I'm an optimist. Learning and thinking will create the knowledge that enables us to change virtually any phenomenon whatsoever, for better or for worse. Knowledge created from learning and thinking may one day prevent stars from collapsing (as stated -- I think -- in David's the Fabric of Reality.)

Since the consequences of learning and thinking can cause virtually anything, learning and thinking can in principle be argued to cause and treat cancer, heart disease, strokes, and virtually any medical/psychiatric condition whatsoever, including attention deficit disorder and obsessiveness. But the causes of these conditions are ultimately so multifactorial, that it is not helpful to say that "learning" causes or treats them, unless one specifies the type of learning that causes or treats them, which can then be evaluated scientifically for accuracy.

Simple (known) chemical changes from medication can precipitate the immediate creation and destruction of attentional capacity and obsessiveness, but not core personality traits and mental retardation. Simple chemical changes can precipitate the immediate creation and destruction of cancer, heart disease, and strokes but not congenital deafness or homosexuality/heterosexuality.

Given our knowledge and the environment we live in, when it is plausibly thought or known that specific chemical changes, but not specific known types of changes in learning, can precipitate a condition and its reversal; the condition is said to be mostly "chemically based". Examples of chemically based conditions include heart disease, cancer, strokes, attention deficits, obsessiveness, and paranoia.

Given our knowledge and the environment we live in, when it is plausibly thought that or known that specific changes in learning, but not changes in chemistry, can precipitate a condition and possibly reverse it; the condition is said to be mostly "learning-based". Relative fear of spiders and certain types of personality characteristic are changed mostly by learning.

Given our knowledge and the environment we live in, if conditions are thought to be created by differences in the overally growth of the organism, which when completed is not changed by learning or changes in medication, the conditions are called "developmentally" based. For these conditions, the overall "structure" of the organism or its brain is thought to be responsible. Developmentally based conditions include many forms of mental retardation, Aspergers, homosexualtiy/heterosexuality, and congential deafness.

Chemicals do not contain information about ethical principles, logical thinking, approaches to problems, and empathy. These critically important hyman attributes are very much learned.

But in some ultimate model of reality, perhaps the behaviors associated with altruism and empathy, according to some reductionists, could be "explained" on a "low" level by chemical reactions. And in some future reality, perhaps the collapse of most stars will be best explained as a consequence of the choices of people.

But in this reality, empathy is a powerful explanatory factor in understanding human relations. And gravity is a powerfull factor in explaining why stars collapse.

So the conditions of this environment -- this reality -- matter. The ease with which individuals are capable of thinking their way out of cancer, heart disease, or attention deficits is certainly relevant. For all practical purposes, people have grave difficulty using thought alone to improve these conditions. So we consider these conditions primarily chemically based, and treat them accordingly.

And when someone is affraid of spiders, we don't talk to them about "chemical imbalances" but instead about how he or she can learn to be more comfortable around these organisms.

Ultimately we can say that virtually anything can be caused by "learning" and by "chemicals". But we apportion causality as suits practicality, given the reality that we have. We just don't know what causes any of these conditions; whether heart disease, cancer, or attention deficits. So man is more spirit than substance when this helps him; but the opposite, when needed as well.