ERBB4 and Cognitive impairment: Furthermore, because both Nrg1 and ErbB4 are highly abundant in the hippocampus (Corfas et al., 1995; Law et al., 2004; Vullhorst et al., 2009) and also because some hippocampus-dependent cognitive deficits were observed in Experiment 1, we examined GFP-labeled CA1 pyramidal neurons to elucidate any neuromorphological alterations of excitatory neurons in the hippocampus.