Simplify the following text for a Grade 13 native English-speaking person.
Original: Î - Aminobutyric acid ( GABA ) ( ; gam-uh uh-mee-noh-byoo-tir-ik as-id ; or the acronym ) is the chief inhibitory neurotransmitter in the mammalian central nervous system .
Simplified: In humans , GABA is also inhibitory neurotransmitter in the mammalian central nervous system .