Piglets in mazes provide insights into human cognitive development

URBANA -- Events that take place early in life almost certainly have consequences for later cognitive development. Establishing the connections is difficult, however, because human infants cannot be used as laboratory subjects.

Rodney Johnson and his collaborators have developed an alternative model for studying infant brain development. Assistant professor Ryan Dilger and I became interested in establishing the neonatal piglet as a model of human brain and cognitive development 3 or 4 years ago, he said.

The idea came to Johnson when a former student, who was working for an infant formula company, asked about finding ways to determine differences in cognitive development between breast-fed infants and infants fed on formula.

Human breast milk is the gold standard, but not every infant can be breast fed. A major goal for many infant formula companies is to improve the formulation to capture all of the benefits of breast milk, he explained.

Johnson and his group had been working with rodent models to study learning and memory; they also had done some research looking at infectious disease in pigs. They wondered if it would be possible to develop tests to look at learning and memory using neonatal piglets.

It seemed like a reasonable idea because the growth and development of the piglet brain is similar to that of the human brain. The brain growth spurt is a perinatal event in both humans and pigs. At birth, the human brain is about 25 percent of adult size. In the first 2 years of life, it reaches 85 to 90 percent of adult size. The piglet brain grows in a similar way in a shorter time.

Johnson's team first developed structural MRI methods for quantifying brain volume in the neonatal piglet. They then used these techniques to determine total brain and brain region volumes in a cohort of male and female domestic pigs, taking repeated measurements every 4 weeks starting at 2 weeks of age and finishing at near sexual maturity at 24 weeks of age.

They found that at 4 weeks, the piglet brain had grown to approximately 50 percent of its maximum volume, and it continued to grow rapidly for the next 8 weeks. Human infant brains grow in a similar way in the postnatal period. The results suggested that environmental insults during this period could affect brain structure and function.

The researchers' next task was to develop a test to assess the piglets' learning and memory, using a T-maze. They thought that this would be easy. They were wrong.

It actually turned out to be very complicated because there were a lot of things that went wrong that we didn't predict, said Johnson. For example, when we first started these studies, we used things like Skittles and apple slices as a reward because that's what people using older pigs had done.