With the rise of imaging genomics, more and more studies have demonstrated that brain structure and function are under strong genetic control 
. As a strong candidate gene that could influence brain development and function, brain-derived neurotrophic factor (BDNF) is involved in regulating neuronal survival, proliferation and differentiation, as well as synaptic plasticity processes 
. A common single nucleotide polymorphism in the human BDNF gene (rs6265) leading to a substitution of methionine (Met) for valine (Val) at codon 66 in the pro-region of the BDNF protein (Val66Met) could result in disruption of activity-dependent BDNF secretion 
. In recent years, structural magnetic resonance imaging (MRI) scans have revealed that the BDNF Val66Met polymorphism can influence human brain morphology. The Met allele carriers showed less gray matter (GM) volume in some brain areas, such as the hippocampus 
, subgenual anterior cingulated 
, dorsolateral prefrontal cortex (DLPFC) 
, amygdale 
, and temporal and occipital lobar regions 
, compared with Val/Val homozygotes. However, these previous studies have provided little information on individuals who are homozygous for the Met allele (Met/Met) because of its small frequency in Caucasians. The Met/Met genotype is rare and is found only about 4% (Met allele frequency: 20% to 30%) of the Caucasian populations 
, which results in rigorous demand on sample size when obtaining information on only Met homozygotes in this race. As a result, the Met/Met homozygotes and the Val/Met heterozygotes were often merged into a group of Met carriers for analyses in most of these studies, which undoubtedly limited the detection of the specific role of the Met/Met genotype on brain structure.
Compared to the Caucasian populations, Asians have a higher Met allele frequency, namely more than 40% 
. In addition, 20–30% of the Met/Met homozygote distribution and nearly 50% of the Met allele frequency exist in the Chinese population 
, which allows analysis of the Met/Met genotype alone to be conducted more readily. To date, data with regards to the relationship between BDNF (rs6265) genotypes and brain structure in the Chinese population is lacking. Moreover, some physiological processes related to BDNF (rs6265) have already been linked racial differences, such as mental diseases in which an association between the Val66Met polymorphism and schizophrenia exists in Scottish, Spanish and American individuals 
, unlike the Chinese population 
. Thus, whether or not the influence of the genetic variant of BDNF (rs6265) on brain anatomy also varies among races is worth discussion. A large-scale general population study on this problem is necessary.
In addition, to our knowledge (online search in PubMed, http://www.ncbi.nlm.nih
. gov/pubmed ), most studies measuring structural brain differences among BDNF(rs6265) genotypes were based on GM volume using voxel-based morphometry (VBM). VBM is a good automatic method to assess volumetric differences over the whole brain. This method offers information on GM volume from cortical and subcortical areas by combining all structure properties (thickness, surface area, and folding), however, these properties are essentially independent from each other. Compared with VBM, the method of cortical thickness measurement provides a direct examination on thickness independent of surface or position variance, and allows for better matching of homologous cortical regions using geometry to do inter-subject registration 
. If these two methods are used toghther, the results driven by dual-analysis would be more credible 
. However, few studies have focused on the relevance of cortical thickness to the BDNF Val66Met polymorphism. Despite a study reporting no relevance of cortical thickness with the rs6265 genotypes 
, a few recent studies have shown that BDNF (rs6265) contributed to the cortical thickness changes in the entorhinal cortex, temporal gyri and DLPFC 
in people at risk of developing Alzheimer’s disease or suffering from trauma. However, it remains unclear whether the cortical thickness in other brain areas was also affected by the BDNF Val66Met polymorphism in healthy subjects.
Therefore, in order to understand the impact of different genotypes of BDNF Val66Met polymorphism on brain structural plasticity, the present study combined for the first time cortical thickness analysis and VBM to investigate the structural brain differences among three BDNF Val66Met genotypes (Val/Val, Val/Met and Met/Met) in healthy young Chinese adults. Moreover, we also observed differences in brain anatomy in Met allele carriers by merging the Val/Met with Met/Met groups, as performed in previous studies, to evaluate the differences caused by grouping methods.