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In Recent Decades Geschwind And Galaburda Hypothesised That The ...

In recent decades Geschwind and Galaburda hypothesised that the overproduction of prenatal testosterone may predispose the foetus to developing dyslexia later in life. They asserted (1985) that elevated exposure of testosterone in the foetus may detract from the development tof the left hemisphere of the brain. This may result in the promotion of the right hemisphere of the brain which can lead to enhanced spatial and mathematical abilities. Sluming and Manning (2000) found that the same kind of trend resulted in enhanced musical ability. Further, Van Gelder et al (2005) used 2D:4D as an indicator for prenatal testosterone and examined it with regard to dyslexia. Reading ability and digit ratio were explored for a sample of almost 400 children. The results showed that no significant differences were found regarding digit ratio and dyslexia, which indicates that there is no relationship between testosterone and 2D:4D for this study. The inconclusive nature of the results is solidified by the fact that no difference was found between the sexes.
Despite the results of the previous study, further evidence for the link between 2D:4D and cognitive functioning can be found in another study by Manning et al (2001). Manning explored the link between digit ratio and autism by measuring 2D:4D in 95 families recruited from the United Kingdom National Autistic Society. Previous research suggested that the condition of autism may arise as a result of contact with augmented levels of testosterone in the womb. It also suggested that there is a negative correlation between 2D:4D and prenatal testosterone. The researchers of this study found that the digit ratios of children with autism, and their families, were lower than those of the normal population. (Family members included parents and siblings.) Some of the children in the study suffered from Asperger syndrome (AS). Children with AS display many of the symptoms of autism but have average or even high intelligence levels. The individuals with AS had higher digit ratios than did children with autism but their ratios were still lower than the averages for the normal population. In addition to this, correlations between digit ratios of children with autism and those of their family members were positive. This study indicates that digit ratio could be an indicator for autism; this could in turn mean that testosterone is part of its aetiology, which would be particularly illuminating as the root causes of autism have long been a mystery.
Digit ratio has also been studied in terms of psychological dysfunction such as psychopathology. Williams et al (2003) looked at 2D:4D and developmental psychopathology in children of preschool age. Preschoolers commonly display behaviours such as low social cognition and hyperactivity, and these possible indicators of later psychopathology could be most evident in this group of children.

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