neurosciencestuff:

Show your fingers to a neuroscientist

By comparing your index and ring fingers, a neuroscientist can tell if you are likely to be anxious, or if you are likely to be a good athlete.

Testosterone: It is well-known that adults whose index finger is shorter than their ring finger were exposed to greater amounts of testosterone when they were in the womb.

Both women and men with this characteristic are — on average — better
equipped to solve mentally demanding 3D rotation tasks as adults. As a
group, they also have better physical and athletic abilities, but are
more prone to having ADHD and Tourette’s syndrome.

Why on earth is this the case?

Both boys and girls are exposed to testosterone in the womb. Everyone
has different levels of male and female sex hormones. Some men have a
lot of testosterone, some have less, and the same applies to women.
Women who have received a lot of prenatal testosterone don’t need much
testosterone as adults.

The level of testosterone in utero affects one’s finger length as an adult.

24 women and a drop of testosterone

“The relationship between the index finger and ring finger in
particular indicates how much testosterone you have been exposed to in
utero,” says Carl Pintzka, a medical doctor and researcher at the
National Competence Service for Functional MRI.

In his doctoral dissertation at NTNU, Pintzka investigated how the
brain functions differently
in women and men. As part of this study, he
tested an established theory about the significance of finger length and
how the brain works.

He measured the finger length of 42 women and gave half of them a
drop of testosterone. The other half were given a placebo. Afterwards,
the women had to solve various mental tasks.

Short index finger, more testosterone

“We could then look at how testosterone levels affect different
abilities in healthy women both in the womb and in adulthood,” says
Pintzka.

An index finger that is relatively short compared to the ring finger
indicates that one has been exposed to a lot of testosterone in utero,
whereas a relatively long index finger suggests a lower exposure to
testosterone in the womb.

“One mechanism behind this relationship is the difference in the
receptor density for oestrogen and testosterone in the various fingers
in utero. This relationship has also been shown to remain relatively
stable after birth, which implies that it’s strictly the foetal hormone
balance that determines this ratio,” says Pintzka.

More testosterone, better sense of place

The relationship between the index finger and ring finger in humans is associated with a variety of abilities in adulthood.

“The greatest effect has been found for various physical and athletic
measures, where high levels of prenatal testosterone are consistently
linked with better capabilities,” Pintzka says. “Beyond this we find a
number of uncertain results, but a general feature is that high levels
of testosterone generally correlate with superior abilities on tasks
that men usually perform better, such as various spatial tasks like
directional sense,” he adds.

Conversely, low levels of testosterone are associated with better
abilities in verbal memory tasks, such as remembering lists of words.
Foetal hormonal balance also likely affects the risk of developing
various brain-related diseases.

… but also more ADHD and autism

Pintzka says studies show that high levels of testosterone in utero
correlate with an increased risk of developing diseases that are more
common in men, such as ADHD, Tourette’s and autism. Low levels of
testosterone are associated with an increased risk of developing
diseases that are more common in women, like anxiety and depression.

His study primarily involved researching how testosterone affects
different spatial abilities in women. The women were asked to navigate a
virtual maze, and to mentally rotate different three-dimensional
objects.

More study needed

According to Pintzka, the study results indicate a trend towards a
positive effect of high testosterone levels on spatial abilities in
utero. He believes that a larger study would be able to show a
significant correlation. Furthermore, the results suggest that these
hormone levels are important both in utero and in adulthood.

In other words, no definite conclusions can be drawn quite yet.
Pintzka found no prenatal hormonal effects on study participants’
ability to navigate a virtual maze.

“The women who scored best on the mental rotation tasks had high
levels of testosterone both prenatally and in their adult lives, while
those who scored worst had low levels in both,” says Pintzka.

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