Insomnia can be based on or aggravated by a neurotransmitter imbalance. Neurotransmitters are chemicals that allow nerve impulses to travel from one nerve cell to another, and include serotonin, acetylcholine, GABA, and the sex hormones testosterone and estrogen. Sleep disorders and such symptoms as depression are especially linked with an imbalance in the neurotransmitter serotonin. Serotonin is manufactured by the body from the amino acid tryptophan. Herbs and foods high in tryptophan that help restore proper serotonin levels in the brain are St. John’s wort, quinoa, spirulina, and soy products.