Reverse optical probing (ROPING) of neocortical circuits.

We describe an optical technique to detect circuits of synaptically connected neurons. By combining calcium imaging of the spontaneous activity of neuronal populations with intracellular recordings from a given neuron, we perform a type of reverse correlation analysis to detect neurons that generate action potentials time-locked to the synaptic currents of the recorded cell. This technique can quickly reveal monosynaptically connected neurons.