Fernando Locatelli
IFIByNE, UBA-CONICET
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Symposia
Computations in neural circuits
Chairs
The ability of animals to recognize a stimulus and respond with a specific and coordinated action involves precise and sophisticated neural computations. Unveiling how the nervous system generates the cognitive functions that relate sensory perception and behavior requires multidisciplinary approaches, including the use of intact behaving animal that enables deciphering complex neuroethological questions such as decision making, sensory perception, and the functional role of the brain’s intrinsic dynamics.
The symposium “Computations in neural circuits” will focus on studies performed on different neural circuits, their physiology, their connectivity and their dynamics in relation to specific cognitive demands and computations.
Two speakers focus their work on understanding the neural computations behind the ability of animals to recognize visual and olfactory cues in zebrafish. Other two speakers focus their work on the integration of multimodal sensory information in relation to escape behavior in goldfish and in coordination of sensory motor information during navigation and locomotion in Drosophila flies.
The talks will summarize results based on behavioral, physiological and neuro-computational approaches.
Speakers
Connectivity and computations of the olfactory bulb
Rainer Friedrich
Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
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In the olfactory bulb (OB), structurally similar odorants evoke overlapping activity patterns across the input channels, the olfactory glomeruli. Neuronal circuits within in the OB reduce the overlap (correlation) between related activity patterns and normalize their variance. Hence, the OB performs a transformation akin to whitening, a fundamental early step in pattern classification. To analyze the underlying mechanisms we measured odor-evoked activity in the OB of a zebrafish larva and subsequently reconstructed the full wiring diagram by volume electron microscopy. This “functional connectomics” approach revealed an overrepresentation of triplet connectivity motifs that privileges multisynaptic reciprocal inhibition among output neurons (mitral cells) with similar tuning. Tuning-dependent multisynaptic connectivity specifically inhibited mitral cells that contributed strongly to pattern correlations. This connectivity was necessary and sufficient to reproduce whitening in generic network models. Hence, whitening in the OB is achieved by higher-order structure in the wiring diagram that is adapted to natural input patterns. These results provide direct insights into the network mechanism underlying a fundamental neural computation and illustrate the potential of “functional connectomics” approaches to analyze complex structure-function relationships in neuronal circuits.
Multisensory integration in the context of escape, from cell circuits to behavior
Violeta Medan
IFIByNE CONICET - FCEN UBA
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Different sensory systems provide animals with valuable information that allows them to identify possible threats and react accordingly. In fish, the Mauthner cell receives inputs from the visual and auditory systems and commands the C-start escape response. We combined optic tectum and auditory stimulation with in vivo intracellular recordings to study multisensory integration in the Mauthner cell of goldfish. We found that weak audio-tectal cues produce a sublinear multisensory enhancement of the Mauthner cell response. Paralleling electrophysiological results, behavioral experiments provided a functional role for multisensory integration. We found the strongest multisensory enhancement when multimodal stimuli have minimum intensity while it disappears as salience increases. In addition, spatial alignment and temporal overlap between auditory and visual cues contribute to enhanced multisensory integration.
Timely multimodal interactions underly flexible control of walking in Drosophila
Eugenia Chiappe
Champalimaud Neuroscience Program
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All animals exhibit stability and flexibility in their locomotive systems to navigate and respond to highly unpredictable habitats on a moment-by-moment bases. These conserved functional principles are thought to emerge largely from the continuous interaction between internally generated neural signals and sensory feedback. However, it remains unclear how canonical computations are formed from these sensorimotor interactions to sustain stability in a flexible manner.
In this talk, I will describe our attempts to answer this question focusing on a visuomotor network in the fly whose function is thought to contribute to gaze and course stability. By performing analysis of behavior in simultaneous with recordings of neural activity, our work shows that this network combines multimodal signals in a timely manner to control the steering movements of the fly continuously but on a moment-by-moment and context-specific bases. This context is set by the instantaneous coordination movement across legs, which in turn is guided by both the behavioral goal of the fly and the current circumstances of the terrain.
Because stability and flexibility are hallmarks of locomotion across animals species, even though their bodies and the environment through which they move can be so different, our findings may provide a framework to examine how CNS may be functionally organized for the visual control of walking stability in other species, or even different modes of locomotion, such as flight.
Principles of functional circuit connectivity: Insights from the zebrafish optic tectum
German Sumbre
Ecole Normale Superieure
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Spontaneous neuronal activity is spatiotemporally structured, influencing brain computations. Nevertheless, the neuronal interactions underlying these spontaneous activity patterns, and their biological relevance, remain elusive. We addressed these questions using two-photon Ca2+ imaging of intact zebrafish larvae to monitor the spontaneous activity fine-structure in the tectum. The spontaneous activity is organized in topographically compact assemblies, grouping functionally similar neurons rather than merely neighboring ones, reflecting the tectal retinotopic map. Assemblies show attractor-like dynamics, improving visual detection in noisy natural environments. These assemblies also emerged in “naive” tecta (tecta of enucleated larvae before the retina connected to the tectum). We thus suggest that the formation of the tectal network circuitry is genetically prone for its functional role. This capability is an advantageous developmental strategy for the prompt execution of vital behaviors, such as escaping predators or catching prey, without requiring prior visual experience.
Mutant zebrafish larvae for the mecp2 gene display an abnormal spontaneous tectal activity suggesting disrupted functional connectivity. These mutant fish show no attractor circuits and an exagerated visual response, suggesting that the functional connectivity of the optic tectum acts as a virtual top-down fovea, improving spatial resolution.