By Rick Weiss
Washington Post Staff Writer
Source: Washington Post
Date: 4 July 2003
Giving new meaning to “sensitivity training,” scientists have developed a simple way to greatly enhance the human body’s ability to feel subtle sensations.
The enhanced sensitivity, achieved with a tiny stimulating device and a single dose of a drug, has reversed fingertip numbness in older people, many of whom have trouble performing everyday tasks such as buttoning shirts or turning switches on and off. Researchers said they suspect it could also help blind people read Braille. And applying the technique to the feet might prevent falls in diabetics who have lost sensation in their toes, which are crucial for balance.
The ability to boost sensory sensitivity, scientists said, could even allow people with normal function to achieve bionic supersensitivity — for work or recreational purposes — enhancing the senses of taste or smell or adding to the tactile pleasure of a romantic caress.
“This indicates that the sensitivity we typically see in normal subjects is not a physical limit,” said Hubert R. Dinse, the neuroscientist who led the work at the Ruhr-University Bochum in Germany.
The new work, described in today’s issue of the journal Science, is the latest in a series of advances that have demonstrated an unexpected capacity to reverse sensory declines in the elderly and enhance those functions in younger people.
Studies have shown that repeated exposure to subtle signals — such as barely perceptible changes in musical tones — can improve sensitivity to those signals, a form of sensory enhancement that has been documented in musicians. Research has shown that these enhanced abilities are the result of the brain gradually reconfiguring itself to devote larger portions to the task at hand. In taxi drivers, for instance, the brain’s hippocampus — which maintains mental maps and a sense of place in the world — grows larger.
Until now, however, scientists did not know how the body translated musical practice, taxi driving or other sensory experiences into anatomical changes in the brain. The new study shows for the first time that the process involves a biochemical pathway already known to play a key role in learning and memory. When scientists gave subjects a drug that “revs up” this pathway, it vastly increased the amount of brain reorganization — or “remodeling” — that occurred during sensory stimulation, and significantly added to the improvement in function.
Geriatricians in particular want to understand and tinker with these biochemical pathways, because the gradual loss of sensory function in old age takes a huge toll on quality of life.
“The incremental loss of vision, hearing, smell and touch tips the balance eventually,” said Daniel Perry, executive director of the nonprofit Alliance for Aging Research. “If you begin to lose these sensory abilities, you’ve really lost the environmental cues that keep you safe and allow you to operate independently. The end of that road is a nursing home.”
In the new experiments, volunteers placed the tip of one index finger on a portable electrical device that delivered a subtle stimulus — similar to the feel of one fingertip gently touching another — about once a second for three hours. As expected, brain scans showed an increase in the amount of gray matter “paying attention” to that finger, and volunteers showed improved “tactile acuity,” measured by the ability to discriminate between two tiny and very closely spaced bumps on a surface.
But that effect was as much as doubled when the subjects were also given a single dose of amphetamine, a drug that energizes a class of brain cells in the NMDA pathway involved in learning and memory. Those who got the drug without the sensory training did not improve at all, indicating that the drug by itself does not enhance tactile sensitivity.
“We were able to change the tactile acuity of 80-year-old subjects to a performance of a 50-year-old,” Dinse said — a 50 percent to 100 percent improvement.
Because of its potential for abuse, amphetamine is not going to be the key to restoring sensory losses in the aged. But the studies are likely to offer a better picture of how the drug bolsters sensory training, Dinse said, and should point the way to safer and simpler chemicals with the same effect.
The higher sensitivity lasted a day or two. But it would not be hard to deliver the fingertip stimulus regularly, Dinse and others said — perhaps with a battery-operated glove that could be worn at night. Some researchers are already developing a similar device to help people who have lost sensitivity in their toes.
Harvard physician Lewis A. Lipsitz and his colleague James J. Collins, a professor of biomedical engineering, have been applying vibrations to the feet of diabetics, who gradually lose sensation because of nerve damage. They have witnessed sizable improvements in those patients’ ability to detect sensations in their feet.
“Now we’re building vibratory insoles that can be put in a shoe,” said Lipsitz, research director at Hebrew Rehabilitation Center for Aged in Boston. “Anything that can enhance information about where the body is in space can help stabilize posture and overcome obstacles and hopefully prevent falls.”
Dinse’s discovery of a pharmacological pathway linked to sensory enhancement could revolutionize efforts to sharpen the senses, agreed University of Toronto neuroscientist Christo Pantev — who has done pioneering work on the effects of musical training on the brain — and Vilayanur S. Ramachandran, director of the center for brain and cognition at the University of California, San Diego. The field of brain remodeling was already exciting, Ramachandran said, but the new study “is even more exciting, because it’s starting to show what the biochemical mechanisms are.”
Others suggested that, in time, the spectrum of human sensation could grow in almost unimaginable ways as biomedical engineers develop drugs or devices for people who are healthy but want to have a richer sensory experience.
