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NeuroVision Report Summary

Project ID: 616509
Funded under: FP7-IDEAS-ERC
Country: Switzerland

Periodic Report Summary 3 - NEUROVISION (The organisation of functional microcircuits in visual cortex)

Determining how the organization of neural circuitry gives rise to its function is a major challenge for understanding the neural basis of perception and behavior. In order to determine how different regions of the neocortex process sensory information, it is necessary to understand how the pattern and properties of synaptic connections in a specific sensory circuit determine the computations it performs. We have begun forging the relationship between synaptic connectivity and neuronal function in primary visual cortex (V1) with the aim of revealing circuit-level mechanisms of sensory processing. To this end, my laboratory has developed a method by which visual response properties of neurons are first characterized with two-photon calcium imaging in vivo, and then synaptic connections between a subset of these neurons are assayed with multiple whole-cell recordings in slices of the same tissue (Ko, Hofer et al, 2011, Nature). Using this approach, we found that connection probability between nearby excitatory neurons is intimately related to the similarity of their responses to visual stimuli. More recently, we discovered a new rule that explains the distribution of the strength of excitatory connections in the neocortex — the few strong connections occur between neurons with most correlated responses, while only weak connections link neurons with uncorrelated responses (Cossell, Iacaruso, et al., 2015 Nature). Although weak connections far outnumber strong connections, each neuron receives the majority of its local excitation from a small number of strong inputs provided by the few neurons with similar responses to visual features. By dominating recurrent excitation, these infrequent yet powerful inputs disproportionately contribute to feature preference and selectivity. Therefore, our results show that the apparently complex organization of excitatory connection strength reflects the similarity of neuronal responses, and suggest that rare, strong connections mediate stimulus-specific response amplification in cortical microcircuits. These data are being combined into a functional, biologically realistic model of the visual cortex circuit (collaboration with A. Silver, UCL).

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