Abbreviated words in excel that possibly associated with neuroimaging

hello, I have downloaded data of the following study.
In the excel file, I have found the abbreviated words as follows.

summary_mean_bg summary_mean_fg summary_p05_bg summary_p05_fg summary_p95_bg summary_p95_fg summary_stdv_bg summary_stdv_fg
anyone know what do they mean?
many thanks.
this is the link of study.