Inhibition is not only directly involved in the generation of these fast oscillations, but also in synchronizing participating neurons, in setting the pace of the oscillations and in maintaining their coherence in space. Among the various types of inhibitory neurons, basket cells play a key role in gamma oscillations (Cardin et al., 2009; Cobb et al., 1995; Sohal et al., 2009). Two important properties of interneurons appear crucial to the generation of synchronized oscillations. First, interneurons are electrically-coupled via gap junctions allowing large populations of interneurons to be synchronized with millisecond precision (Beierlein et al., 2000; Galarreta and Hestrin, 1999, 2001; Gibson et al., 1999; Hestrin and Galarreta, 2005). Second, interneurons make reciprocal synaptic connections onto each other (Bartos et al., 2002; Galarreta and Hestrin, 2002; Gibson et al., 1999; Tamas et al., 1998), a property that models show is important for the robustness of oscillations (Bartos et al., 2007; Vida et al., 2006). Two alternate mechanisms, "PING" (pyramidal-interneuron network gamma oscillations) and "ING" (interneuron network gamma oscillations) have been proposed for the role of inhibitory neurons in the generation
