Biology subjects

Low, K. A.

Publications and source records attributed to Low, K. A..

10 recordsLinked to original sources

bioRxiv2025

Changes in aperiodic (1/f slope) activity during a picture-word interference task: Effects of congruency and sequence manipulations

Aperiodic neural activity (1/f EEG) has been proposed to reflect the balance between excitatory and inhibitory (E/I) inputs, with steeper spectral slopes reflecting increased inhibition and flatter slopes indicating excitation. This activity is also thought to reflect the temporal coordination of neural firing, offering insights into fundamental brain dynamics. Recent studies have shown that the 1/f slope is sensitive to stimulus onset, characterized by initial inhibitory shifts followed by excitatory rebounds, which may reflect cognitive control mechanisms involved in suppressing distractions and preparing goal-directed responses. However, previous research has relied on fixed temporal windows and insufficient control of ERP contamination, limiting our understanding of rapid control dynamics. Here we used newly developed time-resolved analyses to study 1/f spectral slope modulation during a Picture-Word Interference task, focusing on two canonical cognitive control markers: the Congruency Effect (CE) and Congruency Sequence Effect (CSE). Forty-nine participants categorized pictures while ignoring congruent or incongruent words. Behaviorally, we replicated robust CE and CSE patterns. Spectral slope analyses showed that incongruent trials elicited steeper slopes -- consistent with increased inhibition -- particularly in frontal and central regions, reflecting conflict-related control engagement. Moreover, CSE analyses revealed dynamic slope modulations across frontal, central, and occipital components over time, suggesting control adjustments influenced by previous trial congruency. These results provide the first within-trial time-resolved evidence that aperiodic 1/f EEG activity can track both immediate conflict resolution and cognitive adjustments, offering a temporally sensitive neural marker of cognitive control, albeit with effects that are small in magnitude on average.

neuroscience↗

bioRxiv2024

Effects of Aging, Fitness, and Cerebrovascular Status on White Matter Microstructural Health

White matter (WM) microstructural health declines with increasing age, with evidence suggesting that improved cardiorespiratory fitness (CRF) may mitigate this decline. Specifically, higher fit older adults tend to show preserved WM microstructural integrity compared to their lower fit counterparts. However, the extent to which fitness and aging independently impact WM integrity across the adult lifespan is still an open question, as is the extent to which cerebrovascular health mediates these relationships. In a large sample (N = 125, aged 25-72), we assessed the impact of age and fitness on fractional anisotropy (FA, derived using diffusion weighted imaging, DWI) and probed the mediating role of cerebrovascular health (derived using diffuse optical tomography of the cerebral arterial pulse, pulse-DOT) in these relationships. After orthogonalizing age and fitness and computing a PCA on whole brain WM regions, we found several WM regions impacted by age that were independent from the regions impacted by fitness (hindbrain areas, including brainstem and cerebellar tracts), whereas other areas showed interactive effects of age and fitness (midline areas, including fornix and corpus callosum). Critically, cerebrovascular health mediated both relationships suggesting that vascular health plays a linking role between age, fitness, and brain health. Secondarily, we assessed potential sex differences in these relationships and found that, although females and males generally showed the same age-related FA declines, males exhibited somewhat steeper declines than females. Together, these results suggest that age and fitness impact specific WM regions and highlight the mediating role of cerebrovascular health in maintaining WM health across adulthood.

neuroscience↗

bioRxiv2023

Neurovascular Mechanisms of Cognitive Aging: Arteriosclerosis Precipitates Demyelination and Cognitive Decline

