The physiological importance of the cell assembly’s typical ephemeral lifetime is also supported by the fact that this time window temporally overlaps with the duration of AMPA receptor-mediated EPSPs and GABAA receptor-mediated IPSPs (Johnston and Wu, 1995). Furthermore, the temporal interaction between these opposing postsynaptic effects largely determines the period of gamma frequency oscillations observable extracellularly as a local field potential (LFP; Atallah and Scanziani, 2009; Bartos et al., 2007; Bragin et al., 1995; Buzsáki et al., 1983; Csicsvari et al., 2003; Leung, 2004; Mann et al., 2005; Whittington et al., 2000). Finally, this time scale also corresponds to the temporal window of spike timing-dependent plasticity (Magee and Johnston, 1997; Markram et al., 1997; cf., Bi and Poo, 2001). Given the temporal similarity of these basic physiological effects and their functional interactions, the integration time window of τ is therefore a critical reader mechanism that can define the content of gamma wave packet as the fundamental cell assembly. (Reader mechanisms with wider time integration windows can combine several assemblies; see below).
