Cortical representation of fear learning : Illustrationen, Diagramme

During auditory fear conditioning, an animal learns to associate a neutral sound stimulus (CS) with an aversive foot shock (US). Processing of the CS in auditory cortex is altered during and after learning. In this thesis, the role of different subpopulations of neurons during and after fear conditioning is examined. Auditory cortex responses during fear expression are investigated. A subpopulation of calretinin (CR)- positive interneurons and pyramidal cells show an increase in response size to the conditioned stimulus, suggesting the existence of a similar microcircuit in auditory cortex mediating salient sound information during fear expression. Vasoactive-intestinal polypeptide (VIP) – positive interneurons do not show such a CS-evoked increase in response size, hence CR-positive interneurons involved in fear expression are most likely VIP negative. Furthermore, discriminability between the CS and a neutral control sound is increased after fear learning. Taken together, the data suggests the existence of a microcircuit involving CR-positive interneurons and pyramidal cells in auditory cortex which mediates behavioural saliency of sounds during memory expression.