The brain of experienced meditator like Swami Vivekananda and Acharya Rajneesh (née Osho) were quite evolved. Swami Vivekananda was truly an exception. On the verge of gaining enlightenment, he point-blank refused to gain enlightenment in his lifetime.
The evolution of brain is directly linked and proportional to opening of kundalini energy, the cosmic energy lying dormant in base of spine.
The opening of kundalini is always gradual, reaching from chakra to chakra.
Indulging in spirituality as detailed in Bhagavad Gita when seekers, travelers of spiritual path indulged in contemplation (dissolving queries within) their kundalini awakened in stages. Furthermore practice of absolute celibacy for a minimum period of 12 years in continuation is also necessitated.
The brain of normal human beings activated 1 to 2% in its lifetime. But for seekers, travelers of spiritual path situation were different. Enlightened souls like Mahavira, Gautama Buddha, Jesus Christ and Prophet Mohammed used their brain 100%.
The opening of brain directly relates to opening of kundalini spirit. The higher the level of kundalini energy, proportional the activation of brain!
If we desire encompassing the whole cosmos, reaching God in our lifetime then we should indulge in spirituality to awaken our kundalini shakti fully as did Swami Vivekananda.
Kundalini opening activates dormant lying portions of brain in stages and whenever this happened the seeker experienced very heavy headaches that sometimes lasted for days. After the headaches subside it was moments of total lull, ecstasy, absolute bliss.
In present times people of the level of Swami Vivekananda are nowhere to be found. Masses do not understand what yoga meditation was all about. Almost 99% people world over indulging in yoga meditation did it wrong.