by Cassandra R. Elias
You might have lovingly looked down at your nursing babe -- the one with chubby cheeks, thigh rolls and milk drooling from a grinning mouth, saying, "You're my cute little piggy!"
It turns out that your metaphor has some merit.
Besides, eating noisily and looking cute, piglets and babies both experience a period of rapid brain growth soon after birth.
Events in early life almost certainly affect a child's later cognitive development. Researchers find establishing the connections difficult because human babies can't be used as lab subjects for obvious reasons.
Rodney Johnson and his collaborators at the University of Illinois College of Agricultural have developed an alternative model for studying infant brain development. The idea came to Johnson when a student asked about finding ways to determine differences in cognitive development between breastfed infants and infants fed on formula.
"Human breast milk is the gold standard, but not every infant can be breastfed. A major goal for many infant formula companies is to improve the formulation to capture all of the benefits of breast milk," Johnson explained.
The group had been studying learning and memory using rodent models. They'd also done some research on infectious disease in pigs. Would it be possible to develop tests to look at learning and memory using baby pigs?
Johnson's team developed structural MRI methods to measure brain volume in the neonatal piglet. They took repeated measurements every 4 weeks starting at 2 weeks of age and finishing at near sexual maturity at 24 weeks of age.
Baby pigs and baby humans experience a burst in brain growth after birth. At 4 weeks, the piglet brain had grown to approximately 50 percent of its maximum volume. It continued to grow rapidly for the next 8 weeks. Human infant brains grow in a similar way, only slower.
Next researchers developed a test to assess the piglets' learning and memory, using a T-maze. They expected the task to be easy. They were proven wrong.
Things like candies or apple slices work well to motivate older piglets. These newborns had no interest in solid foods. They wouldn't work if the reward was the same as their regular food. The team found a treat they were very willing to work for -- chocolate milk.
The tests took place in a plus-shaped maze with one armed blocked off to form a "T" shape. Piglets were trained to locate the chocolate milk treat in a constant place and direction, using visual cues from outside the maze.
Once the piglets learned the maze, the reward moved to a new location. At first they chose the wrong direction, but choices improved over time.
The study demonstrates that the T-maze can be used to measure cognitive abilities.
Johnson and his collaborators will use these new tests to learn how nutrient deficiencies, infections and other stressors affect the human brain during its period of early, rapid growth.
"We want to know if this will alter the trajectory of normal development in a way that makes them more susceptible to behavioral disorders that occur later in life, such as autism and depression," Johnson said. "Exposure to environmental insults early in life may also reduce stress resilience," he added.
"There is a lot of interest in the concept of programming, the notion that things that occur early in life set that individual up for problems that occur many years later," he continued. "Because the pig brain grows so much like a human brain, we thought this could be a very attractive model."
The researchers have used the piglet model to demonstrate that an iron-deficient diet causes iron depletion in specific brain areas and is accompanied by cognitive deficits. They are using structural MRI and the T-maze task to study how viral pneumonia in the early neonatal period affects brain and cognitive development.
How do you feel about the study and comparing piglets to babies?