Twin Research

Articles

Genetics of Cognition: Outline of a Collaborative Twin Study

Margie Wrighta1 c1, Eco De Geusa2, Juko Andoa3, Michelle Lucianoa4, Danielle Posthumaa5, Yutaka Onoa6, Narelle Hansella7, Caroline Van Baala8, Kai Hiraishia9, Toshikazu Hasegawaa10, Glen Smitha11, Gina Geffena12, Laurie Geffena13, Shigenobu Kanbaa14, Akira Miyakea15, Nick Martina16 and Dorret Boomsmaa17

a1 Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia. margieW@qimr.edu.au

a2 Department of Biological Psychology, Free University, Amsterdam, The Netherlands.

a3 Faculty of Letters, Keio University, Tokyo, Japan.

a4 Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia; Cognitive Psychophysiology Laboratory, School of Psychology and Department of Psychiatry, University of Queensland, Brisbane, Australia.

a5 Department of Biological Psychology, Free University, Amsterdam, The Netherlands.

a6 Faculty of Letters, Keio University, Tokyo, Japan.

a7 Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia; Cognitive Psychophysiology Laboratory, School of Psychology and Department of Psychiatry, University of Queensland, Brisbane, Australia.

a8 Department of Biological Psychology, Free University, Amsterdam, The Netherlands.

a9 Department of Life Sciences (Psychology), University of Tokyo, Tokyo, Japan.

a10 Department of Life Sciences (Psychology), University of Tokyo, Tokyo, Japan.

a11 School of Psychology, University of Queensland, Brisbane, Australia.

a12 Cognitive Psychophysiology Laboratory, School of Psychology and Department of Psychiatry, University of Queensland, Brisbane, Australia.

a13 Cognitive Psychophysiology Laboratory, School of Psychology and Department of Psychiatry, University of Queensland, Brisbane, Australia.

a14 Yamanashi Medical University, Tokyo, Japan.

a15 Department of Psychology, University of Colorado, Boulder, USA.

a16 Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia.

a17 Department of Biological Psychology, Free University, Amsterdam, The Netherlands.

Abstract

Amultidisciplinary collaborative study examining cognition in a large sample of twins is outlined. A common experimental protocol and design is used in The Netherlands, Australia and Japan to measure cognitive ability using traditional IQ measures (i.e., psychometric IQ), processing speed (e.g., reaction time [RT] and inspection time [IT]), and working memory (e.g., spatial span, delayed response [DR] performance). The main aim is to investigate the genetic covariation among these cognitive phenotypes in order to use the correlated biological markers in future linkage and association analyses to detect quantitativetrait loci (QTLs). We outline the study and methodology, and report results from our preliminary analyses that examines the heritability of processing speed and working memory indices, and their phenotypic correlation with IQ. Heritability of Full Scale IQ was 87% in the Netherlands, 83% in Australia, and 71% in Japan. Heritability estimates for processing speed and working memory indices ranged from 33–64%. Associations of IQ with RT and IT (−0.28 to −0.36) replicated previous findings with those of higher cognitive ability showing faster speed of processing. Similarly, significant correlations were indicated between IQ and the spatial span working memory task (storage [0.31], executive processing [0.37]) and the DR working memory task (0.25), with those of higher cognitive ability showing better memory performance. These analyses establish the heritability of the processing speed and working memory measures to be used in our collaborative twin study of cognition, and support the findings that individual differences in processing speed and working memory may underlie individual differences in psychometric IQ.

(Received December 11 2000)

(Accepted December 12 2000)

Correspondence:

c1 Address for Correspondence: Margie Wright, Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, QLD, 4029, Australia.

Metrics