Biology subjects

Kirchhoff, M.

Publications and source records attributed to Kirchhoff, M..

6 recordsLinked to original sources

bioRxiv2026

Not Just Noise: Aperiodic Brain Activity Reflects Corticospinal Excitability

BackgroundElectroencephalography (EEG) can be combined with transcranial magnetic stimulation (TMS) to perform brain-state-dependent stimulation. EEG-TMS studies have shown that corticospinal excitability, as measured via motor evoked potentials (MEPs), is modulated by pre-stimulus periodic EEG features, such as sensorimotor mu-rhythm phase and power. However, the influence of aperiodic brain activity on corticospinal excitability is largely unexplored. ObjectivesWe evaluated the relationship between aperiodic and periodic mu-power, aperiodic exponent, and mu-phase on MEP amplitudes using EEG-TMS. MethodsWe applied 800 single TMS pulses to the left primary motor cortex in 78 healthy adults. We calculated aperiodic/periodic mu-power, aperiodic exponent, and mu-phase for each trial from the pre-stimulus C3-Hjorth transformed EEG. MEP amplitudes were extracted from the right first dorsal interosseous muscle. A linear mixed-effects model assessed relationships between MEP amplitudes and EEG features, with interactions between mu-phase and all other EEG features. ResultsAperiodic and periodic mu-power, aperiodic exponent, and mu-phase significantly modulated MEP amplitudes. Higher aperiodic/periodic mu-power was associated with larger MEP amplitudes, while higher aperiodic exponent was associated with smaller MEP amplitudes. We found a significant interaction effect of aperiodic exponent and mu-phase on MEP amplitude. Aperiodic exponent was negatively associated with MEPs for trough, rising, falling phases, but positively associated with MEPs for peak phase. ConclusionsAperiodic and periodic features of brain activity are reflective of dissociable corticospinal excitability states. Future brain-state-dependent TMS interventions may include aperiodic EEG features, such as aperiodic mu-power and exponent, in addition to the well-established periodic features.

neuroscience↗

bioRxiv2025

Fast and standardized motor-hotspot determination with automated TMS mapping

Determining the optimal stimulation target for motor responses (motor hotspot) and the required intensity for reliably eliciting said responses (motor threshold) are common procedures in transcranial magnetic stimulation (TMS) research and treatments. However, the procedures for determining them are user-dependent, slow, and lack standardization, leading to long stimulation sessions with potentially inadequate outcomes. Partially automated algorithms for determining the motor threshold have been developed, but the motor hotspot is still largely mapped by hand. Automating the hotspot mapping will accelerate the process and improve standardization and accuracy. We developed a fully automated algorithm for finding the motor hotspot with multi-locus TMS and Bayesian optimization. Tested online in five healthy participants, the algorithm located motor hotspots with (mean {+/-} 95% CI) 2.1 {+/-} 0.7 mm and 6 {+/-} 2{degrees} difference from the global best target with only (mean) 47 stimuli. This is a significant improvement from previous motor-mapping algorithms, which do not optimize for stimulation location and orientation simultaneously. This accurate, fast, and user-independent procedure paves the way for faster experimental processes and more streamlined clinical applications.

neuroscience↗

bioRxiv2025

L-selectin shedding regulates functional recovery and neutrophil clearance following spinal cord injury in a sex-dependent manner