Arterial stiffness (arteriosclerosis) has been linked to heightened risks for cognitive decline, and ultimately for Alzheimers disease and other forms of dementia. Importantly, neurovascular outcomes generally vary according to ones biological sex. Here, capitalizing on a large sample of participants with neuroimaging and behavioral data (N = 203, age range = 18-87 years), we aimed to provide support for a hierarchical model of neurocognitive aging, which links age-related declines in cerebrovascular health to the rate of cognitive decline via a series of intervening variables, such as white matter integrity. By applying a novel piecewise regression approach to our cross-sectional sample to support Granger-like causality inferences, we show that, on average, a precipitous decline in cerebral arterial elasticity (measured with diffuse optical imaging of the cerebral arterial pulse; pulse-DOT) temporally precedes an acceleration in the development of white matter lesions by nearly a decade, with women protected from these deleterious effects until approximately age 50, the average onset of menopause. By employing multiple-mediator path analyses while controlling for sex, we show that age may impair cognition via the sequential indirect effects of arteriosclerosis and white matter atrophy on fluid, but not crystallized, abilities. Importantly, we replicate these results using pulse pressure, an independent index of arterial health, thereby providing converging evidence for the central role of arteriosclerosis as an accelerating factor in normal and pathological aging and identifying robust sex-related differences in the progression of cerebral arteriosclerosis and white matter degradation.

neuroscience↗

bioRxiv2023

Event-Induced Modulation of Aperiodic Background EEG: Attention-Dependent and Age-Related Shifts in E:I balance, and Their Consequences for Behavior

The broadband shape of the EEG spectrum, summarized using a 1/fx function, is thought to reflect the balance between excitation and inhibition in cortical regions (E:I balance). This balance is an important characteristic of neural circuits and could inform studies of aging, as older adults show a relative inhibitory activity deficit. Thus far, no studies have leveraged the event-related temporal dynamics of 1/fx activity to better understand the phases of information processing, especially in the context of aging. Here, for the first time, we examined variations of this activity during the foreperiod of a cued flanker task in younger (YA) and older adults (OA), with picture cues varying in task relevance, relative novelty, and valence. We report a biphasic change in the spectral exponent (corresponding to negative slopes in log-log space) after cue presentation, independent of cue-elicited ERPs, with an initial period of increased negativity (indicating cortical inhibition, similar in YA and OA) followed by decreased negativity (indicating cortical excitation, especially in OA). The decrease in the exponent negativity was associated with lower performance and greater congruency costs in the flanker task. Finally, more novel cues reduced the shift towards excitation in OA, partly restoring their E:I balance, and diminishing congruency costs. These findings demonstrate that the broadband shape of the EEG spectrum varies dynamically in a manner that is predictive of subsequent behavior. They also expand our understanding of how neural communication shapes cognition in YA and OA and have implications for neuroscientific models of cognitive processing and age-related cognitive decline.

neuroscience↗

bioRxiv2022

Dynamics of alpha suppression index both modality specific and general attention processes

EEG alpha power varies under many circumstances requiring visual attention. However, mounting evidence indicates that alpha may not only serve visual processing, but also the processing of stimuli presented in other sensory modalities, including hearing. We previously showed that alpha dynamics during an auditory task vary as a function of competition from the visual modality (Clements et al., 2022) suggesting that alpha may be engaged in multimodal processing. Here we assessed the impact of allocating attention to the visual or auditory modality on alpha dynamics, during the preparatory period of a bimodal-cued conflict task. In this task, precues indicated the modality (vision, hearing) relevant to a subsequent reaction stimulus. This task afforded us the opportunity to assess alpha during modality-specific preparation and while switching between modalities. Alpha suppression following the precue occurred in all conditions indicating that it may reflect general preparatory mechanisms. However, we observed a switch effect when preparing to attend to the auditory modality, in which greater alpha suppression was elicited when switching to the auditory modality compared to repeating. No switch effect was evident when preparing to attend to visual information (although robust suppression did occur in both conditions). In addition, waning alpha suppression preceded error trials, irrespective of sensory modality. These findings indicate that alpha can be used to monitor the level of preparatory attention to process both visual and auditory information. These results support the emerging view that alpha band activity may index a general attention control mechanism used across modalities, at least vision and hearing.

neuroscience↗

bioRxiv2021

Modeling spectral changes following stimulation: Is there an event-related shift in 1/f activity?

