When an adult brain suffers an injury, its neurons must struggle harder to rewire than those of young brains. But old tricks can apparently recapture some of the resilience of youth, a new study suggests. After a stroke-like injury, adult rat brains pulse with synchronized electrical waves, more commonly seen in early development, as they try to fix damaged neural circuits.
Neurons in the developing brain readily sprout new branches, or axons, that hook up with other cells. This is one way the developing brain sets up its neural pathways. Although less common in adults, axonal sprouting does occur in the cerebral cortex, the brain's main information processing center, after stroke-like lesions. Researchers suspect that this sprouting may help the brain recover. However, the trigger for sprouting has remained elusive.
To investigate, neuroscientists S. Thomas Carmichael and Marie-Françoise Chesselet of the University of California, Los Angeles, School of Medicine made stroke-like lesions in the brains of adult rats. Within a day, the researchers recorded slow, rhythmic pulses of electrical activity in the area near the lesion. Over several days, the low-frequency pulses spread to the cortex on the opposite side of the brain. After a month, axons from this region had been dispatched to the lesion site. When researchers blocked electrical signals with a toxin, axons failed to sprout. Similar electrical patterns have been recorded on electroencephalographs of stroke patients for decades, notes Carmichael, but it is surprising that this might be a signal for repair. Carmichael and Chesselet report their results in 15 July issue of the Journal of Neuroscience.
This work is "intriguing" and suggests a connection between low-frequency activity and sprouting in the cortex, says neuroscientist Michael Weliky of the University of Rochester in New York. "It opens up an area of study where manipulating or enhancing patterns of neural activity in the brain after stroke could enhance recovery." But the causal link is still missing, says neuroscientist Rafael Yuste of Columbia University in New York City. A more convincing demonstration, he says, would be to prompt new axons by stimulating the brain in a way that mimics the synchronized pulses.