Experience during suckling alters later spatial learning

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Abstract
These experiments explore the role of preweaning experience in learning during the juvenile period. Pups that had been reared with many nipples available reached criterion on an 8-arm radial maze in a few trials; conversely, pups reared with only a few nipples required 3 times the number of trials to reach criterion (Experiment 1). Pups that had been reared with relatively few nipples available rarely nipple-shifted, while those that had been reared with a particularly high density of nipples shifted more frequently (Expt 2). A rearing procedure was devised that allowed precise experimental control of all phases of the suckling experience (Expt 3). Allowing or preventing a single behavior, nipple-shifting, while holding all other variables constant, was sufficient to affect acquisition of the maze task. In Experiment 4, the specificity of the early experience for later tasks was explored using a variety of nonspatial, lever-pressing operants. Rearing condition did not affect acquisition of a lever-pressing operant or of a visual discrimination task. However, pups reared with a high density of nipples responded at higher rates to a variable interval schedule and were more resistant to extinction. The possibility that strategy, rather than learning ability, was affected by rearing condition was assessed using a 2-arm maze task that was structured to present an optimal strategy of either win-shift or win-stay (Expt 5). The ease with which rats acquired the win-stay task was unaffected by rearing condition; all groups performed at about chance levels. However, pups reared with many nipples more readily acquired the win-shift task.