A post mapping serotonin differences across three brain regions to explain why SSRIs "do not work the same for everyone" with autism is circulating. Unlike most infographics circulating on social media, this one traces almost exactly to a real, published postmortem study of human brain tissue. Here is what that study actually found.
The study behind the post
Researchers at Boston University examined postmortem brain tissue from autistic and non-autistic donors, measuring the density of serotonin-related proteins in three regions: the anterior cingulate cortex (ACC), the posterior cingulate cortex (PCC), and the fusiform gyrus. They looked at three specific markers: the serotonin transporter (5-HTT, the protein SSRIs act on), and two serotonin receptor subtypes (5-HT2 and 5-HT1A). The sample included 18 to 19 autistic adults and a similar number of non-autistic adults, plus a separate smaller group of 8 to 9 children in each group for the ACC.
The anterior cingulate cortex: where the differences show up
This is where the study found real, statistically significant differences. Serotonin transporter density was reduced across the autism group as a whole, most pronounced in adults. Serotonin 2 receptor density was reduced in autistic adults but not in autistic children, and while receptor density normally increases with age in non-autistic brains, it appeared to decrease with age in autistic brains. The third marker, the 1A receptor, showed no difference between groups.
Two regions that looked completely normal
In the posterior cingulate cortex and the fusiform gyrus, the researchers found no significant differences in any of the three markers between autistic and non-autistic tissue. This regional specificity is part of what makes the finding credible: the differences were not a blanket, brain-wide pattern, they were confined to one specific region involved in emotion regulation and social processing.
Why this matters for SSRI treatment
SSRIs work by blocking the serotonin transporter, the same protein this study found reduced in the anterior cingulate cortex of autistic adults, but not children. The researchers explicitly flagged this as a reason for caution when prescribing SSRIs to autistic children under 16, since a developing brain with a different serotonin trajectory may respond differently than an adult one. This lines up with decades of mixed clinical trial results for SSRIs in autism, where response has always looked inconsistent without a clear biological explanation, until findings like this one.
What this all adds up to
This is one postmortem study with a modest sample size, and postmortem tissue findings do not automatically predict how someone will respond to medication. But the regional and age-specific pattern it describes gives a genuine biological anchor for something clinicians have long observed anecdotally, that SSRIs affect autistic people inconsistently, and that age may be part of why.
If you are trying to understand your own neurotype before a conversation with a prescriber, our free autism screening can help you organize what you are noticing.
Source: Brandenburg et al., "Differential serotonin transporter (5-HTT) and 5-HT2 receptor density in limbic and neocortical areas of adults and children with autism spectrum disorders: implications for selective serotonin reuptake inhibitor efficacy," Journal of Neurochemistry (2019). Educational summary - not a diagnosis or medical advice. Talk to a prescriber before starting or stopping any medication.