Biology subjects

Rich, R.

Publications and source records attributed to Rich, R..

3 recordsLinked to original sources

bioRxiv2026

Brief Trains of Closed-loop TMS Induce Controllable Power in FM-theta Oscillations

Objective. Frontal-midline theta (FM-theta; 4-8 Hz) oscillations are thought to support cognition. Brief trains of transcranial magnetic stimulation (TMS) can probe these oscillations with high temporal precision but have rarely changed theta power. One possible reason is that prior studies ignored the instantaneous phase of the oscillation, which strongly shapes the cortical response to TMS. We tested whether brief TMS trains triggered at specific FM-theta phases in real time directionally modulate post-train FM-theta power. Approach. Six healthy adults received TMS over dorsomedial prefrontal cortex (Fz) with concurrent electroencephalography during a whole-report working memory task. A beamformer and real-time phase-estimation pipeline triggered four-pulse 6 Hz trains (110% of resting motor threshold) at FM-theta peaks (0 degrees) or troughs (180 degrees), randomized trial by trial. Post-train spectral power was decomposed into total, induced (non-phase-locked) and evoked (phase-locked) components. Main results. Trough-triggered trains transiently increased post-train FM-theta power relative to peak-triggered trains; task performance did not differ. Cluster-based permutation tests showed trough-peak differences in total (4.6-7.1 Hz) and induced (5.0-7.8 Hz) power ~50-440 ms after the train, suggesting amplification of the oscillation . No evoked effect was detected. The total-power effect was robust at the subject level (Cohen's dz = 1.32, p = 0.023). Within-train theta power did not differ between conditions, suggesting a cortical origin. Significance. To our knowledge, this is the first study to lock brief rhythmic TMS trains to the real-time phase of an ongoing oscillation, and to show phase-dependent modulation of FM-theta power after individual trains on timescales relevant to behavior. Open-loop brief-train protocols may have missed such effects by mixing faciliatory and suppressive phases. Phase-locked brief trains offer a precise tool for testing the causal role of oscillations in cognition.

neuroscience↗

bioRxiv2025

Experimental flooding impacts soil biogeochemistry but not aboveground vegetation in a coastal forest

Rising sea levels and intensifying storms increase flooding pressure on coastal forests, triggering tree mortality, ecosystem transitions, and changes to the coastal carbon cycle. However, the mechanisms that drive coastal forest mortality remain elusive due to the complex interplay between belowground and aboveground processes during flooding disturbances and limitations of observations typically reported in coastal forest mortality studies. We used an ecosystem-scale manipulation to simulate hurricane-level flooding of a coastal forest. Monitoring real-time soil conditions and tree physiological responses, we observed consistent impacts on soil biogeochemistry aligned with belowground drivers of tree mortality, but no consistent responses in aboveground vegetation. Our findings provide unprecedented empirically based insight into the earliest stages of a hypothesized forest mortality spiral and offer critical benchmarks for predicting coastal forest resilience in the face of accelerating climate change. Significance StatementChanging sea levels and storms are causing more flooding in coastal forests. This flooding kills trees, changing how coastal ecosystems function, but we do not fully understand what factors determine whether forests survive flooding. We designed an ecosystem-scale experiment to answer this question, with controlled saltwater and freshwater floods equivalent to a hurricane in experimental forest plots. Flooding quickly changed soil conditions, but we have not yet observed consistent tree stress responses. Our study provides the most detailed measurements to date of how coastal forests respond to flooding in real time. These findings will help us better understand the early mechanisms and warning signs of forests threatened by flooding.

systems biology↗

bioRxiv2023

Groundwater redox dynamics across the terrestrial-aquatic interface of Lake Erie coastal ecosystems

Groundwater biogeochemistry in coastal areas is spatially and temporally dynamic because fluctuations in groundwater level may cause alternate redox between distinct hydrological conditions. Recent studies have proposed connections between biogeochemistry and large-scale hydrological processes, specifically focusing on the role of redox-active compounds in changing the oxidation state during flooding and draining events. While water saturation generally results in a shift of redox-active compounds from electron donors to acceptors, the specific mechanisms underlying the transition of groundwater between oxidizing and reducing conditions in response to water level fluctuations are uncertain. To determine the effects of groundwater levels on redox dynamics, we monitored groundwater redox potential across the terrestrial-aquatic interface in Lake Erie coastal areas throughout the high and low-water seasons. In contrast to previously observed responses to flooding in soils, our results revealed patterns of oxidizing redox potentials during high-water and reducing during low-water periods. Furthermore, short-term fluctuations in water table levels significantly impacted the redox potential of groundwater when dissolved oxygen increased, and redox dynamics displayed voltage hysteresis in most events. Based on these findings, we propose that for improved predictions of microbial functions and biogeochemical cycles, redox-informed models should incorporate the antagonistic changes in groundwater redox balance compared to soils and consider the time lags in redox fluctuations. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=92 SRC="FIGDIR/small/544684v1_figu1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@4d7a19org.highwire.dtl.DTLVardef@8b2b92org.highwire.dtl.DTLVardef@d9bc11org.highwire.dtl.DTLVardef@ca3e13_HPS_FORMAT_FIGEXP M_FIG Graphical AbstractConceptual diagram of groundwater redox fluctuations in coastal ecosystems. Large redox fluctuations are derived by dissolved oxygen inputs and smaller more frequent redox fluctuations are led by redox sensitive species leaching from topsoil. C_FIG

ecology↗