Biology subjects

Yi, Y.-J.

Publications and source records attributed to Yi, Y.-J..

6 recordsLinked to original sources

bioRxiv2025

Differences in LC integrity and fMRI activations in healthy aging and MCI associated with successful memory encoding

INTRODUCTIONWe examined whether the decline of delayed episodic memory in old age and MCI is related to structural integrity of the locus coeruleus (LC). We also tested whether LC integrity was associated with encoding-related brain activity, controlling for emotional salience. METHODSParticipants (28 young adults, 28 older adults, 25 MCI) memorized emotional and neutral images during fMRI. Delayed memory was tested four hours later and compared to immediate memory. LC integrity was measured with a neuromelanin-sensitive sequence. RESULTSMCI showed overall memory decline, independent of delay or emotional valence, and reduced LC integrity compared to older adults. Across participants, LC integrity correlated with delayed memory, but did not explain performance within OA or MCI. LC integrity was associated with lower activity related to encoding success and emotional salience. Groups remembered emotional better than neutral images, though memory was greatly impaired in MCI, matching with their reduce LC integrity. DISCUSSIONLC integrity was associated with lower brain activity during encoding and emotional salience processing, no clear relationship with delayed memory performance was observed in MCI.

neuroscience↗

bioRxiv2025

Different dopaminergic circuits defined by D2/D3 receptor availablity patterns show structure-specific links to memory in ageing

Cognitive ageing is marked by progressive decline in episodic memory and dopaminergic function, yet the extent to which individual differences in dopaminergic system integrity influence memory under motivational contexts remains unclear. In this study, we investigated how baseline D2/D3 receptor availability (BPND0) in key dopaminergic pathways relates to reward-modulated memory performance in healthy older adults. Thirty-three healthy seniors (aged 64-85) underwent two session concurrent MR-PET imaging with [1F]fallypride involving scene categorisation task with high- and low-motivational contexts. We quantified BPND0 across nine dopaminergic regions of interest and examined their relationships with recognition memory performance at short ([~]15m) and long ([~]24h) delays. Baseline D2/D3 receptor availability showed high test-retest reliability and regionally distinct profiles, suggesting it reflects a stable neurochemical characteristic in healthy ageing, and principal axis factor analysis revealed two partially independent dopaminergic subsystems (dorsal striatal vs mesolimbic) based on interindividual patterns in receptor densities. Region-specific associations further linked D2/D3 receptor availability to distinct memory outcomes. Higher caudate D2/D3 receptor availability was associated with a liberal response bias (increased hits and false alarms both), whereas higher putamen D2/D3 predicted more durable long-term memory retention. Greater thalamic D2/D3 receptor availability correlated with fewer short-term false memories, while greater D2/D3 receptor availability in the amygdala was associated with better recognition at longer delays. In contrast, higher midbrain (substantia nigra and ventral tegmental area) D2/D3 availability which was linked to poorer reward-related memory performance. These findings suggest several complementary dopaminergic circuits supporting episodic memory. Our results highlight dopaminergic neuromodulation as a key factor in cognitive ageing and a potential target for interventions to bolster memory in late life. Patient consent and ethics approvalAll subjects who were included in this study have provided their consent prior to their participation, following the guidelines of the ethics committee at University Hospital Magdeburg in Magdeburg, Germany.

neuroscience↗

bioRxiv2024

Decoding Salience: A Functional Magnetic Resonance Imaging Investigation of Reward and Contextual Unexpectedness in Memory Encoding and Retrieval

The present study investigated the neuromodulatory substrates of salience processing and its impact on memory encoding and behaviour, with a specific focus on two distinct types of salience: reward and contextual unexpectedness. 46 participants performed a novel task paradigm modulating these two aspects independently and allowing for investigating their distinct and interactive effects on memory encoding while undergoing high resolution fMRI. By using advanced image processing techniques tailored to examine midbrain and brainstem nuclei with high precision, our study additionally aimed to elucidate differential activation patterns in subcortical nuclei in response to reward-associated and contextually unexpected stimuli, including distinct pathways involving in particular dopaminergic modulation. We observed a differential involvement of the ventral striatum, substantia nigra and caudate nucleus, as well as a functional specialisation within the subregions of the cingulate cortex for the two salience types. Moreover, distinct subregions within the substantia nigra in processing salience could be identified. Dorsal areas preferentially processed salience related to stimulus processing (of both reward and contextual unexpectedness) versus ventral areas were involved in salience-related memory encoding (for contextual unexpectedness only). These functional specialisations within SN are in line with different projection patterns of dorsal and ventral SN to brain areas supporting attention and memory, respectively. By disentangling stimulus processing and memory encoding related to two salience types, we hope to further consolidate our understanding of neuromodulatory structures differential as well as interactive roles in modulating behavioural responses to salient events.

