Departments
|
Week of 6 November 1998 |
Vol. II, No. 13 |
Feature
Article
The role of noise in aiding touch
BU researchers develop technology to enhance our tactile sensations
|
|
|
Jim Collins and Kristen
Richardson with the device they use to gauge the
effects of stochastic resonance on people's sense
of touch. Photo by Fred
Sway
|
On November 3, Jim Collins delivered a speech about The Mathematics of the Cell Cycle to a group of journalists at the annual New Horizons in Science Conference, hosted this year by BU. A month before, articles about his stochastic resonance research appeared in The Economist and the Dallas Morning News. When it comes to commanding media attention, Collins has the touch.
And so will the beneficiaries of his research. The reason stochastic resonance -- enhancing a signal by adding noise -- is of such interest to mainstream news sources is its potential to restore tactile sensation to people who have lost it. Although stochastic resonance has been studied in the contexts of physics and sensory biology for several years, Collins, ENG professor of biomedical engineering and codirector of the Center for Biodynamics, and his BU colleagues are the first investigators to attempt to give it medical application.
"Stochastic resonance is a counterintuitive phenomenon," says Collins. "Under certain circumstances, noise can actually be beneficial for the detection of weak signals."
By 'noise,' Collins means any randomly varying signal -- electrical, acoustical, even temperature. Its capacity to boost weak stimuli, he says, can be represented allegorically: Collins' hand gently rocks a marble back and forth in one of the wells of an egg carton. Such movement is an undetectable signal to an observer who can see only the marble's transition between wells.
"Now imagine you stick me on a Green Line train," says Collins. The train's motion, he explains, is noise; coupled with his hand's rocking action, it gets the marble jumping between wells. "This is sufficient to provide the observer with some information about the movement of my hand."
A research effort spearheaded by Bela Suki, ENG assistant professor of biomedical engineering, showed earlier this year that the introduction of noise, in the form of varying air pressure, could improve a patient's response to a mechanical ventilator. Similarly, Collins says, tactile signals too weak to stimulate human sensory neurons can be made palpable by the addition of a small electrical current. This is borne out by research results Collins and his colleagues published in September in the journal Chaos.
"All of our sensory systems work off of threshold-based neurons," he says. "A signal needs to exceed some value before a neuron begins firing, giving information to the brain that indicates there is a stimulus. What happens with aging, and with various conditions and injuries such as stroke and peripheral neuropathy due to diabetes, is that the thresholds get elevated. So we thought that this phenomenon of stochastic resonance, or noise-enhanced sensory dynamics in general, could potentially be exploited to develop new prosthetics that could be used to enhance sensory function for people in whom it is diminished."
Those who have suffered no loss of sensory function also stand to benefit from Collins' research, all of which was conducted on healthy subjects. The investigators applied subthreshold (undetectable) pressure and a slight electrical current to the fingertips of 11 young people. Nearly all of them were able to detect the pressure when the current was also present.
"We were pretty excited about our results," says Kristen Richardson (ENG'00), Collins' research associate and the Chaos article's first author. "We'd done an earlier study in which we'd added mechanical noise -- a little bit of noisy vibration -- to the pressure pulse, and that one had also worked very well.
"Use of the electrical current was the next logical step. It's a little bit more practical in terms of application, something we could actually potentially incorporate in a prosthetic device."
In addition to improving the everyday lives of those whose sense of touch has deteriorated, stochastic resonance could assist healthy individuals in such activities as the use of microsurgical instruments, where heightened sensation would be beneficial.
"It opens up the possibility of developing prosthetics, specifically stimulation gloves and socks, that could be used to lower tactile thresholds for everyone," says Collins.
Currently, such prosthetics exist only in theory. But Collins says he hopes to have some sort of prototype built within a few years.
"The general notion would be to use a computer chip to generate the noise, and then to use existing hardware for stimulation -- hardware that is used already in various clinical settings for therapies, but not for functional enhancement.
"I don't think we're waiting on a breakthrough," he says. "It's a matter of how much funding we can raise to move ahead. Right now, I can't point to a specific year by which we'll have a working clinical device. There's a quote that I like to refer to in these instances, which I've heard attributed both to Niels Bohr and to Yogi Berra: 'Prediction is difficult, especially of the future.' "
Nevertheless, Collins is optimistic. The attention his work has received, both in the specialized and popular media, augurs well for its continuation.
"Interestingly," he says, "it's been a very attractive subject to scientists and to the general public."