Biology subjects

Rolfs, K.

Publications and source records attributed to Rolfs, K..

3 recordsLinked to original sources

bioRxiv2025

High frequency oscillations measured with optically pumped magnetometers from the human retina

Measurement of human neural activity with optically pumped magnetometers (OPMs) is rapidly proliferating, with sensitivity approaching that of cryogenic sensors. Most neuroscience research with OPMs to date has investigated neural responses below 70 Hz, but higher frequencies are also of interest. However, sensitivity to higher frequencies may be limited by both the inherent operating bandwidth of the current generation of zero-field OPMs as well as by their generally lower amplitude. To assess the upper bounds of OPM sensitivity we used the stereotypical retinal response to flashes of light. Retinal responses to light flashes characteristically exhibit a neural response above 70 Hz called the oscillatory potential (OP) when recorded with electroretinography (ERG). Here we adopt the term retinal high frequency oscillation (rHFO) to include measurement of similar activity with OPMs. Our comparison of magnetoretinography (MRG) and ERG shows that rHFO can be measured up to 140 Hz using rubidium-based zero-field OPMs.

neuroscience↗

bioRxiv2021

Improved spatio-temporal measurements of visually evoked fields using optically-pumped magnetometers

Recent developments in performance and practicality of optically pumped magnetometers have enabled new capabilities in non-invasive brain function mapping through magnetoencephalography. In particular the lack of need of cryogenic operating conditions allows for more flexible placement of the sensor heads closer to the brain surface, leading to improved spatial measurement resolution and increased source localisation capabilities. Through the recording of visually evoked brain fields (VEF), we demonstrate that the closer sensor proximity can be further exploited to improve the temporal resolution. We use optically pumped magnetometers (OPMs), and for reference superconducting quantum interference devices (SQUIDs), to measure brain responses to standard flash and pattern reversal stimuli. We find highly reproducible signals with consistency across multiple healthy participants, stimulus paradigms and sensor modalities. The temporal resolution advantage of OPMs is manifest in a fourfold improvement of the ratio of magnetic signal peak height to temporal width, compared to SQUIDs. The resulting capability of improved spatio-temporal signal tracing is illustrated by simultaneous vector recordings of VEFs in the primary (V1) and associative (V2) visual cortex, where a time lag on the order of 10-20 ms is consistently found. This paves the way for further studies of spatio-temporal neurophysiological signal tracking in visual stimulus processing and other brain responses with potentially far-reaching consequences for time-critical mapping of functionality in the healthy and pathological brains.

neuroscience↗

bioRxiv2020

Action potentials induce biomagnetic fields in Venus flytrap plants

Upon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electrophysiological techniques like electroencephalography1, magnetoencephalography2, and magnetic resonance imaging3,4 are used to record this activity and to diagnose disorders. In the plant kingdom, two types of electrical signals are observed: all-or-nothing APs of similar amplitudes to those seen in humans and animals, and slow-wave potentials of smaller amplitudes. Sharp APs appear restricted to unique plant species like the "sensitive plant", Mimosa pudica, and the carnivorous Venus flytrap, Dionaea muscipula5,6. Here we ask the question, is electrical activity in the Venus flytrap accompanied by distinct magnetic signals? Using atomic optically pumped magnetometers7,8, biomagnetism in AP-firing traps of the carnivorous plant was recorded. APs were induced by heat stimulation, and the thermal properties of ion channels underlying the AP were studied. The measured magnetic signals exhibit similar temporal behavior and shape to the fast de- and repolarization AP phases. Our findings pave the way to understanding the molecular basis of biomagnetism, which might be used to improve magnetometer-based noninvasive diagnostics of plant stress and disease.

plant biology↗