neuroscience↗

bioRxiv2024

Early hippocampal high-amplitude rhythmic spikes predict post-traumatic epilepsy in mice

Oscillations, a highly conserved brain function across mammalian species, are pivotal in brain physiology and pathology. Traumatic brain injury (TBI) often leads to subacute and chronic brain oscillatory alterations associated with complications like post-traumatic epilepsy (PTE) in patients and animal models. Our recent work longitudinally recorded local field potential from the contralateral hippocampus of 12 strains of recombinant inbred Collaborative Cross (CC) mice alongside classical laboratory inbred C57BL/6J mice after lateral fluid percussion injury. In this study, we profiled the acute (<12 hr post-injury) and subacute (12-48 hr post-injury) hippocampal oscillatory responses to TBI and evaluated their predictive value for PTE. We found dynamic high-amplitude rhythmic spikes with elevated power density and reduced entropy that prevailed during the acute phase in CC031 mice who later developed PTE. This characteristic early brain oscillatory alteration is absent in CC031 sham controls or other CC and reference C57BL/6J strains that did not develop PTE after TBI. Our work provides quantitative measures linking early brain oscillation to PTE at a population level in mice under controlled experimental conditions. These findings will offer insights into circuit mechanisms and potential targets for neuromodulatory intervention.

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bioRxiv2023

MRI-assessed locus coeruleus contrast and functional response are not associated in young and late middle-aged individuals

The brainstem locus coeruleus (LC) influences a broad range of brain processes, including cognition. The so-called LC contrast is an accepted marker of the integrity of the LC that consists of a local hyperintensity on specific Magnetic Resonance Imaging (MRI) structural images. The small size of the LC has, however, rendered its functional characterization difficult in humans, including in aging. A full characterization of the structural and functional characteristics of the LC in healthy young and late middle-aged individuals is needed to determine to potential roles of the LC in different medical conditions. Here, we wanted to determine whether the activation of the LC in a mismatch negativity task changes in aging and whether the LC functional response was associated to the LC contrast. We used Ultra-High Field (UHF) 7-Tesla functional MRI (fMRI) to record brain response during an auditory oddball task in 53 healthy volunteers, including 34 younger (age: 22.15y {+/-} 3.27; 29 women) and 19 late middle-aged (age: 61.05y {+/-} 5.3; 14 women) individuals. Whole-brain analyses confirmed brain responses in the typical cortical and subcortical regions previously associated with mismatch negativity. When focusing on the brainstem, we found a significant response in the rostral part of the LC probability mask generated based on individual LC images. Although bilateral, the activation was more extensive in the left LC. Individual LC activity was not significantly different between young and late middle-aged individuals. Critically, while the LC contrast was higher in older individuals, the functional response of the LC was not associated with its contrast. These findings show that the age-related alterations of the LC structural integrity may not necessarily be related to changes in its functional response. The results further indicate that LC responses could remain stable in healthy individuals aged 20 to 70.

neuroscience↗

bioRxiv2021

It is the Locus Coeruleus! Or... is it? : A proposition for analyses and reporting standards for structural and functional magnetic resonance imaging of the noradrenergic Locus Coeruleus

The noradrenergic locus coeruleus (LC) in the brainstem shows early signs of protein pathologies in neurodegenerative diseases such as Alzheimers and Parkinsons disease. As the LCs small size (approximately 2.5 mm in width) presents a challenge for molecular imaging, the past decade has seen a steep rise in structural and functional Magnetic Resonance (MR) studies aiming to characterise the LCs changes in ageing and neurodegeneration. However, given its position in the brainstem and small volume, great care must be taken to yield methodologically reliable MR results as spatial deviations in transformations can greatly reduce the statistical power of the analyses at the group level. Here, we suggest a spatial transformation procedure and a set of quality assessment methods which allow LC researchers to achieve the spatial precision necessary for investigating this small but potentially impactful brain structure. Using a combination of available toolboxes (SPM12, ANTs, FSL, FreeSurfer), individual structural and functional 3T LC scans are transformed into MNI space via a study-specific anatomical template. Following this, the precision of spatial alignment in individual MNI-transformed images is quantified using in-plane distance measures based on slice-specific centroids of structural LC segmentations and based on landmarks of salient anatomical features in mean functional images, respectively. Median in-plane distance of all landmarks on the transformed structural as well as functional LC imaging data were below 2 mm, thereby falling below the typical LC width of 2.5 mm suggested by post-mortem data. With the set of spatial post-processing steps outlined in this paper and available for download, we hope to give readers interested in LC imaging a starting point for a reliable analysis of structural and functional MR data of the LC and to have also taken a first step towards establishing reporting standards of LC imaging data.

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