RESULTS: Extracellular single-unit recordings were made from infralimbic (IL) pyramidal cells, IL interneurons and prelimbic (PL) pyramidal cells 2-3 weeks after intra-IL injection of a viral vector encoding channel rhodopsin 2 (ChR2) under the control of the CaMKII promoter (rAAV5/CaMKIIa-ChR2(H134R)-EYFP) or a control vector that lacked the ChR2 sequence (rAAV5/CaMKIIa-EYFP).