This categorical coherence looks for higher level patterns. It could identify the presence of diseases previously unknown, not because it's matching against a list of diseases and their progressions, but because it's identified unknown patterns of neurodegeneration in a patient. In addition to unknown disease progression, this could also identify the combination of drug-induced neurological damage or damage induced by the combination of diseases.
While certain physical neural circuit arrangements are required and while chemistry and genetics are certainly involved to some degree, I believe this merely sets up circuitry that will evolve to reflect metaphysics -- *heady crystals!!* -- In other words, given the proper initial circuitry and given a variety of similar input experiences, the remarkably small spider's brain will inevitably evolve certain key functionalities -- or it will not survive.