This is my translation of an article by Rabbi Yehuda Leib Ashlag TZ"L
Everything that is born is created from its head, and we shall see that this is the brain. And even though is seems that the brain is a rational creation, which has absolutely no connection with the animal soul of the person, this is not so. Rather, all of the person’s life force is drawn from and has its source in the brain, because all the life essence and strength to exist of every living thing sits in the place of primary importance for that particular creature. And because there is no organ more important for man than the brain, therefore, in the brain is found all the power of his existence, and from there comes all of the body’s strength.
And know that the brain is closed within fluid, and within the bones of the skull, and it has no real physical connection with the organs of the body, except for thin veins which are connected with the eyes, and at the end of the brain, a certain kind of organ with "flesh round like Poland" which is the beginning of the spinal chord.
Thus it is that all the thoughts of the brain and its emotional peaks act with their strength on the person and their influence, like pleasure and sorrow, courage and despondency, joy and strength, fill the sinews and arteries with the flow of the life force, making him living and healthy. Conversely, downtroddenness and worry and cause complete death for the living and feeling creature, and according to the measure of their strength will neutralize the life force of the person, as it is written "the poor person is considered dead". His existence is considered "beyond nature", because the life force is measured according to the person’s ability to embrace creation, and his will is dependant upon this. And the person who has become disgusted by life has no life force according to nature, because the nature of living things is to contain and be drawn, with all their essence, to their life force and being.
This can play out is two ways, either that something like poverty and suffering has sucked out a person’s life force, or that he is actually missing part of his force of existence, and due to this lack, he doesn’t receive the influx of life according to the nature of all living things. As is written "evil doers are called living dead", meaning, the evil among the Israel, because they have a seed of Israel within them from their Creator, the addition of "Da’at" (Knowing) of Holiness within their bodies, which differentiates them from all the nations of the world. This is referred to in the holy books as "Helek Elokah Mimal. (A part of G-d from above). And therefore when this part is missing, it is not just a matter of imperfection, rather the person is thought of as dead, and even though he may move, and have other signs of life, he is considered as if he is not living according to nature.
And this is divided in the books to inner light, and surrounding light, meaning that one who lives according to nature , whose will embraces his life in wholeness, lives a life of true delight, and therefore inner light flows within him. This is not the case for someone who can’t bear his own life force and is disgusted by life, and yet is still alive, because his life is drawn towards his existence from without, and he is living the aspect of surrounding light. (And for the former), all the spiritual pleasures are drawn to him in faith, because now his Mishpat (judgement, vision, sentence) is clear to him, integrating his past and present, in that he understands that everything that has happened to him was fair, and with security he will reach his goals. His faith will increase with his every step, and according to this measure his pleasure grows and rises, his will embraces his life completely, and so he is called alive. Unlike the person who doesn’t see fairness in his paths, and doesn’t trust in G-d that he will be lead to his goal, and every step of the way his burden gets heavier, and the doubt increases, until he can no longer believe he will succeed. Thus his worries increase and he becomes disgusted by life, and he then is like a moving dead person (zombie), and his life force and sustenance are drawn to him from the outer surrounding lights . Actually, the place of "Mishpat" is within the brain, while the place of existence, faith, is drawn from the "Mishpat", and it is in the spinal column, and called "Da’at HaMishpat" ("Knowledge of Mishpat").
And if it were possible to inject the spinal column with faith, before the "Mishpat" went out, then we could draw life force to every person, because it would seem that this is not dependent upon the brain. However, this would be very difficult and nearly impossible, except through the brain and its "Mishpat", as stated above.