Not really challenging me, I'm more marvelling at the fact that as giant bags of proteins, we're able to look at our baby and our testicles decide that it's the time to stop doing what they do most of the time.

Cognition is such a handwave IMO - what's the biochemistry behind that? What's the signalling mechanism by which our brain does that? Does that mean with the right external brain signals we can turn off T production?

The implication of cognition having control over the body, which you assert is so well known, is that if we can achieve more control over our cognition we can achieve biochemical control of our body. So the bene gesserit is less fiction than we like to think?