Serotonin and measured intelligence.
Blood serotonin does not predict IQ in typical adults, so high serotonin in autism is illness-linked, not a sign of cognitive level.
01Research in Context
What this study did
Researchers drew blood from healthy adults and gave them an IQ test.
They wanted to see if people with higher serotonin also scored higher.
The team checked each person twice to be sure the level was stable.
What they found
Serotonin numbers stayed the same inside one person, but they did not track with IQ.
High, low, or middle serotonin made no difference to the test score.
The link simply was not there in typical adults.
How this fits with other research
A year earlier, Pritchard et al. (1987) looked at autistic kids and also found no serotonin-IQ tie.
Together, the two papers show the brain chemical is not a ruler for smarts in either group.
Hansen et al. (1989) went a step further: they used a drug to lower serotonin in autistic children, yet IQ and behavior did not budge.
All three studies point to the same take-away—serotonin level and intelligence ride on separate tracks.
Why it matters
You can stop hunting for hidden meaning in a client’s serotonin report.
Whether the lab value is high, low, or average, it tells you nothing about how smart they are.
Spend your time on skill-based goals, not on chasing blood numbers that do not predict learning.
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02At a glance
03Original abstract
Blood serotonin (5HT) has been shown to be elevated in 30% of autistic children and 50% of severely mentally retarded children. Ninety-eight normal adult subjects were studied to determine if there was an inverse relationship between whole blood 5HT in normal adults of average and above-average intelligence. There was a trend toward a negative correlation between whole blood 5HT and Vocabulary scores that would not account for hyperserotonemia in autistic or mentally retarded individuals. Female subjects had significantly greater whole blood 5HT than male subjects. There was no difference in whole blood 5HT collected before and after volume depletion of 450 ml, providing further evidence of the intraindividual stability of whole blood serotonin levels. There was no relationship between age and whole blood 5HT in a group of normal adult subjects.
Journal of autism and developmental disorders, 1988 · doi:10.1007/BF02211873