This Is Your Brain on Drugs

For the Harvard-Northwestern study, published in the April issue of The Journal of Neuroscience, the team scanned the brains of 40 young adults, most from Boston-area colleges. Half were nonusers; half reported smoking for one to six years and showed no signs of dependence. Besides the seven light smokers, nine used three to five days a week and four used, on average, daily. All smokers showed abnormalities in the shape, density and volume of the nucleus accumbens, which “is at the core of motivation, the core of pleasure and pain, and every decision that you make,” explained Dr. Hans Breiter, a co-author of the study and professor of psychiatry and behavioral sciences at Northwestern’s medical school.

Similar changes affected the amygdala, which is fundamental in processing emotions, memories and fear responses.

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Evidence of long-term effects is also building. A study released in 2012 showed that teenagers who were found to be dependent on pot before age 18 and who continued using it into adulthood lost an average of eight I.Q. points by age 38. And last year at Northwestern, Dr. Breiter and colleagues also saw changes in the nucleus accumbens among adults in their early 20s who had smoked daily for three years but had stopped for at least two years.

They had impaired working memories as well. “Working memory is key for learning,” Dr. Breiter said. “If I were to design a substance that is bad for college students, it would be marijuana.”

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Stem Cells Seem Safe in Treating Eye Disease

A treatment based on embryonic stem cells clears a key safety hurdle, and might help restore vision.
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Buy Experiences, Not Things

Forty-seven percent of the time, the average mind is wandering. It wanders about a third of the time while a person is reading, talking with other people, or taking care of children. It wanders 10 percent of the time, even, during sex. And that wandering, according to psychologist Matthew Killingsworth, is not good for well-being. A mind belongs in one place. During his training at Harvard, Killingsworth compiled those numbers and built a scientific case for every cliché about living in the moment. In a 2010 Science paper co-authored with psychology professor Daniel Gilbert, the two wrote that "a wandering mind is an unhappy mind.
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Are We Really Conscious?

Third, what is the relationship between our minds and the physical world? Here, we don’t have a settled answer. We know something about the body and brain, but what about the subjective life inside? Consider that a computer, if hooked up to a camera, can process information about the wavelength of light and determine that grass is green. But we humans alsoexperience the greenness. We have an awareness of information we process. What is this mysterious aspect of ourselves?

Many theories have been proposed, but none has passed scientific muster. I believe a major change in our perspective on consciousness may be necessary, a shift from a credulous and egocentric viewpoint to a skeptical and slightly disconcerting one: namely, that we don’t actually have inner feelings in the way most of us think we do.
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The brain builds models (or complex bundles of information) about items in the world, and those models are often not accurate. From that realization, a new perspective on consciousness has emerged in the work of philosophers like Patricia S. Churchland and Daniel C. Dennett. Here’s my way of putting it:

How does the brain go beyond processing information to become subjectively aware of information? The answer is: It doesn’t. The brain has arrived at a conclusion that is not correct. When we introspect and seem to find that ghostly thing — awareness, consciousness, the way green looks or pain feels — our cognitive machinery is accessing internal models and those models are providing information that is wrong. The machinery is computing an elaborate story about a magical-seeming property. And there is no way for the brain to determine through introspection that the story is wrong, because introspection always accesses the same incorrect information.

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How Exercise May Protect Against Depression

Exercise may help to safeguard the mind against depression through previously unknown effects on working muscles, according to a new study involving mice. The findings may have broad implications for anyone whose stress levels threaten to become emotionally overwhelming.
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