Elsevier

Brain and Language

Volume 92, Issue 3, March 2005, Pages 234-239
Brain and Language

Cerebral lateralization and general intelligence: Gender differences in a transcranial Doppler study

https://doi.org/10.1016/j.bandl.2004.06.104Get rights and content

Abstract

The present study evaluated cerebral lateralization during Raven’s progressive matrices (RPM) paradigm in female and male subjects. Bilateral simultaneous transcranial Doppler (TCD) ultrasound was used to measure mean blood flow velocities (MBFV) in the right and left middle cerebral arteries (MCAs) in 24 (15 females and 9 males) right-handed normal subjects. The female subjects used a left hemisphere strategy, while males used a right hemisphere strategy to successfully solve RPM tasks. This implies that general intelligence is associated with neural systems within one hemisphere that are accessible to a variety of cognitive processes.

Introduction

The determinants of human performance have been a subject of intense debate for over a century. Spearman in 1904, put forward the idea that measures of performance or success in diverse cognitive tests show a pattern of almost universal positive correlation (Jensen, 1987; Spearman, 1904, Spearman, 1923, Spearman, 1927). He postulated the hypothesis of a general intelligence or g factor making some contribution to success in diverse forms of cognitive activity. Subsequently, two contrasting postulates on cortical localization of intelligence were put forward. The first proposes that, processing of any task receives contribution from a large set of components or information-processing functions (Lashley, 1921, Lashley, 1929; Satz, Strauss, & Whitaker, 1990; Thomson, 1951; Thurstone, 1938, Thurstone, 1940). Therefore, any two tasks are likely to share at least some components, giving rise to universal positive correlation. This hypothesis assumes that, general ability is diffusely represented on the whole cortex, and injury to any region of the brain produces an intellectual decrement. Conversely, the second, so-called hierarchic hypothesis postulates that, in the course of evolution some area of the brain has gained a dominant role in sustaining general intelligence (Basso, De Renzi, Faglioni, Scotti, & Spinnler, 1973).

Snow, Kyllonen, and Marshalek (1984) have classified intelligence tests by task complexity, into tests at the center and tests at the periphery. Psychometric tests including RPM (Raven, 1938) and other complex reasoning tests were classified as tests at the center, while simpler tests were placed at the periphery. Applying this construct, irrespective of the views held by both hypotheses, the centrality of the RPM emerges in either case.

Furthermore, it has been suggested that RPM is a good test of intelligence, and should account for a great deal of the reasoning in other tests (Carpenter, Just, & Shell, 1990). It has been suggested that the neural substrate for intelligence lies within prefrontal cortex (Prabhakaran, Smith, Desmond, Glover, & Gabrieli, 1997), and post-rolandic structures (Basso et al., 1973). Recently, positron emission tomography studies have shown selective recruitment of lateral prefrontal cortex in one or both hemispheres (Duncan et al., 2000). Studies of cerebral lateralization of intelligence may implicate one hemisphere, or both, if general abilities were diffusely represented.

Cerebral lateralization could be studied using TCD (Bulla-Hellweg, Vollmer, Götzen, Skreczek, & Hartje, 1996; Cupini et al., 1996; Droste, Harders, & Rastogi, 1989; Evers, Dannert, Rodding, Rotter, & Ringelstein, 1999; Hartje, Ringelstein, Kistinger, Fabianek, & Willmes, 1994; Kelley et al., 1992; Markus & Boland, 1992; Njemanze, 1991, Njemanze, 1996, Njemanze, 2002, Njemanze, 2004; Njemanze, Gomez, & Horenstein, 1992; Rihs, Gutbrod, Steiger, Sturzenegger, & Mattle, 1995; Silvestrini, Troisi, Matteis, Razzano, & Caltagirone, 1994; Varnadore, Roberts, & McKinney, 1997; Vingerhoets & Stroobant, 1999). Studies with TCD have been cross-validated by functional MRI (Schmidt et al., 1999), and reproducibility assessed (Knecht et al., 1998).

The purpose of the present study is to evaluate cerebral lateralization during RPM tasks in females and males. It is postulated that general intelligence is associated with neural systems represented in one hemisphere that are accessible to a variety of cognitive processes. Consequently, unilateral representation of general intelligence will cause MBFV changes in ipsilateral MCA during performance of intelligence tasks. More specifically, the present study evaluates MBFV changes in both MCAs during performance of RPM tasks in both female and male subjects.

Section snippets

Subjects

The studied group included 24 normal volunteers, 15 female and 9 male. Mean age was 25.08 ± 3.16 years (range 21–33); females (25.47 ± 3.5 years) did not differ from males (24.44 ± 2.5 years). All were right-handed as determined using the Edinburgh handedness inventory (mean laterality quotient was 100) (Oldfield, 1971). Subjects had no history of neurological or cardiovascular or respiratory diseases. None was under medication, including contraceptive pills for females or recreational drugs. All

Results

The data obtained with means ± SD and Scheffé test probabilities for post hoc analysis for the different groups are shown in Table 1. The mean Correct score was 50.1 ± 14% for all subjects, and the mean for female subjects did not differ from male (p > .05). The design was a two-way MANOVA comprising: two levels of ANSWER (Wrong and Correct) and two levels of GENDER (Female and Male). There was a main effect of GENDER [F(1,1148) = 26.4, p < .0000003, MSe = 87.6]. There was no main effect of ANSWER (p > 

Discussion

Overall, these results demonstrate that for successful resolution of RPM tasks, females used a left hemisphere strategy while males used the right hemisphere. This implies that general intelligence is associated with neural systems within one hemisphere that are accessible to a variety of cognitive processes. These findings support the hierarchical hypothesis, and agree with results of recent studies, using positron emission tomography (Duncan et al., 2000) and fMRI (Prabhakaran et al., 1997).

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