Our proposed mechanism

We can define the source areas for the association loop to be premotor cortex, posterior parietal cortex and prefrontal cortex, and the target area to be the prefrontal cortex. These areas can arguably be seen as being involved in preparation of higher-level information to be sent to the main output area of the loop, i.e. the prefrontal cortex.

Using our prior analysis of cortical neuroanatomy, we see that, in general, for all four loops, for each connection from the cortex or other area to the basal ganglia there is a direct cortical connection to the target area. Thus each basal ganglia loop forms a connection system which runs parallel to part of the cortical connection system.

So what are the members of the association loop typically doing?
(i) PPC, the posterior parietal cortex is concerned with visual perception to create nonegocentric maps.
(ii) PreMC, the premotor cortex generates descriptions of motor actions at the intention and coordinate level.
(iii) PFC, the prefrontal cortex, generates plans and actions at the relation level. One could write the association as:
if PPC and PreMC and PFC then PFC
so this assertion is upwards, from more concrete towards more abstract information.

Thus we conclude that the basal ganglia build a plan based on lower level inputs and outputs. The end result is rules in the basal ganglia and also for example PFC, of the general form:
(a) in the basal ganglia:
if PPC and PreMC and PFC then PreMCR
and (b) in PFC
PreMCR is a possible action.