Biology subjects

Ralph, M. A. L.

Publications and source records attributed to Ralph, M. A. L..

4 recordsLinked to original sources

bioRxiv2025

Optimising 7T-fMRI for imaging regions of magnetic susceptibility

The temporal signal-to-noise ratio (tSNR) of functional magnetic resonance imaging (fMRI) is particularly poor in ventral anterior temporal and orbitofrontal regions because of B0 and B1+ magnetic field inhomogeneity, a problem that is exacerbated at higher field strengths. In this 7T-fMRI study we compared three methods of improving sensitivity in these areas: parallel transmit, which uses multiple transmit elements, controlled independently, to homogenise the flip angle experienced by the tissue; multi-echo, which entails collection of multiple volumes at different echo times following a single radiofrequency pulse; and multiband, in which multiple slices are acquired simultaneously. We found that parallel transmit and multi-echo increased the magnitude of the BOLD signal change, but only multi-echo increased BOLD magnitude in areas prone to susceptibility artefacts. Multiband and denoising of multi-echo data with independent components analysis (ICA) both improved precision of GLM fit. Exploratory results suggested that multi-echo and ICA denoising can both benefit multivariate analyses. In conclusion, a multi-echo, multiband sequence improved fMRI quality in areas prone to susceptibility artefacts while maintaining sensitivity across the whole brain. We recommend this approach for studies investigating the functional roles of ventral temporal and orbitofrontal regions with 7T fMRI.

neuroscience↗

bioRxiv2025

Transcranial focused ultrasound stimulation of the anterior temporal lobe enhances semantic memory by modulating brain morphology, neurochemistry and neural dynamics

AbstractsUnderstanding neural functioning and plasticity of the brain is a fundamental goal of neuroscience. The ventromedial anterior temporal lobe (ATL) has been suggested as the centre-point of a core transmodal hub for semantic memory, playing a crucial role in the representation of coherent conceptual knowledge. However, non-invasive direct modulation of the ventromedial ATL has remained challenging. Transcranial ultrasound stimulation (TUS) is an emerging neuromodulatory technique that delivers acoustic energy with high spatial precision, making it uniquely suited for targeting deep brain structures non-invasively. In this study, we investigated whether theta-burst TUS (tbTUS) to the ventromedial ATL could enhance semantic memory performance in the adult brain. Using a multimodal neuroimaging approach-- magnetic resonance spectroscopy (MRS), functional MRI (fMRI), and voxel-based morphometry (VBM)--we assessed tbTUS-induced changes in neurochemical concentrations, functional network connectivity, structural plasticity, and semantic memory performance. Compared to control stimulation (ventricle), tbTUS at the ventromedial ATL significantly improved semantic task performance in healthy individuals. MRS analysis revealed that tbTUS decreased GABA and increased Glx levels, reflecting shifts in excitation-inhibition balance. Additionally, tbTUS increased neurometabolites in the ATL, including NAA, creatine and choline, suggesting enhanced neuronal function and metabolism. fMRI analysis demonstrated that tbTUS reduced task-induced regional activity in the ATL and functionally connected semantic regions, while also enhancing intrinsic and effective connectivity across the semantic network. Structural analysis revealed increased grey matter volume in the ATL following tbTUS compared to control stimulation. These findings provide the first convergent evidence that tbTUS can modulate neurochemistry, functional dynamics, and brain morphology to enhance semantic memory function. Our results highlight TUS as a powerful neuromodulatory tool with potential applications in cognitive enhancement and neurorehabilitation, offering a promising intervention for dementia and neurodegenerative disorders.

neuroscience↗

bioRxiv2024

Distributed and integrated representations of tools in human parietal and anterior temporal regions revealed by fMRI-RSA

Classical models of tool knowledge and use are centred on dorsal and ventral parietal pathways. Theories of semantic cognition implicate a "hub-and-spoke" network, centred on the anterior temporal lobe (ATL), that underpins all concepts including tools. Despite their prominence, the two theoretical frameworks have never been brought together and the large discrepancy in the functional neuroanatomy addressed. We undertook a multiple-regression Representational Similarity Analysis (RSA) of task fMRI data with four (motor action, broad function, mechanical function, object structure) feature-based models. The motor action model correlated with the activation patterns in bilateral superior parietal lobules (SPL), while the models of broad function and mechanical effect aligned with the activation patterns in bilateral ATLs. The object-structure model correlated with activation patterns in bilateral middle occipital gyri. The results also showed that the ventral ATL activation patterns corresponded simultaneously with all RDM models except object structure. Furthermore, a standard univariate analysis using tool-familiarity ratings for parametric modulation revealed that classical tool-network regions (frontal, inferior parietal, and posterior middle temporal cortices) were increasingly active as the tool familiarity reduced. These results demonstrate that parietal and ATL regions are both crucial and motivate a major extension and revision of the neuroanatomical framework for tool use. Significance StatementThis study provides definitive evidence for convergent tool representation in human anterior temporal lobe (ATL), outside the traditionally focused parietal lobe as the critical centre for human tool-use ability. For many years the parietal lobe was considered crucial in recognizing and planning use of familiar objects, while regions in temporal lobe received little attention. Our advanced multi-voxel analysis with artefact-resistive fMRI scanning revealed that both non-motor (tool-function) and motor (kinematics for tool use) information convergently represented in the left ventral ATL, while showing other distributed regions encoding distinct types of tool information in anterior temporal and parietal regions. These findings highlight the ATLs crucial role in tool representation and necessitate a significant expansion of neuroanatomical framework for human tool-use ability.

neuroscience↗

bioRxiv2022

Representational similarity learning reveals a graded multi-dimensional semantic space in the human anterior temporal cortex

Neurocognitive models of semantic memory have proposed that the ventral anterior temporal lobes (vATLs) encode a graded and multidimensional semantic space--yet neuroimaging studies seeking brain regions that encode semantic structure rarely identify these areas. In simulations we show that this discrepancy may arise from a crucial mismatch between theory and analysis approach. Utilizing an analysis recently formulated to investigate graded multidimensional representations, representational similarity learning (RSL), we decoded semantic structure from ECoG data collected from the vATL cortical surface while participants named line drawings of common items. The results reveal a graded, multidimensional semantic space encoded in neural activity across the vATL, which evolves over time and simultaneously expresses both broad and finer-grained semantic structure amongst animate and inanimate concepts. The work resolves the apparent discrepancy within the semantic cognition literature and, more importantly, suggests a new approach to discovering representational structure in neural data more generally. Conflict of interestThe Department of Epilepsy, Movement Disorders, and Physiology, Kyoto University Graduate School of Medicine conducts Industry-Academia Collaboration Courses, supported by Eisai Co., Ltd, Nihon Kohden Corporation, Otsuka Pharmaceutical Co., and UCB Japan Co., Ltd.

neuroscience↗