Pollitt, E. | bioRxiv Science

bioRxiv2025

Distinct and complementary mechanisms of oscillatory and aperiodic alpha activity in visuospatial attention

Alpha oscillations are thought to play a key role in visuospatial attention, particularly through lateralisation mechanisms. However, whether this function is driven purely by oscillatory activity or also involves aperiodic neural components remains unclear, making it difficult to develop precise theoretical models of alpha function and attention. Using EEG and concurrent TMS-EEG, this study aimed to (1) disentangle the contributions of oscillatory and aperiodic alpha activity to visuospatial attention and (2) examine their causal roles by differentially modulating aperiodic and oscillatory components. First, across three independent EEG datasets, we found that both oscillatory and aperiodic responses in the alpha band contribute to spatial attention encoding and univariate lateralisation effects. The two signals were uncorrelated across electrodes and their combination yielded stronger effects than either signal separately, suggesting that they may play complementary roles. Then, we used concurrent TMS-EEG to modulate the two signals. Compared to arrhythmic TMS (ar-TMS), rhythmic TMS (rh-TMS), enhanced oscillatory alpha power, especially at the stimulated area, while decreasing aperiodic alpha power across the scalp. Despite these opposing effects, rh-TMS improved visuospatial attention representation carried by both oscillatory and aperiodic alpha signals, suggesting that both signals may support attentional processing through different mechanisms. Moreover, TMS-induced changes in oscillatory and aperiodic alpha decoding differentially predicted behavioural performance, with TMS-induced changes in oscillatory alpha decoding correlating with response errors and changes in aperiodic alpha decoding correlating with response speed. Together these findings reveal a functional dissociation between oscillatory and aperiodic activity in the alpha band. We suggest a dual mechanism for alpha band activity in supporting visuospatial attention, where the two components have distinct but complementary roles. Oscillatory components may primarily support attentional filtering and target prioritization, while aperiodic components may reflect overall neural excitability and cognitive efficiency. Both of these mechanisms contribute to successful visuospatial attention.

neuroscience↗

bioRxiv2024

Staphylococcus aureus gliding comets: formation and observation

Staphylococcus aureus has been shown to move across soft agar surfaces by several different mechanisms. S. aureus can move using either spreading (a form of sliding motility producing generally round/frond like colonies) or by forming comets (slime covered aggregates of cells) that result in long thin dendrites branching out from the central colony. Spreading is agreed to be a form of passive motility whilst the comets are a form of gliding motility (i.e. active). Comets occur under similar conditions to spreading round colonies; however it can be difficult to get the comets to form. Here we examine the variables involved in determining whether comets form as well as report further observations of the comets themselves. We found that the conditions that favoured comet formation (and formed the associated dendrites) occurred over a more limited range than those that enabled spreading motility. Comet formation is very sensitive to the solidifying agents used, the amount of media used and the drying time. We further observed that the comets can propel themselves upwards against gravity unlike spreading motility and that S. aureus formed unusual dense aggregates and strand-like structures within comets unlike the normal growing arrangement of S. aureus observed in spreading. These results may aid others in producing motility assays to study spreading and comet formation in S. aureus and provides further insight into how comets behave.

microbiology↗