The basolateral amygdala complex is involved with, but is not necessary for, rapid acquisition of Pavlovian 'fear conditioning'

A major hypothesis about lateral/basolateral amygdala complex (BLC) functio n in memory proposes that the BLC is the site where conditioned stimulus-un conditioned stimulus (CS-US) associations are formed and permanently stored during Pavlovian 'fear conditioning.' Thus, according to this hypothesis, the BLC is necessary for the acquisition and expression of both discrete-cu e and contextual Pavlovian fear conditioning. This hypothesis clearly requi res that animals with complete lesions of the BLC be completely unable to a cquire Pavlovian fear conditioning. In this experiment, distribution of tra ining and testing trials over three sessions revealed that rats with comple te BLC lesions rapidly acquired a contextual CS-US association (as assessed with freezing behaviour), although their performance, as expected, did not equal that of sham operated controls. Irrespective of the nature of the fr eezing deficit relative to controls, the learning in the BLC-lesioned rats strongly indicates that Pavlovian fear conditioning CS-US associations can be rapidly acquired in the absence of the BLC, and that the BLC cannot ther efore be necessary for their acquisition.