Research into the nature of 1/f-like, non-oscillatory electrophysiological activity has grown exponentially in recent years in cognitive neuroscience. The shape of this activity has been linked to the balance between excitatory and inhibitory neural circuits, which is thought to be important for information processing. However, to date, it is not known whether the presentation of a stimulus induces changes in the parameters of 1/f activity, which are separable from the emergence of event-related potentials (ERPs). Here, we analyze event-related broadband changes in scalp-recorded EEG both before and after removing ERPs to demonstrate their confounding effect, and to establish whether there are genuine stimulus-induced changes in 1/f. Using data from a passive and an active auditory task (n=23), we found that the shape of the post-event spectra differed significantly from the pre-event spectra even after removing the frequency-content of ERPs. Further, a significant portion of this difference could be accounted for by a rotational shift in 1/f activity, manifesting as an increase in low and a decrease in high frequencies. Importantly, the magnitude of this rotational shift was related to the attentional demands of the task. This change in 1/f is consistent with increased inhibition following the onset of a stimulus, and likely reflects a disruption of ongoing excitatory activity proportional to processing demands. Finally, these findings contradict the central assumption of baseline normalization strategies in time-frequency analyses, namely that background EEG activity is stationary across time. As such, they have far-reaching consequences that cut across several subfields of neuroscience. Significance statementInterest in the functional role of the 1/f-like background brain activity has been growing exponentially in neuroscience. Yet, no study to date has demonstrated a clear relationship between information processing and 1/f activity by investigating event-related effects on its parameters. Here, we demonstrate for the first time that stimuli induce rotational changes in 1/f activity, independent from the occurrence of event-related potentials. Not only do these findings suggest that the assumption of stationary background activity in the analysis of neural oscillations is untenable, but they also suggest the presence of large-scale inhibition following stimulus onset, the magnitude of which is dependent on the demands of the task. These findings have far-reaching consequences that cut across several subfields of neuroscience.

neuroscience↗

bioRxiv2021

Dynamics of alpha suppression and enhancement may be related to resource competition in cross-modal cortical regions

In the face of multiple sensory streams, there may be competition for processing resources in multimodal cortical area devoted to establishing representations. In such cases, alpha oscillations may serve to maintain the relevant representations and protect them from interference, whereas theta oscillations may facilitate their updating when needed. It can be hypothesized that these oscillations would differ in response to an auditory stimulus when the eyes are open or closed, as intermodal resource competition may be more prominent in the former than in the latter case. Across two studies we investigated the role of alpha and theta power in multimodal competition using an auditory task with the eyes open and closed, respectively enabling and disabling visual processing in parallel with the incoming auditory stream. In a passive listening task (Study 1a), we found alpha suppression following a pip tone with both eyes open and closed, but subsequent alpha enhancement only with closed eyes. We replicated this eyes-closed alpha enhancement in an independent sample (Study 1b). In an active auditory oddball task (Study 2), we again observed the eyes open/eyes closed alpha pattern found in Study 1 and also demonstrated that the more attentionally demanding oddball trials elicit the largest oscillatory effects. Theta power did not interact with eye status in either study. We propose a hypothesis to account for the findings in which alpha may be endemic to multimodal cortical areas in addition to visual ones.

neuroscience↗

bioRxiv2021

Neural correlates of individual differences in aversion to risk and choice inconsistencies

