Habituation of the acoustic startle response in rats after lesions in the mesencephalic reticular formation or in the inferior colliculus

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Extensive damage to the mesencephalic reticular formation (MRF) in 24 male albino rats altered long-term habituation of the acoustic startle response without disrupting short-term habituation. The MRF lesions did not alter initial startle amplitudes, but the Ss with lesions were unable to attain as low a long-term asymptote of habituation as could 21 control Ss. Subsequent manipulation of stimulus intensity and interstimulus interval revealed no differences in short-term habituation between the 2 groups. Large lesions to the inferior colliculus (IC) of 22 Ss did not disrupt long-term habituation of the acoustic startle response, but these Ss were unable to suppress responding as much as controls to intense stimuli presented rapidly. The deficits in long-term habituation following MRF lesions suggest a disruption of an extrinsic, inhibitory mechanism of habituation. The deficits following IC lesions could have been due either to a disruption of a short-term habituation mechanism or to an increase in response sensitization produced by the lesions. (30 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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