Although mental illnesses are primarily considered human disorders, investigators have attempted to model certain aspects of these disorders in animals to facilitate study of the underlying mechanisms. In such studies, researchers have noted that gene mutations can elicit certain abnormal behaviors in rodents that are very similar to isolated symptoms of mental illness in humans. These behaviors are called endophenotypes. Mutation of proteins that make up the postsynaptic density (PSD), a protein complex located at the ‘receiving’ end of a synapse or electrochemical connection between neurons, have been associated with cognitive defects and mental illnesses in humans. Similarly, mutations in PSD proteins in rodents can produce endophenotypes of mental illnesses. In a recent example, scientists from California Institute of Technology (Pasadena) and University of California, Los Angeles, describe endophenotypes of schizophrenia and autism spectrum disorders associated with null mutations of the gene encoding PSD protein densin-180 in mice.Lab Anim. (NY) 41, 6 (2012).