Infrequent strong connections constrain connectomic predictions of neuronal function (1/3)

How does circuit wiring constrain neural computation? Recent work has
leveraged connectomic datasets to predict the functions of cells and
circuits in the brains of multiple species. However, many of these
hypotheses have not been compared with physiological measurements,
obscuring the limits of connectome-based functional predictions. To
explore these limits, we characterized the visual responses of 43 cell
types in the fruit fly and quantitatively compared them to connectomic
predictions. We show that these predictions are accurate for some response
properties, such as orientation tuning, but are surprisingly poor for
other properties, such as receptive field size. Importantly, strong
synaptic inputs are more functionally homogeneous than expected by chance
and exert a disproportionately large influence on postsynaptic responses.
Finally, we quantitatively define the subset of connections that best
describe the functional differences between cell types. Our results
establish a powerful set of constraints for improving the accuracy of
connectomic predictions.