Amygdala, hippocampus and discriminative fear conditioning to context

Various measures of fear have been shown to condition to a fearful context with different acquisition rates (Antoniadis EA, McDonald RJ. Fear conditio ning to context expressed by multiple measures of fear in the rat, Behav Br ain Res 1999;101(1):1-14). Freezing, locomotion, urination and preference a re 'fast' measures of fear in that they discriminatively condition to conte xt after a single training session, while ultrasonic vocalizations and defe cation are 'slow' measures of fear given that they condition following thre e training sessions. In the present experiment we sought to assess the cont ribution of the amygdala and the hippocampus in this form of learning. Exis ting views differ on the degree of involvement of each memory structure. Th is discord probably emerges from the common use of non-discriminative parad igms and the assessment of a single measure of fear. With the use of a disc riminative paradigm and the assessment of multiple measures of fear, result s indicate that the amygdala is a memory structure that selectively mediate s the conditioning of heart rate, and the hippocampus selectively mediates the conditioning of defecation and body temperature. The conditioning of pr eference, locomotion, freezing and ultrasonic vocalizations, necessitate th e participation of both memory structures while the conditioning of urinati on does not seem to require the participation of either the hippocampus or the amygdala. The proposed view ascribes an equal role in fear conditioning to both the amygdala and the hippocampus. (C) 2000 Elsevier Science B.V. A ll rights reserved.