2/n: Heading direction networks (HDNs) are biological instantiations of ring attractors (RAs), but there are different classes of RAs that incorporate angular velocity signals in different mechanistic ways.

3/n: In fly, functional work, supported by the impressive connectome, show that its HDN is a shifter network made up of three rings: a central ring that encodes heading and two rings that shift the bump CW or CCW. What happens in zebrafish? Structure from function is much trickier there.

4/n: Siyuan developed a framework that is able to distinguish shifter networks from velocity-modulated synaptic networks. The key point is that shifter networks require neurons that have conjunctive heading and angular velocity responses, whereas the alternative does not.