, 2007b). Staurosporine concentration Several recent papers have demonstrated the feasibility of combining

the light activation and/or silencing of neuronal populations with the recording of neuronal activity in both in vitro and in vivo preparations (Han et al., 2009; Sohal et al., 2009; Cardin et al., 2009). For the in vivo studies, however, the distance between the stimulation and recording sites was relatively large, necessitating the use of large-amplitude light intensities (> 30 mW) to stimulate the neurons within the recorded area. Among other problems, such imprecise stimulation hinders the clean separation of local and more global network effects. In this article we describe the fabrication and example applications of integrated miniature optoelectronic devices that enable both large neuronal ensemble recordings and simultaneous localized optical perturbation of neurons in behaving animals (a brief description Angiogenesis inhibitor of these methods has been reported: Royer et al., 2008). All experiments were conducted in accordance with institutional regulations (Janelia Farm Institutional Animal Care and Use Committee). To obtain devices

(fiber-based optoelectronic probes or ‘optrode’: Deisseroth et al., 2006; Zhang et al., 2007a) that enable both the recording and optical stimulation of local populations of neurons, we equipped commercially available silicon probes with micron-scale light guides by placing chemically etched optical fibers onto their shanks. The silicon probe models we used (Buzsaki32; Buzsaki64 from NeuroNexus Inc., Ann Arbor, MI, USA) have either four or eight shanks. The shanks are 250 μm apart and bear eight recording sites each (160 μm2 each site; 1–3 MΩ impedance) arranged in a staggered configuration with 20 μm vertical separation (Fig. 1C; also Bartho et al., 2004, Csicsvari et al., 2003, Wise and Najafi, 1991). An eight-shank silicon probe records from 50 to 140 well-clustered neurons in the hippocampus and neocortex (Fujisawa et al., 2008; Pastalkova et al., 2008). As light guides, we used single-mode optical fibers

(125 μm in diameter, Thorlabs no. 460HP), because their light-guiding properties are less affected Dipeptidyl peptidase by the etching due to their small core diameter (3.5 μm). Because light is emitted from the fiber end with the shape of a cone (∼30° angle), the volume of excited tissue at the level of the recording sites depends on how far above them the fiber ends. For some applications, light modulation needs to be restricted to only the brain volume monitored by the silicon probe, which means that the optical fiber should end < 100 μm above the recording sites. However, critical factors in recording numerous neurons are the small size and smooth profile of the electrode, which minimize capillary and neuronal damage during penetration in the brain (Buzsaki, 2004; Kipke et al., 2008).