Biology subjects

Postans, M.

Publications and source records attributed to Postans, M..

6 recordsLinked to original sources

bioRxiv2025

Fornix subdivisions and spatial learning: a diffusion MRI study

The fornix is the major white matter tract linking the hippocampal formation with distal brain sites. Human and animal lesion studies show that the connections comprising the fornix are vital for specific attributes of episodic and spatial memory. The fornix, however, interconnects the hippocampal formation with an array of subcortical and cortical sites and it is not known which specific connections support spatial-mnemonic function. To address this, making use of a partly previously published dataset (Hodgetts et al., 2020), we applied a novel deterministic tractography protocol to diffusion-weighted magnetic resonance imaging (dMRI) data from a group of healthy young adult humans who separately completed a desktop-based virtual reality analogue of the Morris water maze task. The tractography protocol enabled the two main parts of the fornix, delineated previously in axonal tracing studies in rodents and primates, to be reconstructed in vivo, namely the pre-commissural fornix (connecting the hippocampus to the medial prefrontal cortex and the basal forebrain) and the post-commissural fornix (connecting the hippocampus to the medial diencephalon). We found that inter-individual differences in pre-commissural - but not, surprisingly, post-commissural - fornix microstructure (indexed by free water corrected fractional anisotropy, FA) were significantly correlated with individual differences in spatial learning, indexed by reduction in search error as individuals learned to navigate to a hidden target location from multiple starting points. This study provides novel evidence that flexible and/or precise spatial learning involves a hippocampal-basal forebrain/prefrontal network underpinned in part by the pre-commissural fornix.

neuroscience↗

bioRxiv2022

The association between real-world experiential diversity and event cognition

Parsing experience into meaningful events or units, known as event segmentation, may be critical for structuring episodic memory, planning, and navigating the spatial and social world. However, little is known about what factors shape inter-individual differences in event segmentation. Here, we show that individuals with greater variation in their daily social and spatial lives (experiential diversity) displayed more fine-grained event segmentation during a movie-viewing task. Further analyses revealed that this relationship held after considering potential confounds, such as anxiety and loneliness, and was primarily driven by variation in social experiential diversity. These results support the view that event segmentation can occur proactively based on social and spatial environmental dynamics learned in the wild and provide a potential cognitive pathway through which isolation impacts cognitive health.

animal behavior and cognition↗

bioRxiv2021

Subiculum - BNST Structural Connectivity in Humans and Macaques

Invasive tract-tracing studies in rodents implicate a direct connection between the subiculum and bed nucleus of the stria terminalis (BNST) as a key component of neural pathways mediating hippocampal regulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. A clear characterisation of the connections linking the subiculum and BNST in humans and non-human primates is lacking. To address this, we first delineated the projections from the subiculum to the BNST using anterograde tracers injected into macaque monkeys, revealing evidence for a monosynaptic subiculum-BNST projection involving the fornix. Second, we used in vivo diffusion MRI tractography in macaques and humans to demonstrate substantial subiculum complex connectivity to the BNST in both species. This connection was primarily mediated through the fornix, with additional connectivity via the amygdala, consistent with rodent anatomy. Third, utilising the twin-based nature of our human sample, we found that microstructural properties of these tracts are moderately heritable (h2 [~] 0.5). In a final analysis, we found no evidence of any significant association between subiculum complex-BNST tract microstructure and indices of perceived stress/dispositional negativity and alcohol use, derived from principal component analysis decomposition of self-report data. We did, however, find subiculum complex-BNST tract microstructure associations with BMI, age, and sex. Our findings address a key translational gap in our knowledge of the neurocircuitry regulating stress.

neuroscience↗

bioRxiv2019

The role of the pre-commissural fornix in episodic autobiographical memory and simulation

