Q:

What is this ceiling beam called above interior wall?

I'm attempting to add ethernet to a bedroom. This will involve drilling a hole from the attic to route the cables behind the drywall. I expected to see 2x4 above the interior wall but found a tongue and groove 2x6 as shown in the photos below. It runs in parallel with the ceiling joists and ends about an inch away from the roof overhang. House is in California and built in 1958.
Does this beam have a name and what is the purpose? Can I drill down through it to route cables?

A:

That board is likely nailed to the top of the 2x4 wall framing and provides a nailing surface for the ceiling finish material. Yes, you can drill through it. It’s called a nailer, is not structural, and is not a beam. 

