The Old Parts of the Brain are Fast but Dumb
Above is a great audio clip on how the old parts of the brain can govern behaviour.
Note Asprey is talking about an untraumatised brain. Even without trauma, the old parts of our brain are easily distractable, prone to trigger random eating, focused on sex and biased to hardwired reflexes in response to danger. In a sensitised nervous system the reptile and mammalian elements react even quicker and limit the prefrontal cortex even more.
I like the idea of the energy economy of the body being stacked to deal with reptile brain, then mammal brain, and only then conscious processing. So, for example, if there is inflammation or toxicty in your liver (Asprey is very keen on not stressing the liver with molds) then the resources of your system will be diverted to the liver by the reptile brain. You will not be able to think clearly or maintain energy, focus and willpower.
Watching the video made be think of an old friend - Mike The Headless Chicken. Another example of how many of functions can be done without thinking. For Asprey that is scary - we need to learn how to exert control on these unconscious systems or they will control us. He likes meditation, gratitude, sleep and clean diet, all aided by bio feedback, as good starting points to influence what is happening in the old parts of your brain.