Perspective: A new era of comparative connectomics

Abstract

Morphological studies on brains have recently entered a new phase of circuit analysis identified under the newly designated area of connectomics, the study of brain wiring diagrams exact at synapse level that can now be produced by means of electron microscopy and automated reconstruction. The most comprehensive examples come from the brains of invertebrates with few neurons, which Nature provides in great abundance especially among marine larval invertebrates. Two complete examples, the nematode C. elegans and the larva of the ascidian Ciona intestinalis, are now published; others are in the pipeline. Each species has its advantages and champions, especially clearly so in Drosophila, which offers outstanding opportunities for functional analysis of complex behaviours using genetics-based methods. Collectively, these offer an ultimate prospect for the causal analysis of behaviour. In addition, the availability of multiple connectomes from behaviourally different species will reveal features of the network design that are common to all, and that enable comparison with networks from different levels of biological organization, as well as with those from networks that have evolved from human technologies.