Biology subjects

Panagiotaropoulos, T.

Publications and source records attributed to Panagiotaropoulos, T..

3 recordsLinked to original sources

bioRxiv2026

From Coarse to Rich: Successive Waves of Visual Perception in Prefrontal Cortex

The ventrolateral prefrontal cortex (vlPFC) is well known for its involvement in high-level functions such as cognitive control and language. However, vlPFCs role in visual processing is less clear. Here, we investigated how neuronal ensembles in the vlPFC dynamically encode different types of visual information. Using chronic recording of spiking activity, we investigated vlPFCs representational geometry in a macaque monkey passively viewing a large set of naturalistic images, and compared this to representations in deep neural networks (DNNs). We found that the vlPFC processes visual information in two stages. First, an "early" response from 50 to 90 ms after stimulus onset encodes the low spatial frequency component of an image. It contains sufficient information to form a coarse estimate of the position and category of a salient object. Then, from 100 ms on, the representational geometry changes and contains much richer information. This late period contains non-categorical information typically present in conscious experiences such as the orientation of a face and natural scenes in the background. The late window also enables sub-category identification, which is boosted by the low spatial category prior. These results suggest that the vlPFC has a dual role in natural vision: first forming fast low-spatial-frequency-based priors shaping feed-forward visual processing, and subsequently maintaining a detailed and rich representation of a visual scene. SignificanceWhat information does the prefrontal cortex represent during natural vision, and how does this relate to conscious experience? Theories of consciousness differ sharply on whether prefrontal activity reflects detailed perceptual content or only high-level, task-related information. Using dense neural recordings during passive viewing of thousands of naturalistic images, we show that the ventrolateral prefrontal cortex processes visual information in two distinct stages: an early, coarse estimate of the visual scene is followed by a richer, high-dimensional representation that includes sub-category identity and other perceptual details. These findings reveal that prefrontal circuits encode more of the content of visual experience than previously assumed, even in the absence of a task.

neuroscience↗

bioRxiv2025

Neural Activity dynamic in Primate Cortex Across Consciousness Levels: Insights from High-Density Neuropixel Recording

This study investigates the anesthesia mechanisms induced by sevoflurane and how it modulates neural activity in the posterior parietal cortex (PPC) and prefrontal cortex (PFC) in Non Human Primates (NHPs) using high density Neuropixel probes. Spiking and local field potentials (LFPs) were recorded in two macaque monkeys under going four sevoflurane concentrations (2%, 3%, 4%, and 6%). We aimed to (i) quantify the emergence of anesthesia-induced Up/Down state dynamics, (ii) track changes in oscillatory power and inter-regional synchrony, and (iii) determine whether frontal and parietal areas exhibit differential sensitivity to rising and falling anesthetic depth. Across different anesthetic levels, we observed characteristic slow oscillations in delta range in both PFC and PPC, with neurons transitioning between high-firing "Up" states and near-silent "Down" states. Deeper anesthesia extended Down states, suppressed mean firing rates, and reduced the frequency and duration of Up states. In M1, no single units were detected in PFC, and only a few were recorded in M2. We suspect misalignment of the probe with PFC pyramidal cells and extensive suppression in PFC as the main reasons. Recurrent Neural Networks (RNN) was used to extract Up/Down states from LFP activities, based one the pattern observed in the PPC. The PPC [->] PFC information flow observed in Transfer Entropy analysis suggests that even under anesthesia, some level of feedforward-like interactions may persist. Up states originate in deep cortical layers and propagate toward superficial layers, following a bottom-up progression, indicating that deep-layer pyramidal neurons, which receive strong thalamic input, may be the primary drivers of Up states. The short Up states under deep anesthesia might represent a failed ignition attempt, where the brain momentarily tries to reactivate but cannot sustain functional activity due to global inhibition. LFP analyses revealed that although the absolute delta power remains high at different anesthetic levels, the relative delta band power is anti correlated with anesthetic depth, due to sporadic short (20ms to 40ms) burst in gamma (30-100 Hz) that appeared transient in nature. Lower sensitivity to anesthesia dose changes were observed in PFC as compared to PPC. This could explain why anesthesia first impairs cognitive function before affecting basic sensory responses. These results indicates that the traditional Up/Down state models might oversimplify anesthetic brain dynamics. While anesthesia is often described as a state of simple global slow-wave oscillations, the observed Up/Down state durations are not uniform, they fluctuate, follow non-trivial transition patterns, and differ between PFC and PPC.

neuroscience↗

bioRxiv2025

Anaesthesia disrupts mesoscale signal propagation in spite of enhanced responsivity in frontal but not in parietal cortex

Loss of consciousness under anaesthesia is accompanied by widespread silencing of neurons, and disruption of cortical dynamics. Yet, how this affects mesoscale signal propagation within higher-order associative areas, crucially implicated in theories of consciousness, remains poorly understood. Here we combined intracortical microstimulation, and simultaneous multielectrode recordings in the ventrolateral prefrontal cortex (vlPFC) and the posterior parietal cortex (PPC) of macaques across wakefulness, and graded depths of anaesthesia. Spiking responses revealed distinct regimes: in the PFC, higher-amplitude stimulation elicited a delayed single rebound after sustained inhibition, whereas in the PPC, a faster and double-rebound profile emerged. Despite enhanced local spiking and LFP responsivity under anaesthesia, we found a strong and selective suppression of lateral signal propagation in the PFC - a breakdown strikingly absent in the PPC. This dissociation suggests that anaesthesia disrupts consciousness not merely by silencing cortical populations, but by impairing mesoscale integrative processes critical for neuronal dynamics at multiple scales. Our findings demonstrate in a causal and spatially-resolved manner, that lateral signal spread within higher-order cortex is a key mechanism underlying conscious awareness, and its loss under anaesthesia.

neuroscience↗