Metabolic mapping of brain regions associated with behavioral extinction in preweanling rats

Fluorodeoxyglucose autoradiography, quantitative image analysis, and a mult ivariate tool (partial least squares) were used to assess distributed patte rns of brain activation in postnatal day 17 and day 12 rat pups engaged in extinction of instrumental behavior. Pups were trained in a straight alley runway on an alternating reward schedule, or on a pseudorandom reward sched ule, injected with fluorodeoxyglucose, and then shifted to continuous nonre ward (extinction). Another group at each age served as handled controls. Da y 17 pups trained on the alternating schedule demonstrated faster extinctio n rates compared to those trained on the pseudorandom schedule, a phenomeno n known as the partial reinforcement extinction effect. No differences were found between day 12 groups. Partial least-squares analysis revealed age-r elated increases in fluorodeoxyglucose uptake across all three training con ditions in the cingulate and frontal cortices, amygdala, midline thalamic n uclei, cerebellum, and in several brainstem regions. Training-related incre ases common to both age groups were found in the orbital frontal cortex, li mbic thalamus, gigantocellular reticular nucleus, the somatosensory system, and cerebellum. Age-dependent training effects were found in the interposi tus and medial cerebellar nuclei wherein fluorodeoxyglucose uptake increase d in the day 12 alternation and pseudorandom groups relative to controls. D ay 12 pups trained on the alternating schedule demonstrated increased uptak e in the anterior dorsal thalamus relative to pseudorandom and control pups . Hence, a large-scale neural system comprised by somatosensory, cerebellar , and brainstem regions govern extinction behavior in preweanling rats. Rec ruitment of limbic structures may allow the older pups to modify extinction behavior based on prior learning. (C) 2001 Published by Elsevier Science B .V.