Biology subjects

Mander, B. A.

Publications and source records attributed to Mander, B. A..

7 recordsLinked to original sources

bioRxiv2026

Longitudinal Alterations in Sleep EEG Biomarkers of Memory Consolidation in Middle-Aged and Older Adults

The precise coordination of slow oscillations (SO) and sleep spindles during non-rapid eye movement (NREM) sleep supports memory consolidation and may serve as a sensitive marker of cognitive aging. However, longitudinal changes in their oscillatory dynamics in midlife and older age remain poorly understood. Using polysomnography with high-density EEG at two timepoints over [~]2.5 years, we examined changes in local NREM slow wave (SW), sleep spindle (occurring in the 11-16 Hz sigma range), and SO-sigma coupling strength in cognitively unimpaired middle-aged to older adults at risk for Alzheimers disease. Fronto-central SO-sigma power coupling strength significantly declined over time, independent of changes in multiple measures of SW and sleep spindle expression. Local declines in multiple sleep spindle measures were also observed. Greater baseline levels of cerebrospinal fluid (CSF) neurogranin, a postsynaptic protein abundantly expressed in the dendritic spines of the hippocampus and cerebral cortex and implicated in calcium-dependent synaptic plasticity, predicted the magnitude of longitudinal decline in SO-fast sigma coupling strength, which in turn predicted episodic memory performance changes. These findings suggest that longitudinal changes in local sleep oscillatory dynamics are related to decreased synaptic integrity and may serve as an early indicator of memory decline in older adults at risk for Alzheimers disease.

neuroscience↗

bioRxiv2024

Engagement in moderate-intensity physical activity supports overnight emotional memory retention in older adults

ImportancePreserving the ability to vividly recall emotionally rich experiences contributes to quality of life in older adulthood. While prior work suggests that moderate-intensity physical activity (MPA) may bolster memory, it is unclear whether this extends to emotionally salient memories consolidated during sleep. ObjectiveTo investigate associations between engagement in physical activity (PA) and overnight emotional memory retention and examine whether theoretically replacing 30-minutes of lower-intensity activity with MPA is associated with better consolidation. Design, Setting, and ParticipantsA cross-sectional study of 40 community-dwelling older adults free of neurological and psychiatric disorders. Data were collected from May 2018 to July 2022 and analyzed from January to July 2024. ExposuresParticipants completed an overnight polysomnography (PSG) with emotional memory tested before and after sleep and a self-report questionnaire assessing habitual PA. Main Outcome(s) and Measures(s)Emotional memory performance was assessed via recognition memory or mnemonic discrimination performance. Overnight memory retention was calculated by subtracting immediate test from delayed test performance for both recognition memory and mnemonic discrimination, with more negative scores indicating lower memory retention. Frequency and duration of MPA, light-intensity PA, non-exertive activity, and sedentary behavior were calculated from the Community Health Activities Model Program for Seniors (CHAMPS) Activities Questionnaire for Older Adults. Isotemporal substitution modelling evaluated whether statistically reallocating time spent in sedentary and lower-intensity activity to MPA was associated with better overnight memory retention. ResultsData from 40 participants were analyzed ({square}age=72.3{+/-}5.8, 26 female). Better overnight emotional recognition memory retention was associated with the frequency ({beta}=0.663, SE=0.212, p=0.003) and duration ({beta}=0.214, SE=0.101, p=0.042) of MPA. No relationships were found with mnemonic discrimination or neutral recognition memory. Statistically modelling the replacement of 30 minutes of lower-intensity activity with MPA was associated with better overnight retention of emotional memories ({beta}=0.108, SE=0.048, p=0.030), but not neutral ({beta}=-0.029, SE=0.069, p=0.679). Conclusions and RelevanceMPA may enhance sleep-dependent consolidation of emotional memories in older adults. Modest increases in MPA may yield significant benefits for sleep-dependent emotional memory retention. These findings may guide interventions to preserve memory function and inform public health recommendations by demonstrating that substituting even short durations of low-intensity activity for MPA could produce significant cognitive gains relevant for maintaining quality of life in older adulthood.

neuroscience↗

bioRxiv2024

Cerebrovascular pathology mediates associations between hypoxemia during rapid eye movement sleep and medial temporal lobe structure and function in older adults

Obstructive sleep apnea (OSA) is common in older adults and is associated with medial temporal lobe (MTL) degeneration and memory decline in aging and Alzheimers disease (AD). However, the underlying mechanisms linking OSA to MTL degeneration and impaired memory remains unclear. By combining magnetic resonance imaging (MRI) assessments of cerebrovascular pathology and MTL structure with clinical polysomnography and assessment of overnight emotional memory retention in older adults at risk for AD, cerebrovascular pathology in fronto-parietal brain regions was shown to statistically mediate the relationship between OSA-related hypoxemia, particularly during rapid eye movement (REM) sleep, and entorhinal cortical thickness. Reduced entorhinal cortical thickness was, in turn, associated with impaired overnight retention in mnemonic discrimination ability across emotional valences for high similarity lures. These findings identify cerebrovascular pathology as a contributing mechanism linking hypoxemia to MTL degeneration and impaired sleep-dependent memory in older adults.

