To infer that someone's cognitive function is on the lower end of the spectrum by alluding to "Sped". Sonic is widely regarded as a very speedy character and sonic is an attempt to play on the word sped. Attaching Sonic to the brain means sped brain for lack of a better phrase.
*Plays game*
John: "Kill him, he is one shot."
Bob: *Misses every shot*
John: Do you have sonic brain?
John: "Kill him, he is one shot."
Bob: *Misses every shot*
John: Do you have sonic brain?
by Pogopawee March 19, 2021
When some one is obsessed with the Sonic The Hedgehog franchise, and it consumes their mind. Stuck playing Sonic games every day.
by Wonkobonko April 19, 2023