Medial prefrontal lesions attenuate conditioned reflex facilitation but donot affect prepulse modification of the eyeblink reflex in rabbits

Conditioned reflex facilitation occurs when the amplitude of the eyeblink ( EB) unconditioned reflex (UR) is increased as a result of prior pavlovian c onditioning. Prepulse modification of the EB reflex is produced by precedin g the unconditioned stimulus (US) by a brief low-level neutral stimulus. Th is study examined both conditioned EB facilitation and prepulse modificatio n in rabbits with either medial prefrontal (mPFC) lesions or sham lesions. Conditioned reflex facilitation was assessed by comparing EB UR amplitude p rior to and after pavlovian EB conditioning. Animals that received CS/US pa ired presentations showed evidence of conditioned reflex facilitation, but animals with unpaired training did not. However, this increase in EB UR mag nitude in the paired groups was smaller in animals with mPFC lesions,. comp ared to those with sham lesions. In two subsequent experiments different gr oups of sham and lesion animals received an intense burst of white noise pr eceded by tones with different interstimulus interval durations to assess p repulse modification. Unlike conditioned facilitation, prepulse modificatio n was unaffected by mPFC lesions.