Opioid peptides such as dynorphin and hemorphin likely contribute to imbalances in excitatory/inhibitory (E/I) function and subsequent cognitive deficits in AD, as they have been supposed to disrupt the activity of a number of neurotransmitters over the course of the disease, including glutamate, GABA, acetylcholine, and noradrenaline [204]. This evidence concerns the gene PDYN and Alzheimer disease.