The finding that mature rats exposed to classical odor-shock conditioning soon learn to avoid the odor as a way of also avoiding the shock certainly qualifies for the school of the blooming obvious. What is less apparent, and in fact little known, is that rat pups show “paradoxical learning;” pups still confined to the nest show a strong odor preference in this classical training paradigm. This attraction to anything, even pain, occurs regardless of maternal presence.

In a paper published last year in Nature Neuroscience, Moriceau and Sullivan present a compelling series of studies of the time period just after complete dependence, when the pups are beginning to walk outside of the nest. During this time the pup requires continued interactions with the mother, but also the ability to learn outside the nest. A teenage rat as it were. During this time period the investigators found that maternal presence suppresses stress-induced corticosterone release. That is all good, but surprisingly, maternal presence also results in a strong preference for an odor paired with a shock. When the mother was absent the pup learned to avoid the odor, but when the mother was present our teenage rats learned to prefer the odor, even when paired with subsequent pain.

On the surface this seems to be some weird stuff. Why would the presence of the mother be linked with paradoxical learning? Good question. It may be that maternal presence provides such an “approach” motivation that “avoidance” needs to be learned later in life. My suspicion is that the most relevant finding from this study is the fundamental nature of the maternal bond. This study suggests the impact of the maternal bond does not diminish after the animal begins to achieve some degree of independence. We don’t know what paradoxical learning during this transition period really means in these animals. But it is clear that the maternal bond exhibits an extremely strong effect on brain development during this time period equivalent to human adolescence.

Further Reading:

Moriceau S, Sullivan R. Maternal presence serves as a switch between learning fear and attraction in infancy” Nature Neuroscience 2006;9:1004-1006.