Brain networks for working memory and factors of intelligence assessed in males and females with fMRI and DTI

Article history: Received 24 September 2009 Received in revised form 21 March 2010 Accepted 22 March 2010 Available online 28 April 2010 Neuro-imaging studies of intelligence implicate the importance of a parietal–frontal network. One unresolved issue is whether this network underlies a general factor of intelligence (g) or other specific cognitive factors. A second unresolved issue is whether males and females use different parts of this network. Here we obtained intelligence factors (general, speed of reasoning, spatial, memory, andnumerical) froma large set of tests completedby6929 young adults, 40ofwhom(21 males, 19 females) also completed DTI and fMRI during a working memory n-back task. Within brain areas activatedduring this task, correlationswere computed betweenpercent activation and scores on the intelligence factors. Themain findings were: (1) individual differences in activation during the n-back task were correlated to the general intelligence factor (g), as well as to distilled estimates (removing g) of speed of reasoning, numerical ability, and spatial ability, but not to memory, (2) the correlations were mainly bilateral for females and unilateral for males, and (3) differences in the integrity of the axonal connections were also related to the functional findings showing that integrity of interhemispheric connections was positively correlated to some intelligence factors in females but negatively correlated in males. This study illustrates the potential for identifyingaspects of the neural basis of intelligenceusing a combinationof structural and functional imaging. © 2010 Elsevier Inc. All rights reserved.