Regrowing Damaged Neurons
Ultimately, treatment for brain and spinal cord damage will depend on our ability to trigger development of new neurons and to coax injured neurons to regrow their connections. The latter approach is the more promising in the short term, but it requires overcoming the central nervous system's mechanisms for discouraging that growth. Two new studies appear to represent significant breakthroughs. In the first, researchers used a knockout procedure to produce mice lacking the gene resonsible for a molecule (PTEN) that inhibits axon growth. Then they crushed the optic nerve; ordinarily, the axons would not regrow, and about 80% of the neurons would die. Over a period of 28 days, 50% of the neurons survived and about 10% of the axons regrew, some as much as 4 millimeters. Science, Vol 322, 963-966. The second study blocked the activity of the Nogo and PirB receptors on the neuron surface that respond to growth-inhibiting proteins found in the neurons' myelin. Using neurons grown in a culture dish, this strategy produced an almost total elimination of myelin inhibition of axonal regrowth. Science, Vol 322, 967-970.
Brain Evolution Studies Go Micro
Scientists trying to puzzle out how the human brain accounts for our unique abilities have focused on anatomical features like our thicker cortex, greater brain to body size ratio, and larger frontal lobes. Now the focus is turning to the microscopic level. This article discusses the proposed roles of Von Economo neurons (linked to aspects of social cognition), "minicolumns" (which probably make our brains more efficient), different organization of the planum temporale (important in language), and the greater number and activity of astrocytes (which support synapse formation). Science, Vol 315, 1208-1211.
Score Another One for Plasticity
Following amputation of a hand, the motor cortex reorganizes itself and the hand area of the motor cortex slowly takes over some of the control of muscles in the arm. But what happens if the patient receives a hand transplant? For the first time, we have evidence that the cortex accepts the alien hand just like its own. Two patients who received transplant of both hands after work accidents learned to perform tasks like using screwdriver and pliers and rewiring an electrical socket. French researchers demonstrated that the motor cortex had accepted the foreign hands by using transcranial magnetic stimulation to activate the cortical area while observing the resulting hand movements. Proceedings of the National Academy of Sciences Vol 106, 7197-7202.
