When does the comment block with schema information for the model get updated by rails?

Seems like output of the annotate_models plugin. Just install it and run annotate in your rails root and the schema information will update automatically. Ideally, run it after each migration.

You could also use the annotate-models gem. It's a bit less intrusive as there's no plugin needed.

Usage:

% gem install annotate
% annotate
Annotated Product, User, Role