AO_SCPLOWBSTRACTC_SCPLOWWhen making financial choices, most people prefer smaller but more certain gains to larger but more uncertain ones with the same expected value (risk aversion). However, attitudes toward risk may vary greatly also within individuals (choice inconsistency). To examine the brain dynamics implementing risky and inconsistent decisions, we recorded event-related brain potentials (ERPs) from 24 adults engaged in a task requiring choices between certain but smaller gains and uncertain but larger ones. Choice consistency and risk aversion were quantified for each individual. Participants were classified into three groups according to their attitude toward risk. Relative neutrality to risk was accompanied by a higher consistency across trials than risk aversion or proneness. Choice consistency was related to the amplitude of the positive ERP peaking near 200 ms after stimulus onset (P200), while risk aversion was related to modulation of the medial frontal negativity (MFN) and to the amplitude of a late positive potential (LPP). Late ERP activity was related to the modulation of value signals by risk levels and associated with individual differences in behavior. Overall, this study suggests that individual differences in attitude toward risk and choice consistency are associated with distinct brain dynamics.

neuroscience↗

bioRxiv2020

The impact of 1/f activity and baseline correction on the results and interpretation of time-frequency analyses of EEG/MEG data: A cautionary tale

Typically, time-frequency analysis (TFA) of electrophysiological data is aimed at isolating narrowband signals (oscillatory activity) from broadband non-oscillatory (1/f) activity, so that changes in oscillatory activity resulting from experimental manipulations can be assessed. A widely used method to do this is to convert the data to the decibel (dB) scale through baseline division and log transformation. This procedure assumes that, for each frequency, sources of power (i.e., oscillations and 1/f activity) scale by the same factor relative to the baseline (multiplicative model). This assumption may be incorrect when signal and noise are independent contributors to the power spectrum (additive model). Using resting-state EEG data from 80 participants, we found that the level of 1/f activity and alpha power are not positively correlated within participants, in line with the additive but not the multiplicative model. Then, to assess the effects of dB conversion on data that violate the multiplicativity assumption, we simulated a mixed design study with one between-subject (noise level, i.e., level of 1/f activity) and one within-subject (signal amplitude, i.e., amplitude of oscillatory activity added onto the background 1/f activity) factor. The effect size of the noise level x signal amplitude interaction was examined as a function of noise difference between groups, following dB conversion. Findings revealed that dB conversion led to the over- or under-estimation of the true interaction effect when groups differing in 1/f levels were compared, and it also led to the emergence of illusory interactions when none were present. This is because signal amplitude was systematically underestimated in the noisier compared to the less noisy group. Hence, we recommend testing whether the level of 1/f activity differs across groups or conditions and using multiple baseline correction strategies to validate results if it does. Such a situation may be particularly common in aging, developmental, or clinical studies.

neuroscience↗

bioRxiv2020

Spontaneous alpha oscillations and low-frequency activities are related to complementary aspects of cognitive control in younger and older adults

The resting-state human EEG power spectrum is dominated by alpha (8-12 Hz) and theta (4-8Hz) oscillations, and also includes non-oscillatory broadband activity inversely related to frequency (1/f activity). Gratton (2018) proposed that alpha and theta oscillations are both related to cognitive control function, though in a complementary manner. Alpha activity is hypothesized to facilitate the maintenance of representations, such as task sets in preparation for expected task conditions. In contrast, theta activity would facilitate changes in representations, such as the updating of task sets in response to unpredicted task demands. Therefore, theta should be related to reactive control (which may prompt changes in task representations), while alpha may be more relevant to proactive control (which implies the maintenance of current task representations). Less is known about the possible relationship between 1/f activity and cognitive control, which was analyzed here in an exploratory fashion. To investigate these hypothesized relationships, we recorded eyes-open and eyes-closed resting-state EEG from younger and older adults and subsequently tested their performance on a cued flanker task, expected to elicit both proactive and reactive control processes. Results showed that alpha power and 1/f slope were smaller in older than younger adults, whereas theta power did not show age-related reductions. Resting alpha power and 1/f slope were predictive of proactive control processes, whereas theta power was related to reactive control as measured by the cued flanker task. All predictive associations were present over and above the effect of age, suggesting that these resting-state EEG correlates could be indicative of trait-like individual differences in cognitive control performance, which may be already evident in younger adults, and are still similarly present in healthy older adults.

neuroscience↗