Involvement of the amygdala in evaluating the biological significance of conditioned stimuli.

The destruction of the amygdala in cats and dogs causes the animals to stop responding adequately to signals of various biological significance; the curves of change in the amplitude and probability of appearance of EPs in the sensorimotor cortex lose the maxima characteristic of intact animals at frequencies of 0.8, 1.6, and in the band from 2.0 to 3.0 kHz, which are the format frequencies of certain communicational signals in cats. The assumption of a signal (food) significance by an indifferent stimulus, earlier without any biological meaning, finds reflection in the neuronal activity of the amygdala, which begins to respond to this signal as if to an unconditioned stimulus. On the basis of the above factors, the role of the amygdala is discussed in the evolution of the biological significance of conditioned stimuli and the differentiation of the afferent influences that reach it.