Empirical assessment of changing sample-characteristics in task-fMRI over two decades: An example from gustatory and food studies

Over the past two decades, functional neuroimaging has not only grown into a large field of research, but also substantially evolved. Here we provide a quantitative assessment of these presumed in sample composition and data analysis, using fMRI studies on food/taste research published between 1998 and 2019 as an exemplary case in which the scientific objectives themselves have remained largely stable. A systematic search for papers written in English was done using multiple databases and identified 426 original articles that were subsequently analyzed. The median sample size significantly increased from 11.5 to 35.5 while the ratio of male to female subjects remained stable. There were, however, more papers involving female subjects only, rather than male subjects only, since 2003. There was a decline in uncorrected results and statistical correction by false-discovery rate. Reflecting a trend toward more conservative thresholding, the number of foci reported per paper did not change significantly and sample size (power) did not correlate with the number of reported foci. The median journal impact factor and the normalized number of citations (citations per year) of the papers, in turn, showed a significantly decreasing trend. Number of citations negatively correlated to sample size, publication year but positively correlated to journal impact factor, and was also influenced by statistical correction method. There was a decreasing trend in studies recruiting both left-handed and right-handed subjects. In summary, the present paper quantifies several large-scale trends that have often been anecdotally discussed and reveals the changing nature of neuroimaging studies that may be considered when pursuing meta-analytic approaches.