How is epigenetic memory expressed in neurons?
There are (at least) two ways epigenetic traits are inherited.  The important background in both cases is gene expression: there is a misconception that genes are for this or that, where the reality is that most traits come from an overlap of several genes expressing themselves in different ratios.  As a simple example, consider two varieties of bird of the same species, but one has a longer beak.  One might conclude that the genes involved in the morphology of the beak were expressed longer or in greater quantity in the bird with the bigger beak.  Epigenetics describes inherited expression schemes.

The well known method of epigenetic transfer is DNA methylation.  The DNA itself is not actually changed, but the methylation sites act like tags, altering the expression rate of those particular genes.  Another way is through histones, which are part of packing and unpacking DNA between storage and use.  Alterations in histones can also alter gene expression.