Qualitative and quantitative analyses of hoarding in medial frontal cortex rats using a new behavioral paradigm

The study demonstrates novel features of rat hoarding, patterns of recovery from medial frontal cortex damage that are behaviorally dependent, and new methodology for studying hoarding. Rats were placed in a covered cage connected to an alley at the end of which were food pellets varying in size between 20 and 500 mg. Food pellet size directed movements: small food pellets were swallowed immediately, medium sized pellets were held in the paws and eaten, and large pellets were carried back to the cage. After bilateral ablations of the medial frontal cortex, hoarding ceased immediately postoperatively and then partially recovered. Thereafter, food pellets were treated as being smaller than they actually were. The medial frontal cortex rats also hoarded fewer multiple pellets, had slower hoarding speeds, and showed reduced hoarding in 24-h hoarding tests. They were more responsive to illumination changes: as illumination was reduced and finally reversed between the hoarding alley and home cage, they, unlike control rats, reduced and then ceased hoarding. Equivalent change was not produced by eye patches. Damage to medial frontal cortex may change an animal's sensitivity to the many cues provided by the food, the environment, and previous experience in such a way that hoarding responses become increasingly controlled by the immediate, simple, stimulus features of the environment.