A Genetic Investigation of the Covariation Among Inspection Time, Choice Reaction Time, and IQ Subtest Scores

Abstract

Information processing speed, as measured by elementary cognitive tasks, is correlated with higher order cognitive ability so that increased speed relates to improved cognitive performance. The question of whether the genetic variation in Inspection Time (IT) and Choice Reaction Time (CRT) is associated with IQ through a unitary factor was addressed in this multivariate genetic study of IT, CRT, and IQ subtest scores. The sample included 184 MZ and 206 DZ twin pairs with a mean age of 16.2 years (range 15-18 years). They were administered a visual ( -figure) IT task, a two-choice RT task, five computerized subtests of the Multidimensional Aptitude Battery, and the digit symbol substitution subtest from the WAIS-R. The data supported a factor model comprising a general, three group (verbal ability, visuospatial ability, broad speediness), and specific genetic factor structure, a shared environmental factor influencing all tests but IT, plus unique environmental factors that were largely specific to individual measures. The general genetic factor displayed factor loadings ranging between 0.35 and 0.66 for the IQ subtests, with IT and CRT loadings of −0.47 and −0.24, respectively. Results indicate that a unitary factor is insufficient to describe the entire relationship between cognitive speed measures and all IQ subtests, with independent genetic effects explaining further covariation between processing speed (especially CRT) and Digit Symbol.

A non-invasive method to relate the timing of neural activity to white matter microstructural integrity

“…Individual differences in white matter physiology, particularly myelination have been proposed to contribute to variation in information processing speed (Luciano et al 2004) consistent with recent reports of correlations between FA and cognitive reaction time (Bucur et al 2007;Gold et al 2007;Madden et al 2004;Manoach et al 2007;Nestor et al 2007;Tuch et al 2005;Westerhausen et al 2006). Here we report relations between FA and the latency of evoked neural responses, which are presumably more proximal measures of neuronal function than are behavioral measures of latency.…”

“…A recently developed imaging technique, diffusion tensor imaging (DTI), can be used to investigate whether individual differences in the microstructural integrity of white matter tracts contributes to inter-individual variability in the timing of neural activity. White matter physiology, particularly myelination, has been proposed to contribute to Individual differences in cognitive processing speed (e.g., Luciano et al 2004) based on the wellestablished role of myelin thickness and axon diameter in determining conduction velocity (Waxman 1980). Recent reports of relations between DTI measures of fractional anistropy (FA) -an indirect measure of myelination (Harsan et al 2006) and other WM microstructural properties (Beaulieu 2002) -and cognitive reaction time support the proposal of a white matter contribution to variability in processing speed (Bucur et al 2007;Gold et al 2007;Madden et al 2004;Manoach et al 2007;Nestor et al 2007;Tuch et al 2005;Westerhausen et al 2006).…”

Genome-wide Scan of IQ Finds Significant Linkage to a Quantitative Trait Locus on 2q

“…The findings from behavioural genetic studies are somewhat aligned with this view in that verbal IQ shows a larger contribution to variation from the common environment than does performance IQ/visuo-spatial ability (Casto et al, 1995;Rietveld et al, 2000;Wainwright et al, 2004). Further distinction between verbal and performance abilities is provided by results which show independent verbal and performance genetic factors in addition to the general genetic cognitive factor (Luciano et al, 2004a;Petrill et al, 1996a;Rijsdijk et al, 1998). Specific genetic influences on individual IQ subtests tend to be significant, but small in magnitude (Luciano et al, 2003;Pedersen et al, 1994).…”

Whole genome association scan for genetic polymorphisms influencing information processing speed

“…Psychometric speed measures, such as digit symbol, contribute to the estimation of a person's full scale IQ, typically forming part of a first-order perceptual speed factor. Multivariate genetic analyses have found evidence for genetic pleiotropy among varied measures of processing speed (chronometric and psychometric) and, importantly, among speed and more complex cognitive abilities, notably IQ (Luciano et al, 2004;Rijsdijk et al, 1998). For chronometric speed measures, common genes have been shown to influence the variation in processing speed and IQ rather than there being a causal relationship between the two (Luciano et al, 2005), although in an older sample (50-89 years) and using psychometric speed measures a directional relationship from speed to spatial and memory abilities explained the genetic covariance (Finkel et al, 2009).…”

“…Some of these have been associated with psychiatric diseases characterised by cognitive impairment of some sort (e.g., dyslexia, Alzheimer's disease (AD)), while others are involved in metabolic syndromes which are known to have negative effects on cognition. The association with immune system related disorders is also interesting because a polymorphism in TNF-alpha (which encodes a proinflammatory cytokine) has been associated with processing speed in the elderly (Baune et al, 2008).The speed measures were inter-correlated, and in the Brisbane sample have been shown to be genetically related (Luciano et al, 2004), we therefore expected some overlap between these measures in the GWA results. Only one of the top hits overlapped across measures (2-choice and 8-choice RT) and this SNP was not located near any known gene.…”