Subject: left-handers
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Left-handers are often excluded from neuroscience and neurogenetics studies in order to reduce variance in the data. In this Perspective from Nature Reviews Neuroscience, Willems et al. discuss the potential of studying this substantial but often-ignored portion of the population. (£) http://bit.ly/1eqq8Ya
Nature Reviews Neuroscience | Perspectives | Opinion

On the other hand: including left-handers in cognitive neuroscience and neurogenetics

Journal name:
Nature Reviews Neuroscience
Year published:
DOI:
doi:10.1038/nrn3679
Published online

Abstract

Left-handers are often excluded from study cohorts in neuroscience and neurogenetics in order to reduce variance in the data. However, recent investigations have shown that the inclusion or targeted recruitment of left-handers can be informative in studies on a range of topics, such as cerebral lateralization and the genetic underpinning of asymmetrical brain development. Left-handed individuals represent a substantial portion of the human population and therefore left-handedness falls within the normal range of human diversity; thus, it is important to account for this variation in our understanding of brain functioning. We call for neuroscientists and neurogeneticists to recognize the potential of studying this often-discarded group of research subjects.

At a glance

Figures

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  1. Hemispheric activation differences in left- and right-handers during action verb reading.
    Figure 1: Hemispheric activation differences in left- and right-handers during action verb reading.

    Participants were asked to read action verbs involving hand actions (for example, 'to throw') or non-hand actions (for example, 'to laugh'). The graph shows the differences in activation in the premotor cortex (Brodmann area 6) between the two conditions. In right-handed participants, the difference in activation between hand-related and non-hand-related action conditions was most pronounced in the left hemisphere, which conforms to their hand preference (that is, right-handers preferentially use their right hand for performing manual actions, and motor control of the right hand is mainly governed by the left motor cortex). In left-handers, the pattern was reversed. Error bars represent SEM. There was a statistically significant three-way interaction effect between hemisphere (left versus right), group (left-handers versus right-handers) and action verb (manual versus non-manual). Figure is reproduced, with permission, from Ref. 55 © (2010) SAGE Publications.

  2. Language and visuospatial activations in left-handers with typical and atypical language lateralization.
    Figure 2: Language and visuospatial activations in left-handers with typical and atypical language lateralization.

    Activation in the language network during a word-generation task is shown in blue. Left-handed individuals with typical language lateralization (panel a) show more activation in left-hemispheric language regions than in right-hemispheric regions, whereas the reverse is true for left-handed individuals with atypical, right-lateralized language function (panel b). A set of regions activated during a visuospatial attention task (shown in green) was also differentially lateralized in these two groups. In left-handed individuals in whom language is left-lateralized (typical), activation was most pronounced in the right hemisphere (panel a), whereas in left-handed individuals in whom language was right-lateralized (atypical), activation was most pronounced in the left hemisphere (panel b). This study was conducted in left-handers because of the greater variability in language lateralization in left-handers. By actively looking for atypically lateralized individuals within the left-handed population, the issue of co-lateralization of linguistic and visuospatial functions could be addressed. Figure is reproduced from Ref. 82.

  3. Left- and right-handers show differences in lateralization during face perception.
    Figure 3: Left- and right-handers show differences in lateralization during face perception.

    Parts of the extrastriate cortex are selectively sensitive to the perception of faces or bodies, and these areas are sometimes dubbed the fusiform face area (FFA), and the extrastriate body area (EBA) and fusiform body area (FBA), respectively. The FFA in particular is thought to be right-lateralized, and the figure shows that this may in fact not be the case for left-handers. Left- and right-handed participants were asked to view pictures of faces, bodies and chairs (control stimuli), and the extent of activation was quantified. The graphs show the extent of activation (in number of voxels on the y axis) in four extrastriate visual areas when participants viewed faces or bodies compared with the extent of activation during the viewing of chairs. a | The typical right-lateralization of the FFA in right-handers is absent in left-handers. b | Right-handers show a similar right-lateralization in the EBA, and left-handers again show no statistically significant lateralization in this area. c | There is no statistically significant lateralization in the FBA in either left-handers or right-handers. d | The human motion area MT (hMT), which is a visual area that is sensitive to motion, also did not show any lateralization effect of handedness. These findings indicate that right-lateralization does not occur in all functional areas in the visual system but is specific for the FFA and EBA in right-handers. Statistically significant differences between activity in the left versus right hemisphere are indicated by an asterisk. Figure is reproduced, with permission, from Ref. 99 © (2010) Oxford University Press.

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Affiliations

  1. Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands.
    Max Planck Institute for Psycholinguistics, 6525 XD Nijmegen, The Netherlands.

    • Roel M. Willems,
    • Simon E. Fisher &
    • Clyde Francks

  2. Department of Experimental Psychology, Ghent University, Ghent, 9000, Belgium.

    • Lise Van der Haegen

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The authors declare no competing interests.

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  • Roel M. Willems

    Roel M. Willems is a senior researcher at the Donders Institute for Brain, Cognition and Behaviour and at the Max Planck Institute for Psycholinguistics, Nijmegen, the Netherlands. He obtained his Ph.D. from Radboud University Nijmegen, on the neural integration of information from speech and gestures. He previously held positions at the Radboud University Nijmegen and the University of California, Berkeley, USA, during which he investigated the role of the motor cortex in language understanding. He investigates the neural basis of our language capacities, and his current main interest is the role of mental simulation in the comprehension of literature. Roel M. Willems's homepage.

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  • Lise Van der Haegen

    Lise Van der Haegen is a postdoctoral researcher at the Department of Experimental Psychology at Ghent University, Belgium. She is a member of the Center for Reading Research group and is supported by a grant from the Research Council of Ghent University. For her Ph.D. degree she investigated the need for interhemispheric communication in visual word reading by comparing left- and right-handed subjects with a clear typical or atypical language organization. Current research focuses on the relationship between the hemispheric specialization of language sub-processes and non-language-related cognitive functions. Lise Van der Haegen's homepage.

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  • Simon E. Fisher

    Simon E. Fisher is Director of the Max Planck Institute for Psycholinguistics Nijmegen, the Netherlands, and a professor of language and genetics at the Donders Institute for Brain, Cognition and Behaviour in Nijmegen. Before this, he was a Royal Society research fellow, leading a group at the Wellcome Trust Centre for Human Genetics at the University of Oxford, UK. As a neurogeneticist investigating human cognitive traits, he was co-discoverer of FOXP2, the first gene to be implicated in a speech and language disorder. His subsequent research has used language-related genes as molecular windows into critical neural pathways. He received several awards in recognition of this work, including the Francis Crick Lecture and the Eric Kandel Young Neuroscientists Prize. Simon E. Fisher'shomepage.

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  • Clyde Francks

    Clyde Francks completed his D.Phil. (2002) and postdoctoral studies in the human neurogenetics laboratory of Anthony Monaco at the University of Oxford, UK, on the genetics of dyslexia and handedness. He then worked as a manager in the pharmaceuticals industry (GlaxoSmithKline), leading collaborations with academic institutes on genetic studies of schizophrenia and smoking. In 2010, he moved back to full-time academic research to start a group investigating the genetics of human brain lateralization and its links to cognitive variation at the Max Planck Institute for Psycholinguistics, Nijmegen, the Netherlands (an institute of the Max Planck Society), where he is a W2 (German academic scale) senior investigator. He is also a research fellow at the Donders Institute for Brain, Cognition and Behaviour in Nijmegen. Please see the Genetics of Handedness project website.

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