Complementary Sensory and Associative Microcircuitry in Primary Olfactory Cortex

The three-layered primary olfactory (piriform) cortex is the largest component of the olfactory cortex. Sensory and intracortical inputs converge on principal cells in the anterior piriform cortex (aPC).Wecharacterize organization principles of the sensory and intracortical microcircuitry of layer II and III principal cells in acute slices of rat aPC using laser-scanning photostimulation and fast two-photon population Ca²⁺ imaging. Layer II and III principal cells are set up on a superficial-to-deep vertical axis. We found that the position on this axis correlates with input resistance and bursting behavior. These parameters scale with distinct patterns of incorporation into sensory and associative microcircuits, resulting in a converse gradient of sensory and intracortical inputs. In layer II, sensory circuits dominate superficial cells, whereas incorporation in intracortical circuits increases with depth. Layer III pyramidal cells receive more intracortical inputs than layer II pyramidal cells, but with an asymmetric dorsal offset. This microcircuit organization results in a diverse hybrid feedforward/recurrent network of neurons integrating varying ratios of intracortical and sensory input depending on a cell’s position on the superficial-to-deep vertical axis. Since burstiness of spiking correlates with both the cell’s location on this axis and its incorporation in intracortical microcircuitry, the neuronal output mode may encode a given cell’s involvement in sensory versus associative processing

Analysis of Excitatory Microcircuitry in the Medial Entorhinal Cortex Reveals Cell-Type-Specific Differences

SummaryMedial entorhinal cortex (MEC) plays an important role in physiological processes underlying navigation, learning, and memory. Excitatory cells in the different MEC layers project in a region-specific manner to the hippocampus. However, the intrinsic microcircuitry of the main excitatory cells in the superficial MEC layers is largely unknown. Using scanning photostimulation, we investigated the functional microcircuitry of two such cell types, stellate and pyramidal cells. We found cell-type-specific intralaminar and ascending interlaminar feedback inputs. The ascending interlaminar inputs display distinct organizational principles depending on the cell-type and its position within the superficial lamina: the spatial spread of inputs for stellate cells is narrower than for pyramidal cells, while inputs to pyramidal cells in layer 3, but not in layer 2, exhibit an asymmetric offset to the medial side of the cell's main axis. Differential laminar sources of excitatory inputs might contribute to the functional diversity of stellate and pyramidal cells