Biology subjects

Naidoo, R.

Publications and source records attributed to Naidoo, R..

7 recordsLinked to original sources

bioRxiv2026

Increased activity without changes in coupling between somata and apical dendrites during visual mismatches

Leading theories of cortical function posit that sensory processing involves a comparison between top-down predictions and bottom-up sensory data. Tests of these theories have been hampered by experimental challenges related to simultaneously recording top-down and bottom-up signals in response to sensory stimuli that either do or do not match internally-generated predictions. Here, we conduct dual-plane 2-photon calcium imaging near-simultaneously from distal apical dendrites and somata of pyramidal neurons in each of 4 different regions of mouse visual cortex while the mice are presented with visual sequences that can either match or mismatch previously habituated visual stimuli. Specifically, we examine the responses in the distal apical dendrites and cell bodies of pyramidal neurons while mice view either movie clips that reverse unexpectedly or Gabor patch sequences that have orientations that do not match habituated patterns. We find that in response to unexpected reversals in natural movies, both the apical dendrites and somata show increased activity that decreases over repeated exposures, consistent with a prediction error response. However, we do not find any clear evidence for increased activity in response to mismatches in Gabor sequences, beyond possible release from adaptation effects. We additionally use volumetric images to connect dendritic and somatic compartments and examine the coupling between connected dendrites and cell bodies in layer 5 pyramidal neurons. We do not find evidence for changes in coupling in response to mismatch stimuli, either for natural movies or Gabor sequences. Our results are consistent across four regions of visual cortex. We also observe that increased responses to reversals in natural movies are stronger in layer 2/3 than layer 5 pyramidal neurons. Altogether, these data suggest that visual cortex is sensitive to deviations from previously-experienced naturalistic inputs. Our data do not suggest that this mismatch sensitivity extends to artificial stimuli, nor do they support theories of prediction error causing changes in the coupling between apical dendrites and somata.

neuroscience↗

bioRxiv2026

Moving object generates topographic responses in the majority of entorhinal neurons

Vision is crucial in generating a complex array of responses in rodents during spatial exploration and in humans during memory tasks. These tasks involve other variables too, e.g. multisensory cues in rodents and complex memories in humans. Further, there are major differences between the medial and lateral entorhinal cortical (MEC and LEC) functional cell types. To understand the contribution of purely visual information to entorhinal responses, we presented a simple, moving vertical bar of light to head-fixed mice, without any task or reward. Surprisingly, 66% (2391/3601) of the MEC broad spiking neurons were significantly modulated by the bar position on the screen. Visual tuning in MEC had a pronounced dorsoventral topography --the tuning strength dropped from 79% in the dorsal most quartile to 40% in the ventral most quartile. Unlike major differences in spatial and other codes between MEC and LEC during free foraging experiments, LEC cells showed very similar visual tuning (392/606, 65%), including the dorso-ventral gradient in LEC5. Additionally, the majority of putative interneurons, from MEC as well as LEC, showed similar, widespread visual tuning, unlike spatial tasks. Neurons also encoded the object motion direction (naso-temporal vs. temporo-nasal visual motion) with changes in mean rate, tuning strength and/or tuning location. Such directional nature of visual tuning indicates significant history-dependence or sequence encoding. Consistently, replacing the continuous motion by randomly flashing bar of light abolished bar-tuning in two-thirds of continuous bar-tuned cells and substantially altered tuning in the rest. These results reveal the contribution of purely visual inputs in generating anatomically organized responses in the majority of entorhinal neurons. The prevalence and similarity of visual tuning across all layers of MEC as well as LEC exceeds that of other known functional cell types (like grid cells in MEC or egocentric object tuning/time-cells in LEC) during spatial navigation tasks and could be foundational in understanding entorhinal complexity.

neuroscience↗

bioRxiv2026

Psilocybin collapses visual change detection and drives cortical dynamics toward a state of surprise

Psilocybin profoundly alters visual perception, yet the neuronal mechanisms underlying these effects remain unclear. Here we combined large-scale Neuropixels recordings with cell-type specific optogenetics in head-fixed mice performing a visual change-detection task. Psilocybin severely impaired task performance without overt motor deficits. In cortex, the drug modestly suppressed activity of layer 5 neurons while preserving representations of image identity. By contrast, psilocybin imposed a 4-Hz oscillation on visually evoked activity that preferentially affected neurons encoding image change rather than image identity. Under psilocybin, expected image repetitions aberrantly recruited change-encoding ensembles and shifted cortical population dynamics towards trajectories normally evoked by genuine stimulus changes. These effects were strongest in somatostatin-expressing (SST) interneurons in visual cortex. The strength of this modulation depended on image structure and was greatest for images with clear, continuous contours, which preferentially recruited change-encoding ensembles. These findings demonstrate that psilocybin drives internally generated cortical surprise signals, providing a circuit mechanism for altered perception in the acute psychedelic state.

neuroscience↗

bioRxiv2026

Pheno-MYCN maps the morphological footprint of MYCN amplification in paediatric neuroblastoma

