We evaluated the effects of input inactivation on the magnitude of tone responses as indicated by responses in the first 3 s bin after tone onset. We limited our

analysis to cells showing significant tone responses (Z > 2.58; p < 0.01) either before or after input inactivation. We found that 20% of PL cells (n = 34/172) were tone responsive prior to input inactivation, similar to our previous report ( Burgos-Robles et al., 2009). Inactivation of BLA and vHPC produced opposite effects. Averaging over all tone responsive neurons (n = 26/78, 33%), BLA inactivation significantly decreased tone responsiveness (t25 = 3.52 [paired]; p = 0.002; see Figure 2A, top, bottom). This effect was due to decreased tone responses of pyramidal neurons (t21 =

2.81 [paired]; p = 0.011; Figure 2A, bottom inset) and interneurons (t3 = 4.11 [paired]; p = 0.03; Figure S2). In contrast to Dinaciclib manufacturer BLA, vHPC inactivation increased tone responses (for example, see Figure 2B, top). Averaging over all tone responsive PL neurons (n = Y-27632 supplier 25/95, 26%), vHPC inactivation significantly increased tone responsiveness (t24 = −2.26 [paired] p = 0.03; Figure 2B, bottom). This effect was due to increased tone responses of pyramidal neurons (t18 = 2.12 [paired]; p = 0.048; Figure 2B, bottom inset) and not to interneurons (t5 = 0.75 [paired]; p = 0.48; Figure S2). These opposing effects of BLA and vHPC inactivation could be detected as early as 300 ms after tone onset. To evaluate within-cell changes, we tracked the tone responses Bay 11-7085 (TRs) of each cell before and after

inactivation in conditioned rats. Cells were classified as significantly tone responsive if they fired >2.58 SD, (p < 0.01) above baseline rate within the first 3 s bin. Inactivation of BLA caused the majority of the 26 PL cells to lose their TRs, a small proportion to become TR, and some to remain TR (Figure 2C). This suggests that BLA is the major route by which conditioned tones can influence PL. In contrast to BLA, inactivation of vHPC resulted in most of the 25 PL neurons either becoming TR or remaining TR, with a smaller number losing their TR (Figure 2D). Thus, despite the typical heterogeneity of single-cell responses, the pattern of responses we observed supports the idea that BLA communicates conditioned responses to PL, whereas vHPC gates those responses. To test whether these effects of BLA and vHPC converge onto single PL cells, we implanted a subset of rats with cannulas in both structures. Out of 10 PL neurons tested, we found 3 that were TR and 7 that were not TR. Notably, 2 of these 7 non-TR cells (from different rats) revealed evidence of BLA and vHPC convergence. Figure 3 shows the tone responses of these neurons, which were not initially TR (top panel), but became significantly TR after vHPC inactivation (middle panel).