How to get Devise's current_user in ActiveRecord callback in Rails?

I'm using Devise and Rails 3.2.16. I want to automatically insert who created a record and who updated a record. So I have something like this in models:

before_create :insert_created_by
before_update :insert_updated_by

private
def insert_created_by
  self.created_by_id = current_user.id
end
def insert_updated_by
  self.updated_by_id = current_user.id
end

Problem is that I get the error undefined local variable or method 'current_user' because current_user is not visible in a callback. How can I automatically insert who created and updated this record?

If there's an easy way to do it in Rails 4.x I'll make the migration.