Gamma aminobutyric acid (or GABA for short) is an inhibitory neurotransmitter – it makes a neuron less likely to fire. GABA is important, not only in damping down brain activity, but also in controlling the precise timing of the neural impulses. It allows groups of neurons to synchronize their activity and transmit signals across the brain.
In a 2001 paper, John P Hussman speculated that GABA might be implicated in autism. To date, the evidence has been fairly indirect. However, a paper published last week in Current Biology claims to provide the first direct evidence linking autism symptoms to GABA dysfunction.