Anatomically, the BLA represents a nuclear extension of the temporal neocortex and the CEA represents a ventrocaudal extension of the striatum (Pitkänen et al., 1997 and Swanson and Petrovich, 1998). The flow of information between the BLA and CEA is largely unidirectional with LA neurons projecting to CEl directly

and indirectly to CEm via the basolateral nucleus (BL) and through a network of inhibitory interneurons in the intercalated cell masses (ITC) (Krettek and Price, 1978, Paré and Smith, 1993, Paré and Smith, 1998 and Paré et al., 1995). CEm projects to several brain regions that mediate fear responses, GS-1101 mouse such as freezing, tachycardia, and stress hormone release, and axonal projections from BLA to CE are critical for the expression of these responses after fear conditioning (Ciocchi et al., 2010, Haubensak et al., 2010, Jimenez and Maren, 2009 and Paré et al., 2004). That is, after fear this website conditioning, it has recently been shown that aversive CSs come to suppress the inhibitory influence of CEl on CEm and drive the expression of conditional fear responses (Ciocchi et al., 2010 and Haubensak et al., 2010). This reveals that CEl normally inhibits CEm and the regulation of this inhibition appears to be essential

for the expression of fear and anxiety (Tye et al., 2011). Multimodal sensory information reaches both regions of the amygdala, and this affords an opportunity for the convergence of CS and US information within these areas. Indeed, substantial data indicate that the lateral nucleus (LA) is a critical sensory interface of the amygdala that mediates CS-US association formation during fear conditioning (Blair et al., 2001 and Maren, 1999). For example, auditory and somatic Adenylyl cyclase stimuli excite LA neurons at short latencies (Johansen et al., 2010 and Romanski et al., 1993), and fear conditioning greatly augments responses of LA neurons to auditory CSs (Goosens et al., 2003, Goosens and Maren, 2004, Herry et al., 2008, Hobin et al., 2003, Johansen et al., 2010, Maren, 2000, Quirk et al., 1997 and Repa et al., 2001). Bernstein and colleagues have also recently shown that individual LA neurons exhibit increases in the expression of the immediate early gene Arc

that reflects CS-US convergence in these cells (Barot et al., 2009). The convergence of CS and US information in the LA engenders associative plasticity that increases the efficacy of CS inputs onto LA neurons (Blair et al., 2001 and Maren, 1999). For example, fear conditioning increases CS-evoked extracellular field potentials in the LA in vivo (Rogan and LeDoux, 1995 and Tang et al., 2001), and LA neurons exhibit conditioning-related changes in synaptic transmission measured ex vivo (McKernan and Shinnick-Gallagher, 1997, Rumpel et al., 2005 and Tsvetkov et al., 2002). In addition to these electrophysiological correlates of conditioning, LA neurons exhibit changes in gene expression and protein phosphorylation after fear conditioning (Lamprecht et al., 2009, Ploski et al.