Chuckle. By sheer coincidence I happened to be watching Earl’s recent interview with “Giants’ Shoulders” on YouTube. The like just happened to be the top post, my “golf ball marker” since Bluesky still doesn’t yet allow unread posts in chronological order!

Looks good for bottom-up stimuli like retinotopy, but what about expts (in humans) with high emotional valence, or attentional effects? Surely top-down cognitive processes could confound during the control blocks. (And might cause some interesting non-linearities in physiology, too.)

The autonomic nervous system? A cyclic in sympathetic nervous activity should cause respiratory and EDA changes, plus muscle tone changes, etc.

A bit outside my expertise, but I’d start by looking at cyclic changes in arousal. Breathing will likely reflect the same processes.
I think it may be tantamount to asking why breathing rate & depth ever change during rest. Presumably it’s autonomic?