While loss of NRG1-ErbB4 signalling is detrimental (Li et al. 2007; Agarwal et al. 2014), excessive NRG1-ErbB4 activity (as seen in schizophrenia) is also associated with synaptic dysfunction resulting from suppression of LTP-induced NMDA receptor function (Pitcher et al. 2011; Agarwal et al. 2014; Luo et al. 2014). This evidence concerns the gene ERBB4 and schizophrenia.