To what degree do you think the human consciousness is reliant upon the body and the brain?
Various forms of dualism found in much of Christianity over the centuries, have most definitely taken a few of their ques from Platonic dualism. Classically understood, the human soul was trapped inside of the prison of the body, awaiting escape at the time of death. It could be thought that if the true person is something that is ultimately immaterial, then perhaps it is inconsequential how the “prison” of the body is really treated. Watching out for one’s health, for example, really does not matter if a disembodied afterlife—even with a resurrection to follow in some far off distant eschaton—is the next stage of existence.
The idea that what a person does to himself or herself physically, does not have a spiritual effect, is utterly absurd. Much of how people consider and value themselves is by what they see in the morning in the bathroom mirror. Your average person makes decisions every day that affect to what degree of maintenance, improvement, and/or comfort will be allowed for the body. If people choose to either pamper or abuse themselves, such an environment can lead to extremes ranging from hedonism to self-mutilation. Most people on Earth today, whether they be rich or poor, do not fall into such a paradigm. However, a person’s daily attitude and decision making abilities can certainly be affected by the kinds of substances ingested, or by how much they exercise. If people do not eat healthy meals, or get a reasonable amount of sleep every night, or even get a good amount of fresh air, their ability to think properly can be hampered. This can, in turn, affect one’s connection to the supernatural.
Those who hold to anthropological models like that of either holistic dualism, or more especially emergent dualism, do certainly recognize that how one treats the body has a definite effect on the human mind or consciousness, and one’s personality. In the view of William Hasker,
“[M]ental properties are ‘emergent’ in the following sense: they are properties that manifest themselves when the appropriate material constituents are placed in special, highly complex relationships….The mind…comes into existence when the constituents of its ‘material base’ are arranged in a suitable way—in this case, in the extremely complex arrangement found in the nervous system of humans.”
Hasker’s basic conclusion is that when all of the parts needed for a human person to develop are in place, namely the body, brain, neurological system, blood, and other chemicals—the essential personality or mind will emerge from this. Yet in too many cases witnessed throughout history, various stimuli-constituents, either witnessed or experienced by people externally, or taken or felt by them internally, can negatively impact the development of a personality.
An easy point in case to understand is how many people make decisions—sometimes poor decisions—when under or lacking the influences of various chemical substances. Most frequently, alcohol or drug abuse are cited as examples of how people can make really poor, or just flat stupid decisions when things count, and this can surely relate to spiritual decisions and matters as well. Yet, what about those who do not drink alcohol or use illegal drugs like heroine or cocaine? Obviously, many people are highly affected by nicotine, which most often comes from smoking cigarettes, and the stereotypical chain smoker needs his one or two packs a day to be efficient. Furthermore and far more common, those who need to drink large quantities of caffeine or consume large amounts of sugar every day, are surely not immune to making poor decisions. The human brain, which operates as the “hardware,” to the “software” of the human mind, must function at peak efficiency in order for the best reasoning skills and decision making processes to be employed.
When the body is not operating at an optimal level—being given a fair amount of exercise, a balanced diet, regular excretions, and yes for some people even a regular amount of married sexual intercourse—one’s mind, consciousness, or immaterial spirit can be resultantly affected. Some of this can relate to self-confidence or self-perception. Everyone who works a regular nine-to-five job, five days a week, recognizes that without the availability of weekends (think: Shabbat), and most especially vacation days, that (severe) exhaustion can set in. People tend to make very poor decisions when they are exhausted. This can affect relationships and proper communication between a husband and wife, parents and their children, but most especially how Believers are to regularly pray, study the Scriptures, and gather with other brothers and sisters in the Lord. If people are not trying to be reasonably healthy, then their relationship with God can be prone to suffer.
It might be said that for many people of faith—especially those with various disabilities or incurable diseases which they have to face for many years—that they might tend to look more beyond their physical condition to the time when they get to die and see their Lord in Heaven, being rid of their pain and frustrations. This is not for most of us. We have to live normally each day in relative health, recognizing how a positive physical state affects our relationship with the Heavenly Father. No one has any Biblical right to treat the human body as anything else than “wonderfully made” (Psalm 139:14), because how we treat our outer physical self will undoubtedly influence our inner spiritual self, and in many cases vice versa. Until the time of death when temporary disembodiment will take its affect, we are embodied beings. What we do to ourselves physically will often affect us spiritually.
 Possible references to this include, but are not limited to: Plato Phaedo 81b; Phaedrus 250c; Cratylus 400c; Marcus Aurelius Meditations 3.7.
Consult the FAQ, “Dualism,” for a further review.
 William Hasker, The Emergent Self (Ithaca and London: Cornell University Press, 1999), pp 189-190, 190-191.