“…More specifically, biological variables that have been associated with low self-esteem and depression include reduced hippocampal volume (Pruessner et al, 2005), higher cortisol stress response (Pruessner, Hellhammer, & Kirschbaum, 1999), specific patterns of prefrontal electroencephalography alpha activity (De Raedt, Franck, Fannes, & Verstraeten, 2008;Putnam & McSweeney, 2008), variations in the oxytocin receptor gene (Saphire-Bernstein et al, 2011), and reduced cardiac vagal tone (Martens, Greenberg, & Allen, 2008). Future research should examine whether these factors contribute (e.g., as third variables, moderators, or mediators) to the explanation of the effect of low self-esteem on depression (for an example, see Scarpa & Luscher, 2002). We can only speculate as to why depression and anxiety are differentially linked to low self-esteem.…”