On travel I usually bring as many back issues of 
Harper's that I haven't yet read.  And so I was fascinated to read in the December issue 
an article on the possible prevention of psychosis (subscription required).  This article bears upon not only whatever responsibility we may have for the recent violence in Tuscon Arizona, and yet another reason why "he was insane, and there was nothing we could have done" was an inadequate response, but also the nature of mind and consciousness  and sanity, and its relation to 
kensho (見性 ), 
satori (悟り ) and other meditative states.
If you can get a copy of this article, I strongly suggest you read the whole thing, because I'm touching on only a tiny part of this article:
It is impossible to predict the precise moment when a person has  embarked on a path toward madness, since there is no quantifiable point  at which healthy thoughts become insane. It is only in retrospect that  the prelude to psychosis can be diagnosed with certainty. Yet in the  past decade, doctors have begun to trace the illness back to its  earliest signs. [T]he First Episode  Psychosis Clinic at the University of Illinois Medical Center ... is one of about sixty clinics in the United States  that work to help people experiencing early psychotic symptoms maintain a  grasp on reality. About a third of these programs focus exclusively on  patients who appear to be in what is known as the prodrome, the aura  that precedes a psychotic break by up to two or three years. During this  phase, people often have mild hallucinations—they might spot a  nonexistent cat out of the corner of their eye or hear their name in the  sound of the wind—yet they doubt that these sensations are real. They  still have “insight”—a pivotal word in psychiatric literature,  indicating that a patient can recognize an altered worldview as a sign  of illness, not a revelation. 
By working with people when they are still  skeptical of their own delusions, doctors hope to stop the disease  before it has really begun. Three years ago, the results of a study of  nearly 300 patients who sought treatment because of “recurring unusual  thoughts,” “unusual sensory experiences,” or “increased suspiciousness”  were published by the North American Prodrome Longitudinal Study, a  collaboration of eight prodromal outpatient clinics. The researchers  found that 35 percent of patients had a psychotic break within two and a  half years of enrolling at a clinic...
Although the DSM [(Diagnostic and Statistical Manual of Mental Disorders )] is written by the country’s leading  psychiatrists, the neurological mechanisms behind mental disorders are  too poorly understood to have much bearing on the way the manual  separates health from pathology. Instead, the fifty-eight-year-old book  guides psychiatrists toward diagnoses with checklists of behavioral  signs that require a “minimal amount of inference on the part of the  observer” (according to the 1987 edition). The outer limits of normality  are decided by committee, with definitions of illness deferring to  consensus opinion. A “delusion,” one of the five key symptoms listed for  schizophrenia, is a “false belief . . . firmly sustained despite what  almost everyone else believes.” A “bizarre delusion,” a more severe  symptom, has gone through numerous revisions. In one edition of the  manual, it had to have “patently absurd” content with “no possible basis  in fact”; in the next, it involved “a phenomenon that the person’s  culture would regard as totally implausible.” After the revision, 10  percent of patients who were previously deemed schizophrenic were given a  new diagnosis, the majority of them because their delusions were no  longer bizarre.
The DSM is designed to avoid the slippery spaces between  disorders, the complaints not easily named or seen. Perhaps more than  any other disorder, the psychosis risk syndrome puts pressure on the  logic of the entire enterprise, as it forces doctors to break down the  process of losing one’s mind. They have to identify delusions before the  patient really believes in them. When does a strong idea take on a  pathological flavor? How does a metaphysical crisis morph into a medical  one? At what point does our interpretation of the world become so fixed  that it no longer matters “what almost everyone else believes”? Even  William James admitted that he struggled to distinguish a schizophrenic  break from a mystical experience. 
 There are, as I've said, many "take-aways" in this artcle, among them:
- There is, evidently, some kind of a continuum between total full-fledged psychotic break from reality and "normal" behavior and...
- Those that experience it often, if not inevitably are aware that their beliefs aren't necessarily normal
- And they are often suffering from the delusions they are having 
- And we have a responsibility, I think, to try to understand this process, 
- But since we stigmatize the ill and the mentally ill, that's problematic.
More to the point of what I want to say, is I was somewhat struck by what the sufferers of prodrome (pre-psychotic break syndrome) were expressing and my own Zen practice as well as tiny tiny bit I know about neurology; you can't help but be.
Our "self" is something our brain creates for us, and there isn't "one" place in the brain this "self" can be said to reside.  And yet it is just this "self" that apparently suffers in a psychotic break.  The questions that one clinic asks possible prodrome patients include:
Do you daydream a lot or find yourself preoccupied with  stories, fantasies, or ideas?
Do you think others ever say that your interests are unusual or  that you are eccentric?
Do familiar people or surroundings ever seem strange?  Confusing? Unreal? Not a part of the living world? Alien? Inhuman?
Have you ever felt that you might not actually exist? Do you  ever think that the world might not exist?
 There are, it seems to me, a number of 
koans embedded in each of those questions.  Do you daydream a lot? What is a lot? What is a daydream? What is the living world? What is alien? What is inhuman? What does it mean to exist?  How do we know the world exists?
The other question, "Do you think others ever say that your interests are unusual or that you  are eccentric?" is even more interesting: I suppose (I hope) the answer to this question doesn't allow the imaginative to be swept into a psychotic diagnosis.
The fact that in  
kensho (見性 ), "seeing into one's nature,"  one sees that one's nature is 
sunyata, is clearly not to say that one's nature is one rock solid unchanging essence. (Or not.)  Is this the same as a psychotic break? Different?  
I think the difference between a Zen practice, including 見性 and a psychotic break is several:
- We generally aren't suffering because we are questioning everything.
- We aren't usually existentially disturbed at the consideration, and acting within, the premise that the self is a construct of the mind; rather, we are for whatever reason, reassured by it, because we understand this is the nature of all beings.
- We try  not to be attached to beliefs and delusions, including the belief in non-attachment.
Also, there is a strong link between the incidences of psychosis and deprivation - whether it's a deprivation caused by being a minority, or by being economically disadvantaged, the incidence of psychosis seems to increase.
We have a responsibility to find out these issues to their core, and to try to help those who need it.  I would also venture - again as a rank nonspecialist who is clearly writing from the most his most ignorant parts - I would venture that the use of mindfulness based methods might be applied to these prodrome people with interesting results.  It's a study that begs to be done, if it's not already being done, simply because the links between the mystical states and the psychotic break are striking.