Using the zebrafish larva as the experimental model and a multidisciplinary approach, including twophoton calcium imaging to monitor activity of neural networks, motor behaviours, genetic engineering techniques to label, monitor and manipulate activity of specific neurons or entire circuits and mathematical methods for data analysis, we are studying the following subjects:
1) Multimodal sensory perception:
we are studying the neural basis of sensory perception using different sensory modalities asking the question if the neural correlates of sensory perception are unique of each sensory modality or a comprehensive common one for all modalities. More precisely, we are using visual illusion to study the neural network mechanisms that enable the emergence of visual perception. In parallel, we are using microfluidic devices to present gustatory stimuli with unprecedented spatiotemporal resolution, permitting to present rapid, non-perceived, stimuli and longer, perceived stimuli.
2) Ongoing spontaneous activities:
In absence of sensory stimulation sensory brain areas remain active. These ongoing spontaneous (OS) neuronal activities were traditionally considered as random independent biophysical noise with no functional value for brain computations. However, in the last decades it was shown that OS activities are capable of interacting meaningfully with sensory-induced neuronal inputs, both at the single neuron and the network level. OS activities are structured according to the coarse functional and anatomical circuitry and partially account for both the variability of stimulus-evoked neuronal responses and fluctuations in human motor behaviour . Furthermore, it was suggested that neuronal responses to stimuli are only mild modulations of OS activity structure, the latter representing an internal statistical model of the environment that samples the constrained repertoire of possible neuronal responses. Nevertheless, the origin of this structured OS activities and its biological relevance still remain elusive. Using zebrafish larvae we showed for the first time, the fine structure of the coherent OS activities of a significant fraction of the largest sensory brain region in an intact, awake, vertebrate. More specifically, we have found that the OS network activities showed spatiotemporal dynamics organised in distinct neuronal assemblies. These OS assemblies, primarily composed of neighbouring neurons, reconstructed the OT functional retinotopic map. These neuronal assemblies were tuned to visual objects corresponding to the angular size of zebrafish's natural prey at different positions in the larva's field of view (FoV), and showed angular tuning preferences that resembled prey-detection performance. Moreover, these assemblies consisted of ?preferred? network states, generated through a winner-take-all mechanism and attractor-like dynamics. Therefore, the OT coherent OS activities emerge from its intrinsic circuitry, optimised for a vital behaviour (prey detection),
3) Functional incorporation of new-born neurons to already established neural circuits:
Newborn neurons originate from a process called neurogenesis. This process is defined by the division of neural stem cells (NSCs) into daughter cells that then differentiate, migrate and give rise to functional neurons. Several observations highlight the requirement of electrical activity of the migrating neurons to sustain their survival and integration). However, the neurophysiological mechanisms underlying their incorporation into functional neural circuits remain elusive. For this purpose, we are using state-of-the-art genetic techniques to label new-born neurons while we monitor their morphology and activity, as well as the activity of the neighbouring matured neurons, while presenting visual stimuli or recording spontaneous activities. So far, we can follow the functional connectivity map during development, where some random connections appear during the early stages, while later, a connectivity pattern becomes evident, forming functional assemblies as those observed to emerge from the dynamics of the ongoing spontaneous activities (project 1).