neuroscience↗

bioRxiv2023

Medial temporal lobe functional network architecture supports sleep-related emotional memory processing in older adults

Memory consolidation occurs via reactivation of a hippocampal index during non-rapid eye movement slow-wave sleep (NREM SWS) which binds attributes of an experience existing within cortical modules. For memories containing emotional content, hippocampal-amygdala dynamics facilitate consolidation over a sleep bout. This study tested if modularity and centrality--graph theoretical measures that index the level of segregation/integration in a system and the relative import of its nodes--map onto central tenets of memory consolidation theory and sleep-related processing. Findings indicate that greater network integration is tied to overnight emotional memory retention via NREM SWS expression. Greater hippocampal and amygdala influence over network organization supports emotional memory retention, and hippocampal or amygdala control over information flow are differentially associated with distinct stages of memory processing. These centrality measures are also tied to the local expression and coupling of key sleep oscillations tied to sleep-dependent memory consolidation. These findings suggest that measures of intrinsic network connectivity may predict the capacity of brain functional networks to acquire, consolidate, and retrieve emotional memories.

neuroscience↗

bioRxiv2022

Human REM sleep controls neural excitability in support of memory formation

Sleep oscillations provide a key substrate to facilitate memory processing, the underlying mechanism of which may involve the overnight homeostatic regulation of plasticity at a synaptic and whole-network level. However, there remains a lack of human data demonstrating if and how sleep enhances memory consolidation and associated neural homeostasis. We combined intracranial recordings and scalp electroencephalography (EEG) in humans to reveal a new role for rapid eye movement (REM) sleep in promoting the homeostatic recalibration of optimal excitation/inhibition-balance. Moreover, the extent of this REM-sleep homeostatic recalibration predicted the success of overnight memory consolidation, expressly the modulation of hippocampal-- neocortical excitability favoring remembering rather than forgetting. The findings describe a novel, fundamental role of human REM sleep in maintaining neural homeostasis, thereby enhancing long-term memory.

neuroscience↗

bioRxiv2020

Coupling between slow-waves and sharp-wave ripples organizes distributed neural activity during sleep in humans

Hippocampal-dependent memory consolidation during sleep is hypothesized to depend on the synchronization of distributed neuronal ensembles, organized by the hippocampal sharp-wave ripples (SWRs, 80-150 Hz) and subcortical/cortical slow-waves (0.5-4 Hz). However, the precise role of SWR-slow-wave interactions in synchronizing subcortical/cortical neuronal activity is unclear. Here, we leverage intracranial electrophysiological recordings from the human hippocampus, amygdala, temporal and frontal cortices, to examine activity modulation and cross-regional coordination during SWRs. Hippocampal SWRs are associated with widespread modulation of high frequency activity (HFA; 70-200 Hz) a measure of local neuronal activation. This peri-SWR HFA modulation is predicted by the coupling between hippocampal SWRs and local subcortical/cortical slow-waves. Finally, local cortical slow-wave phase offsets during SWRs predicted functional connectivity between the frontal and temporal cortex. These findings suggest a selection mechanism wherein hippocampal SWR and cortical slow-wave synchronization governs the transient engagement of distributed neuronal populations supporting hippocampal-dependent memory consolidation.

neuroscience↗

bioRxiv2019

An Electrophysiological Marker of Arousal Level in Humans

Deep non-rapid eye movement sleep (NREM) - also called slow wave sleep (SWS) - and general anesthesia are prominent states of reduced arousal linked to the occurrence of slow oscillations in the electroencephalogram (EEG). Rapid eye movement (REM) sleep, however, is also associated with a diminished arousal level, but is characterized by a desynchronized, wake-like EEG. This observation challenges the notion of oscillations as the main physiological mediator of reduced arousal. Using intracranial and surface EEG recordings in four independent data sets, we establish the 1/f spectral slope as an electrophysiological marker that accurately delineates wakefulness from anesthesia, SWS and REM sleep. The spectral slope reflects the non-oscillatory, scale-free measure of neural activity and has been proposed to index the local balance between excitation and inhibition. Taken together, these findings reconcile the long-standing paradox of reduced arousal in both REM and NREM sleep and provide a common unifying physiological principle -- a shift in local Excitation/ Inhibition balance -- to explain states of reduced arousal such as sleep and anesthesia in humans.\n\nSignificance StatementThe clinical assessment of arousal levels in humans depends on subjective measures such as responsiveness to verbal commands. While non-rapid eye movement (NREM) sleep and general anesthesia share some electrophysiological markers, rapid eye movement sleep (REM) is characterized by a wake-like electroencephalogram. Here, we demonstrate that non-oscillatory, scale-free electrical brain activity -- recorded from both scalp electroencephalogram and intracranial recordings in humans -- reliably tracks arousal levels during both NREM and REM sleep as well as under general anesthesia with propofol. Our findings suggest that non-oscillatory brain activity can be used effectively to monitor vigilance states.

neuroscience↗