A Model Circuit for Cortical Temporal Low-Pass Filtering

We propose that the low-pass characteristics in the temporal and velocity domain of area 17 cells are generated by the abundant excitatory connections between cortical neurons. We have incorporated this anatomical feature in a model circuit in which simple cells' firing is initiated by geniculocortical excitatory synaptic input, with a short time course, and firing is maintained by feedback corticocortical excitatory synapses, which have a longer time course. The low-pass performance of the model is demonstrated by computing the model simple cells' velocity response curves (VRC) elicited by moving bars, and comparing these to those of its LGN (lateral geniculate nucleus) inputs. For the same parameter set, the VRCs of sustained and transient LGN cells are transformed into VRCs typical of central area 17 and central area 18 cells, respectively.