…fically need chains of three neurons; rather these chains are a signature of loops in the real CA3. That is, if we take a chains of chains that end up linking each neuron back to itself, we get a loop: a set of neurons that connect to each other in turn, and end up connecting back to the start neuron. That way, if only a small number of these neurons gets an input, they can each help make the next in the loop fire, which will make the next fire, and so on. Completing the pattern. But this is just a guess, an example of how any bit of good science inspires ideas, hypotheses, creative offshoots that could be tested, probed, added or discarded.
So the answer was: yes, the real CA3 can do pattern completion. The ancient theory was correct. But there are all sorts of things we still don’t know. How, for instance, do these motifs actually help? The paper offers one clue: if they left the “chain” motif out of the model, it failed. So, somehow, the existence of many sets of three neurons linked in a chain allows pattern completion to happen.