NRG1 and Cognitive impairment: Interestingly, either haploinsufficiency of Nrg1 or overexpression of Nrg1 (Deakin et al., 2009, 2012; Kato et al., 2010) in mice can result in some types of cognitive deficits, which implies a possible U-shaped relationship between Nrg1 expression and cognitive function, which has been reported for the COMT gene (Honea et al., 2009).