For anyone on HN seriously interested in this topic, I would wholeheartedly recommend the recently published &quot;The Mind Illuminated&quot; book written by Culadasa, professor of neuroscience and a _very_ accomplished meditator. [ <a href="http:&#x2F;&#x2F;www.amazon.com&#x2F;dp&#x2F;0990847705" rel="nofollow">http:&#x2F;&#x2F;www.amazon.com&#x2F;dp&#x2F;0990847705</a> ]<p>For all the other commenters asking why Mindfulness and Concentration are used as technical terms  - that&#x27;s because they correspond to Sati and Samadhi - terms in Pali used by the Buddha.<p>One of the takeaways of the book mentioned above is that concentration is NOT a state of being concentrated on a single object. It&#x27;s a state of unification of the mind that persists regardless of its current object. The other important information (obvious for any serious meditator) is that, once reached, it DOESN&#x27;T require lot of force to sustain. On the contrary - it&#x27;s a much more energy efficient mode of functioning. That&#x27;s why in the 4th Jhana (one of the most advanced states of concentration) the breath completely subsides. It wouldn&#x27;t be possible if it required so much force. BTW it doesn&#x27;t mean that the oxygen intake stops completely as there&#x27;s still some absorption caused by the air diffusion in the lungs and through the skin (cutaneous respiration).<p>Again, I really recommend the book by Culadasa for anyone even remotely interested. It&#x27;s amazing from theoretical point of view and even more concerning meditation practice.