Whitening of odor representations by specific network connectivity

One of the fundamental questions in neuroscience is how computational functions of neuronal circuits are determined by their connectivity. The olfactory bulb decorrelates and normalizes patterns of sensory input, resulting in a transformation referred to as whitening that supports pattern classification. To analyze the underlying mechanisms we measured odor-evoked activity throughout the OB of a zebrafish larva and reconstructed the wiring diagram in the same specimen by volume electron microscopy. This functional connectomics approach revealed an overrepresentation of triplet connectivity motifs that privilege disynaptic reciprocal inhibition among co-tuned output neurons. This connectivity resulted in strong inhibition of neuronal responses to common features of correlated sensory input patterns. In generic network models, this connectivity was necessary and sufficient to reproduce whitening of naturalistic inputs. These results reveal a specific network topology that is adapted to the statistical structure of olfactory inputs and mediates whitening by feature suppression.