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In a finding that is a major advance in spinal cord injury research, U.S. scientists report that regenerating axons can be guided to their correct targets where they can re-form connections after spinal cord injury.

Previous research showed that severed axons — long, slender projections of a nerve cell that conduct electrical impulses — can be coaxed to regenerate into and beyond sites of spinal cord injury. But it hasn’t been clear how to guide these axons to the precise target, according to a news release from the University of California, San Diego.

In experiments on rats, researchers at the UCSD School of Medicine found that regenerating axons can be guided to the correct target using a nervous system growth factor called neurotrophin-3 (NT-3).

When the growth hormone was placed in the correct target, axons grew into it and formed electrical connections called synapses. When the growth factor was placed in the wrong target, the researchers found that the axons grew into that target as well, according to the study published online Aug. 2 in the journal Nature Neuroscience.

“The ability to guide regenerating axons to a correct target after spinal cord injury has always been a point of crucial importance in contemplating translation of regeneration therapies to humans,” senior author Dr. Mark Tuszynski, director of UCSD’s Center for Neural Repair, said in a news release.

“While our findings are very encouraging in this respect, they also highlight the complexity of restoring function in the injured spinal cord,” he said.

A new study in Bronx seniors provides yet more evidence that keeping your brain active for fun can keep dementia at bay.

Dr. Charles B. Hall of the Albert Einstein College of Medicine in Bronx, New York, and his colleagues found that every day per week that a person engaged in one of six mentally stimulating leisure activities delayed the onset of dementia by about two months.

Hall and his colleagues had previously shown that people with more years of education who developed dementia did so later than less educated individuals. In the current study, he said, “it was the cognitive activity that mattered, not the education.”

In the current study, published in Neurology, Hall and his team looked at 101 people who developed dementia. All were participating in the Bronx Aging Study, which has been following 488 people since the early 1980s.

All of the study participants, who ranged in age from 75 to 85, had reported their years of formal education at the study’s outset, as well as how often each week they read, wrote, did crossword puzzles, played board or card games, participated in group discussions, or played music. A person scored 1 for each day that they did each activity. The study participants, all of whom were dementia free at the beginning of the study, underwent cognitive testing every 12 to 18 months.

The higher a person’s score on the activity scale, the later the onset of accelerated mental decline, Hall and his colleagues found. For example, a person in the top 25 percent based on their activity scale, who engaged in 11 “activity days” a week, started their accelerated decline 1.29 years later, on average, than a person in the bottom 25 percent, with four activity days a week.

But once that decline began, it happened faster in people with higher activity scores.

The findings back up the idea of “cognitive reserve,” Hall noted, which is the theory that education and brain exercise build extra capacity into the brain so it can better handle the damage to neurons caused by Alzheimer’s disease. But once that damage reaches a certain point, a person will develop dementia.

Being more mentally active “might keep you out of a nursing home for a year or two,” Hall said. “But it’s not going to prevent Alzheimer’s disease unfortunately, at least that’s the theory, and this is evidence toward that theory.” Eventually, he said, the disease “would overwhelm whatever reserve you had.”

Hall and his colleagues are now investigating which of the six activities in the current study might give the most brain-preserving “bang for the buck.” Studies will need to tease out whether education and later-life mental activities have effects that are independent of one another.

With what we know now, he added, engaging in these activities could help-and it certainly won’t hurt. “You might get depressed from not being able to do a crossword puzzle, but there’s really very little of a downside here.”