Biology subjects

Seenivasan, P.

Publications and source records attributed to Seenivasan, P..

3 recordsLinked to original sources

bioRxiv2024

Connectome-driven neural inventory of a complete visual system

Vision provides animals with detailed information about their surroundings, conveying diverse features such as color, form, and movement across the visual scene. Computing these parallel spatial features requires a large and diverse network of neurons, such that in animals as distant as flies and humans, visual regions comprise half the brains volume. These visual brain regions often reveal remarkable structure-function relationships, with neurons organized along spatial maps with shapes that directly relate to their roles in visual processing. To unravel the stunning diversity of a complex visual system, a careful mapping of the neural architecture matched to tools for targeted exploration of that circuitry is essential. Here, we report a new connectome of the right optic lobe from a male Drosophila central nervous system FIB-SEM volume and a comprehensive inventory of the flys visual neurons. We developed a computational framework to quantify the anatomy of visual neurons, establishing a basis for interpreting how their shapes relate to spatial vision. By integrating this analysis with connectivity information, neurotransmitter identity, and expert curation, we classified the [~]53,000 neurons into 727 types, about half of which are systematically described and named for the first time. Finally, we share an extensive collection of split-GAL4 lines matched to our neuron type catalog. Together, this comprehensive set of tools and data unlock new possibilities for systematic investigations of vision in Drosophila, a foundation for a deeper understanding of sensory processing.

neuroscience↗

bioRxiv2022

Cross-strata co-occurrence of ripples with theta-frequency oscillations in the hippocampus of foraging rats

Background and motivationBrain rhythms have been postulated to play central roles in animal cognition. A prominently reported dichotomy of hippocampal rhythms, driven primarily by historic single-strata recordings, assigns theta-frequency oscillations (4-12 Hz) and ripples (120-250 Hz) to be exclusively associated with preparatory and consummatory behaviors, respectively. However, due to the differential power expression of these two signals across hippocampal strata, reports of such exclusivity require validation through simultaneous multi-strata recordings and cross-strata analysis of these oscillatory patterns. MethodologyWe assessed co-occurrence of theta-frequency oscillations with ripples in multi-channel recordings of extracellular potentials across hippocampal strata from foraging rats. We detected all ripple events from an identified stratum pyramidale (SP) channel based on rigorous thresholds relating to the spectro-temporal and spatial characteristics of ripples. We then defined theta epochs based on theta oscillations detected from each of the different channels spanning the SP to the stratum lacunosum-moleculare (SLM) through the stratum radiatum (SR). We calculated the proportion of ripples embedded within theta epochs. ResultsWe found [~]20% (across rats) of ripple events (in SP) to co-occur with theta epochs identified from SR/SLM channels, defined here as theta ripples. All characteristics of theta ripples were comparable with ripples that occurred in the absence of theta oscillations. Furthermore, the power of theta oscillations in the immediate vicinity of theta ripples was similar to theta power across identified theta epochs, together validating the identification process of theta ripples. Strikingly, when theta epochs were instead identified from the SP channel, such co-occurrences were significantly lower in number. The reduction in the number of theta ripples was consequent to progressive reduction in theta power along the SLM-SR-SP axis. We assessed the behavioral state of rats during ripple events and found most theta ripples to occur during immobile periods. We confirmed that across sessions and rats, the theta power observed during exploratory theta epochs was comparable with theta power during immobile theta epochs. In addition, the progressive reduction in theta power along the SLM-SR-SP axis was common to both exploratory and immobile periods. Finally, we found a strong theta-phase preference of theta ripples within the third quadrant [3{pi}/2-2{pi}] of the associated theta oscillation. ImplicationsOur analyses provide direct quantitative evidence for the occurrence of ripple events nested within theta oscillations in the rodent hippocampus. These analyses emphasize that the prevalent dichotomy about the manifestation of theta-frequency oscillations and ripples needs to be reevaluated, after explicitly accounting for the differential stratum-dependent expression of these two oscillatory patterns. The prevalence of theta ripples expands the potential roles of ripple-frequency oscillations to span the continuum of encoding, retrieval, and consolidation, achieved through interactions with theta oscillations.

neuroscience↗

bioRxiv2019

Efficient phase coding in hippocampal place cells

Hippocampal place cells encode space through phase precession, whereby neuronal spike phase progressively advances during place-field traversals. What neural constraints are essential for achieving efficient transfer of information through such phase codes, while concomitantly maintaining signature neuronal excitability specific to individual cell types? We developed a conductance-based model for phase precession in CA1 pyramidal neurons within the temporal sequence compression framework, and defined phase-coding efficiency using information theory. We recruited an unbiased stochastic search strategy to build a model population that exhibited physiologically observed heterogeneities in intrinsic properties. Place-field responses elicited from these models matched signature sub- and supra-threshold place-cell characteristics, including phase precession, sub-threshold voltage ramps, increases in theta-frequency power and firing rate during place-field traversals. Employing this model population, we show that disparate parametric combinations with weak pair-wise correlations resulted in models with similar high-efficiency phase codes and similar excitability characteristics. Mechanistically, the emergence of such parametric degeneracy was dependent on the differential and variable impact of individual ion channels on phase-coding efficiency in different models, and importantly, on synergistic interactions between synaptic and intrinsic properties. Furthermore, our analyses predicted a dominant role for calcium-activated potassium channels in regulating phase precession and coding efficiency. Finally, change in afferent statistics, manifesting as input asymmetry, induced an adaptive shift in the phase code that preserved its efficiency, apart from introducing asymmetry in sub-threshold ramps and firing profiles during place-field traversals. Our study postulates degeneracy as a potential framework to attain the twin goals of efficient temporal coding and robust homeostasis.\n\nSIGNIFICANCE STATEMENTNeuronal intrinsic properties exhibit significant baseline heterogeneities, and change with activity-dependent plasticity and neuromodulation. How do hippocampal neurons encode spatial locations through the precise timings of their action potentials in the face of such heterogeneities? Here, employing a unifying synthesis of the temporal sequence compression, efficient coding and degeneracy frameworks, we show that there are several disparate routes for neurons to achieve high-efficiency spatial information transfer through such temporal codes. These disparate routes were consequent to the ability of neurons to produce precise encoding through distinct structural components, critically involving synergistic interactions between intrinsic and synaptic properties. Our results point to an explosion in the degrees of freedom available to a neuron in concomitantly achieving efficient coding and excitability homeostasis.

neuroscience↗