Conditioned taste aversion is an unusual form of associative learning in which long delays between conditional stimulus taste (CS) and unconditioned stimulus illness (US) suggest stimulus encoding by novel mechanisms. Recent data suggest that stimulus inputs are encoded by inducible bZIP proteins, the kinetics of which match the temporal features of the CS and US in taste aversion learning. Blockade of US-induced c-Fos translation in the brain stem by antisense oligonucleotides specifically blocks both acquisition and extinction of a learned taste aversion, but does not impair sensory processing of either CS or US, suggesting that c-Fos antisense blocks associative events within NTS necessary to support taste aversion learning.