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.