Corticocortical signaling drives activity in a downstream area rapidly and scalably

How effectively does activity in an upstream cortical area drive activity in a downstream area? To address this, we combined optogenetic photostimulation with multi-unit electrophysiology to study a parietofrontal corticocortical pathway from retrosplenial cortex to posterior secondary motor cortex in mice. Photostimulation in the upstream area produced local activity that decayed quickly. This activity in turn drove downstream activity that arrived rapidly (5-10 ms latencies), and scaled in amplitude across a wide range of stimulus parameters as an approximately constant fraction (~0.2) of the upstream activity. A model-based analysis could explain the corticocortically driven activity with exponentially decaying kernels (~20 ms time constant) and small delay. Reverse (antidromic) driving was similarly robust. The results show that corticocortical signaling in this pathway drives downstream activity in a mostly linear manner. The regular and predictable responses further suggest that precise stimulation driven control of cortical population activity should be possible.