Effects of infant and adult amygdaloid lesions upon acquisition of two-way active avoidance by the adult rat: Influence of rearing conditions

When performed in the adult rat, bilateral and complete amygdalectomy resulted in a clear deficit in the acquisition of a 2-way active avoidance in a shuttle-box. When performed in the 7 day old rat pup, the same complete lesion resulted in no disruption of acquisition of the 2-way AA task by the rats when adult, irrespective of the environmental conditions in which they were reared from weaning. However, isolation-reared rats showed shorter response latencies than did group-reared rats. When the amygdaloid lesion was restricted to the centromedial area of the amygdala, operations carried out at 7 days resulted in a reliable impairment of the 2-way active avoidance in the initial phase of the acquisition, but only when the rats had been group-reared from weaning. The same lesion resulted in a reliable improvement in acquisition when the rats had been reared in isolation. In short, the degree of recovery of function with respect to 2-way AA acquisition following a bilateral amygdaloid lesion depends on the age at which the lesion is carried out (at infant or adult age), on the extent of the lesion (complete or restricted to the CM area) and on the rearing conditions (in groups or in isolation).