Emotional learning enhances stimulus-specific top-down modulation of sensorimotor gating in socially reared rats but not isolation-reared rats

Abstract

Prepulse inhibition (PPI), the suppression of the startle reflex by a preceding sensory stimulus (prepulse), can be top-down modulated in both humans and rats. This study investigated whether emotional-learning-induced enhancement of PPI in rats is prepulse specific. The results show that in socially reared rats, PPI elicited by a narrowband-noise prepulse on the broadband-noise background (masker) was enhanced after the prepulse became fear conditioned. This fear-conditioning-modulated PPI was further enhanced by introducing a perceived spatial separation between the conditioned prepulse and the broadband-noise masker. However, these PPI enhancements disappeared if the conditioned prepulse was replaced by a different narrowband-noise prepulse that was not fear conditioned. In isolation-reared rats, who had both enhanced baseline startle and reduced PPI before conditioning, neither fear conditioning of the prepulse nor perceived spatial separation between the conditioned prepulse and noise masker could enhance PPI. Thus, the emotional-learning-induced enhancement of PPI in socially reared rats is prepulse specific, indicating that auditory processing interacts with mnemonic signaling in the formation of top-down modulation of PPI. Since the deficiency of attentional modulation of PPI in schizophrenic patients is correlated with the symptom severity, the deficiency of top-down modulations of PPI in isolation-reared rats is useful for modeling schizophrenia.