Abnormal levels of __________ are linked to anxiety disorders, seizures, and insomnia.

GABA (gamma-aminobutyric acid) is the brain’s main inhibitory neurotransmitter: it helps calm neural activity. Abnormally low GABA activity can contribute to excessive brain activity, which is associated with anxiety, seizures, and insomnia. The correct choice is GABA (gamma-aminobutyric acid).

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