Campana, G. | Search bioRxiv

bioRxiv2025

Sparks fade with distance: The effect of electric field distribution on global motion perception using different tES techniques

Previous evidence has shown that high frequency transcranial random noise stimulation (hf-tRNS) decreases motion coherence thresholds when a cephalic montage (i.e., return over Cz) is used. Extracephalic montages have also been employed to modulate behavioral performance, eliminating stimulation of regions under the return electrode. In this study, we examined the effects of different transcranial electrical stimulation (tES) protocols on visual motion discrimination, placing the return electrode on the ipsilateral arm. We assessed the impact of electrode localization using hf-tRNS, anodal, cathodal transcranial direct current stimulation (tDCS), and Sham stimulation over hMT+, a brain region involved in global motion perception. Motion direction discrimination was measured using random dot kinematograms (RDKs). Due to the increased distance between the stimulation and return electrodes in this montage, we expected a smaller reduction in motion discrimination thresholds compared to our previous study. The results suggest that increased interelectrode distance mitigates the efficacy of hf-tRNS. Additionally, no significant effects were observed with the other tES protocols tested. Our findings imply that the positioning of the two electrodes affects current flow characteristics, leading to reduced neuromodulation. These results underscore the importance of stimulation configuration, particularly the effect of interelectrode distance on performance. Given the widespread application of brain stimulation techniques in clinical and cognitive research, our results can guide future studies in carefully considering this further aspect of stimulation montage configurations.

neuroscience↗

bioRxiv2016

The food web of Potter Cove (Antarctica): complexity, structure and function

Knowledge of the food web structure and complexity are central to better understand ecosystem functioning. A food-web approach includes both species and energy flows among them, providing a natural framework for characterizing species ecological roles and the mechanisms through which biodiversity influences ecosystem dynamics. Here we present for the first time a high-resolution food web for a marine ecosystem at Potter Cove (northern Antarctic Peninsula). Eleven food web properties were analyzed in order to document network complexity, structure and topology. We found a low linkage density (3.4), connectance (0.04) and omnivory percentage (45), as well as a short path length (1.8) and a low clustering coefficient (0.08). Furthermore, relating the structure of the food web to its dynamics, an exponential degree distribution (in- and out-links) was found. This suggests that the Potter Cove food web may be vulnerable if the most connected species became locally extinct. For two of the three more connected functional groups, competition overlap graphs imply high trophic interaction between demersal fish and niche specialization according to feeding strategies in amphipods. On the other hand, the prey overlap graph shows also that multiple energy pathways of carbon flux exist across benthic and pelagic habitats in the Potter Cove ecosystem. Although alternative food sources might add robustness to the web, network properties (low linkage density, connectance and omnivory) suggest fragility and potential trophic cascade effects.

ecology↗