Never mind sugar and spice and puppy dogs’ tails; this is what divides the boys from the girls. A study based on the brain scans of youngsters has shown why girls prefer a best friend while boys gravitate towards packs.

The research found that girls are hardwired to understand individual relationships, while boys’ brains are more attuned to the complex dynamics and internal competition within a gang.

The study, conducted by researchers at the National Institute of Mental Health in the United States, gauged the effects of a process familiar to many households: children becoming more interested in interacting with their peers as they grow older.

The study used magnetic resonance imaging scanners to monitor the brains of 34 young people, aged nine to 17, as they were shown pictures of new people they could choose to meet. The tests showed that the circuitry in the brain responsible for sizing people up became more active in girls as their age increased, but not in boys.

Daniel Pine, the child psychiatrist who led the study, says the social differences between girls and boys intensify around adolescence.

“One-on-one individual relationships tend to become very important for girls around adolescence, while aspects of relationships that manifest in competitions, such as in sporting events, become very common among boys,” he said.

The scans suggest that as girls progress from childhood to adolescence, certain areas of their brain become increasingly stimulated when they are faced with a one-to-one social encounter.

If the girl is interested in the person, her hypothalamus (associated with hormone secretion), hippocampus (linked to learning), insula (which affects feelings) and nucleus accumbens (motivation and reward) are all activated. Boys, by contrast, show a slight decline in activity in these areas, indicating they are less stimulated by personal interactions than girls are.

“Complex behaviours such as how girls perceive social clues are shaped both by things that are intrinsic to people — part of who they are — but also by things out in the environment,” Pine said.

In addition, the research has provided clues as to why teenage girls are more prone to anxiety and depression. The parts of the brain that showed increased activity in social situations are also those related to depression.

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