Abstract
We investigated effects of sign language use and auditory deprivation from birth on the volumes of three cortical regions of the human brain: the visual cortex surrounding the calcarine sulcus in the occipital lobe; the language-related cortex in the inferior frontal gyrus (pars triangularis and pars opercularis); and the motor hand region in the precentral gyrus. The study included 25 congenitally deaf participants and 41 hearing participants (of which 16 were native sign language users); all were right-handed. Deaf participants exhibited a larger calcarine volume than hearing participants, which we interpret as the likely result of cross-modal compensation and/or dynamic interactions within sensory neural networks. Deaf participants also had increased volumes of the pars triangularis bilaterally compared to hearing signers and non-signers, which we interpret is related to the increased linguistic demands of speech processing and/or text reading for deaf individuals. Finally, although no statistically significant differences were found in the motor hand region for any of the groups, the deaf group was leftward asymmetric, the hearing signers essentially symmetric and the hearing non-signers were rightward asymmetric – results we interpret as the possible result of activity-dependent change due to life-long signing. The brain differences we observed in visual, motor, and language-related areas in adult deaf native signers provide evidence for the plasticity available for cognitive adaptation to varied environments during development.
Highlights
Across the lifespan, the structural and functional plasticity of the mammalian brain is expressed through a variety of mechanisms and pathways
Auditory regions of the brain are an obvious candidate for plastic changes, and we have shown that deaf people have decreased white matter in and around Heschl’s gyrus, the anatomical landmark for the primary auditory cortex (Emmorey et al, 2003); this finding was later replicated by Shibata (2007)
Volumes of major brain regions are often correlated for size (Allen et al, 2002), before undertaking group-wise comparisons of regional brain volumes, it is important to examine if overall brain size is an important covariable
Summary
The structural and functional plasticity of the mammalian brain is expressed through a variety of mechanisms and pathways. Multiple changes in brain structure and function have been detected in musicians compared to non-musicians (Gaser and Schlaug, 2003; Wan and Schlaug, 2010). Another way brain plasticity has been investigated is by studying individuals whose sensory experiences or cognitive demands, often beginning in childhood, are profoundly different from normal experience. Blind individuals show changes in brain anatomy that correlate with the length of time blindness has been experienced, with early-onset blind individuals showing more pronounced changes than late-onset individuals (Noppeney, 2007; Leporé et al, 2010a)
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