p026fig01.18 Inverted U as a function of arousal. A Golden Mean at intermediate levels of arousal generates a combination of behavioral threshold, sensitivity, and activation that can support typical behaviors.  Both underarousal and overarousal lead to symptoms that are found in mental disorders.<BR>||  Behavior vs arousal.<TABLE border="1"><TR><TD><B>depression</b></td><TD><B>under-aroused</b></td><TD><B>over-aroused</b></td></tr><TR><TD><B>threshold</b></td><TD>elevated</td><TD>low</td></tr><TR><TD><B>excitable above threshold</b></td><TD>Hyper</td><TD>Hypo</td></tr></table> "UPPER" brings excitability "DOWN".