Biology subjects

Dwarakanath, A.

Publications and source records attributed to Dwarakanath, A..

5 recordsLinked to original sources

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↗

bioRxiv2020

Prefrontal state fluctuations control access to consciousness

Access of sensory information to consciousness is thought to be mediated through ignition of neural activity in the prefrontal cortex (PFC). Ignition occurs once activity elicited by sensory input crosses a threshold, which has been shown to depend on brain state fluctuations. However, the neural correlates of fluctuations and their interaction with the neural representations of conscious contents within the PFC remain largely unknown. To understand the role of prefrontal state fluctuations in conscious access, we combined multielectrode intracortical recordings with a no-report binocular rivalry (BR) paradigm that induces spontaneously-driven changes in conscious perception. During BR, antagonistic coupling of two prefrontal states, characterised by dominance of low frequency (1-9Hz) or beta (20-40Hz) local field potentials (LFP), reflect competition between two states of visual consciousness; perceptual update and stability, respectively. Low frequency perisynaptic bursts precede spontaneous transitions in conscious perception, signalling upcoming perceptual update of conscious content. We therefore show that it is a global cortical state that seems to drive internal switches, rather than the spiking activity of selective neuronal ensembles, which subsequently, only report the active percept. Beta band bursts were found to be correlated with periods of stable conscious perception, and selectively synchronised the neural ensemble coding for the consciously perceived stimulus. Similar ongoing fluctuations in the LFPs, with dynamics resembling the distribution of perceptual dominance periods during BR, dominated the prefrontal cortex during resting-state, thus pointing to their default, endogenous nature. Our results suggest that the two modes of conscious perception: perceptual update, and stability, can be associated with distinct prefrontal cortical states.

neuroscience↗

bioRxiv2020

Decoding the contents of consciousness from prefrontal ensembles

Multiple theories attribute to the primate prefrontal cortex a critical role in conscious perception. However, opposing views caution that prefrontal activity could reflect other cognitive variables during paradigms investigating consciousness, such as decision-making, monitoring and motor reports. To resolve this ongoing debate, we recorded from prefrontal ensembles of macaque monkeys during a no-report paradigm of binocular rivalry that instigates internally driven transitions in conscious perception. We could decode the contents of consciousness from prefrontal ensemble activity during binocular rivalry with an accuracy similar to when these stimuli were presented without competition. Oculomotor signals, used to infer conscious content, were not the only source of these representations since visual input could be significantly decoded when eye movements were suppressed. Our results suggest that the collective dynamics of prefrontal cortex populations reflect internally generated changes in the content of consciousness during multistable perception. One sentence summaryNeural correlates of conscious perception can be detected and perceptual contents can be reliably decoded from the spiking activity of prefrontal populations.

neuroscience↗

bioRxiv2017

Non-monotonic spatial structure of interneuronal correlations in prefrontal microcircuits

Correlated fluctuations of single neuron discharges, on a mesoscopic scale, decrease as a function of lateral distance in early sensory cortices, reflecting a rapid spatial decay of lateral connection probability and excitation. However, spatial periodicities in horizontal connectivity and associational input as well as an enhanced probability of lateral excitatory connections in the association cortex could theoretically result in non-monotonic correlation structures. Here we show such a spatially non-monotonic correlation structure, characterized by significantly positive long-range correlations, in the inferior convexity of the macaque prefrontal cortex. This functional connectivity kernel was more pronounced during wakefulness than anesthesia and could be largely attributed to the spatial pattern of correlated variability between functionally similar neurons during structured visual stimulation. These results suggest that the spatial decay of lateral functional connectivity is not a common organizational principle of neocortical microcircuits. A non-monotonic correlation structure could reflect a critical topological feature of prefrontal microcircuits, facilitating their role in integrative processes.\n\nSignificance statementThe spatial structure of correlated activity of neurons in lower-order visual areas has been shown to linearly decrease as a measure of distance. The shape of correlated variability is a defining feature of cortical microcircuits as it constrains the computational power and diversity of a region. We show here for the first time a non-monotonic spatial structure of functional connectivity in the pre-frontal cortex where distal interactions are just as strong as proximal interactions during visual engagement of functionally similar PFC neurons. Such a nonmonotonic structure of functional connectivity could have far-reaching consequences in rethinking the nature and the role of prefrontal microcircuits in various cognitive states.

neuroscience↗