Myths of neuropsychology: Intelligence, neurometabolism, and cognitive ability

Recently, Dodrill (1999) revised a previously described "Myth of neuropsych ology'' (1997) to state: "Just as below average performances on neuropsycho logical tests are found when intelligence is below average, to that same de gree above average performances on neuropsychological tests are expected wh en intellectual abilities are above average.'' This study addresses the rel ationship between intellectual and neuropsychological performance in the co ntext of Magnetic Resonance Spectroscopy (MRS) measurements of the neuromet abolite N-acetylaspartate (NAA). When subjects were stratified by Full Scal e IQ (Average, High Average, Superior) they differed significantly in terms of total neuropsychological performance [F(2,47 = 17.63; p <.001] and the neuronal marker NAA [F( 2,47) = 3.25; p <.05]. Regression analysis across g roups demonstrated that FSIQ and NAA were independently related to Total z- score [F(1,47) = 29.43; p <.0001] and accounted for over half the variance (r(2) of model =.56). The concurrent relationship of FSIQ and NAA to total neuropsychological performance suggests that the relationship between measu res sensitive to intellectual ability and neuropsychological performance is real, and does not reflect arbitrary psychometric or scaling properties of the WAIS-III.