Last week's article in Science looked at the effects of the anesthetic/dissociative drug ketamine ("vitamin K" or "Special K" on the street) in brain cell function in rats, concluding "that ketamine might be useful in treating depression because it increases brain activity instantly - so there is no need to wait weeks or months for the drug to take effect."
Another article from Nature Reviews Neuroscience reviewed the state of the art in psychedelic science and found that "countless studies show that hallucinogens promote healthy neural activity in the brain. The researchers also created a chart to show what test subjects' states of mind are, according to studies, when under the influence of various substances."
Go to Lanny-Yap (great site!) for links to the articles.