Microstructural properties of the vertical occipital fasciculus explain the variability in human stereoacuity

Abstract

Stereopsis is a fundamental visual function that has been studied extensively. However, it is not clear why depth discrimination (stereoacuity) varies more significantly among people than other modalities. Previous studies reported the involvement of both dorsal and ventral visual areas in stereopsis, implying that not only neural computations in cortical areas but also the anatomical properties of white matter tracts connecting those areas can impact stereopsis and stereoacuity. Here, we studied how human stereoacuity relates to white matter properties by combining psychophysics, diffusion MRI (dMRI), and quantitative MRI (qMRI). We performed a psychophysical experiment to measure stereoacuity, and in the same participants we analyzed the microstructural properties of visual white matter tracts based on two independent measurements, dMRI (fractional anisotropy, FA) and qMRI (macromolecular tissue volume; MTV). Microstructural properties along the right vertical occipital fasciculus (VOF), a major tract connecting dorsal and ventral visual areas, were highly correlated with measures of stereoacuity. This result was consistent for both FA and MTV, suggesting that the structural-behavioral relationship reflects differences in neural tissue density, rather than differences in the morphological configuration of fibers. fMRI confirmed that binocular disparity stimuli activated the dorsal and ventral visual regions near VOF endpoints. No other occipital tracts explained the variance in stereoacuity. In addition, the VOF properties were not associated with differences in performance on a different psychophysical task (contrast detection). These series of experiments suggest that stereoscopic depth discrimination performance is, at least in part, constrained by dorso-ventral communication through the VOF.

Altered functional connectivity of cortical networks in semantic variant Primary Progressive Aphasia

“…Connectivity between the FFA and SPL may be mediated by the vertical occipital fasciculus (VOF), which has projections to the posterior intraparietal sulcus of the dorsal attention network and the fusiform gyrus of the visual association network (Budisavljevic et al, 2018;Takemura et al, 2016;Yeatman et al, 2014). Supporting the functional evidence of dorsal attention and visual association network communication, the VOF has been implicated in reading (Greenblatt, 1973(Greenblatt, , 1976), depth perception (Oishi et al, 2018), and object related motor actions (Budisavljevic et al, 2018). Although the VOF connects regions of the visual association and dorsal attention networks, the white matter architecture that would support direct connectivity between the nodes of interest in this study (the SPL and FFA) is not understood.…”

BOLD fMRI signals of visual white matter encode visuotopic information and predict effective connectivity between visual areas

“…Vertical occipital fasciculus (VOF) is the fiber bundle connecting dorsolateral and ventrolateral visual cortex (20, 21). It plays critical roles in processing higher level visual information, such as stereopsis, object category information, and visual-motor control signals (20–22). To the best of our knowledge, the retinotopic organization of VOF has not been investigated.…”

Perspectives given by structural connectivity bridge the gap between structure and function

“…At a cellular/ molecular level, the type of synapses will impact the underlying neural circuitry with quite different functional implications (Bargmann and Marder 2013). At a macroscopic level, there is increasing evidence from dMRI studies showing that differences in white matter bundles can explain behavioural diversity among human individuals (Catani et al 2007;Thiebaut de Schotten et al 2011;Huber et al 2018;Oishi et al 2018), as well as impact precision medicine (Forkel et al 2014Takemura et al 2019;Forkel and Thiebaut de Schotten 2020).…”