Fig. 8

Schematics of the shifter circuit in the EB–PB system. a In the EB–PB system, the PEN neurons form a shifter circuit by sending the signals from the PEI–EIP feedback circuit to the neighbor EB regions. We illustrate how the shifter circuit is formed in the b and c. b Consider the PEI neurons which innervates R0–R7 regions. Each PEI neuron sends signals from one EB region to one PB dual region and the signals are sent back to the same PB region by an EIP neuron. Note that an EIP neuron actually innervates three EB regions, but two of them belong to the same dual region. For the simplicity, we only depict the innervation of the dual region for each EIP neuron. c To build a shifter circuit for the PEN neurons, we first copy the innervation patterns of the PEI neurons and then shift the innervation sites in PB rightward by one region but leave the innervation sites in EB unchanged. To accommodate the change, we need to add a new PB region, R8, to the right side of PB. A new EIP neuron (gray dashed line) that innervates R8 has also to be added in order to complete the shifter circuit. Note that here we only depict the neurons innervating the right side of PB. The neurons innervating the left side of PB are simply the mirror images of the neurons in the right side