Department of General Psychology, University of Padua, Italy Peter Kramer, Dipartimento di Psicologia Generale, Università di Padova, Via Venezia 8, 35131 Padova, Italy E-mail: peter.kramer{at}unipd.it Psychologists and psychiatrists tend to be little aware that (a) microbes in our brains and guts are capable of altering our behavior; (b) viral DNA