Are faster brains also smarter?

Danielle Posthuma¹, Dorret I. Boomsma¹, G. Caroline C. van Baal¹, and Eco J.C. de Geus<sup>1

1</sup>Department of Biological Psychology, Vrije Universiteit, Amsterdam, The Netherlands

The idea that rapid central nervous system processing may correspond to a smarter brain has been proposed in earlier studies and has recently been confirmed by studies reporting positive relations between inspection time and IQ (Posthuma, D., de Geus, E.J.C., and Boomsma, D.I., submitted,Behav. Genet. Luciano, M., Smith, G.A., Wright, M.J., Geffen, G.M., Geffen, L.B., and Martin, N.G., in press, Intelligence). An alternative way to index speed of central nervous system processing is through the assessment of brain oscillations via electroencephalographic (EEG) recording. The dominant frequency (peak frequency) with which an adult human brain oscillates is around 10 cycles per second, but large differences exist in individual peak frequencies. Earlier studies have related peak frequency positively to intelligence, arguing that a faster oscillating brain reflects rapid information processing associated with higher intelligence. This theory, however, still needs to be proven. In the present study data from 271 extended twin families (688 participants) were collected as part of a large ongoing project on the genetics of adult brain function and cognition. IQ was assessed with the Dutch version of the WAIS-IIIR. Individual peak frequencies were picked according to the method described by Klimesch (Klimesch, W, 1999, Brain. Res. Rev. 29,169-195). Results of structural equation modeling indicated that both peak frequency and IQ were moderately to highly heritable (47% and 89% resp.). The phenotypic correlation between alpha peak frequency and IQ, however, was 0.02. These results suggest that peak frequency can not be used as an intermediate phenotype for IQ and that genetic loci important for the speed with which the brain oscillates are not related to IQ.