Neuropsychological and functional magnetic resonance imaging (MRI) evidence suggests that the ability to vividly remember our personal past, and imagine future scenarios, involves two closely connected regions: the hippocampus and ventromedial prefrontal cortex (vmPFC). Despite evidence of a direct anatomical connection from hippocampus to vmPFC, it is unknown whether hippocampal-vmPFC structural connectivity supports both past and future-oriented episodic thinking. To address this, we applied diffusion-weighted magnetic resonance imaging (dMRI) and a novel deterministic tractography protocol to reconstruct distinct subdivisions of the fornix previously detected in axonal tracer studies, namely pre-commissural (connecting the hippocampus to vmPFC) and post-commissural (linking the hippocampus and medial diencephalon) fornix, in a group of healthy young adult humans who undertook an adapted past-future autobiographical interview. As predicted, we found that inter-individual differences in pre-commissural - but not post-commissural - fornix microstructure (fractional anisotropy) was significantly correlated with the episodic richness of both past and future autobiographical narratives. Notably, these results remained significant when controlling for both non-episodic narrative content and grey matter volumes of the hippocampus and vmPFC. This study provides novel evidence that reconstructing events from ones personal past, and constructing possible future events, involves a distinct, structurally-instantiated hippocampal-vmPFC pathway. Significance StatementA novel anatomically-guided protocol that allows the pre-commissural and post-commissural fornix fibers to be separately reconstructed in vivo (Christiansen et al., 2016) was applied to reconstruct the pre-commissural subdivision of the white matter fornix tract (anatomically linking the hippocampal formation to the vmPFC) and investigate its contribution to episodic memory and future simulation. We demonstrated that the amount of episodic details contained in past and future narratives, collected via an adapted autobiographical interview, was positively correlated with pre-, but not post-, commissural fornix microstructure. These findings highlight how inter-individual variation in the pre-commissural subdivision of the fornix underpins the construction of self-reflective, contextual events - for both the past and future.

neuroscience↗

bioRxiv2018

Uncovering a role for the dorsal hippocampal commissure in episodic memory

The dorsal hippocampal commissure (DHC) is a white matter tract that provides inter-hemispheric connections between temporal lobe brain regions. Despite the importance of these regions for learning and memory, there is scant evidence of a role for the DHC in successful memory performance. We used diffusion-weighted MRI (DW-MRI) and white matter tractography to reconstruct the DHC across both humans (in vivo) and nonhuman primates (ex vivo). Across species, our findings demonstrate close consistency between the known anatomy and tract reconstructions of the DHC. Anterograde tract-tracer techniques also highlighted the parahippocampal origins of DHC fibers in nonhuman primates. Finally, we derived Diffusion Tensor MRI (DT-MRI) metrics from the DHC in a large sample of human subjects to investigate whether inter-individual variation in DHC microstructure is predictive of memory performance. The mean diffusivity of the DHC was correlated with performance in a standardised episodic memory task; an effect that was not reproduced in a comparison commissure tract - the anterior commissure. These findings highlight a role for the DHC in episodic memory, and our tract reconstruction approach has the potential to generate further novel insights into the role of this previously understudied white matter tract in both health and disease.

neuroscience↗

bioRxiv2018

Increased posterior default mode network activity and structural connectivity in young adult APOE-ε4 carriers: a multi-modal imaging investigation

Young adult APOE-{varepsilon}4 carriers show increased activity in posterior regions of the default mode network (pDMN), but how this is related to structural connectivity is unknown. Thirty young adults (half APOE-{varepsilon}4 carriers, the other half APOE-{varepsilon}3{varepsilon}3/{varepsilon}2{varepsilon}3; mean age 20 years) were scanned using both diffusion and functional magnetic resonance imaging. Diffusion tractography was used to quantify the microstructure (mean diffusivity, MD; fractional anisotropy, FA) of the parahippocampal cingulum bundle (PHCB), which links pDMN and the medial temporal lobe. APOE-{varepsilon}4 carriers had lower MD and higher FA relative to non-carriers in PHCB. Further, PHCB microstructure was selectively associated with pDMN activity during a scene discrimination task known to be sensitive to Alzheimers disease (AD). These findings are consistent with a lifespan view of AD risk, where early-life structural and functional brain changes in specific, vulnerable networks leads to increased neural activity that may ultimately trigger amyloid-{beta} deposition.

neuroscience↗