During the acute phase of spinal cord injury (SCI), neutrophils infiltrate in large numbers and can exacerbate inflammation, secondary tissue damage, and neurological deficits. L-selectin is a signaling and adhesion receptor that has been shown to facilitate neutrophil recruitment and secondary injury after SCI. During neutrophil activation, L-selectin is typically cleaved or shed from the cell surface and augmenting L-selectin shedding can improve hindlimb recovery and tissue sparing following SCI in male mice. However, it is unclear how endogenous L-selectin shedding regulates neutrophil responses and functional recovery after SCI, particularly when also considering sex as a biological variable. In this study, we investigated the sex-dependent role of endogenous L-selectin shedding in neutrophil function and long-term outcomes in a murine thoracic contusion model of SCI. We found that endogenous L-selectin shedding improves long-term functional recovery and white matter sparing in female, but not male, mice. In addition, we demonstrate that L-selectin shedding alters neutrophil accumulation in a sex-dependent manner. While L-selectin shedding does not mediate neutrophil activation or effector functions, we found that neutrophil clearance is facilitated by L-selectin shedding in female mice alone. These results demonstrate that endogenous L-selectin shedding is a critical and sex-dependent mediator of neutrophil accumulation and clearance, as well as long-term functional outcomes, after SCI.

neuroscience↗

bioRxiv2025

Mature neutrophils promote long-term functional recovery after spinal cord injury in a sex-dependent manner

Neutrophils are abundant and complex innate immune cells that act as first responders to tissue injury, with critical roles in combating infection and initiating would healing. Following spinal cord injury (SCI), neutrophils are the first peripheral immune cells to infiltrate the injured spinal cord in large numbers. Despite the growing body of evidence demonstrating sex differences in neutrophil function, sex as a biological variable in neutrophil responses following SCI has yet to be thoroughly investigated. Here we provide novel evidence that neutrophil responses differ by sex following SCI with divergent effects on long-term outcomes. We show substantial sex-dependent shifts in the phenotype of circulating and intraspinal neutrophils across time following SCI. Depletion of neutrophils immediately after SCI reveals a previously unidentified role for mature neutrophils in promoting long-term functional recovery in a sex-dependent manner. Mechanistically, mature neutrophils acquire an inflammation-resolving phenotype in the acutely injured spinal cord and depletion of mature neutrophils exacerbates long-term macrophage accumulation following SCI in a sex-dependent manner. Collectively, our findings provide the first account of marked sex differences in the response of neutrophils to SCI and elucidate a novel and sex-dependent role for mature neutrophils in promoting resolution of inflammation and long-term recovery following SCI.

neuroscience↗

bioRxiv2020

Drone-derived canopy height predicts biomass across non-forest ecosystems globally

Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, yet are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely-sensed biomass products and are undersampled by in-situ monitoring. Current global change threats emphasise the need for new tools to capture biomass change in non-forest ecosystems at appropriate scales. Here we assess whether canopy height inferred from drone photogrammetry allows the estimation of aboveground biomass (AGB) across low-stature plant species sampled through a global site network. We found mean canopy height is strongly predictive of AGB across species, demonstrating standardised photogrammetric approaches are generalisable across growth forms and environmental settings. Biomass per-unit-of-height was similar within, but different among, plant functional types. We find drone-based photogrammetry allows for monitoring of AGB across large spatial extents and can advance understanding of understudied and vulnerable non-forested ecosystems across the globe.

ecology↗

bioRxiv2017

Biological Self-organisation and Markov blankets

Biological self-organisation is a process of spontaneous pattern formation; namely the emergence of coherent and stable systemic configurations that distinguish themselves from their environment. This process can occur at various spatial scales: from the microscopic (giving rise to cells) to the macroscopic (the emergence of organisms). Self-organisation at each level is essential to account for the hierarchical organisation of living organisms (organelles within cells, within tissues, within organs, etc.). In this paper, we pursue the idea that Markov blankets - statistical boundaries separating states that are external to a system from its internal states - emerge at every possible level of the description of the (living) system. Through simulations, we show that the concept of a Markov blanket is fundamental in defining biological systems and underwrites the nature and form of interactions between successive levels of hierarchical structure. We demonstrate the validity of our argument using simulations, based on the normative principle of variational free energy minimisation. Specifically, we adopt a top-down approach to provide a proof of concept for the claim that the self-organisation of Markov blankets (and blankets of blankets) underwrites the self-evidencing, autopoietic behaviour of living systems.

systems biology↗