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
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.
Nicholls, M. E. R., Chapman, H. L., Loetscher, T. & Grimshaw, G. M.The relationship between hand preference, hand performance, and general cognitive ability. J. Int. Neuropsychol. Soc.16, 585–592 (2010).
Badzakova-Trajkov, G., Häberling, I. S. & Corballis, M. C.Magical ideation, creativity, handedness, and cerebral asymmetries: a combined behavioural and fMRI study. Neuropsychologia49, 2896–2903 (2011).
Groen, M. A., Whitehouse, A. J. O., Badcock, N. A. & Bishop, D. V. M.Does cerebral lateralization develop? A study using functional transcranial Doppler ultrasound assessing lateralization for language production and visuospatial memory. Brain Behav.2, 256–269 (2012).
Tzourio-Mazoyer, N.et al. Left hemisphere lateralization for language in right-handers is controlled in part by familial sinistrality, manual preference strength, and head size. J. Neurosci.30, 13314–13318 (2010).
Aziz-Zadeh, L., Wilson, S. M., Rizzolatti, G. & Iacoboni, M.Congruent embodied representations for visually presented actions and linguistic phrases describing actions. Curr. Biol.16, 1818–1823 (2006).
Longcamp, M., Anton, J. L., Roth, M. & Velay, J. L.Premotor activations in response to visually presented single letters depend on the hand used to write: a study on left-handers. Neuropsychologia43, 1801–1809 (2005).
De Nooijer, J. A., van Gog, T., Paas, F. & Zwaan, R. A.When left is not right: handedness effects on learning object-manipulation words using pictures with left- or right-handed first-person perspectives. Psychol. Sci.24, 2515–2521 (2013).
Van den Berg, F. E., Swinnen, S. P. & Wenderoth, N.Involvement of the primary motor cortex in controlling movements executed with the ipsilateral hand differs between left- and right-handers. J. Cogn. Neurosci.23, 3456–3469 (2011).
Dassonville, P., Zhu, X. H., Uurbil, K., Kim, S. G. & Ashe, J.Functional activation in motor cortex reflects the direction and the degree of handedness. Proc. Natl Acad. Sci. USA94, 14015–14018 (1997).
Verstynen, T., Diedrichsen, J., Albert, N., Aparicio, P. & Ivry, R. B.Ipsilateral motor cortex activity during unimanual hand movements relates to task complexity. J. Neurophysiol.93, 1209–1222 (2005).
Yovel, G., Tambini, A. & Brandman, T.The asymmetry of the fusiform face area is a stable individual characteristic that underlies the left-visual-field superiority for faces. Neuropsychologia46, 3061–3068 (2008).
Siddiqui, T. J., Pancaroglu, R., Kang, Y., Rooyakkers, A. & Craig, A. M.LRRTMs and neuroligins bind neurexins with a differential code to cooperate in glutamate synapse development. J. Neurosci.30, 7495–7506 (2010).
Sommer, I., Ramsey, N., Kahn, R., Aleman, A. & Bouma, A.Handedness, language lateralisation and anatomical asymmetry in schizophrenia: meta-analysis. Br. J. Psychiatry J. Ment. Sci.178, 344–351 (2001).
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.
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.
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.
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.