Abstract EN:

The local cortical network connectivity significantly deviates from a random network, giving rise to fine structure at the neuron-to-neuron level. In this study, we have investigated the effects of these fine structures on network dynamics and function. We have investigated two types of fine structure, namely, excess bidirectionality and feature specific connectivity. The study of the effects of excess bidirectionality was conducted in a conductance-based model of layer 2/3 in rodent V1. Through large scale numerical simulations, we showed that excess bidirectional connections in the inhibitory population leads to slower dynamics. Remarkably, we found that bidirectional connections between inhibitory cells are more efficacious in slowing down the dynamics than those between the excitatory cells. Additionally, bidirectional connections between inhibitory cells increases the trial-to-trial variability, while between the excitatory and inhibitory populations it reduces the variability leading to improved coding efficiency. Our results suggest that the strong reciprocal connections between excitatory and PV+ cells that have been experimentally reported can improve coding efficiency by reducing the signal-to-noise ratio. The second part of this work involved an analytical study of a model of layer 2/3 rodent V1 with binary neurons. In our study, we assumed that neurons in layer 4 were selective to stimuli orientation. Our results account for the changes in tuning properties observed during the critical period in mouse V1. Prior to the critical period, the connectivity between pyramidal neurons in the mouse V1 is non-specific. Following previous studies of spiking networks, we analytically demonstrated that with such connectivity, layer 2/3 neurons in our model develop orientation selectivity. A small fraction of strong feature specific connections between pyramidal cells have been reported in the mouse V1 after the critical period. We showed that, in spite of their small number, such connections can substantially impact the tuning of layer 2/3 cells to orientation: excitatory neurons become more selective and through non-specific global changes in their synaptic strengths, the inhibitory cells become more broadly tuned.