A recent study comparing personalities and brain scans of only children to children with siblings had surprising results
Researchers in China – a country well known for having enforced a one-child policy for more than 30 years – recruited 126 only children and 177 non-only children for the study.
According to the study paper, the participants were all right-handed, healthy individuals with no history of psychiatric or neurological disorders.
Each completed a self-report questionnaire and had their personality traits assessed based on a five-factor model of personality, including: neuroticism, extraversion, openness, agreeableness, and conscientiousness.
Creativity was assessed using a measure of divergent thinking, and MRI scans of participants’ brains were also collected.
Analyses were used to explore the association between grey matter volume and individual differences in behaviours.
Based on behavioural results alone, only children exhibited higher creativity scores and significantly lower agreeableness scores compared with the non-only children.
Analyses of the whole brain revealed that only children had greater supramarginal gyrus volumes than the non-only children, a section of the brain thought to be involved with language perception and processing.
Conversely, only children had smaller medial prefrontal cortexes and volume of the parahippocampal gyrus – a region that plays an important role in both spatial memory and navigation.
Creativity scores were significantly positively correlated with grey matter volume in the right supramarginal gyrus, while the agreeableness scores were significantly and positively correlated with grey matter volume mainly in the medial prefrontal cortex.
“Creativity refers to the ability to change existing thinking patterns, break with the present, and build something new. Only children might have more opportunities for independent activity, and independence is strongly related to creative thinking,” the authors suggest.
Meanwhile, “agreeableness has been linked to psychological mechanisms that allow for the understanding of others’ emotions, intention and mental states”, they say.
There were no significant differences in general intelligence found between the only children and non-only children.
“On the neural level, our results provide the first evidence that there are differences in anatomical structures … that may play an important role in emotional regulation and self-control between only children and non-only children.
“More broadly, our results may reveal that differences in the family environments between only and non-only children may contribute to the differences in the behaviour and anatomical structures between these two samples,” the researchers conclude.