8 ± 1.0 cells per mouse; KO: 17.4 ± 2.1 cells per mouse; Figure 2A) and analyzed units (CT: n = 48; KO: n = 92) with significant activity on the track (place field peak > 1 Hz). Fine quantification PD-0332991 mw revealed no differences in these responses across multiple measures (Figure 2; see also Figure S1). Specifically, single units in KO exhibited normal place field sizes (F(1,138) = 0.01, NS; Figure 2B), normal firing rates within place fields (F(1,138) = 0.56, NS; Figure 2C), no difference in the normal tendency of units to fire more in one direction than another (F(1,138) = 0.19, NS; Figure 2D),

and no difference in sparsity (F(1,138) = 0.85, NS; Figure 2E), which is a measure of the localization of place fields (Jung et al., 1994). In addition, no difference was observed in spatial information index (F(1,138) = 0.02, NS; Figure 2F), which measures how informative about position a spike from a place cell is (Markus et al., 1994), and spatial coherence (F(1,138) = 0.92, NS; Figure 2G), which measures the local smoothness of a firing rate pattern of spikes (Muller and Kubie, 1989). Next, to determine whether excitability might be evident in the precise timing of single spikes, we further examined run-time unit activity

on a finer timescale. Since hippocampal single units exhibit complex LY294002 nmr spikes, made up of a burst of several spikes occurring 2–10 ms apart (Quirk and Wilson, 1999), we first measured the number of spikes during bursts. Both KO and CT units exhibited similar numbers of spikes per burst (F(1,142) = 0.01, NS; Figure 2H) and a similar percentage of burst spikes (F(1,142) = 0.40, NS; Figure 2I). Interestingly, however, we found that

bursts in KO tended to be faster, as measured by burst interspike interval (CT: 5.70 ± 0.70 ms; KO: 4.99 ± 0.78 ms; F(1,142) = 29.16, p < 10−6; Figure 2J), and extracellular spike amplitude attenuation, which is associated with complex spikes (Harris et al., 2001 and Quirk and Wilson, 1999), was also increased in KO (CT: 2.84% ± 0.39%; KO: 5.93% ± 0.38%; F(1,142) = 31.36, p < 10−6; Figure 2J). Taken together, these results indicated that the spatial representation at the level of single science cells in KO appears to be preserved during exploratory behavior, in spite of the bias toward enhanced synaptic strength, with little change in spike timing during bursts. Since the place responses of single units in calcineurin KO were largely normal during run, we next examined whether unit activity during immobile periods, specifically SWRs, was also unaltered. In both KO and CT mice, single units exhibited spikes during SWR events (Figure 3A). Place cells in KO, however, fired more than double the number of spikes during each SWR event as compared to those in CT (CT: 1.11 ± 0.14 spikes per SWR; KO: 2.56 ± 0.54 spikes per SWR; F(1,81) = 4.84, p < 0.05; Figure 3B).