Mapping pavlovian conditioning effects on the brain: Blocking, contiguity,and excitatory effects

Pavlovian conditioning effects on the brain were investigated by mapping ra t brain activity with fluorodeoxyglucose (FDG) autoradiography. The goal wa s to map the effects of the same tone after blocking or eliciting a conditi oned emotional response (CER). In the tone-blocked group, previous learning about a light blocked a CER to the tone. In the tone-excitor group, the sa me pairings of tone with shock US resulted in a CER to the tone in the abse nce of previous learning about the light. A third group showed no CER after pseudorandom presentations of these stimuli. Brain systems involved in the various associative effects of Pavlovian conditioning were identified, and their functional significance was interpreted in light of previous FDG stu dies. Three conditioning effects were mapped: 1) blocking effects: FDG upta ke was lower in medial prefrontal cortex and higher in spinal trigeminal an d cuneate nuclei in the tone-blocked group relative to the tone-excitor gro up. 2) Contiguity effects: relative to pseudorandom controls, similar FDG u ptake increases in the tone-blocked and -excitor groups were found in audit ory regions (inferior colliculus and cortex), hippocampus (CA1), cerebellum , caudate putamen, and solitary nucleus. Contiguity effects may be due to t one-shock pairings common to the tone-blocked and -excitor groups rather th an their different CER. And 3) excitatory effects: FDG uptake increases lim ited to the tone-excitor group occurred in a circuit linked to the CER, inc luding insular and anterior cingulate cortex, vertical diagonal band nucleu s, anterior hypothalamus, and caudoventral caudate putamen. This study prov ided the first large-scale map of brain regions underlying the Kamin blocki ng effect on conditioning. In particular, the results suggest that suppress ion of prefrontal activity and activation of unconditioned stimulus pathway s are important neural substrates of the Kamin blocking effect.