Neuroscience. New brain cells prompt new theory of depression

No one knows what causes depression, although many neuroscientists blame an imbalance of brain chemicals, so-called neurotransmitters, especially those that affect the brain's pleasure responses. Now a few neuroscientists are converging on a radical, but complementary, theory: that depression may be caused by a lack of new cell growth in the brain. The recent discovery that the brain keeps producing neurons into adulthood has given this highly speculative theory at least one leg to stand on.     

Neuroscience. Where the brain monitors the body

Researchers haven't known exactly where in the brain all the signals that allow an animal to keep track of its limbs are located, but now a team may have located some of the neurons that first make these multisensory connections. On page 1782, researchers report evidence that a small region of the parietal cortex of the monkey brain known as area 5 may enable the monkey to integrate many sources of information about its body and thereby update its mental model of what the body is doing. The researchers based this conclusion on their finding that some area 5 neurons fire at their fastest rates when the visual feedback from a monkey's arm matches the sensory feedback, an indication that the neurons are sensitive to both streams of information.     

Neuroscience. A critical issue for the brain

The notion that there is a "critical period" for learning in the first 3 years of life has cropped up widely in media reports recently. But although critical periods have been well documented for the development of sensory systems in the brain, especially vision, researchers differ over whether they exist for the development of the brain functions that underlie complex learning and thinking skills. Scientists do agree, however, that where critical periods do exist, they are not sharply defined, nor are they unique to the first 3 years of life, as has been conveyed in the media. The message should give hope to adults who may not learn with the ease of early childhood, but can still do it.