CORRESPONDENCE LINK TO ORIGINAL ARTICLE is: how are inter-individual brain differences related to intra-individual brain differences? Beyond IQ comparisons: The answer to this question, which can be addressed with (quantitative and molecular) intra-individual training differences genetic studies and brain imaging, lies in determining whether intra-individual dif- Olivier Houdé ferences (for example, the executive training effects described above) take the same form in all individuals. If they do not, genes As stated by Deary, Penke and Johnson depends on intra-individual variability4. For involved in intelligence might be closely in their recent article (The neuroscience example, we carried out an imaging study to linked, through endophenotypes, to this dou- of human intelligence differences. Nature investigate what happened before and after ble system of differences both in children12,13 Rev. Neurosci. 11, 201–211 (2010))1, it is training in error inhibition (an executive and in adults. 5 important to recognize that people differ not function) in a deductive-logic task . We found Olivier Houdé is at the Department of Psychology, only in their general cognitive ability (that a clear shift (or switch) in regional cerebral Paris Descartes University, Sorbonne, 46 rue Saint- is, intelligence quotient (IQ)), but probably blood flow (rCBF) from the posterior part Jacques, 75005 Paris, France. also in how they use their brain to reach of the brain before training to the e-mail: [email protected] particular levels of performance. Going fur- pre frontal part after training. Hence, the doi:10.1038/nrn2793-c1 ther, we need to learn about how the same same brain can be used differently in 1. Deary, I. J., Penke, L. & Johnson, W. The neuroscience brains can be used differently for the same the same deductive-logic task. We also of human intelligence differences. Nature Rev. tasks. In differential and developmental found a similar change in rCBF from the Neurosci. 11, 201–211 (2010). 2. Lautrey, J. in Dictionary of Cognitive Science psychology, such phenomena are known as pre-training rest period to the post-training (ed. Houdé, O.) 98–100 (Psychology Press, New York, ‘intra-individual differences’2,3. rest period6. Such results provide insight into 2004). 3. Sternberg, R., Lautrey, J. & Lubart, T. Models of Human the intra-individual differences that lead the Intelligence: International Perspectives (American Intraindividual brain differences human brain towards logical intelligence7. Psychological Association, Washington, 2003). 4. Houdé, O. & Tzourio-Mazoyer, N. Neural foundations In their Review, Deary, Penke and Johnson of logical and mathematical cognition. Nature Rev. examine only inter-individual IQ dif- A double system of differences Neurosci. 4, 507–514 (2003). 5. Houdé, O. et al. Shifting from the perceptual brain to ferences. I agree with their definition of Interestingly, this so-called ‘fluid’ (as the logical brain: the neural impact of cognitive human intelligence as a general capability opposed to ‘crystallized’)8 aspect of intel- inhibition training. J. Cogn. Neurosci. 12, 721–728 (2000). that involves the ability to reason and think ligence — in this example, how the brain 6. Mazoyer, B., Houdé, O., Joliot, M., Mellet, E. & abstractly, but I disagree with their sole focus responds to training in error inhibition Tzourio-Mazoyer, N. Regional cerebral blood flow increases during wakeful rest following cognitive on inter-individual differences. In the field — differed between subjects. Indeed, a com- training. Brain Res. Bull. 80, 133–138 (2009). of reasoning and abstract thinking (that is, parison between subjects who were able or 7. Changeux, J.-P. The Physiology of Truth (Harvard University Press, Cambridge, 2004). logico-mathematical cognition), some brain unable to shift from making errors to logical 8. Cattell, R. B. Intelligence: Its Structure, Growth, and imaging studies have confirmed over the responses after error inhibition training Action (Elsevier Science, New York, 1987). 9. Houdé, O. et al. Access to deductive logic depends on past decade that human intelligence also showed that success in the deductive-logic a right ventromedial prefrontal area devoted to task involved (in subjects who were able to emotion and feeling: evidence from a training paradigm. NeuroImage 14, 1486–1492 (2001). shift) activation in the right ventromedial 10. Damasio, A. The Feeling of What Happens: Body and Glossary prefrontal cortex, which is known to sustain Emotion in the Making of Consciousness (Harcourt 9,10 Brace, New York, 1999). Executive function logical intuition . Together, these results 11. Fuster, J. Cortex and Mind: Unifying Cognition (Oxford Also called cognitive control, it includes inhibition (resisting argue for brain variability in human intel- University Press, New York, 2003). 12. Diamond, A., Briand, L., Fossella, J. & Gehlbach, L. habits, temptations or distractions), switching (adjusting to 11 ligence, dynamic-network cognition and Genetic and neurochemical modulation of prefrontal change) and working memory (mentally holding and using differential training effects. cognitive functions in children. Am. J. Psychiatry 161, information). 125–132 (2004). Considering this double system of intra- 13. Rueda, M., Rothbart, M., McCandliss, B., Endophenotype individual and inter-individual variability, Saccomanno, L. & Posner, M. Training, maturation, and genetic influences on the development of A quantifiable phenotype with an assumed intermediate the crucial question for the neuroscience of executive attention. Proc. Natl Acad. Sci. USA 102, role in the pathway from genes to complex phenotypes. human intelligence, beyond IQ comparisons, 14931–14936 (2005). NATURE REVIEWS | NEUROSCIENCE www.nature.com/reviews/neuro © 2010 Macmillan Publishers Limited. All rights reserved.