MYCN amplification has long been a prognostic marker in paediatric neuroblastoma, yet is typically assayed in bulk, alongside rather than within the heterogeneous tissue architecture pathologists assess. This leaves a gap: MYCN status alone cannot localise MYCN-associated biology, while morphology alone cannot assign molecular risk. Motivated by our finding that the two together identify high-risk cases missed by either, we developed Pheno-MYCN, a weakly supervised framework linking slide-level MYCN prediction to interpretable morphological sub-populations on routine H&E whole-slide images. The aim is not a stronger classifier: prediction probes what MYCN amplification does to the tissue, its evidence open to pathological scrutiny. Across 189 slides, Pheno-MYCN resolved each into phenotypic clusters that expert review mapped to neuroblastoma morphologies. Cell-level profiling revealed MYCN amplification "marked" every sub-population, through a different feature in each: densely cellular yet disorganised tumour with sparser, less diverse networks; chiefly abundance in necrotic and haemorrhagic regions. MYCN-amplified-like tissue was identifiable per slide from these features alone (AUC 0.93-1.00, leave-one-slide-out) and traced as a continuous gradient within tumours. Thus MYCN amplification leaves a concrete, interpretable footprint that can be read and localised on routine H&E, offering a low-cost means to flag and map it where molecular testing is limited.

cancer biology↗

bioRxiv2026

Mapping small-scale ephemeral surface water to inform transfrontier conservation planning in southern Africa

Reliable freshwater access drives terrestrial wildlife movements and habitat use globally. The small, rain-fed seasonal pools critical for dryland wildlife persistence are vulnerable to rising temperatures and unstable precipitation regimes projected under climate change. In southern Africa, which is expected to warm rapidly by 2100, the drying and disappearance of surface water may cause a breakdown in seasonal migrations of large, area-sensitive, and water-dependent wildlife species. Furthermore, the disappearance of ephemeral water may concentrate wildlife around remaining surface water, increasing resource competition and human-wildlife conflict. An accurate understanding of the dynamics and drivers of seasonal surface water will therefore be crucial to wildlife and human health as climate change intensifies. Here, we present a framework and empirical analysis of fine-scale surface water mapping in the Kavango Zambezi Transfrontier Conservation Area (KAZA), the worlds largest terrestrial conservation area (520,000km2). From 2019-2025, we implemented Otsu thresholding on median Automated Water Extraction Index Sentinel-2 MSI imagery (10m), creating >35 quasi-monthly KAZA-wide Ephemeral Surface Water (ESW) rasters (mean accuracy 87%, compared to 50% for a 30m Global Surface Water (GSW) product). Low wet season (November-May) rainfall drove led to low surface water fill from February-May, especially after multiple drought years (2023-2024), suggesting a critically vulnerable time for water-dependent wildlife. Finally, we assessed the applicability of our ESW map for wildlife movement analyses. African savanna elephant (Loxodonta africana) are known to visit water approximately every 48 hours; a useful water map should reflect this dependence. We calculated water visitation rates using GPS data from 27 individual elephant and a threshold distance of T = 200m, and found that 99% of GPS tracks maintained ESW visitation rates under 48 hours, compared to only 29% of tracks for GSW visitation. These results were robust when T was varied, and ESW similarly outperformed random controls and several other water products, making ESW an effective proxy for actual water use in animal movement models. As climate change threatens seasonally ephemeral surface water, fine-resolution tools such as ESW will help conservation scientists and managers to understand and predict the drivers of wildlife movements at the scale of wildlife needs.

ecology↗

bioRxiv2021

Functional Connectivity of the World's Protected Areas

Rapid environmental change threatens to isolate the worlds wildlife populations and intensify biodiversity loss. Global policies have called for expanding and connecting the worlds protected areas (PAs) to curtail the crisis, yet how well PA networks currently support wildlife movement, and where connectivity conservation or restoration is most critical, have never been mapped globally. Here, we map the functional connectivity (how animals move through landscapes) of the worlds terrestrial PAs for the first time. Also, going beyond existing global connectivity indices, we quantify national PA-connectedness using an approach that meaningfully represents animal movement through anthropogenic landscapes. We find that reducing the human footprint may improve national PA-connectivity more than adding new PAs; however, both strategies are critical for improving and preserving connectivity in places where the predicted flow of animal movement is highly concentrated. We show that the majority of critical connectivity areas (CCAs) (defined as globally important areas of concentrated animal movements) remain unprotected. Of these, 72% overlap with previously-identified global conservation priority areas, while 3% of CCAs occur within moderate to heavily modified lands. Conservation and restoration of CCAs could safeguard connectivity of the worlds PAs, and dovetail with previously identified global conservation priorities.

ecology↗

bioRxiv2019

ICONIC MANAKINS AND DESPICABLE GRACKLES: COMPARING BIRD-RELATED CULTURAL ECOSYSTEM SERVICES ACROSS BIRDWATCHERS, FARMERS, AND URBANITES IN NORTHWESTERN COSTA RICA

Despite the great cultural and economic benefits associated with birdwatching and other bird-related cultural ecosystem services (CES), little is known about the bird-related CES perceived by people, and how they differ across stakeholder groups and species. The goal of this study was to explore CES across three stakeholder groups in northwestern Costa Rica. We conducted surveys (n=404 total) in which we presented farmers (n=140), urbanites (n=149), and birdwatchers (n=115) with pictures and songs of bird species and collected participants ratings on items designed to measure multiple CES. We found bird-related CES were perceived as six different constructs: identity, bequest, education, birdwatching, acoustic aesthetic, and disservices. The three stakeholder groups varied across these constructs and across species. Specifically, birdwatchers ranked species higher in terms of their education scores and lower in disservices scores compared to the other two groups. Positive correlations across CES, and negative correlations with disservices, suggest that the affect heuristic (by which generalized positive or negative feelings sway judgements of risks and benefits) might be informing bird-related CES. Our approach represents a novel method for assessing CES that can be adapted and modified for different taxa and multiple geographical contexts.

ecology↗