sub menu (sub nav) active state?

[ihstiv]

Hey Guys,
I'm not having any luck figuring out a relatively easy way to style the sub menu/nav items so that they have an active state when viewing the CMS page (for example).

Here's an example of the page we'd like to have the 'tattoo artist interviews' sub nav menu item highlighted with a bold or different background color CSS style:
http://www.lastsparrowtattoo.com/6-tattoo-artist-interviews.html

Thanks in advance for any ideas or suggestions.

Cheers