Deviance Detection in Rat Auditory Cortex Figure 13. Comparing the leave-one-out model predictions with experimental observations. A-F. Comparison of the average LFP responses at the six stimulation conditions and four values of Df (thin lines, the same in all panels) with the predicted responses from models in which one condition (denoted at the title of each panel) was left out of the training data (thick lines). Error bars: s.e.m. The data of the left-out condition is displayed in saturated color, while the data for the conditions that were part of the training set are displayed in faded colors. doi:10.1371/journal.pone.0023369.g013 interactions’) with Df of 11% or smaller. They used a slower rate of presentation, longer stimuli and higher probability of the deviant stimulus relative to those used in the current study. The pattern of their results is roughly consistent with ours, and the lower sensitivity in their study may be due to the large-scale averaging inherent in epidural recordings. Malmierca and co-workers demonstrated significant SSA in rat inferior colliculus (IC) [7,21] and in rat medial geniculate body (MGB) [10]. SSA with similar characteristics was also found in the MGB of mice [9]. Although adapting neurons were found in all IC and MGB subdivisions, SSA was much weaker and essentially non-existent at the rates used here in the ventral division of the MGB in rats [10]. It was mostly found outside the ventral division of the MGB in mice as well [9]. Given that the ventral division of the MGB is the major ascending input to the auditory cortex, these results suggest that much of the SSA measured in auditory cortex is actually generated in auditory cortex, with a possible small contribution from the MGB. Indeed, Szymanski et al. [22] showed that SSA in rat auditory cortex increased away from layer IV, suggesting an important contribution of cortical processing to cortical SSA. All of these studies used only the Standard, Deviant and Equal conditions, which makes it impossible to dissect out the contribution of pure adaptation to the Deviant responses, as we could do using the additional control conditions in the current paper. Two recent reports demonstrated SSA in auditory cortex of awake rats as well. Von Behrens et al. [11] found SSA that was somewhat weaker than that reported here, but they used longer tones and longer ISIs than those used for most of the data reported here. Farley et al. [12] used, in addition to the Deviant condition, the so called ‘control’ condition of the MMN literature, which is equivalent to the ‘Diverse-broad’ condition used in this paper [17]. They found significant SSA to frequency shifts, and found the responses to tones in the Deviant and in the Diverse-broad conditions to be essentially equivalent on average. These findings are rather similar to those we report here. Farley et al. [12] concluded that there is no deviance sensitivity in A1 of rats. However, the additional conditions we used in this paper allowed us to show that under a model of pure adaptation the responses in the Deviant condition should be smaller than in the Diverse-broad conditions (Fig. 9). Thus, the observed near equality of the responses in these two conditions (Figs. 5C and 5D) is actually surprising, and indicates the presence of true deviance sensitivity. We turn now to justify these statements. Mechanisms of SSA Adaptation of the responses to tones of a given frequency is obviously induced by the presentation of the same tone frequency, but also by the presentation of tones of adjacent frequencies. Cross-frequency adaptation became significant at frequency separations between 21% and 44% (Fig. 7). This range is substantially narrower than the tuning width of either LFP or multiunit clusters (e.g. [23]), but is consistent with the width of the adaptation channels estimated by the models (Fig. 11B). Thus, PLoS ONE | www.plosone.org 13 August 2011 | Volume 6 | Issue 8 | e23369