Biology subjects

Riddle, J.

Publications and source records attributed to Riddle, J..

5 recordsLinked to original sources

bioRxiv2026

Transcranial Random Aperiodic Stimulation Improves Working Memory Precision

Aperiodic neural activity, historically dismissed as noise, is independently modulated from neural oscillations during visual working memory maintenance. In the context of aging, flatter trait aperiodic activity is associated with poorer visual working memory performance. Here, we causally test the role of aperiodic neural activity in visual working memory in younger adults. We introduce a novel noninvasive neurostimulation method, transcranial random aperiodic stimulation (tRAS), to causally manipulate aperiodic activity to be either steeper or flatter. In a randomized, double-blind, placebo-controlled, crossover neurostimulation design (n = 30), we show that online noninvasive tRAS improves visual working memory precision when aperiodic activity is causally steepened. Our novel stimulation method paves the way for causal studies of non-oscillatory, aperiodic activity in human cognition, aging, and disease.

neuroscience↗

bioRxiv2025

Aperiodic neural timescales in prefrontal cortex dilate with increased task abstraction

Navigating everyday environments requires that the brain perform information processing at multiple different timescales. For example, while watching a movie we use sensory information from every video frame to construct the current movie scene, which itself is continuously integrated into the narrative arc of the film. This critical function is supported by sensory inputs propagating from dynamic sensory cortices to association cortices, where neural activity remains more stable over time. The hierarchical organization of cortex is therefore reflected in a gradient of neural timescales. While this propagation of inputs up the cortical hierarchy is facilitated by both rhythmic (oscillatory) and non-rhythmic (aperiodic) neural activity, traditional measures of oscillations are often confounded by the influence of aperiodic signals. The reverse is also true: traditional measures of aperiodic neural timescales are influenced by oscillations. This makes it difficult to distinguish between oscillatory and timescale effects in cognition. Here, we analyzed electroencephalography (EEG) data from participants performing a cognitive control task that manipulated the amount of task-relevant contextual information, called task abstraction. Critically, we separated aperiodic neural timescales from the confounding influence of oscillatory power. We hypothesized that neural timescales would increase during the task, and more so in high-abstraction conditions. We found that task abstraction dilated the aperiodic neural timescale, as estimated from the autocorrelation function, over prefrontal cortical regions. Our findings suggests that neural timescales are a dynamic feature of the cerebral cortex that change to meet task demands. Significance StatementThough often thought of as indexing anatomical brain structure, neural timescales have recently come under the spotlight for their variability across different task conditions. Here, we investigated whether neural timescales dynamically change during cognitive tasks that require a greater level of contextual control. Previous work quantified neural timescales using the autocorrelation function, but this approach conflates oscillatory and aperiodic contributions to the timescale. Thus, we decomposed the neural timescale into oscillatory and aperiodic components, and found that aperiodic-derived timescale measures dynamically change with contextual control. Oscillatory power also exhibits change in response to task demands, reaffirming previous findings. These results together suggest that both established oscillatory and novel aperiodic measures of neural timescales can dynamically change to meet task demands.

neuroscience↗

bioRxiv2024

Condensin-mediated restriction of retrotransposable elements facilitates brain development in Drosophila melanogaster.

Neural stem and progenitor cell (NSPC) maintenance are essential for ensuring that organisms are born with proper brain volumes and head sizes. Microcephaly is a disorder in which babies are born with significantly smaller head sizes and cortical volumes. Mutations in subunits of the DNA organizing complexes, condensins have been identified in microcephaly patients. However the molecular mechanisms by which condensin insufficiency causes microcephaly remain elusive. We previously identified conserved roles for condensins in repression of retrotransposable elements (RTEs). Here, we show that condensin subunit knockdown in NSPCs of the Drosophila larval central brain increases RTE expression and mobility which causes cell death, and significantly decreases adult head sizes and brain volumes. These findings suggest that unrestricted RTE expression and activity may lead to improper brain development in condensin insufficient organisms, and lay the foundation for future exploration of causative roles for RTEs in other microcephaly models.

neuroscience↗

bioRxiv2020

Progesterone modulates theta oscillations in the frontal-parietal network

The neuroactive metabolites of the steroid hormones progesterone (P4) and testosterone (T) are GABAergic modulators that influence cognitive control, yet the specific effect of P4 and T on brain network activity remains poorly understood. Here, we investigated if a fundamental oscillatory network activity pattern related to cognitive control, frontal midline theta (FMT) oscillations, are modulated by steroids hormones, P4 and T. We measured the concentration P4 and T using salivary enzyme immunoassay and FMT oscillations using high-density electroencephalography (EEG) during the eyes-open resting state in fifty-five healthy female and male participants. Electrical brain activity was analyzed using Morlet wavelet convolution, beamformer source localization, background noise spectral fitting, and phase amplitude coupling analysis. Steroid hormone concentrations and biological sex were used as predictors for scalp and source-estimated theta oscillations and for top-down theta-gamma phase amplitude coupling. Elevated concentrations of P4 predicted increased FMT oscillatory amplitude across both sexes, and no relationship was found with T. The positive correlation with P4 was specific to the frontal-midline electrodes and survived correction for the background noise of the brain. Using source localization, FMT oscillations were localized to the frontal-parietal network. Additionally, theta amplitude within the frontal-parietal network, but not the default mode network, positively correlated with P4 concentration. Finally, P4 concentration correlated with increased coupling between FMT phase and posterior gamma amplitude. Our results suggest that P4 concentration modulates brain activity via upregulation of theta oscillations in the frontal-parietal network and increased top-down control over posterior cortical sites. Significance StatementThe neuroactive metabolites of the steroid hormones progesterone (P4) and testosterone (T) are GABAergic modulators that influence cognitive control, yet the specific effect of P4 and T on brain network activity remains poorly understood. Here, we investigated if a fundamental oscillatory network activity pattern related to cognitive control, frontal midline theta (FMT) oscillations, are modulated by steroids hormones, P4 and T. Our results suggest that P4 concentration modulates brain activity via upregulation of theta oscillations in the frontal-parietal network and increased top-down control over posterior cortical sites.

neuroscience↗

bioRxiv2019

Network-targeted, multi-site direct cortical stimulation enhances working memory by modulating phase lag of low frequency oscillations

Working memory, an important component of cognitive control, is supported by the coordinated activation of a network of cortical regions in the frontal and parietal cortices. Oscillations in theta and alpha frequency bands are thought to coordinate these network interactions. Thus, targeting multiple nodes of the network with brain stimulation at the frequency of interaction may be an effective means of modulating working memory. We tested this hypothesis by identifying regions that are functionally connected in theta and alpha frequency bands and intracranially stimulating both regions simultaneously in participants undergoing invasive monitoring. We found that in-phase stimulation resulted in improvement in performance compared to sham stimulation. In contrast, anti-phase stimulation did not affect performance. In-phase stimulation resulted in decreased phase lag between regions within working memory network while anti-phase stimulation resulted in increased phase lag suggesting that shorter phase lag in oscillatory connectivity may lead to better performance. The results support the idea that phase lag may play a key role in information transmission across brain regions. More broadly, brain stimulation strategies that aim to improve cognition may be better served targeting multiple nodes of brain networks.

neuroscience↗