Smooth Brain is a slang expression for the disorder known by medical professionals as Lissencephaly.
It is a disorder where the patient’s brain lacks gyri or brain folds, resulting in a smooth appearance for the center of the nervous system.
Online, the phrase “Smooth Brain” is used both humorously and as an insult to call someone intellectually impaired. It is also frequently included in image macros and GIFs, mocking people with a low IQ.
The phrase “Smooth Brain” started emerging in the English language in the 19th century, especially after 1850, predominantly in medical environments, however it needed over a century to become a widely accepted affront.
It was first defined as an insult on Urban Dictionary in 2011, and began appearing on forums and message boards like Reddit and 4chan in the following years.
Memes concerning the phenomenon of lissencephaly started emerging in 2019, on sites like me.me, Reddit or Imgflip.
The phrase started seeing more widespread use following the image macros, becoming a new trend among insults, widely embraced across the web.
“Smooth Brain” has become a staple of internet culture, and today it may be encountered in the comment section of any social media site, as well as YouTube videos and a wide array of image macro memes across the web.