Introduction of acoustic stimulation during acquisition and resistance to extinction in the normal and hippocampally damaged rat.

The basic experimental question in each of three experiments was whether exposure to acoustic stimulation in acquisition of an FR chain would increase -persistence in the subsequent extinction of that response. Other factors manipulated in the experiments were (a) the manner of introduction of the tone stimulus (gradual increase in intensity or terminal intensity from the outset), (b) locus of introduction of tone in the response chain (at beginning or end), and (c) the interaction of tone-in-acquisition treatment with presence or absence of hippocampal lesions in the subjects. The findings were that introduction of the tone in acquisition increased resistance to extinction (a) more greatly under terminal than under gradual conditions, (b) both when it was introduced at the beginning and at the end of the response chain, and (c) in operated controls but not in rats with lesions of the hippocampus.