Fear and the modification of acoustically evoked potentials during conditioning.

Abstract

Experiments were performed to determine if movement had been responsible for observed changes in acoustically evoked potentials in the rat during conditioning. In one, peripheral auditory mechanisms operative during movement were bypassed by using electrical stimulation of cochlear nucleus or cochlea to evoke auditory potentials as a conditioned emotional response was established with a photic conditional stimulus (CS). In another, differences in movement during control and photic CS conditions were eliminated by behavioral techniques and by sampling click-evoked potentials in periods of no movement. In both situations, amplitudes of late components of potentials recorded from auditory cortex, medial geniculate body and inferior collieulus were directly related to strength of the conditioned emotional response. Early components of these responses and responses of ventral cochlear nucleus did not show this relationship. Unconditioned fear was also accompanied by increases in amplitudes of evoked potentials. Fear was apparently responsible for the systematic changes during aversive conditioning.