Single-unit spikes were separated from all other spikes using unsupervised spike sorting (see Experimental Procedures). Multiunits were all spikes left after identification of single-unit spikes, and spike time was defined as the time of the peak of the voltage deviation. As shown in the histograms in Figures 2B1–2B3, synchronization is precise, with spikes from different units firing within <250 μs (in the Supplemental Text available online, we rule out artifactual spike pairing). Precise synchronous firing was also found
when a single unit was compared HIF cancer to a multiunit (Figure 2B3) and when multiunits were compared to each other (not shown). Hereafter we define synchronized spikes as spikes that happen within less than 250 μs. The average fraction of synchronized spikes was significantly different from the
fraction of synchronized spikes arising by chance (compare red line to histograms in Figures 2B1–2B3, and see Experimental Procedures) and ranged from 0.9% for single-unit pairs (SU×SU, n = 138) to 6.0% for multiunit pairs (MU×MU, n = 2578; see Table 1). As shown in Figure 2A, synchronized spikes were sparse in single-unit pairs. Sparseness in these SU×SU synchronized trains made it difficult to calculate statistics for changes in firing rate elicited by odors. Therefore when evaluating Veliparib datasheet odor-induced changes we used synchronized trains estimated from multiunit pairs. Importantly, in the Supplemental Text and in Figure S1 (available online), we show that the percent of synchronized spikes in MU×MU pairs is consistent with the makeup of the multiunit spikes by single units, and in Figure S2 we show that the waveforms of the synchronized multiunit spikes do not differ from those of the rest of the spikes in the multiunit. Finally, an autocorrelogram of the synchronized spike trains in the RA shows a weak oscillatory pattern (at ∼5 Hz, Figure 2B4) consistent with changes in simultaneous synchronized
firing associated with breathing. Figure 3Ai shows the development of differential responsiveness to new odors by synchronized spike trains through a go-no go session. As shown in an earlier study for spikes Astemizole from individual units (Doucette and Restrepo, 2008), in the first 20-trial block, the synchronized spike trains do not respond differentially to the two odors (Figures 3Ai and 3B), and the mouse does not respond differentially to the odors (Figure 3C). In contrast, after 60–100 trials (three to five blocks), the animal develops a differential behavioral response and the synchronized spike trains respond with excitation to the rewarded odor, and with inhibition to the unrewarded odor. Responses were classified as divergent using a t test corrected for multiple comparisons through false discovery rate (FDR) with a significant p value in at least two blocks in a session (see Experimental Procedures).