Deviance Detection in Rat Auditory Cortex Figure 4. Typical responses to all conditions (Df = 44%). A. Responses of LFP and MUA recorded at the same site as Figs. 1 and 3 to f1 and f2 in all stimulus conditions, sorted by frequency. Insets: the amplitudes of the responses, normalized by the responses at the corresponding deviant-alone condition. The raster plots display only 25 representative responses in the standard and equal-probability conditions, as in Fig. 1. B. Responses recorded in the same recording site as A to sequences with different f1 and f2. C,D. Additional examples of the responses to all sequences, recorded from another rat. doi:10.1371/journal.pone.0023369.g004 recording locations, both conditions held (LFP: 29/214, 14%; MUA: 17/85, 20%; see for example the MUA responses in Fig 4A, 13.3 kHz and Fig. 4D, 10.8 kHz). Dependence of SSA on Df To assess the bandwidth over which cross-frequency adaptation contributes to SSA, we presented the same types of sequences with Figure 5. Summary of the responses to all conditions (Df = 44%). A and B. Average (bar plots) and distributions (summarized as box plots) of the responses (normalized with respect to the corresponding deviant-alone response) to both frequencies in each of the six conditions, in all sets recorded with Df = 44%. The number of cases included in each column is displayed underneath it (not all sets included all the six conditions). A. LFP, including 114 sets recorded from 60 individual sites in 22 rats. B. MUA, including 49 sets recorded from 35 sites in 18 rats. C and D. The normalized response to in the Deviant condition (abscissa) versus the normalized response to the same tone in the Diverse-broad condition (ordinate). Each point represents one of the main frequencies (either f1 or f2) of a set in a specific recording site. C. LFP, (r = 0.62, df = 212, p,,0.001). D. MUA (r = 0.40, df = 83, p,0.001). doi:10.1371/journal.pone.0023369.g005 Df’’s of 10%, 21% and 96%. Figure 6 shows typical responses to stimulus pairs with these three values of Df, recorded from three different animals. With Df = 10%, all conditions except Deviant- alone showed strong adaptation, probably due to proximity between different frequencies in the same sequence. The least adapted responses occurred in the Diverse-broad condition that spanned the broadest frequency band. Nevertheless, the LFP response to each frequency when deviant was stronger than the response to the same frequency when standard; the same occurred for the MUA responses to f2 (11.6 kHz). With Df = 21%, the contrast between the responses to the same frequency in different conditions was larger and the pattern of responses became qualitatively similar to that of Df = 44%. With Df = 96% the two frequencies were presumably too far apart to elicit cross-frequency adaptation, except maybe for the Diverse-narrow condition where frequencies were still rather densely packed. These data, for all values of Df, are summarized in Fig. 7. The responses were normalized to the Deviant-alone responses of the same set (as in Fig. 5). Clearly, cross-frequency adaptation strongly affected the responses for Df = 10%, and didn’t affect much the responses at Df = 44%. At Df = 21%, there was some decline in the size of the responses, suggesting that this was the effective bandwidth of cross-frequency adaptation. SSA was nevertheless evident in both LFP and MUA at all Df, even in the strongly reduced responses at Df = 10%. Dependence of SSA on ISI The dependence of SSA on ISI was studied with Df = 44%. In two rats, responses were collected for ISI of 500 ms and 1000 ms. In another group of four rats ISIs of 300, 700, 1200 and 1800 ms were used. SSA was evident at all ISIs, as illustrated by the responses in individual examples (Fig. 8A): in all of these cases, the responses to a frequency when Deviant (red) was larger than the responses to the same frequency when Standard (blue). The population average for each group (Fig. 8B) showed a decrease in SSA as ISI increased (Fig. 8C), but SSA was significant even with ISIs of 1800 ms both in individual recording sites and in the population average. To check the significance of the different apparent trends of response magnitudes in the two groups of rats, a 3-way ANOVA was performed, the factors being the groups of rats (two levels), conditions (six levels), and short vs. long ISIs (two levels: in the first group 500 ms was considered as short ISI, 1000 ms as long ISI, while in the other group we coded 300 ms and 700 ms as short ISIs, 1200 and 1800 ms as long ISIs). The main effect of ISI on the size of LFP responses was not significant (F(1,868) = 3.31, p = 0.07), and even the interaction between ISI and the group of rats was only borderline significant (F(1,866) = 4.35, p = 0.04). We conclude that the difference in trends in the two groups, even if present, is small. Modeling SSA The data suggest that the responses to tone sequences are shaped by ‘adaptation channels’ whose width is about 20% of their center frequency. To check whether this mechanism is sufficient to account for the data, we turned to modeling. The model describes the effects of tone presentations at all frequencies on the responses to tones at the center frequency, fo, of the adaptation channel. PLoS ONE | www.plosone.org 6 August 2011 | Volume 6 | Issue 8 | e23369