Understanding and being able to read facial expressions of other people is a key to successful social interaction. It seems the male hormone testosterone can impair the process of identifying and empathizing and it can interact with the brain during fetal development manifesting itself with a telltale indicator: second digit-to-fourth digit ratio on the right hand. Testosterone modifies the brain’s processing capacity, which in turn alters social behaviors. A study was conducted to examine whether oral testosterone administration to females would impair their ability to identify people by their facial expressions.
Autism is a disorder that manifests in childhood where the child lacks the mental ability to identify and read others’ facial expressions, thereby affecting social behavior. The disorder is more commonly seen in males and literature suggests that exposure to testosterone during fetal growth negatively impacts the brain. This gets reflected in their childhood development of various cognitive skills. Moreover, studies also suggest that fetal exposure to testosterone is reflected in a lower length ratio of index to ring finger of the right hand. Males who are generally exposed to intrauterine testosterone more than females have a lower index-to-ring finger ratio. Based on these findings, the authors hypothesized that if testosterone was administered to adult females who have lower index-to-ring finger length ratio, their cognition ability to identify people by facial expression would be impaired.
* Female volunteers in the age range of 20 to 25 years were recruited. They received testosterone in the first phase and then a placebo in the second phase of the study.
* Volunteers underwent a computerized generated test “reading the mind in the eyes (RMET),” where pictures of individuals with different facial expressions were shown to the participants one at a time.
* Volunteers described the possible expression of each photo by ticking one of the four sentences that best described the expression.
* Finger ratio was measured from a scanned photo of the right hand of the volunteers.
* Testosterone administration significantly affected the volunteer’s ability to read facial expressions compared to placebo, as shown by a decrease in the performance in “the reading the mind in the eyes” test.
* This inability was strongly correlated with volunteers who had a lower digit ratio, suggesting a high prenatal testosterone exposure.
* A negative correlation was also found in the placebo group, between salivary testosterone and the ability to read facial expressions.
Similar studies, in which the female hormone oxytocin was administered to both young healthy males and males with autism and Asperger syndrome showed an improvement in recognition of facial expressions. With a high possibility of interdependence between steroid hormones (e.g. testosterone) and peptide hormones (e.g. oxytocin) in the development of autism, further studies should have an integrative approach to fully understand autism.
The study showed that a lower digit ratio (which suggests a high prenatal brain processing by testosterone) in an individual strongly correlates with the impaired ability to infer facial expressions when exposed to testosterone. The findings perhaps suggest the underlying reasons autism is a male prevalent disorder. The fetal brain processed by testosterone negatively affects social functioning behavior during development in early adolescence and adulthood, where the testosterone levels are again increased. The “data provide unique insights into the psychobiology of social intelligence and open up opportunities for further research in human social neuroendocrinology,” conclude the study authors. Further research needs to be conducted to look into the effect of similar correlation on other cognitive behaviors like sexual desire or social dominance.
For More Information:
Testosterone Administration Impairs Cognitive Empathy in Women Depending on Second-to-Fourth Digit Ratio
Publication Journal: PNAS, January 2011
By Jack van Honk; Dennis J. Schutter; Utrecht University, Utrecht, The Netherlands, and the University of Cape Town, South Africa
*FYI Living Lab Reports Are Summaries of the Original Research.