Biology subjects

Umla-Runge, K.

Publications and source records attributed to Umla-Runge, K..

4 recordsLinked to original sources

bioRxiv2024

Multimodal MEG and microstructure-MRI investigations of the human hippocampal scene network

Although several studies have demonstrated that perceptual discrimination of complex scenes relies on an extended hippocampal network, distinct from an anterotemporal network supporting the perceptual discrimination of faces, we currently have limited insight into the specific functional and structural properties of these networks. Here, combining electrophysiological (magnetoencephalography, MEG) and microstructural (multi-shell diffusion MRI, dMRI) imaging in healthy human adults (30 female/10 male), we show that both hippocampal theta power modulation and fibre restriction of the fornix (a major input/output pathway of the hippocampus) independently related to accuracy during scene, but not face, perceptual discrimination. Conversely, microstructural features of the inferior longitudinal fasciculus (a long-range occipito- anterotemporal tract) correlated with face, but not scene, perceptual discrimination accuracy. Our results provide new mechanistic insight into the neurocognitive systems underpinning complex scene and face perception, providing support for multiple-system representation-based accounts of the medial temporal lobe. Significance StatementIn contrast to theories positing segregated cortical areas for perception and memory, the specialized representations of the hippocampus may support both the perception and memory of visual scenes. To investigate, we utilised the unique window into hippocampal electrophysiological activity offered by Magnetoencephalography (MEG). We found hippocampal theta activity modulations in the hippocampus and posteromedial cortex during scene, versus face and shape-size, perceptual oddity discrimination, the magnitude of which correlated with scene, but not face or shape- size, discrimination accuracy. Moreover, multimodal white matter imaging revealed that tissue restriction of the fornix - the major hippocampal output tract - independently predicted scene discrimination performance. Our multimodal MEG-microstructure study provides novel evidence that the hippocampus and connected structures conjointly support online scene processing.

neuroscience↗

bioRxiv2022

A Role for the Fornix in Temporal Sequence Memory

Converging evidence from studies of human and nonhuman animals suggests that the hippocampus contributes to sequence learning by using temporal context to bind sequentially occurring items. The fornix is a white matter pathway containing the major input and output pathways of the hippocampus, including projections from medial septum, and to diencephalon, striatum, and prefrontal cortex. If the fornix meaningfully contributes to hippocampal function, then individual differences in fornix microstructure might predict sequence memory. Here, we tested this prediction by performing tractography in 51 healthy adults who had undertaken a sequence memory task. Microstructure properties of the fornix were compared with those of tracts connecting medial temporal lobe regions, but not predominantly the hippocampus: the Parahippocampal Cingulum bundle (PHC) (conveying retrosplenial projections to parahippocampal cortex) and the Inferior Longitudinal Fasciculus (ILF) (conveying occipital projections to perirhinal cortex). Using principal components analysis, we combined Diffusion Tensor Imaging and Neurite Orientation Dispersion and Density Imaging measures obtained from multi-shell diffusion MRI into two informative indices, the first (PC1) capturing axonal packing/myelin, the second (PC2) capturing microstructural complexity. We found a significant correlation between fornix PC2 and implicit reaction-time indices of sequence memory, indicating that greater fornix microstructural complexity is associated with better sequence memory. No such relationship was found with measures from the PHC and ILF. This study highlights the importance of the fornix in aiding memory for objects within a temporal context, potentially reflecting a role in mediating network communication within an extended hippocampal system.

neuroscience↗

bioRxiv2021

Evidence against altered excitatory/inhibitory balance in the posteromedial cortex of young adult APOE E4 carriers: a resting state 1H-MRS study

A strategy to gain insight into early changes that may predispose people to Alzheimers disease is to study the brains of younger cognitively healthy people that are at increased genetic risk of AD. The Apolipoprotein (APOE) E4 allele is the strongest genetic risk factor for AD, and several neuroimaging studies comparing APOE E4 carriers with non-carriers at age ~20-30 have detected hyperactivity (or reduced deactivation) in posteromedial cortex (PMC), a key hub of the default network (DN) which has a high susceptibility to early amyloid deposition in AD. Transgenic mouse models suggest such early network activity alterations may result from altered excitatory/inhibitory (E/I) balance, but this is yet to be examined in humans. Here we test the hypothesis that PMC fMRI hyperactivity could be underpinned by altered levels of excitatory (glutamate) and/or inhibitory (GABA) neurotransmitters in this brain region. Forty-seven participants (20 APOE E4 carriers and 27 non-carriers) aged 18-25 underwent resting-state proton magnetic resonance spectroscopy (1H-MRS), a non-invasive neuroimaging technique to measure glutamate and GABA in vivo. Metabolites were measured in a PMC voxel of interest and in a comparison voxel in the occipital cortex (OCC). There was no difference in either glutamate or GABA between the E4 carriers and non-carriers in either MRS voxel, nor in the ratio of glutamate to GABA, a measure of E/I balance. Default Bayesian t-tests revealed evidence in support of this null finding. Results suggest that PMC hyperactivity in APOE E4 carriers is unlikely to be associated with, or indeed may precede, alterations in local resting-state PMC neurotransmitters, thus informing the spatio-temporal order and the cause/effect dynamic of neuroimaging differences in APOE E4 carriers. HighlightsO_LIHyperactivity in posteromedial (PM) network in people at AD genetic risk (APOE E4) C_LIO_LISuch PM network hyperactivity may initiate pathogenic cascade that triggers AD C_LIO_LIAPOE mouse models suggest hyperactivity driven by excitatory/inhibitory imbalance C_LIO_LIUsing 1H-MRS at 3T we studied PMC E/I balance in young adult APOE E4 carriers C_LIO_LIFound evidence against altered E/I balance in young adult APOE E4 carriers C_LI

neuroscience↗

bioRxiv2018

Neurochemical correlates of scene processing in the precuneus/posterior cingulate cortex: a multimodal fMRI and 1H-MRS study

Precuneus/posterior cingulate cortex (PCu/PCC) are key components of a midline network, activated during rest but also in tasks that involve construction of scene or situation models. Despite growing interest in PCu/PCC functional alterations in disease, the underlying neurochemical modulators of PCu/PCCs task-induced activity are largely unstudied. Here, a multimodal imaging approach was applied to investigate whether inter-individual differences in PCu/PCC fMRI activity, elicited during perceptual discrimination of scene stimuli, were correlated with local brain metabolite levels, measured during resting-state 1H-MRS. Forty healthy young adult participants (12 male) completed an fMRI perceptual odd-one-out task for scenes, objects and faces. 1H-MRS metabolites N-acetyl-aspartate (tNAA), glutamate (Glx) and {gamma}-amino-butyric acid (GABA+) were quantified via PRESS and MEGA-PRESS scans in a PCu/PCC voxel and an occipital (OCC) control voxel. Whole brain fMRI revealed a cluster in right dorsal PCu/PCC that showed a greater BOLD response to scenes versus faces and objects. When extracted from an independently defined PCu/PCC region of interest, scene activity (versus faces and objects and also versus baseline) was positively correlated with PCu/PCC, but not OCC, tNAA. A complementary fMRI analysis restricted to the PCu/PCC MRS voxel area identified a significant PCu/PCC cluster, confirming the positive correlation between scene-related BOLD activity and PCu/PCC tNAA. There were no correlations between PCu/PCC fMRI activity and Glx or GABA+ levels. These results demonstrate, for the first time, that scene activity in PCu/PCC is linked to local tNAA levels, identifying a neurochemical influence on inter-individual differences in the task-driven activity of a key brain hub.

neuroscience↗