Effects of lesions of the amygdala, pyriform cortex, and stria terminalis on two types of exploration by rats

Bilateral lesions were made in three groups of rats, selectively destroying the corticomedial amygdala, the pyriform cortex, or the dorsal stria terminalis. During Phase 1 of the experiment, the behavior of each rat was observed in an open-field apparatus for 4 consecutive days for 5 min per day. This phase permitted an evaluation of exploration that occurs when a rat is forced into contact with novelty. During Phase 2, a novel object was placed in the center of the open field and the procedure was repeated for 4 more days. This phase permitted an evaluation of the exploration that occurs when a rat can interact voluntarily with novelty. Lesions of the corticomedial amygdala increased contact with novelty during Phase 1 and increased exploration of the novel object during Phase 2. Stria terminalis lesions produced the same pattern, except that contact and exploration were decreased. Pyriform lesions decreased exploration only during Phase 2. These data show that the effect of lesions of the amygdala and related structures on exploration are different when different types of exploration are measured. The role of the amygdala and its afferent and efferent neural connections in mediating the two types of exploration studied is discussed.