Biology subjects

Ptito, M.

Publications and source records attributed to Ptito, M..

5 recordsLinked to original sources

bioRxiv2026

Temporal dynamics of cognitive map formation in early- and late-onset blindness

Cognitive maps encode spatial relationships between locations and support flexible navigation. However, how these mental representations form in blindness remains unclear. Here, we introduce a multisensory virtual navigation paradigm that monitors non-visual cognitive map formation over time. Sixteen early blind (EB), 17 late blind (LB), and 29 sighted controls (SC) learned the layout of a tactile maze and, in a virtual version, repeatedly performed pointing (judgment of relative directions) and navigation (reaching locations) tasks. Thus, this experiment tracked both functional and spatio-cognitive components of cognitive map formation across multiple learning stages and showed that EB accumulated knowledge more slowly than SC. In addition, both EB and LB had reduced pointing accuracy under viewpoint changes, indicating difficulty translating cognitive maps into first-person perspectives. Yet, navigation and pointing improved in all groups, and a subset of EB and LB achieved expert-level performance. In sum, this study provides a scalable framework for tracking the temporal dimension of cognitive map formation in blindness and other neurological conditions, informing how spatial knowledge is acquired and translated into navigation behavior. Importantly, it suggests that allocentric cognitive map formation in blindness is an experience-dependent process that varies across time and individuals. Observed spatial disadvantages in both blind groups may result from adaptive strategies that constrain the use of allocentric cognitive maps, independent of prior visual experience.

neuroscience↗

bioRxiv2026

Temporal Dynamics of Cortical State Plasticity Following Adult Vision Loss

The adult brain retains a capacity for adaptation, yet the long-term sequence of plasticity remains poorly understood. To address this, we performed longitudinal mesoscopic calcium imaging of the dorsal cortex in spontaneously behaving adult mice before and after bilateral enucleation (BE). We uncovered behaviour-dependent and spatially distinct changes in cortical activity organised into two sequential, overlapping windows. An early window, spanning from day 1 to week 3-5, was marked by reduced activity in visual and retrosplenial cortices during locomotion, with movements suppressing rather than enhancing activity, as is typically observed. A second, delayed window (week 1 to week 7-10, peaking around 3 weeks) was characterised by increased slow-wave activity in primary visual cortex (V1) and lateromedial visual area (LM), indicative of heightened excitability. Consistently, activity increased--rather than decreased--at the transition from locomotion to quiescence. In parallel, we observed a rapid, long-lasting, and behaviour-dependent reorganisation of cortical network structure. Together, these findings demonstrate that cortical states in the adult brain are dynamic and can undergo substantial, months-long plasticity. The temporal and spatial dissociations between windows identified suggest distinct plasticity mechanisms in the circuit regulating cortical states. Therefore, our study provides a spatiotemporal framework to guide future investigations into the mechanisms of plasticity in the mature brain.

neuroscience↗

bioRxiv2023

Bridging the 3D geometrical organisation of white matter pathways across anatomical length scales and species

We used diffusion MRI and x-ray synchrotron imaging on monkey and mice brains to examine the organisation of fibre pathways in white matter across anatomical scales. We compared the structure in the corpus callosum and crossing fibre regions and investigated the differences in cuprizone-induced demyelination mouse brains versus healthy controls. Our findings revealed common principles of fibre organisation that apply despite the varying patterns observed across species; small axonal fasciculi and major bundles formed laminar structures with varying angles, according to the characteristics of major pathways. Fasciculi exhibited non-straight paths around obstacles like blood vessels, comparable across the samples of varying fibre complexity and demyelination. Quantifications of fibre orientation distributions were consistent across anatomical length scales and modalities, whereas tissue anisotropy had a more complex relationship, both dependent on the field-of-view. Our study emphasises the need to balance field-of-view and voxel size when characterising white matter features across length scales.

neuroscience↗

bioRxiv2020

Axon morphology is modulated by the local environment and impacts the non-invasive investigation of its structure-function relationship

Axonal conduction velocity, which ensures efficient function of the brain network, is related to axon diameter. Non-invasive, in vivo axon diameter estimates can be made with diffusion magnetic resonance imaging, but the technique requires 3D validation. Here, high resolution, 3D synchrotron X-ray Nano-Holotomography images of white matter samples from the corpus callosum of a monkey brain reveal that blood vessels, cells and vacuoles affect axonal diameter and trajectory. Within single axons, we find that the variance in diameter and conduction velocity correlates with the mean diameter, contesting the value of precise diameter determination in larger axons. These complex 3D axon morphologies drive previously reported 2D trends in axon diameter and g-ratio. Furthermore, we find that these morphologies bias the estimates of axon diameter with diffusion magnetic resonance imaging and, ultimately, impact the investigation and formulation of the axon structure-function relationship.

neuroscience↗

bioRxiv2018

Uncovering a role for the dorsal hippocampal commissure in episodic memory

The dorsal hippocampal commissure (DHC) is a white matter tract that provides inter-hemispheric connections between temporal lobe brain regions. Despite the importance of these regions for learning and memory, there is scant evidence of a role for the DHC in successful memory performance. We used diffusion-weighted MRI (DW-MRI) and white matter tractography to reconstruct the DHC across both humans (in vivo) and nonhuman primates (ex vivo). Across species, our findings demonstrate close consistency between the known anatomy and tract reconstructions of the DHC. Anterograde tract-tracer techniques also highlighted the parahippocampal origins of DHC fibers in nonhuman primates. Finally, we derived Diffusion Tensor MRI (DT-MRI) metrics from the DHC in a large sample of human subjects to investigate whether inter-individual variation in DHC microstructure is predictive of memory performance. The mean diffusivity of the DHC was correlated with performance in a standardised episodic memory task; an effect that was not reproduced in a comparison commissure tract - the anterior commissure. These findings highlight a role for the DHC in episodic memory, and our tract reconstruction approach has the potential to generate further novel insights into the role of this previously understudied white matter tract in both health and disease.

neuroscience↗