COMT and Cognitive impairment: Accordingly, several drug classes, based on their modulation of specific components of catecholamine neurotransmission, have been developed or are proposed for the treatment of cognitive impairments in psychiatric disorders, including D1R agonists, D3R antagonists, Alpha 2A adrenergic receptor agonists and antagonists, norepinephrine transporter blockers, and catechol-O-methyltransferase inhibitors (Millan et al., 2012).