Fig. 4: Microcircuit implementation of GLE: key components.

Representation neurons form the forward pathway (red), error neurons form the backward pathway (blue). Both classes of neurons are pyramidal (PYR), likely located in different layers of the cortex. Lateral connections enable information exchange and gating between the two streams. The combination of retrospective membrane and prospective output dynamics allow these neurons to tune the temporal shift of the transmitted information. Errors are also represented in dendrites, likely located in the apical tuft of signal neurons, enabling local three-factor plasticity to correct the backpropagated errors.