The human brain can adapt to changing demands even in adulthood, but MIT neuroscientists have now found evidence of it changing with unsuspected speed. Their findings suggest that the brain has a network of silent connections that underlie its plasticity.

The brain’s tendency to call upon these connections could help explain the curious phenomenon of “referred sensations,” in which a person with an amputated arm “feels” sensations in the missing limb when he or she is touched on the face. Scientists believe this happens because the part of the brain that normally receives input from the arm begins “referring” to signals coming from a nearby brain region that receives information from the face.

“We found these referred sensations in the visual cortex, too,” said senior author Nancy Kanwisher of the McGovern Institute for Brain Research at MIT, referring to the findings of a paper being published in the July 15 issue of the Journal of Neuroscience. “When we temporarily deprived part of the visual cortex from receiving input, subjects reported seeing squares distorted as rectangles. We were surprised to find these referred visual sensations happening as fast as we could measure, within two seconds.”

Many scientists think that this kind of reorganized response to sensory information reflects a rewiring in the brain, or a growth of new connections.

“But these distortions happened too quickly to result from structural changes in the cortex,” Kanwisher explained. “So we think the connections were already there but were silent, and that the brain is constantly recalibrating the connections through short-term plasticity mechanisms.”

First author Daniel Dilks, a postdoctoral researcher in Kanwisher’s lab, first found the square-to-rectangle distortion in a patient who suffered a stroke that deprived a portion of his visual cortex from receiving input. The stroke created a blind region in his field of vision. When a square object was placed outside this blind region, the patient perceived it as a rectangle stretching into the blind area – a result of the the deprived neurons now responding to a neighboring part of the visual field.

“But the patient’s cortex had been deprived of visual information for a long time, so we did not know how quickly the adult visual cortex could change following deprivation,” Dilks said. “To find out, we took advantage of the natural blind spot in each eye, using a simple perceptual test in healthy volunteers with normal vision.”

Blind spots occur because the retina has no photoreceptors where the optic nerve exits the eye, so the visual cortex receives no stimulation from that point. We do not perceive our blind spots because the left eye sees what is in the right eye’s blind area, and vice versa. Even when one eye is closed, we are not normally aware of a gap in our visual field.

It takes a perceptual test to reveal the blind spot, which involves covering one eye and moving an object towards the blind spot until it “disappears” from view.

Dilks and colleagues used this test to see how soon after the cortex is deprived of information that volunteers begin to perceive shape distortions. They presented different-sized rectangles just outside the subjects’ blind spot and asked subjects to judge the height and width at different time points after one eye was patched.

The volunteers perceived the rectangles elongating just two seconds after their eye was covered – much quicker than expected. When the eye patch was removed, the distortions vanished just as fast as they had appeared.

“So the visual cortex changes its response almost immediately to sensory deprivation and to new input,” Kanwisher explained. “Our study shows the stunning ability of the brain to adapt to moment-to-moment changes in experience even in adulthood.”

Notes:

Chris Baker (NIH) and Yicong Liu (MIT undergraduate student) contributed to this study, which was supported by the NIH and NIMH.

Written by Cathryn Delude, McGovern Institute, MIT News Office

Scientists are finding that the adult human brain is far more malleable than they once thought. Your behavior and environment can cause substantial rewiring of your brain or a reorganization of its functions.

Studies have shown that exercise can improve the brain’s executive skills, which include planning, organizing and multitasking. What you eat can also influence how effectively your brain operates.

Activities such as listening to music, playing video games and meditating may boost cognitive performance as well.
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Amputees sometimes experience phantom limb sensations, feeling pain, itching or other impulses coming from limbs that no longer exist. Neuroscientist Vilayanur S. Ramachandran worked with patients who had so-called phantom limbs, including Tom, a man who had lost one of his arms.

Ramachandran discovered that if he stroked Tom’s face, Tom felt like his missing fingers were also being touched. Each part of the body is represented by a different region of the somatosensory cortex, and, as it happens, the region for the hand is adjacent to the region for the face. The neuroscientist deduced that a remarkable change had taken place in Tom’s somatosensory cortex.

Ramachandran concluded that because Tom’s cortex was no longer getting input from his missing hand, the region processing sensation from his face had slowly taken over the hand’s territory. So touching Tom’s face produced sensation in his nonexistent fingers.

Continue reading this article at: Six Ways

NEW YORK (Reuters Health) – Declining mental function is often seen as a problem of old age, but certain aspects of brain function actually begin their decline in young adulthood, a new study suggests.

The study, which followed more than 2,000 healthy adults between the ages of 18 and 60, found that certain mental functions — including measures of abstract reasoning, mental speed and puzzle-solving — started to dull as early as age 27.

Dips in memory, meanwhile, generally became apparent around age 37.
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More good news on the neurobics front: Reading books, playing games or engaging in computer activities or crafts like pottery or quilting helps keep the brain young into old age, according to a new report. And while reading was good for the brain, watching too much TV seemed to be bad for it.

The findings, to be presented at the American Academy of Neurology’s 61st Annual Meeting in Seattle in late April, add to a growing body of evidence that mental challenges, or “neurobics,” like crossword puzzles and word games help keep memory and thinking sharp.

The research, from the Mayo Clinic in Rochester, Minn., involved a random sampling of 1,321 men and women in their 70s and 80s. Among the participants, 197 had mild cognitive impairment, a form of memory loss that sometimes precedes Alzheimer’s disease. The remainder had no memory problems.
Interested in reading the full article? Follow the link: Keeping the Brain Young