Brain diffusion study uncovers different connectivity patterns for high intelligence among boys and girls

May 22, 2007

Before the dawn of political correctness, there was a time when girls were made of sugar and spice and everything nice, and boys were made of snips and snails and puppy dog tails. Now, functional MRI is confirming that boys and girls really don't think alike. Brain structures and functions that facilitate intelligence in girls are different for boys.

Before the dawn of political correctness, there was a time when girls were made of sugar and spice and everything nice, and boys were made of snips and snails and puppy dog tails. Now, functional MRI is confirming that boys and girls really don't think alike. Brain structures and functions that facilitate intelligence in girls are different for boys.

Vincent J. Schmithorst, Ph.D, a research instructor in pediatric brain imaging at Children's Hospital in Cincinnati, based that conclusion on a study of 303 normal boys and girls ranging in age from five to 18.

His research, presented Monday, examined the relationship between narrative processing and interhemispheric functional connectivity in the brains of boys and girls.

The children were asked to perform a narrative comprehension task while undergoing perfusion MRI in a 3T scanner. The experiment involved listening to a 30-second story that was interrupted several times by random tones. The children's recollection of the story was tested afterward.

No significant differences were seen between boys and girls for age, IQ, or task performance, according to Schmithorst. Task performance was correlated with IQ.

By evaluating brain activation patterns, Schmithorst and pediatric neurosurgeon Dr. Scott L. Holland found functional activation in several regions of brain relevant to IQ, including the superior temporal gyri, posterior superior temporal gyri (including Wernicke's area, on the left hemisphere), the superior medial frontal gyri; and

the left inferior frontal gyrus (Broca's area).

Schmithorst and Holland then calculated a time course for each region and conducted a connectivity analysis.

They found that the more intelligent girls greatly depended on neuronal networks connected to the left posterior superior temporal gyrus, including Wernicke's area, and its right hemisphere analog.

In general, boys depended more on connectivity with Broca's area, and the right posterior superior temporal gyrus - the right hemisphere homologue of Wernicke's area.

"This pattern had a significant effect for boys, but either no effect or a negative effect for girls," Schmithorst said.

The Cincinnati Children's Hospital group also found an interaction between IQ, sex, and the connections linking Wernicke's area and its right hemisphere homologue and the right posterior superior temporal gyrus. In these regions, there was a large effect for the youngest boy, but it disappeared among the older boys.

 

"Our research shows that the picture is more complex than simply saying that girls are allied with a more connected architecture than boys," Schmithorst said. "It most likely reflects differences in their information-processing schemes."

The research on boys and girls extends from studies showing that the brains of women and men process information differently. Adult women generally perform more neural processes but have fewer neurons than men, Schmithorst said. He pointed to recent studies indicating that compared to men, there are more regions of a woman's brain where white matter density and N-acetylaspartate (NAA) concentrations correlate with IQ.

Correlations have been established between the shape of the splenium (posterior section) of the corpus callosum and cognitive performance. Published research based on diffusion tensor imaging at the Children's Hospital in Cincinnati has demonstrated differences in white matter microstructure.

"White matter microstructural differences also correlate with IQ. This suggests that white matter and connectivity in the brain may be important things to look at," Schmithorst said.

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