Yogic dhyana originates in back brain, based on past experience.
Asana & Pranayama
Yogic dhyana commences with pranayama. Pranayama to samadhi is a single continuous process.
Prana kriya touches 350 nadis (channels) within.
Pranayama regulates breath by desha (region), kala (duration), samkhya (cycles).
Breath driven to touch pranic manas (mind), loosen grip of mental vasanas (tendencies).