Animals were anesthetized under isofluorane (1–3% in oxygen) and placed in a stereotactic head frame on a temperature-controlled heating pad. A craniotomy and a durotomy were performed above region of interest. The animals were injected with 50–500nl of the indicated virus at a rate of 10–25nl/min using a sharp glass pipette (25–35 mm diameter) that was left in place for 5–15 min after the injection to minimize backflow. The craniotomy site was covered with sterile bone wax, the surgical opening was closed with Vetbond and the animals were returned to their home cage for at least one week. The injection sites were defined by the following coordinates : Mice somatosensory cortex S1: 1.0mm posterior, 3.0mm lateral, 0.7 / 0.4mm ventral relative to bregma; Mice hippocampus CA1: 1.6mm posterior, 1.8mm lateral, 1.2mm ventral relative to bregma; Mice striatum: 0.5mm posterior, 2.0mm lateral, 3.2mm ventral relative to bregma; Zebra Finches HVC: 0,2mm anterior, 2.1 / 2.3 / 2.5mm lateral, 0.4mm ventral relative to the bifurcation of the sagittal sinus; Gerbils auditory cortex A1: 3.0mm anterior, 6.5mm lateral, 0.3mm ventral relative to lambda; Ferrets visual cortex V1: 2.0mm anterior, 7.5mm lateral, 0.25 / 0.4mm ventral relative to lambda. Marmosets visual cortex V1: 15mm anterior, 5mm lateral, 1mm ventral relative to bregma. For zebra finches, the craniotomy was covered with a silicone elastomer (Kwik-Cast; WPI). For the subset of animals used for in vivo recording, a thin cover glass (3 mm, #1 thickness, Warner Instruments) was affixed to the skull using cyanoacrylate to create a chronic optical window over HVC. For ferrets, the scalp was retracted and a custom titanium headplate adhered to the skull using C&B Metabond (Parkell). One coverglass (5mm diameter, #1.5 thickness, Electron Microscopy Sciences) was adhered to a custom titanium cannula using optical adhesive (Norland Products) and placed onto the brain to gently compress the underlying cortex and dampen biological motion during imaging. The cranial window was hermetically sealed using a stainless steel retaining ring (5/16″ internal retaining ring, McMaster-Carr), Kwik-Cast (World Precision Instruments), and Vetbond (3M). For marmosets, the craniotomy was covered with an artificial dura made from bovine cells and the bone flap was fixed in place using Vetbond (3M). Following placement of the bone flap, the skin was sutured closed.