What part of a DS is this?

[campercarl]

So I was digging through some boxes when I found I had this odd looking cartridge type thing.

At first glance I thought it was some sort of accessory for the DS. There's a imprint on the side saying Nintendo DS Lite so I was right about that, but soon I realized that this thing wasn't listed under any DS Lite accessory to ever exist. So what is it? A piece of a DS Lite that has been removed? A third party accessory?
I was stumped, so that's when I decided it would be smart to ask you guys.

More pictures of it:

[Veilor]

I googled and found this http://techforums.nintendo.com/message/112301 seems it's for the Guitar Hero controller/buttons.

[campercarl]

I googled and found this http://techforums.nintendo.com/message/112301 seems it's for the Guitar Hero controller/buttons.

Yep that would be it! Turns out it the peripheral comes with 2 adapters. One for DS and DS lite. The Lite one is already screwed in when you first get it, so when I got the game I must of removed it to put the original adapter on without keeping track of were I placed the DS Lite adapter. Good thing I found it though, thanks alot!