Biology subjects

Demeyere, N.

Publications and source records attributed to Demeyere, N..

4 recordsLinked to original sources

bioRxiv2025

Sleep-like slow waves in wakefulness index post-stroke behavioural alterations

Increases in high-amplitude, low-frequency EEG oscillations during non-rapid eye movement (NREM) sleep serve as markers of neuronal silencing, which disrupts functional connectivity and is associated with a loss of awareness and responsiveness. Cortical slowing likewise occurs during wakefulness, upon sleep deprivation, and accompanies performance deterioration. Recent work has revealed similar oscillations (termed sleep-like slow waves) following stroke in brain regions close or connected to a brain lesion, offering a plausible but untested mechanism for stroke-related behavioural impairment. Here, we simultaneously recorded EEG and behavioural performance while 30 unilateral stroke patients (12 left hemisphere, 18 right hemisphere) and 27 age-matched healthy adults completed a computerised perceptual decision-making task. Sleep-like slow waves occurred more frequently in stroke patients relative to healthy controls. Furthermore, there was a significant correlation between slow wave occurrence and the accuracy and speed of perceptual reports in stroke patients, suggesting that variations in the occurrence of slow waves may contribute to cognitive heterogeneity post-stroke. Evidence that sleep-like slow waves predict deficits in perceptual decision-making following stroke indicates that stroke-induced lesions can destabilize cortical networks extending beyond the damaged regions, thereby contributing to broader cognitive impairments.

neuroscience↗

bioRxiv2025

Methodological choices strongly modulate the sensitivity and specificity of lesion-symptom mapping analyses

Lesion mapping results can vary substantially as a function of specific analysis parameters, but the extent to which individual methodological choices interact to modulate the sensitivity and specificity of results is not clear. Here, we employed a large-scale simulation approach to inform practical recommendations for lesion symptom mapping studies. Routine clinical imaging from 959 stroke survivors (mean age = 72.5, 49.3% female) was used to conduct 384,780 lesion mapping analyses based on simulated behavioural data. Each simulated analysis used different combinations of plausible sample inclusion criteria, analysis parameters (e.g., correction factors), analysis types (e.g., univariate vs. multivariate), and underlying target correlates. Simulated analysis accuracy (Dice similarity coefficient and percent coverage of target correlates) was compared across designs. Overall, analysis accuracy varied widely and was substantially modulated by the specific design used. Analyses that maximised lesion coverage by including large and diverse samples reliably outperformed analyses using more restricted samples. Analyses using direct total lesion volume controls outperformed analyses using other (or no) volume corrections across all accuracy measures. False discovery rate corrections yielded the best performance in terms of target coverage, while permutation corrections yielded the best Dice coefficients. While multivariate approaches were more accurate than univariate analyses in terms of Dice coefficient, univariate analyses generated higher target hit rates and percent target coverage. These results identify specific analysis designs suitable for studies aiming to maximise their sensitivity and/or specificity to underlying critical correlates, while highlighting the inferential strengths and weaknesses of these complementary approaches.

neuroscience↗

bioRxiv2023

Neurophysiological mechanisms underlying post-stroke deficits in contralesional perceptual processing

Slowed responding to sensory inputs presented in contralesional space is pervasive following unilateral cerebral stroke, but the causal neurophysiological pathway by which this occurs remains unclear. To this end, here we leverage a perceptual decision-making framework to disambiguate information processing stages between sensation and action in 30 unilateral stroke patients (18 right hemisphere, 12 left hemisphere) and 27 neurologically healthy adults. By recording neural activity using electroencephalography (EEG) during task performance, we show that the relationship between strokes in either hemisphere and slowed contralesional response times is sequentially mediated by weaker target selection signals in the contralateral hemisphere (the N2c ERP), and subsequently delayed evidence accumulation signals (the centroparietal positivity). Notably, asymmetries in CPP and response times across hemispheres are associated with everyday functioning. Together, these data suggest a plausible neurophysiological pathway by which post-stroke contralesional slowing arises and highlight the utility of neurophysiological assessments for tracking clinically relevant behaviour.

neuroscience↗

bioRxiv2017

Dissociating ego- and allocentric neglect after stroke: prevalence, laterality and outcome predictors

Visuospatial neglect is a neuropsychological condition commonly experienced after stroke, whereby a patient is unable to attend to stimuli on their contralesional side. We aimed to investigate whether egocentric and allocentric neglect are functionally dissociable and differ in prevalence, laterality and outcome predictors. A consecutive sample of 366 acute stroke patients completed the Broken Hearts test from the Oxford Cognitive Screen. A subsample of 160 patients was followed up 6 months later. We evaluated the association between egocentric and allocentric neglect, contrasted the prevalence and severity of left-sided versus right-sided neglect, and determined the predictors of persistence versus recovery at follow up. Clinically, we found a double dissociation between ego- and allocentric neglect, with 50% of the neglect patients showing only egocentric neglect and 25% only allocentric neglect. Importantly, patients with only allocentric neglect did not demonstrate any egocentric spatial bias in the locations of the allocentric errors. Left-sided egocentric neglect was more prevalent and more severe than right-sided egocentric neglect, though right-sided neglect was still highly prevalent in the acute stroke sample (35%). Leftsided allocentric neglect was more severe but not more prevalent than right-sided allocentric neglect. Overall recovery of neglect was high: 81% of egocentric and 75% of allocentric neglect patients recovered. Severity of neglect was the only significant behavioural measure for predicting recovery at 6 months.

neuroscience↗