I think that the brain has a much better “body needs” sensor than the limbic system. The basal ganglia (BG) performs reinforcement learning which predicts the outcome of a situation in terms of how good or bad it will be for the animal. I think that information in the basal ganglia is routed to the PFC, where it is process and analysed. The result is a loop between Unsupervised Learning and Reinforcement Learning.
You should read my post in that thread too:
Some more details: The Striatum has two populations of cells D1 and D2, one population only activates in the presence of dopamine, the other in the absence. Dopamine here encodes the expected value, which is an output of reinforcement learning. D1 and D2 cells are learning to represent their input from the cortex, as Hebbian learning tends to do, but their ability to learn is gated on the current level of dopamine, so that they learn to detect only the things which are present when they’re allowed to learn. These cells then represent things which have a value to the animal; everything the animal cares about should show up somewhere in the Striatum.
N.B. I think that working memory cells could activate themselves via the Cortex->BG->Thalamus->Cortex pathway, which can only persist if the BG deems the subject matter valuable.