Stress during early life can affect human cognitive development, but characterizing these effects is challenging, in part because of a lack of appropriate research subjects. A suitable model would be one whose brain development is similar to that of humans and whose cognitive abilities can be evaluated objectively. Rodney Johnson and his colleagues at University of Illinois at Urbana-Champaign recently developed a model that meets these requirements—the neonatal piglet.

First, they used magnetic resonance imaging (MRI) to quantify piglets' brain development from the ages of 2 weeks to 24 weeks, when the piglets were near sexual maturity. Total brain volume increased 121–130% during this period. The piglets' brains reached about 50% of maximum volume at the age of 4 weeks and grew to about 95% of maximum volume by the age of 21–23 weeks ( Dev. Neurosci. published online 6 July 2012 doi:10.1159.000339311). This large postnatal increase in piglet brain volume is similar to that of human neonates: at birth, the human brain is ∼25% of its adult size, growing to 85–90% within the first 2 years of life.

Next, Johnson's team created a 'T'-shaped maze task to evaluate piglets' learning. Two-week-old piglets were trained to locate a reward in a constant location within the maze by using visual cues placed outside the maze. Their performance improved over time, and they had mastered the task within 5 d (Anim. Cogn. 15, 667–676; 2012). The reward location was then changed, and piglets were tested again. Their performance was initially much worse, as expected, but improved over time. The results show that a T-maze task can be used to assess cognition in neonatal piglets.

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But developing the T-maze task was itself a challenge. “[T]here were a lot of things that went wrong that we didn't predict,” Johnson indicated in a press release. For example, the piglets ignored the food rewards that the researchers initially offered but were finally motivated to perform the maze task when the reward was changed to chocolate milk. And the researchers had to add a 'start box' from which the piglets could enter the maze, because the piglets reacted badly when researchers carried them into the maze in initial trials.

Johnson's group plans to use the MRI and T-maze techniques to evaluate the effects of early life exposure to stressors on postnatal brain development. “This is the type of interesting question we can pursue now that the piglet model is in place,” he said.