodal and electrophysiological data.

Background: Although characteristically defined by motor, cognitive and neuropsychiatric symptoms, there is mounting evidence that the visual cortex is one of the earliest cortical regions to be affected by degeneration in HD. [1] Examining localized structure-function relationships in HD can help differentiate between network-wide changes that are specific to the presence of the Huntingtin gene (HTT) mutation and those which represent natural biological variability.

Method: Participants were recruited from the Leiden site of the international multicenter Track-On HD study and comprised of 20 HD gene-mutation carriers (mean age 49.2 years, 12 female) and 24 healthy controls (mean age 52.5 years, 16 female). We obtained multimodal 3-T MRI (cortical thickness, diffusion tensor imaging tractography, resting state fMRI effective connectivity) and electrophysiological data (visual evoked potentials). Furthermore, task performance on two well-established visual processing tasks were obtained: Map Search and Symbol Digit Modalities Test.

Results: Using principal component analysis, we identified patterns that indicate a close relationship between structural organization of the visual system and efficient functional processing. One such pattern related higher primary visual cortical thickness, lower diffusivity in the visual pathway and higher effective connectivity between the visual thalamic region and primary and association regions of the visual cortex. This was common to both controls and HD participants suggesting a naturally occurring pattern that was not substantially influenced by the HTT mutation. However, HD participants had higher diffusivity in white matter tracts of the visual pathway, less efficient top-down processing and reduced VEP responsivity.

Conclusion: These findings suggest that HD may be associated with a less effective visual processing system. However, the lack of correlation with visual task performance indicates a possible dissociation between behavior and the assessed properties of the visual network in the brain at rest or alternatively, the possible effects of compensatory processes.

References: [1] Odish OFF, Reijntjes RHAM, van den Bogaard SJA, et al. Progressive microstructural changes of the occipital cortex in Huntington’s disease. Brain Imaging Behav. 2018; 12:1786-1794.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/multimodal-characterization-of-the-visual-network-in-huntingtons-disease/