Check out this essay in The Wilson Quarterly by Charles Barber - "The Brain: A Mindless Obsession." There's a lot of neuro-activity going on out there, but in spite of the excitement and hype and neuro-everything claims the truth is we know hardly anything about how the brain works. Barber's analysis makes us look like medievalists when it comes to understanding things like depression, or how Prozac actually works. Among other things this is due to the outrageous complexity of the physical brain.
Barber writes, re. psychiatric disorders: "if anything has been gleaned from the last two decades of work in the genetics of psychiatric disorders, it is that the origins of these maladies are terribly complex. No individual gene for a psychiatric disorder has been found, and none likely will ever be. Psychiatric disorders are almost certainly the product of an infinitely complex dialogue between genes and the environment." If in fact such a "dialogue" is infinitely complex we can never expect to gain a complete or perhaps even a near-complete understanding.
Another quote, to give you a flavor of the essay: "The state of the art right now is that we can read brains—to some very crude extent—but we can’t even begin to read minds. Wall Street Journal science writer Sharon Begley has coined the term “cognitive paparazzi” to describe those who claim they can. “What does neuroscience know about how the brain makes decisions? Basically nothing,” says Michael Gazzaniga, director of the SAGE Center for the Study of the Mind at the University of California, Santa Barbara."
And: "There are currently no standard ways of treating or assessing mental illness based on brain images. The only unequivocal clinical use of imaging is in detecting raw abnormalities. “The only thing imaging can tell you is whether you have a brain tumor or some other gross neurological damage,” says Paul Root Wolpe of the University of Pennsylvania’s Center for Bioethics. The unfortunate fact remains that the most accurate way of gauging the thoughts and feelings of others is simply by asking them what they are thinking and feeling.
Steven Pinker, again: “We are still clueless about how the brain represents the content of our thoughts and feelings. Yes, we may know where jealousy happens—or visual images or spoken words—but ‘where’ is not the same as ‘how.’”"
When might we expect to understand "how" the brain works? "The brain is the most complicated object in the universe. Nobel Prize–winning psychiatrist Eric Kandel has written, “In fact, we are only beginning to understand the simplest mental functions in biological terms; we are far from having a realistic neurobiology of clinical syndromes.” Neuroscientist Torsten Wiesel, another Nobelist, scoffed at the hubris of calling the 1990s “The Decade of the Brain.” “We need at least a century, maybe even a millennium,” he said, to comprehend the brain."
Finally, look at this quote from Francis Crick, reducing "mind" to the physical activity of the brain: “‘You,’ your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. As Lewis Carroll’s Alice might have phrased it: ‘You’re nothing but a pack of neurons.’”"
But if that's true, then Crick's claim that the mind is nothing but the physical activity of the brain is itself nothing but the physical activity of the brain. What could it mean to argue for the "truth" of such a theory?