A previously proposed hypothesis for the opposite effects of the COMT Val158Met genotypes on cognition is that there may be an optimum level of dopamine signaling in a healthy individual’s brain and that healthy individuals with the val/val genotype and those individuals with schizophrenia start off on different points on an inverted-U curve model and thus are affected differently by the COMT Val158Met genotype [27]. The gene discussed is COMT; the disease is schizophrenia.