Scientists unmask brain's hidden potential

August 27, 2008

Previous research has found that when vision is lost, a person's senses of touch and hearing become enhanced. But exactly how this happens has been unclear.

Now a long-term study from the Berenson-Allen Center for Noninvasive Brain Stimulation at Beth Israel Deaconess Medical Center (BIDMC) demonstrates that sudden and complete loss of vision leads to profound – but rapidly reversible -- changes in the visual cortex. These findings, reported in the August 27 issue of the journal PLOS One, not only provide new insights into how the brain compensates for the loss of sight, but also suggest that the brain is more adaptable than originally thought.

"The brain's ability to reorganize itself is much greater than previously believed," explains senior author Alvaro Pascual-Leone, MD, PhD, Director of the Berenson-Allen Center and Professor of Neurology at Harvard Medical School (HMS). "In our studies [in which a group of sighted study subjects were blindfolded for five days], we have shown that even in an adult, the normally developed visual system quickly becomes engaged to process touch in response to complete loss of sight. The speed and dynamic nature of the changes we observed suggest that rather than establishing new nerve connections – which would take a long time – the visual cortex is unveiling abilities that are normally concealed when sight is intact."

Or, as first author Lotfi Merabet, OD, PhD, describes, "In a sense, by masking the eyes, we unmask the brain's compensatory potential."

The scientists had previously shown that study subjects with normal vision who are blindfolded for a five-day period performed better than non-blindfolded control subjects on Braille tests. Subsequent brain scans found that blindfolded subjects also experienced dramatic changes in the brain's visual cortex.

In this study, the authors set out to determine the origins of these outcomes: Were they the result of new nerve connections being developed? Or were latent capabilities in the brain's visual cortex being "unmasked" in response to the loss of sight?

"We recruited 47 subjects to participate in the study," explains Merabet, Assistant Professor of Ophthalmology and Neurology at HMS. "Half of the study participants remained completely blindfolded, 24 hours a day, for a total of five days under the careful watch of the staff of BIDMC's General Clinical Research Center. The other half were only blindfolded for testing, but spent the rest of the day seeing normally. During their stays, both sets of study participants underwent intensive Braille instruction for four to six hours a day from a professional instructor from the Carroll Center for the Blind."

The study participants also underwent serial brain scans (known as fMRI or functional magnetic resonance imaging) at both the beginning and end of the five-day study period.

As predicted, the researchers found that the subjects who were blindfolded were superior at learning Braille than their non-blindfolded counterparts. Furthermore, the brain scans of the blindfolded subjects showed that the brain's visual cortex had become extremely active in response to touch (in contrast to the initial scan in which there was little or no activity). Twenty-four hours after the blindfolds were removed, the subjects were re-scanned, whereby it was discovered that their visual cortices were no longer responsive to tactile stimulation – in other words, reading Braille no longer activated "sight" among the study subjects. Finally, using transcranial magnetic stimulation (TMS) to transiently block the function of the visual cortex, the scientists demonstrated that disruption of the visual cortex impaired tactile function and Braille reading after five days of blindfolding – but not a day after the blindfold was removed and never in the control subjects.

"This extremely rapid adaptation indicates that functions that are normally inhibited in the brain's visual cortex will come to the surface when they are needed," adds Merabet. "We believe that over time, if these adaptive functions are sustained and reinforced, they will eventually lead to permanent structural changes."

"Our brain captures different types of information from the world -- sounds, sights, smells or tactile sensations," adds Pascual-Leone. "The impressions we form require us to merge these various different elements, but science's traditional view of brain function is that it is organized in separate and highly specialized systems."

But, he says, as the results of this research demonstrate, that is not the case.

"Our study shows that these views are incorrect and illustrate the potential for the human brain to rapidly and dynamically reorganize itself," notes Pascual-Leone. "We have shown that even in an adult, the normally developed visual system quickly becomes engaged to process touch in response to complete loss of sight. And we believe that these principles may also apply to other sensory loss, such as deafness or loss of function following brain injury."

Source: Beth Israel Deaconess Medical Center

Explore further: Researchers demonstrate 'mind-reading' brain-decoding tech

Related Stories

Researchers demonstrate 'mind-reading' brain-decoding tech

October 23, 2017
Researchers have demonstrated how to decode what the human brain is seeing by using artificial intelligence to interpret fMRI scans from people watching videos, representing a sort of mind-reading technology.

Novel technology ties brain circuits to alertness

November 2, 2017
Stanford University investigators have for the first time tied several brain circuits to alertness.

Study unveils changes in the brain during extended missions in space

November 1, 2017
It's been 55 years since NASA astronaut John Glenn successfully launched into space to complete three orbits aboard the Friendship 7 Mercury spacecraft, becoming the first American to orbit the Earth. The evolution of spaceflight, ...

Researchers want to heal the brain. Should they enhance it as well?

October 18, 2017
Despite obvious benefits for people with otherwise untreatable conditions, there could be downsides to brain-machine interfaces being developed to treat disease or drive prosthetic limbs. As researchers get better at building ...

Right brain also important for learning a new language

October 17, 2017
Novel language learning activates different neural processes than was previously thought. A Leiden research team has discovered parallel but separate contributions from the hippocampus and Broca's area, the learning centre ...

Virtual reality reduces phantom pain in paraplegics

October 30, 2017
Virtual reality reduces phantom body pain in paraplegics and creates the illusion that they can feel their paralyzed legs being touched again. The results could one day translate into therapies to reduce chronic pain in paraplegics.

Recommended for you

Hibernating ground squirrels provide clues to new stroke treatments

November 17, 2017
In the fight against brain damage caused by stroke, researchers have turned to an unlikely source of inspiration: hibernating ground squirrels.

Age and gut bacteria contribute to multiple sclerosis disease progression

November 17, 2017
Researchers at Rutgers Robert Wood Johnson Medical School published a study suggesting that gut bacteria at young age can contribute to multiple sclerosis (MS) disease onset and progression.

Molecular guardian defends cells, organs against excess cholesterol

November 16, 2017
A team of researchers at the Harvard T. H. Chan School of Public Health has illuminated a critical player in cholesterol metabolism that acts as a molecular guardian in cells to help maintain cholesterol levels within a safe, ...

Prototype ear plug sensor could improve monitoring of vital signs

November 16, 2017
Scientists have developed a sensor that fits in the ear, with the aim of monitoring the heart, brain and lungs functions for health and fitness.

Ancient enzyme could boost power of liquid biopsies to detect and profile cancers

November 16, 2017
Scientists are developing a set of medical tests called liquid biopsies that can rapidly detect the presence of cancers, infectious diseases and other conditions from only a small blood sample. Researchers at The University ...

FDA to crack down on risky stem cell offerings

November 16, 2017
U.S. health authorities announced plans Thursday to crack down on doctors pushing stem cell procedures that pose the gravest risks to patients amid an effort to police a burgeoning medical field that previously has received ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.