Activating the Apple Thunderbolt Display speakers when Macbook Pro is docked

Sometimes, I don't get access to the Display Audio that my Thunderbolt Apple Display provides when I dock to the machine with my MacBook Pro. The clunky way to solve this, is a reboot. I've tried using the Apple Preferences (Sound), but that fails to provide the option, unless I reboot. Here is what my system_profiler shows as available Sound/Devices after the reboot (and when the Apple Preferences does give me the option to select the bigger Thunderbolt display):

Devices:

    Built-in Input:

      Input Channels: 2
      Manufacturer: Apple Inc.
      Current SampleRate: 44100
      Transport: Built-in

    Built-in Output:

      Default System Output Device: Yes
      Manufacturer: Apple Inc.
      Output Channels: 2
      Current SampleRate: 44100
      Transport: Built-in

    Display Audio:

      Default Input Device: Yes
      Default Output Device: Yes
      Input Channels: 1
      Manufacturer: Apple Inc.
      Output Channels: 2
      Current SampleRate: 44100
      Transport: USB

Any ideas how to 'wake-up' the Thunderbolt connection to recognize the third item (Display Audio) without resorting to a reboot? Ideally, that would at least activate it as an option in the Apple Preferences menu.

Here's a picture of the Preferences:

I've experienced this annoyance too. Rebooting can be very inconvenient when I have a lot of work open. Unplug/plugging the monitor doesn't seem to help. After reading the answer above, I started to log out, canceled it and for some reason the display audio option was restored. Woohoo! I'll repeat same procedure next time and see if this was just luck.