Interindividual Variation in Fornix Microstructure and Macrostructure Is Related to Visual Discrimination Accuracy for Scenes But Not Faces

Abstract

Transection of the nonhuman primate fornix has been shown to impair learning of configurations of spatial features and object-in-scene memory. Although damage to the human fornix also results in memory impairment, it is not known whether there is a preferential involvement of this white-matter tract in spatial learning, as implied by animal studies. Diffusion-weighted MR images were obtained from healthy participants who had completed versions of a task in which they made rapid same/different discriminations to two categories of highly visually similar stimuli: (1) virtual reality scene pairs; and (2) face pairs. Diffusion-MRI measures of white-matter microstructure [fractional anisotropy (FA) and mean diffusivity (MD)] and macrostructure (tissue volume fraction, f) were then extracted from the fornix of each participant, which had been reconstructed using a deterministic tractography protocol. Fornix MD and f measures correlated with scene, but not face, discrimination accuracy in both discrimination tasks. A complementary voxelwise analysis using tract-based spatial statistics suggested the crus of the fornix as a focus for this relationship. These findings extend previous reports of spatial learning impairments after fornix transection in nonhuman primates, critically highlighting the fornix as a source of interindividual variation in scene discrimination in humans.

Temporal lobe contribution to perceptual function: A tale of three patient groups

“…For example, in one study combining measurements of white matter structure, functional selectivity and behavior in the same subjects, two parallel white matter tracts were uncovered, one connecting to face-and one to place-selective regions and the diffusion properties correlated with behavioral profile for face or place processing (Gomez et al, 2015). Even more pertinent are the findings from recent studies of the contribution of the inferior longitudinal fasciculus, ILF, and the fornix in perceptual discrimination tasks similar to those used here (Hodgetts et al, 2015;Postans et al, 2014). Microstructure of the fornix, a principal tract linking the HC with adjacent cortical and subcortical structures, was correlated with perceptual discriminations of scenes but not faces, and, conversely, microstructure of the ILF, the main ventral pathway to the anterior temporal lobe was correlated with perceptual discriminations of faces but not of scenes.…”

“…Functional MRI studies show activation of MTL during perception using tasks similar to those employed in the neuropsychological studies alluded to above, with differential recruitment of the HC and PrC for scene and object/face discriminations, respectively (Barense, Henson, Lee, & Graham, 2010;Erez, Cusack, Kendall, & Barense, 2015;Hodgetts et al, 2015;Lee, Scahill, & Graham, 2008;Mundy, Downing, Dwyer, Honey, & Graham, 2013;Mundy, Downing, & Graham, 2012;O'Neil, Cate, & Kohler, 2009). Emerging investigations using diffusion MRI also reveal similar functional dissociations; using the same tasks as above, interindividual differences in scene and face perceptual discrimination accuracy was associated with interindividual variability in two white matter tracts connected to the HC and PrC, respectively (Hodgetts et al, 2015;Postans et al, 2014).…”

Category specificity in the medial temporal lobe: A systematic review

“…This evidence is preliminary due to the small number of studies, but it offers a compelling complement to the neuroimaging and lesion studies. Both studies found associations between structural measures of the fornix white matter and scene perception (Hodgetts et al, ; Postans et al, ). The fornix is the major white matter projection originating from the hippocampus (Aggleton & Brown, ).…”

White matter pathways supporting individual differences in epistemic and perceptual curiosity

“…The hippocampus is a medial temporal lobe structure supporting the encoding and recall of long-term memory (Burgess et al, 2002; Davachi, 2006; Eichenbaum et al, 2007; Murray et al, 2018). Given that the hippocampus has been implicated in a number of processes critical to curiosity, including exploration, reward seeking and novelty detection (O’Keefe and Nadel, 1978; Murray et al, 2017; Kumaran and Maguire, 2009; Voss et al 2017), we investigated the relationship between curiosity and the fornix - the principal tract linking the hippocampus with sites beyond the temporal lobe (Postans et al, 2014; Rudebeck et al, 2009). Regarding the relationship between curiosity and fornix microstructure, we performed analyses targeting the microstructure of the whole fornix, but also the anterior and posterior hippocampal fornix segments that correspond to the functional subdivisions of the anterior and posterior hippocampus, respectively (Christiansen et al, 2017; Saunders and Aggleton, 2007).…”