Much of channeling, psychic work and telepathic communication happens via your connection to your Higher Self. Higher Self is partly responsible for your intuitive hints and ideas. Other spirits also can send you messages via your Higher Self or directly. When you telepathically connect to someone or when you are channeling information from an other-dimensional being, the information comes from that being to their Higher Self, then to your Higher Self, then back to you.
Importantly, only the basic functions of your mind are in your physical brain. More sophisticated functions, such as creativity, talents, and higher mental functions come from the interaction of your physical brain with your spirit. Different spiritual bodies of yours are involved in higher thought processes: etheric, mental, emotional, astral, and other bodies. The communication to these bodies goes from neurons directly and via some of your chakras.
Heart has its own spiritual mind which is very intuitive and knows the future often better thank your brain mind. Integration of all your minds and all your chakras is a life-long process.
People with Alzheimer's and dementia are often unable to communicate with their soul and partly lose the abilities to retrieve memories and information from the spiritual mind. You can see how their thinking is very superficial and lacks connection to reality. Drunken people and ones under the influence of psychoactive drugs might have these connections impaired or overly stimulated. Some drugs like coffee and nicotine ground the mind to this physical reality and block spiritual uplifting. This might help mindless physical work but blocks higher intuitive and creative thinking. This is why most of Reiki people, psychics and channelers exclude coffee and nicotine. Some psychoactive drugs and some psychiatric disorders like schizophrenia and manic depressive disorder, distort brain chemistry leading to detachment of the mind from this physical reality - the mind would still be active and spiritually connected, but it would have trouble of staying grounded, its perception of this reality is weakened and it has trouble telling the difference between this reality, alternative realities and dreams. To us, their perception would be delusional, while in fact, they are simply telling us things which happen in dreams and parallel timelines. Modern psychiatric drugs rebalance brain chemistry to ground patients to this reality, this improves the ability of these people to live their physical life but damages their ability to connect to spirit and thus slows down their spiritual growth. Understanding the spiritual part of psychiatric disorders is necessary for a better way of helping the patients.