Abstract
Evidence for experience-dependent structural brain change in adult humans is accumulating. However, its time course is not well understood, as intervention studies typically consist of only 2 imaging sessions (before vs. after training). We acquired up to 18 structural magnetic resonance images over a 7-week period while 15 right-handed participants practiced left-hand writing and drawing. After 4 weeks, we observed increases in gray matter of both left and right primary motor cortices relative to a control group; 3 weeks later, these differences were no longer reliable. Time-series analyses revealed that gray matter in the primary motor cortices expanded during the first 4 weeks and then partially renormalized, in particular in the right hemisphere, despite continued practice and increasing task proficiency. Similar patterns of expansion followed by partial renormalization are also found in synaptogenesis, cortical map plasticity, and maturation, and may qualify as a general principle of structural plasticity. Research on human brain plasticity needs to encompass more than 2 measurement occasions to capture expansion and potential renormalization processes over time.
Highlights
Following Lövdén et al (2010, 2013), we define plasticity as the inherent ability of the brain to undergo macroscopic structural change in response to altered environmental demands
Plastic changes are triggered in the presence of a prolonged mismatch between the functional supply of brain structure and the experiential demands of the environment that cannot be accommodated by flexibility
We report that individuals training fine motor skills of writing and tracing with their nondominant left hand displayed significant expansion of gray matter volume of both left and right primary motor cortex relative to a control group
Summary
Following Lövdén et al (2010, 2013), we define plasticity as the inherent ability of the brain to undergo macroscopic structural change in response to altered environmental demands. Other studies have reported gray matter changes after 2 weeks of mirror reading (Ilg et al 2008), 7 days of juggling training (Driemeyer et al 2008), a few days of signature writing (Hamzei et al 2012), and even after only 2 sessions of practice in a complex whole-body balancing task (Taubert et al 2010) or hours of training on color subcategories (Kwok et al 2011). This suggests that changes in gray matter volume may emerge quite rapidly
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