structural:reformatting, quality:correction, information:filtering
Role of CpG sites in memory

In 2016 Halder et al. using mice, and in 2017 Duke et al. using rats, subjected the rodents to contextual fear conditioning, causing an especially strong long-term memory to form. At 24 hours after the conditioning, in the hippocampus brain region of rats, the expression of 1,048 genes was down-regulated (usually associated with 5mCpG in gene promoters) and the expression of 564 genes was up-regulated (often associated with hypomethylation of CpG sites in gene promoters). At 24 hours after training, 9.2% of the genes in the rat genome of hippocampus neurons were differentially methylated. However while the hippocampus is essential for learning new information it does not store information itself. In the mouse experiments of Halder, 1,206 differentially methylated genes were seen in the hippocampus one hour after contextual fear conditioning but these altered methylations were reversed and not seen after four weeks. In contrast with the absence of long-term CpG methylation changes in the hippocampus, substantial differential CpG methylation could be detected in cortical neurons during memory maintenance. There were 1,223 differentially methylated genes in the anterior cingulate cortex of mice four weeks after contextual fear conditioning.