By James Tillman

WASHINGTON, DC, October 28, 2009 (—Recent animal research backs previous sociological research by indicating that children raised by single mothers may experience reduced brain development, leading to an increase in aggressive behavior, according to an article in the Wall Street Journal.

The findings come from research on degus, which are small rodents related to guinea pigs.  Degu parents usually raise their pups together.  When deprived of their father, however, degu pups exhibited developmental changes in the amygdala, the part of the brain related to emotional responses and to fear, and in the orbitofrontal cortex, or OFC, the brain's decision-making center.

According to Anna Katharina Braun, director of the Institute of Biology at the Otto von Guericke University in Magdeburg, the balance between these two parts of the brain is critical to normal emotional and cognitive functioning: if the OFC isn't active, the amygdala “goes crazy, like a horse without a rider.” 

Thus, an analysis of the degus' behavior indicated that the fatherless animals showed more impulsive behavior, and engaged in more play-fighting or aggressive behavior with their siblings than did the pups raised by both parents.

In the study, published in the journal Neuroscience, half the degus were raised by two parents while the other half were raised by a single mother after the father was removed from the cage one day after the birth of his offspring.

In two-parent families, Dr. Braun and her colleagues found that degu mothers and fathers cared for their pups in similar ways, including sleeping next to or crouching over them, licking and grooming them, and playing with them. 

In single-parent families, on the other hand, the frequency of the mother's interaction with her pups did not change greatly, which meant that those pups experienced significantly less touching and interaction than those with two parents.

Researchers then looked at the neurons – the cells in the body that process and transmit information – of pups at day 21, when they were weaned from their mothers, and at day 90, which is considered adulthood for the species.

Neuron functioning is related to the number and length of neurons' dendrites – branch-like protrusions from neurons related the handling of information.  Dendritic spines (twig-like protrusions from a neuron's dendrites) also help the neuron receive messages from other neurons.

The researchers found that at 21 days, fatherless animals had less dense dendritic spines than did animals raised by both parents.  Although the density of the spines was the same by day 90, the length of some types of dendrites was significantly shorter in some parts of the brain, even in adulthood, in fatherless animals.

“It just shows that parents are leaving footprints on the brain of their kids,” says Dr. Braun.

The wiring between certain brain regions in the degus is very similar to that in humans.  “So on that level,” says Dr. Braun, “we can assume that what happens in the animal's brain when it's raised in an impoverished environment … should be very similar to what happens in our children's brain.”

Other researchers have found similar results in different animals.  Xia Zhang of the University of Ottawa and his colleagues in China have found that voles separated from their fathers exhibited more anxious behavior and were less social than those who were not separated.  Their study was published in July in the journal Behavioral Processes.

Such neurological research backs a host of sociological studies that have tracked the negative developmental effects of single-parent households.

For instance, a 2004 study in the Journal of Research on Adolescence indicated that growing up without a father was associated with higher odds of incarceration later in life, even after controlling for other factors.  Those who grew up in households without ever experiencing the presence of a father tended to have the highest odds of incarceration.

Similarly, a 2006 study in the Journal of Divorce and Remarriage indicated that adolescents living in single-parent families were more likely to report depressive tendencies and use of illegal drugs when compared to those living in families with two biological parents.

Approximately 25% of the children living in the US live with only one parent, according to a 2008 press release by the United States Census Bureau.


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