The RAC/RAS has been postulated as the “Searchlight of Attention” since this paper by F. Crick:
http://www.pnas.org/content/pnas/81/14/4586.full.pdf
If you google the term “searchlight of attention” you can see that many papers since this one explore this concept (pro and con) and add considerable insight to the workings of this structure.
It is certainly an important adjunct to the interplay between the Thalamus and Cortex - I am not sure if the attention function should be a stand-alone feature apart from the data path or an inseparably part of function of these structures.
My personal take runs something like this; I see that the thalamus does at least two different functions in relation to the cortex.
One is closely related to the feedback path in the general direction through various hierarchies as described in the first post above.
There is nothing controversial here. I will add that this path is in parallel with the direct corticocortical pathways. I see the cortico-thalamic-cortical loop as being a command and control pathway where the cortico-cortical pathway is an information pathway.
The second function is also a control function but with a very different purpose - to activate or coordinate the basic information processing method of the cortex. It would be very wasteful to activate large swaths of the cortex where this is no information to be processed. The signal that something is to be recognized and/or learned would be a widespread “surprise” signal from local areas of the cortex. I see that this would trigger the start of traveling waves in that area of the cortex. Due to the map-spanning connections of the thalamus this same C&C function would be relayed to corresponding areas of related maps.
You may have seen this before but I invite you to read it again in light of this discussion:
With these thoughts in mind - the RAS is positioned to compare the (relatively) local activity between the cortex and thalamus. Given the two functions I have outlined above - and assuming that form follows function - where would this fit in for comparing the activity levels of the two structures?
One uses bursting to signal surprise, one uses bursting to jump-start activity. The RAS is looking for something and bursting seems like a very easy to detect to signal that could be sensed. What if it is simply acting to equalize activity between the two structures? In the process it would act to detect surprise and activate processing on the related information pathway, all using simple and relatively local functions.
This is agnostic as the WHAT/WHERE functions and is instead - a cortex wide processing method. Please note: Hierarchy/pathways is established here by genetic programming and is outside the scope of this discussion.