Acoustically evoked potentials in the rat during conditioning.

Acoustically evoked potentials were recorded from unanesthetized rats in a series of experiments designed to study changes in sensory evoked potentials during conditioning. It is shown that when clicks a re established as conditional stimuli (CS) in conditioned emotional response (CER) situations , click-evoked potentials recorded from central auditory structures and from mesencephalic reticular formation exhibit appreciable amplitude increases. Similar increases were found with Sidman avoidance conditioning. These changes in evoked potentials during aversive conditioning were not related to acquired discriminative o r conditional properties of the acoustic stimulus , since similar changes in click-evoked potentials were found when a CER was brought under control of a photic CS. These alterations in click-evoked potentials were shown to be independent of movement o r movement-related variables. Potentials evoked in central auditory structures by electrical stimuli applied to the cochlear nucleus o r within the cochlea also revealed increases in amplitude during acquisition of a CER. In one experiment nearly all movement was eliminated in both CS and control conditions through methods of behavioral control. Data-sampling techniques provided a further control for residual differences in amount of movement in the two periods. These procedures did not eliminate increases in amplitudes of click-evoked potentials during aversive conditioning. In general, whenever behavioral measures indicated that rats were frightened, acoustically evoked potentials evidenced increased amplitudes, whether o r not a CS was present. In all experiments only changes in late components of acoustically evoked potentials were consistently related to observed behavioral changes. It is concluded that changes in sensory evoked potentials observed during conditioning are not related to what may be considered the neural substrate of conditioning, but, in aversive conditioning situations at least , they a re associated with fear elicited initially as an unconditioned response to noxious stimulation and later as a conditioned response.