Professor Trevor Robbins describes the GABA (or GABAergic) system, whose main function in the brain is inhibition.
The GABAergic system is one of the two important amino acid systems in the brain. The glutamate system is responsible for fast signaling, for excitation. The GABA system is responsible for fast signaling inhibition. So, it is like the off switch in an electrical network, it responds very quickly.
The cortex, the neocortex and the hippocampus are made up of networks of neurons which work by on and off switches, by glutamate and GABAergic neurons. So, GABA is a very interesting neurotransmitter because drugs such as the benzodiazepines or Liprium work by affecting GABA. They enhance GABAergic function and hence produce anxiolysis or anxiety reduction.