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. Author manuscript; available in PMC: 2021 Jun 30.
Published in final edited form as: Neuroimage. 2020 Oct 21;225:117479. doi: 10.1016/j.neuroimage.2020.117479

Figure 10. Dual counterstream architecture of inter-areal pathways.

Figure 10.

A) Parent neurons at L3 and L5 have FF projections (red) to higher order areas reciprocated by FB projections (blue) in L2 and the L6. Simultaneous tracer injections in high and low areas show that the upper layer counterstream has near 100% segregation, i.e. the FF (FB) neurons do not send axon collaterals to lower (higher) order areas. However the evidence that the FF and FB pathways form continuous streams, as depicted here is indirect; what crucially remains to be elucidated are the laminar details on the connectivity and the cellular targets. B) the canonical microcircuit showing the two FB pathways targeting L2 and L6. Modified from (Douglas and Martin, 1991); C) the incorrectly assumed serial processing (lower) between areas that is not observed in the cortex, where instead each areas project to all upper and lower stream areas (all to all). (panel A from (Markov et al., 2014b));