I am interested in evolutionary origins, core functions, and basic principles of "neural" components in organisms and lifecycle stages lacking a nervous system - such as sponges or placozoans, aneural larval stages, and diverse organisms inherently aneural outside animals - and how their molecules to systems sense, interpret, and control behavior in the species - and what this suggests for human in a comparative context to the brain.
Put another way, I think its really interesting to take genetic components of the human brain and look for homologs in genomes, transcriptomes, and cell-types of organisms, like a sponge or an early-stage larval snail, or a single-cell alga - which have no nervous system or aren't even animals (see also Ocean To Brains) - and see which, if any, brain components are present - where and/or when they are expressed - and what they might be doing. When we see human brain components in these seemingly novel non-neural contexts - basically, when we see brain parts in non-brain situations, even in other tissues in human - it can highlight deep evolutionary origins of the brain and can broaden our thinking and understanding of the components themselves - of how nervous systems first arose and now function - of how simple and complex brains have elaborated independently in parallel and repeatedly (see also Big Brains) - and it can critically and uniquely highlight fundamental principles and core functions that provide insight into ourselves - and new ideas for understanding disease and finding new approaches in medicine.
Cilia, ion channels, and cellular communication is increasingly recognized for potential roles in the deep origins and early evolution nervous systems and brains in animals. In this context, mechanosensory ciliary systems, like the apical tuft-prototroch system used for larval swimming in molluscs, annelids, and other phyla, are of particular interest. I have found in the marine snail Lottia (see adult snail image) that pre-neural larval swimming behaviors are increasingly complex (see 15-hour larval swimming gif) and non-motile putatively mechanosensory cilia of the apical tuft at the anterior tip of the larva and motile cilia of the prototroch, which forms a ring that separates head and trunk and is used for swimming (see larval images in movement of cillia image), may have a sensory-processing-response system that integrates cilia, ion channels, and cellular communication components. Importantly, the apical tuft and prototroch later in development are linked under neural control, including serotonergic apical ganglia that innervate the prototroch (see preneural expression in 15-hour serotonin IHC image). Thus, a functional understanding of preneural and neural control of the apical-tuft protoch system, how they individually operate and potentially integrate, could provide novel insights into general nervous system and specific potentially ancient (conserved across phyla) neural circuit function and evolution.