Most of the brain's signaling is excitatory — neurons telling other neurons to fire. The brain stays organized only because a counterweight system constantly says not yet, not here, not all at once. That counterweight is GABA.
GABA is the dominant inhibitory neurotransmitter in the central nervous system. About forty percent of synapses in cortex use it. When GABA binds its receptor on the receiving neuron, the receiving neuron becomes less likely to fire. That is the entire mechanism. It is not exciting. It is essential.
Remove the GABA brake and the brain seizes. That is not metaphor. Antibodies against the GABA-A receptor produce status epilepticus. Drugs that block GABA-A — picrotoxin, bicuculline — produce uncontrollable convulsions in the laboratory. The system runs to runaway excitation in seconds.
Three classes of drugs work by enhancing the GABA brake. Benzodiazepines bind a site on GABA-A and increase the receptor's response to GABA when GABA is present — they are positive allosteric modulators, not agonists. Barbiturates work similarly, but at high doses can open the channel without GABA at all, which is why barbiturate overdose is so much more lethal than benzodiazepine overdose. Alcohol potentiates GABA-A through partly overlapping and partly distinct mechanisms.
All three produce sedation, anxiolysis, and muscle relaxation. All three produce tolerance with chronic use. And — most importantly clinically — all three produce a shared withdrawal syndrome. When the brain has adapted to chronic GABA potentiation by downregulating its own GABA tone, abrupt removal of the potentiator leaves the brake too weak to hold. The result is unopposed excitation: tremor, agitation, autonomic instability, and in severe cases, seizure and death.
This is why benzodiazepine withdrawal must be tapered, not stopped. It is why severe alcohol withdrawal is treated with benzodiazepines — you are substituting one GABA potentiator for another with a longer half-life and slower offset. And it is why combining alcohol with benzodiazepines is dangerous in the other direction: the brake becomes too strong, respiratory drive fails, and the patient stops breathing.
Hold onto the image. GABA is the brake. Everything that enhances it produces sedation and seizure-protection. Everything that removes it abruptly produces excitation and seizure-risk.