patterns are not only associated with increased but also by selectively decreased firing of inhibitory interneurons in both neocortex and hippocampus (Figure 9B; Gentet et al., 2010; Rao et al., 1999; Wiebe and Staubli 2001; Wilent and Nitz, 2007). Such well-defined suppression of inhibitory neurons in a neural sentence may facilitate the emergence of new assemblies, suppressed by the same interneurons in other parts of the sentence. How can inhibitory neurons play such a two-faced role: to be part of an assembly and also suppress competing assemblies? Since assembly members are typically drawn from sparsely firing neurons of a large neuron network (Fujisawa et al., 2008; Harris et al., 2003; Sakata and Harris, 2009), only a few principal cells are typically active in a given volume of tissue at any given time. Although interneurons are expected to respond to all of their principal cell inputs more or less equally, in a given short time window only one or a few strongly active principal cells discharge them, thereby essentially ‘copying’ the principal cell’s firing pattern. In turn, the transient ally interneuron can suppress the activity of competing principal cells in the vicinity of their (mostly local) axon collaterals. As a result,
