CIBR has extensive expertise and resources for the measurement of neuronal ensemble activity in head-fixed, behaving rodents and in brain slices maintained alive in vitro. For the former, CIBR uses a Plexon multichannel recording system capable of simultaneously recording 256 extracellular single units and 64 local field potentials using custom-fabricated fixed arrays of microelectrodes and robotic insertion of up to 16 independently-controllable microelectrodes within 1 mm2. This is currently being used in collaborative research between the Welsh, Turner, and Ramirez labs, in conjunction with integrated multi-channel optogenetic stimulation via simultaneously-implanted optoelectrode arrays. For in vitro ensemble recordings, CIBR is one of the few sites in the world that has implemented the use of “array 2-photon microscopy” to allow for wide field-of-view, real-time imaging of neuronal activity using calcium indicators with subcellular resolution. This is accomplished using a LaVision Biotech instrument that splits a high-power pulsed infrared laser beam into 64 beamlets, which can either be swept as an array over the tissue to increase speed and image brightness, or steered as independent beam arrays to user-defined regions of interest for 2-photon optogenetic stimulation in conjunction with single- or paired-patch clamp recordings of visually-identified neurons.