The effects of perirhinal lesions on fear conditioning to auditory and visual stimuli

The perirhinal cortex (PER) appears to be necessary for fear conditioning to discontinuous auditory cues but not to continuous auditory cues. This line of research led to a hypothesis of PER functioning called "stimulus unitization" in which the PER acts to bind temporally discontinuous cues into a single representation for learned associations. The current study assessed the role of the PER in a three day fear conditioning paradigm by randomly assigning animals to one of eight groups based on two factors: surgical condition (Sham vs Lesion) and conditioned stimulus (Continuous Tone, Discontinuous Tone, Continuous Light, or Discontinuous Light). Perirhinal lesions significantly reduced freezing to auditory and visual cues during fear acquisition regardless of stimulus features. Furthermore, there was no effect of perirhinal lesions to context-elicited freezing. Finally, the results suggest that there may be a difference in the saliency of auditory cues compared with visual cues.