| Over the past few decades, Pavlovian conditioning procedures have been utilized to advance our understanding of the neural systems involved in the production of fear. While much is known about the neural systems involved in the production of fear, little is known about the neural systems involved in the inhibition of fear. In rats, the inhibition of fear can be examined using a feature-negative discrimination procedure in which a noise stimulus acquires the ability to inhibit fear to a light which signals danger. Because the “safety” properties of this noise must be transmitted through auditory pathways in the brain, identification of these auditory pathways will help to identify a component of the neural circuit involved in the inhibition of fear.; The purpose of the present study was to examine the effects of lesions of structures within the auditory system in an effort to disrupt the detection of the noise inhibitor. To accomplish this, four experiments were conducted in which rats were first given feature-negative discrimination training followed by lesions of the inferior colliculus (IC), mediate geniculate body (MGB), auditory thalamus (ADT), or auditory cortex (CTX). Next, rats were tested for the ability to inhibit fear in the presence of the noise safety signal. The results of these experiments indicated that bilateral lesions of either the IC or ADT disrupted the ability of the noise inhibitor to inhibit fear to a light CS. In contrast, lesions largely restricted to the MGB or CTX did not disrupt the inhibition of fear. These results suggest that an auditory pathway(s) which includes the IC and ADT is used to detect the safety properties previously conditioned to an auditory stimulus. |
