Biology subjects

Andrews, S. C.

Publications and source records attributed to Andrews, S. C..

5 recordsLinked to original sources

bioRxiv2025

Resting-State EEG Aperiodic Exponent Moderates the Association Between Age and Memory Performance in Older Adults

Memory functions are susceptible to age-related cognitive decline, making it essential to explore the underlying neurophysiological mechanisms that contribute to memory function during healthy ageing. Resting-state EEG (rsEEG) parameters, particularly the aperiodic exponent, a marker of cortical excitation-inhibition balance, and individual alpha peak frequency, a correlate of neural processing efficiency, have demonstrated associations with ageing and cognitive functions. This study investigated associations between these rsEEG markers and performance across multiple memory systems in healthy older adults (n = 99) aged 50-84 years, specifically the direct associations of these markers on memory across episodic, working, and visual short-term memory systems, assessed via computerised tasks, as well as their moderating effects on age-memory relationships. While no direct associations were seen between rsEEG markers and memory performance across tasks beyond the contribution of age, gender and education, results revealed significant moderating effects of the aperiodic exponent on age-related performance in episodic and visual short-term memory. Notably, for individuals with a higher exponent, age was not significantly associated with episodic or visual short-term memory performance, whereas those with average and lower exponent values showed poorer performance with older age. These findings suggest that average and lower aperiodic exponents may reflect a marker of decrement in age-related memory performance and higher exponents may index an underlying protective mechanism against age-related memory decline. This investigation extends the current understanding of cognitive ageing mechanisms by identifying the aperiodic exponent as a potential biomarker explaining individual differences in cognitive ageing trajectories in older adult populations, particularly in episodic and visual short-term memory systems, and establishes a framework for studying neuroprotective mechanisms and developing interventions to preserve cognitive function in older adults.

neuroscience↗

bioRxiv2025

Relationships between GABA+ and Glx concentrations with age and inhibition in healthy older adults

Inhibition represents a core executive function which underlies the ability to suppress interfering and/or distracting stimuli, thereby building resistance against task-irrelevant information. However, the impact of ageing on inhibitory functioning and the potential role of neuroplasticity - largely driven by predominant excitatory (glutamatergic) and inhibitory (GABAergic) neurochemicals - remains poorly understood. In this study, we investigated age relationships with neurochemical concentrations (GABA+ and Glx) and examined the associations between these neurochemicals and inhibitory sub-components in the context of healthy ageing. To this end, participants completed three inhibition tasks (i.e., flanker, Stroop and go/no-go), each measuring a different sub-component process, via the PsyToolkit platform. MRS data was acquired in the sensorimotor (SM1; n=71, mean age (SD) = 68.3 ({+/-}9.7) years, 39 females) and prefrontal (PFC; n=58, mean age (SD) = 67.6 ({+/-}9.6) years, 30 females) regions using a HERMES sequence and analysed using OSPREYs pipeline. After correcting for gender and education, semi-partial correlations (rho) revealed no significant relationships between age and GABA+ or Glx concentrations in either the SM1 or PFC regions. Furthermore, through partial correlations (rho), after correcting for age, gender and education, we identified a significant negative relationship between SM1 Glx concentrations and go/no-go error rates, such that greater concentrations of Glx in the SM1 region were associated with greater accuracy on the go/no-go task. The null age-neurochemical results suggest that GABA+ and Glx may not uniformly decline during healthy ageing. This finding suggests that the relationship between older age and neurochemistry may be more nuanced than previously reported. In addition, our neurochemical-behavioural findings provide neurochemically-and-spatially specific evidence that SM1 Glx concentrations may be important for response inhibition. This result indicates a role for the glutamatergic system in supporting inhibition over the normal course of ageing.

neuroscience↗

bioRxiv2025

Neurophysiological Correlates of Modifiable Dementia Risk Factors in Cognitively Unimpaired Older Adults

The 2024 Lancet Commission on Dementia estimates that up to 45% of dementia cases could be prevented by addressing modifiable risk factors, emphasising both prevention opportunities and the need to understand the biological mechanisms. This study investigated neurophysiological mechanisms underlying modifiable dementia risk factors in cognitively unimpaired older adults. Seventy-nine cognitively unimpaired older adults underwent MRI brain scans, with spectroscopy measurements taken from the sensorimotor cortex (SMC) and prefrontal cortex (PFC), using a Hadamard Encoding and Reconstruction of MEGA-Edited Spectroscopy (HERMES) sequence, optimised for measuring GABA+. Modifiable dementia risk scores were calculated using the Assessment for Cognitive Health and Dementia Risk (CogDrisk). Hierarchical linear regression analyses revealed a significant negative relationship within the SMC, with lower GABA+ ({beta} = -0.249, p = 0.009) associated with higher risk scores. In the PFC, lower tNAA and tCho concentrations significantly predicted higher risk scores ({beta} = -0.168 and -0.170, respectively). These findings suggest that GABAergic system alterations may underlie the pathophysiology of modifiable dementia risk in healthy ageing, whilst changes in tNAA and tCho may reflect early alterations in neuronal integrity. These region-specific neurochemical findings may help identify potential early biomarkers for dementia risk, and suggest new therapeutic pathways for preventive interventions.

