The modifications of chitta are destroyed by Dhyan.
There are three states to the mind, which the modern sciences acknowledge – the conscious, the unconscious and the subconscious state. Dhyan pertains to the fourth state of mind, the super conscious state or the turaiya state. In dhyan, there is no pratyaya [an object of focus]. There is poorna, or you may call it shoonya. The five senses are at rest. You don’t focus on anything. You are there but you are everywhere, yet you are nowhere. You let go, depending on your karmas, divinity takes over you and the Guru guides you into the higher realms and into reality, siddhis are a by-product. In such a state, vrittis of chitta dissolve.