Differential effects of prenatal testosterone on lateralization of handedness and language

Differential effects of prenatal testosterone on lateralization of handedness and language

Lust, Jessica M; Geuze, Reint H; Vsn de Beek, Cornielieke; Cohen-Ketten, S; Peggy T; Bourna, Anke; Groothuis, Ton G.G. Neuropsychology, Vol 25 (5), Sep 2011, 581-589. doi: 10.1037/a0023293

Research has shown that prenatal exposure to testosterone may influence cerebral lateralization. This is well-supported in animal research. Two main theories have emerged for why this may be:

1.      Testosterone, most notably in males, will delay the growth of parts of the left hemisphere. Oppositely, this will promote the growth of the right hemisphere, possibly to the point of causing language and handedness to become predominant in the right hemisphere

2.      Larger corpus callosums are often found in males who don’t strictly favor one hand, indicating more hemisphere communication. This theory contrasts the first, saying that higher prenatal testosterone levels will decrease the corpus callosum and increase left hemisphere dominance for language and right handedness.

In this study, the researchers used samples of amniotic fluid from mothers in their 30’s to test for prenatal testosterone levels. Later, when the children these women were pregnant with were 6 years old, their functional lateralization was assessed.

The researchers hypothesized that there would be a shift toward left-handedness as a function of increased PT exposure, if the first theory was to be supported. They also hypothesized that there would be a shift toward right-handedness with increased PT exposure, if the second theory was to be supported. They finally predicted an increase in the strength of handedness as a function of increased PT.

There were 67 children, all tested by the same psychologist on ten measures of handedness appropriate for their age level, such as drawing, hammering, stirring, cutting, etc. Then, the children were tested on language lateralization. In a listening task, two different sets of three syllables were spoken into a child’s left and right ear simultaneously. The child would be instructed to pay attention to just one ear at a time and repeat the syllables back in order. The psychologist recorded accuracy.

The only significant result was a negative correlation between strength of handedness and PT. As PT increased, the strength of handedness decreased. This surprised the researchers. Research also seemed to indicate that higher PT levels related to stronger lateralization of language.