neuroscience↗

bioRxiv2025

Age-related Inhibitory Decline: Examining Inhibition Sub-Components and their Impact on Sustained Attention in Healthy Ageing

ObjectiveThe inhibition deficit hypothesis postulates that inhibitory functioning declines with age, which negatively impacts other cognitive abilities. Yet still, the impact of healthy ageing on inhibitory functioning remains unclear, with the multifaceted nature of inhibition often an overlooked factor. Moreover, no prior study has empirically tested whether inhibitory sub-components explain differential age-effects in sustained attention - an open question that this work aims to address. MethodIn this cross-sectional study, we investigated the inhibition deficit hypothesis in a sample of eighty healthy older adults (mean age = 67.78 years, 44f). We utilised the PsyToolkit platform to administer three inhibition tasks (i.e., flanker, Stroop, and go/no-go), each targeting a distinct sub-component process, along with the Sustained Attention to Response Task (SART). ResultsSemi-partial correlations (rho) of the three inhibition sub-component measures (correcting for gender and education) with age resulted in significant positive relationships with task performance on the Stroop and go/no-go, such that older individuals had more pronounced Stroop effects and worse go/no-go accuracy, respectively. Lastly, go/no-go performance completely mediated the relationship between ageing and sustained attention performance, whilst Stroop effects partially mediated this association. ConclusionAge-related declines were observed in specific inhibition tasks, which speaks against a general inhibition deficit in healthy ageing and cautions against conflating these sub-components into a generalised concept of inhibition. The mediation findings demonstrate that inhibitory sub-components account for age-related declines in sustained attention, over and beyond ageing itself via an indirect path, representing an important cognitive domain to maintain throughout ageing. Key pointsO_ST_ABSQuestionC_ST_ABSAre different inhibitory sub-components associated with age, and do they mediate age-related changes in sustained attention? FindingsDifferent inhibition tasks were uncorrelated, demonstrating specific relationships with age and providing evidence that select inhibition tasks can explain differential age-effects in sustained attention. ImportanceThis study lends support for the inhibition deficit hypothesis and underlines the importance of considering inhibitions multifaceted nature. Next stepsFuture research should adopt longitudinal designs to examine causal relationships

animal behavior and cognition↗

bioRxiv2023

Ageing attenuates exercise-enhanced motor cortical plasticity

Cardiorespiratory exercise is known to modulate motor cortical plasticity in young adults, but the influence of ageing on this relationship is unknown. Here, we compared the effects of a single session of cardiorespiratory exercise on motor cortical plasticity in young and older adults. We acquired measures of cortical excitatory and inhibitory activity of the primary motor cortex using transcranial magnetic stimulation (TMS) from 20 young (M {+/-} s.d. = 25.30 {+/-} 4.00 years) and 20 older (M {+/-} s.d. = 64.10 {+/-} 6.50 years) healthy adults. Single and paired pulse TMS measures were collected before and after a 20-minute bout of high-intensity interval cycling exercise or an equivalent period of rest, and again after intermittent theta burst stimulation (iTBS). In both young and older adults, exercise led to an increase in glutamatergic excitation and a reduction in gamma-aminobutyric acid (GABA) inhibition. However, in contrast to younger adults, older adults showed an attenuated plasticity response to iTBS following exercise. These results demonstrate an age-dependent decline in cortical plasticity and indicate that a preceding bout of high-intensity interval exercise may be less effective for enhancing primary motor cortex plasticity in older adults. Our findings align with the hypothesis that the capacity for cortical plasticity is altered in older age. Key pointsO_LIExercise enhances motor cortical plasticity in young adults, but how ageing influences this effect is unknown. C_LIO_LIHere, we compared primary motor cortical plasticity responses in young and older adults before and after a bout of high-intensity interval exercise, and again after a plasticity-inducing protocol - intermittent theta burst stimulation. C_LIO_LIIn both young and older adults, exercise led to an increase in glutamatergic excitation and a reduction in gamma-aminobutyric acid (GABAergic) inhibition. C_LIO_LIOur key result was that older adults showed an attenuated plasticity response to theta burst stimulation following exercise, relative to younger adults. C_LIO_LIOur findings demonstrate an age-dependent decline in exercise-enhanced cortical plasticity and indicate that a preceding bout of high-intensity interval exercise may be less effective for enhancing primary motor cortex plasticity in older adults. C_LI

neuroscience↗