Section: New Results

Hierarchy of neural organisation in the zebra fish spinal cord: causality analysis of in-vivo calcium imaging data

Participants : Fabrizio de Vico Fallani [correspondant] , Martina Corazzol, Jnena Sternberg, Kevin Fidelin, Claire Wyart, Mario Chavez.

The recent development of genetically encoded calcium indicators enables monitoring in vivo the activity of neuronal populations. Most analysis of these calcium transients relies on linear regression analysis based on the sensory stimulus applied or the behavior observed. To estimate the basic properties of the functional neural circuitry, we propose a network-based approach based on calcium imaging recorded at single cell resolution. Differently from previous analysis based on cross-correlation, we used Granger causality estimates to infer activity propagation between the activities of different neurons. The resulting functional networks were then modeled as directed graphs and characterized in terms of connectivity and node centralities. We applied our approach to calcium transients recorded at low frequency (4 Hz) in ventral neurons of the zebrafish spinal cord at the embryonic stage when spontaneous coiling of the tail occurs. Our analysis on population calcium imaging data revealed a strong ipsilateral connectivity and a characteristic hierarchical organization of the network hubs that supported established propagation of activity from rostral to caudal spinal cord. Our method could be used for detecting functional defects in neuronal circuitry during development and pathological conditions.

Figure 5. Rostro-caudal distribution of the nodal delta centrality in the representative zebrafish embryo. Panel a) The normalized ipsi value is represented for each node (motoneuron) as a colored circle superimposed on the field of view. The larger the circle, the more central is the node in terms of its tendency to act as a transmitter (red color, positive value) or receiver (blue color, negative value) hub of information flow. Panel b) The same normalized ipsi centrality values are here represented within the neuronal GC network. Statistically significant GC influences are illustrated as directed arrows. The thicker the arrow the stronger the GC value is. Inter-hemicord directed links are illustrated in gray color for the sake of simplicity.

More details in [9] .