Biology subjects

Seymour, J.

Publications and source records attributed to Seymour, J..

3 recordsLinked to original sources

bioRxiv2025

A catastrophic marine mortality event caused by a complex algal bloom including the novel brevetoxin producer, Karenia cristata (Dinophyceae)

Harmful algal blooms of Karenia brevis (Dinophyceae) are a global anomaly, occurring in one location worldwide, causing severe marine and acute human impacts via brevetoxins (BTX). During 2025 an unprecedented, currently ongoing, mass marine mortality occurred in South Australia, across an area of [~]20,000 km2, persisting for >6 months, resulting in the deaths of [~]106 marine animals of >550 taxa, with human health impacts. Using custom metabarcoding, long-read sequencing and targeted quantitative PCR, we characterized the microalgal assemblage. Karenia cristata dominated over the sampling area, in an assemblage with four other Karenia species with varied abundances spatially and temporally. High abundances of K. cristata appeared in the austral autumn, and hydrodynamic processes appear to have entrained cells coastward in the semi-enclosed seas. We isolated the species and characterized it using light and electron microscopy, liquid chromatography mass spectrometry and toxicity assays. We show for the first time that the rare and little known K. cristata produces significant BTX with a profile (BTX-2, -3, -B5), differing from K. brevis, with toxicological effects. These findings reveal a novel, significant BTX-producing Karenia, which considering its substantial detrimental marine ecosystem impacts, is an emerging international threat with unknown consequences in changing ocean conditions.

ecology↗

bioRxiv2021

The Listening Zone of Human Electrocorticographic Field Potential Recordings

Intracranial electroencephalographic (icEEG) recordings provide invaluable insights into neural dynamics in humans due to their unmatched spatiotemporal resolution. Yet, such recordings reflect the combined activity of multiple underlying generators, confounding the ability to resolve spatially distinct neural sources. To empirically quantify the listening zone of icEEG recordings, we computed the correlations between signals as a function of distance (expressed as full width at half maximum; FWHM) between 8,752 recording sites in 71 patients implanted with either subdural electrodes (SDE), stereo-encephalography electrodes (sEEG), or high-density sEEG electrodes. As expected, for both SDE and sEEG electrodes, higher frequency signals exhibited a sharper fall off relative to lower frequency signals. For broadband high gamma (BHG) activity, the mean FWHM of SDEs (6.6 {+/-} 2.5 mm) and sEEGs in gray matter (7.14 {+/-} 1.7 mm) was not significantly different, however the FWHM for low frequencies recorded by sEEGs was 2.45 mm smaller than SDEs. White matter sEEG electrodes showed much lower power for frequencies 17 to 200 Hz (q < 0.01) and a much broader decay (11.3 {+/-} 3.2 mm) than gray matter electrodes (7.14 {+/-} 1.7 mm). The use of a bipolar referencing scheme significantly lowered FWHM for sEEG electrodes, as compared with a white matter reference or a common average reference. These results outline the influence of array design, spectral bands, and referencing schema on local field potential recordings and source localization in icEEG recordings in humans. The metrics we derive have immediate relevance to the analysis and interpretation of both cognitive and epileptic data.

neuroscience↗

bioRxiv2021

Sensing Local Field Potentials with a Directional and Scalable Depth Array: DISC

A variety of electrophysiology tools are available to the neurosurgeon for diagnosis, functional therapy, and neural prosthetics. However, no tool can currently address these three critical needs: (i) access to all cortical regions in a minimally invasive manner; (ii) recordings with microscale, mesoscale, and macroscale resolutions simultaneously; and (iii) access to spatially distant multiple brain regions that constitute distributed cognitive networks. We present a novel device for recording local field potentials (LFPs) with the form factor of a stereo-electroencephalographic electrode but combined with radially positioned microelectrodes and using the lead body to shield LFP sources, enabling directional sensitivity and scalability, referred to as the DISC array. As predicted by our electro-quasistatic models, DISC demonstrated significantly improved signal-to-noise ratio, directional sensitivity, and decoding accuracy from rat barrel cortex recordings during whisker stimulation. Critically, DISC demonstrated equivalent fidelity to conventional electrodes at the macroscale and uniquely, revealed stereoscopic information about current source density. Directional sensitivity of LFPs may significantly improve brain-computer interfaces and many diagnostic procedures, including epilepsy foci detection and deep brain targeting.

bioengineering↗