Oh yeah let me just plug in an fmri and find out if someone is definitively experiencing “joy”. That’s high level somewhat subjective emotion, not pain. Neurological understanding is not nearly as advanced as you think it is. I spent my post doc doing fmri research; the best thing you could come up with here is “areas of the brain associate with pleasure are highly activated” but even that doesn’t necessarily indicate the baby feels overwhelmed. Maybe I’m wrong and there’s some fancier neuroscientist out their that can read baby brains but I doubt it