Emotional states displayed by an animal or a human can seriously affect behavior of their conspecifics. The amygdala plays a crucial role in the processing of emotions. In this study, we describe an experimental rat model of between-subject transfer of emotional information and its effects on activation of the amygdala. The rats were kept in pairs, and one animal (designated as ''demonstrator'') was treated to specific behavioral training of either foot-shockreinforced context conditioning or just exposure to a novel context. We next examined the influence of the demonstrators on the exploratory behavior of their cagemates (called ''observers'') and the observers' performance of the acoustic startle response. We report that we can distinguish both groups of observers from the control animals (as shown by startle-response measure) and distinguish between observers (by means of indexing the exploration), with respect to whether they were paired with demonstrators treated to different experimental conditions. Furthermore, we show that the observers have most of their amygdala activated (as revealed by c-Fos mapping) to the same level as the demonstrators and, in the case of the central amygdala, to an even higher level. Moreover, the level of c-Fos expression in the observers reflected the specific behavioral treatment of the demonstrators with whom they were paired. Thus, in this study, we have shown that undefined emotional information transferred by a cohabitant rat can be evaluated and measured and that it evokes very strong and information-specific activation of the amygdala.c-Fos ͉ emotion ͉ social communication ͉ brain mapping ͉ empathy E motions coordinate homeostasis of an organism in a complex, dynamic environment and participate in regulation of social behaviors. Emotional states displayed by an animal or a human can seriously affect the behavior of conspecifics. This fact has been demonstrated in numerous studies involving simulated and real panic situations, in which the presence of a leader determines the time of achieving the goal of a safe exit (1, 2). The escape panic could happen in life-threatening situations, such as fires in crowded buildings, but sometimes, interestingly, it seems to emerge without any apparent cause. This kind of panic is probably provoked by the specific emotional behavior of some members of the crowd.It is well known that the elaborate emotional systems of social species, such as humans, allow the recognition of very subtle emotional signals. Most of the functional imaging studies in humans have used emotional facial expressions as social signals presented to a subject to associate differences in the social content of stimuli with differences in the activity of the neural structures engaged in the processing of such stimuli (3). The results of these studies clearly pointed to the amygdala being involved in the processing of negatively valenced stimuli of biological importance (4-6). The neuroimaging studies also revealed that fearful faces are especially effective in activa...

Understanding the function of the distinct amygdaloid nuclei in learning comprises a major challenge. In the two studies described herein, we used c-Fos immunolabeling to compare the engagement of various nuclei of the amygdala in appetitive and aversive instrumental training procedures. In the first experiment, rats that had already acquired a bar-pressing response to a partial food reinforcement were further trained to learn that an acoustic stimulus signaled either continuous food reinforcement (appetitive training) or a footshock (aversive training). The first training session of the presentation of the acoustic stimulus resulted in significant increases of c-Fos immunolabeling throughout the amygdala; however, the pattern of activation of the nuclei of the amygdala differed according to the valence of motivation. The medial part of the central amygdala (CE) responded, surprisingly, to the appetitive conditioning selectively. The second experiment was designed to extend the aversive versus appetitive conditioning to mice, trained either for place preference or place avoidance in an automated learning system (INTELLICAGE). Again, much more intense c-Fos expression was observed in the medial part of the CE after the appetitive training as compared to the aversive training. These data, obtained in two species and by means of novel experimental approaches balancing appetitive versus aversive conditioning, support the hypothesis that the central nucleus of the amygdala is particularly involved in appetitively motivated learning processes.

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