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Prenatal Testosterone Exposure and Hemispheric Asymmetry for Language and Spatial Memory: A Prospective Cohort Study
Autism is among the most severe, prevalent and heritable of all neurodevelopmental disorders. However, the factors causing autism are still unclear. Any aetiological theory must incorporate a plausible explanation of the core cognitive abilities of individuals with autism. It has long been speculated that developmental language difficulties may reflect failure to develop typical lateralisation. Hemispheric differences for function are among the most replicated findings in all of neuropsychology. Typically, the most crucial areas involved in language production are found in the left hemisphere, while the right hemisphere is more specialized for visuospatial functions. It has been suggested that differing concentrations of prenatal testosterone may underpin variations in cerebral lateralisation. However, research in this area has been limited by indirect measures of cerebral lateralisation (i.e. handedness) and prenatal testosterone (i.e. 2D:4D digit ratio).
Objectives:
The aim of this study is to investigate whether levels of circulating testosterone are associated with hemispheric asymmetry for language and spatial memory, using functional Transcranial Doppler Ultrasonography (fTCD) to measure hemispheric asymmetry. fTCD uses ultrasound to measure the blood flow in the left and right middle cerebral arteries. It was hypothesised that higher fetal testosterone concentrations would be associated with reduced left hemisphere activation for language and increased right hemisphere activation for spatial memory. A secondary aim is to examine whether cognitive abilities in adulthood are related to variations in prenatal testosterone and hemispheric asymmetry.
Methods:
Umbilical cord serum testosterone concentration was used as a surrogate measure of prenatal testosterone exposure. Samples taken immediately after delivery in a subset of the Western Australian Pregnancy Cohort Study were assayed for testosterone by liquid chromatography-mass spectrometry. fTCD sessions were conducted with subset of male participants from the cohort (20 high umbilical testosterone; 20 low umbilical testosterone). Recordings were taken while the participants completed a word generation task and a visual short-term memory task. Participants also completed a number of tasks assessing verbal and non-verbal abilities.
Results:
A Laterality Index (LI) was calculated by computing the relative difference in blood flow velocity between the two hemispheres. No significant differences were found between the high and low testosterone groups for word generation LI, t (38) = -.688, p = .50, or spatial memory LI, t (38) = -.244, p = .81. Verbal and non-verbal ability was not significantly related to prenatal testosterone concentration or hemispheric asymmetry (p> .05).
Conclusions:
Results show no relationship between umbilical testosterone levels and hemispheric asymmetry for language or spatial memory. This is in contrast with previous research using various proxy measures. In addition, cognitive abilities in typically developing adults were not related to prenatal testosterone exposure or hemispheric asymmetry. The current study is the first to have used a neuroimaging technique, to measure hemispheric asymmetry, in conjunction with a relatively direct measure of prenatal testosterone exposure. The findings indicate that prenatal testosterone exposure may not be related to the development of cerebral lateralisation.