How Brain Reorganizes After Damage / How Dyslexic Brains Differ

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How Brain Reorganizes After Damage / How Dyslexic Brains Differ

Friday, October 08, 1999

Reuters Health -- After a head injury, the cortex -- the " thinking "

part of the brain -- can shift some brain functions from damaged to

undamaged regions, according to a report published in The Journal of

Neuroscience.

Previous research revealed that damage to the brain results in a

process termed plasticity, in which the brain reorganizes itself, with some

areas of the brain increasing in size and taking on functions of nearby

damaged areas.

In this study, Drs. Jayson and Dostrovsky of the

University of Toronto in Ontario, Canada, attempted to shed some light on

the role of the cortex and the thalamus in plasticity. The thalamus, an area

deep inside the brain, receives information about senses and body movement,

and relays this information to the cortex.

The scientists damaged specific areas of the brains of male rats and

placed electrodes in the brains to monitor how it changed in response to the

injuries.

The researchers found that simultaneous damage to the cortex and the

thalamus prevented plasticity or reorganization from occurring. However, if

they injured the thalamus, which set the process of plasticity in motion,

and then waited one week before injuring the cortex, they did see

significant changes in the structure of the thalamus, indicating that

reorganization had taken place.

and Dostrovsky conclude that in order for more primitive areas

of the brain (such as the thalamus) to adapt, it needs instruction from the

more evolved brain -- the cortex. An undamaged cortex can send signals that

help the thalamus to adapt to injury, but once the changes have been made,

the thalamus can maintain itself, the researchers say.

In an interview with Reuters Health, Dostrovsky said that the research

may have applications " to rehabilitation following strokes and trauma and

also for prevention of side effects in neurosurgery, " such as " removal of

tumors, and epilepsy surgery. "

Dostrovsky also commented that this study only relates to

reorganization of the thalamus " and it is not clear whether plasticity at

other levels (of the brain) will be similarly dependent on the cortex. "

SOURCE: The Journal of Neuroscience 1999;19.

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Dyslexic Children's Brains Differ From Normal Kids'

Dyslexia, a reading disorder, is the most common learning disability,

affecting an estimated 5 percent to 15 percent of children. Now a new

interdisciplinary study shows that dyslexic children use nearly five times

the brain area as normal children to perform a simple language task.

The study also shows, for the first time, that there are chemical

differences in the brain function of dyslexic and non-dyslexic children.

The research, published in the current issue of the American Journal of

Neuroradiology by an interdisciplinary team of researchers at the University

of Washington, also provides new evidence that dyslexia is indeed a

brain-based disorder.

The researchers, headed by developmental neuropsychologist Virginia

Berninger and neurophysicist Todd s, used a novel noninvasive

technique called proton echo-planar spectroscopic imaging (PEPSI) to explore

the metabolic brain activity of six dyslexic and seven non-dyslexic boys

during oral language tasks.

PEPSI is about 32 times faster than conventional magnetic resonance

spectroscopy. Software developed at the university enabled the researchers

to detect specific brain chemicals, including lactate.

Lactate is a by-product of energy metabolism produced by neurons when

the brain is activated. The study measured levels of brain lactate

activation. Most, but not all, of this brain activity took place in the left

anterior, or frontal, lobe of the brain, which is known to be one of the

centers for expressive language function.

" The dyslexics were using 4.6 times as much area of the brain to do the

same language task as the controls, " said s, a professor of

radiology. " This means their brains were working a lot harder and using more

energy than the normal children. "

" People often don't see how hard it is for dyslexic children to do a

task that others do so effortlessly, " added Berninger, a professor of

educational psychology. " There are learning differences in children. We

can't blame the schools or hold teachers accountable for teaching dyslexic

children unless both teachers and the schools are given specialized training

to deal with these children. "

The 13 boys in the study were between 8 and 13 years of age and the

dyslexic and control groups were well-matched in age, IQ and head size, but

not in reading skills. The controls were reading at a level above normal for

their age and had a history of learning to read easily. The dyslexics had

delayed reading skills and were reading well below average for their age.

Their families also had a history of multi-generational dyslexia that was

confirmed in a concurrent family genetics study.

Once fitted with earphones, the boys were asked to perform four tasks

while their brains were being imaged. Three of the tests involved pairs of

words and the fourth used pairs of musical tones.

In the language tests, the boys heard a series of word pairs that

consisted of pairs either of two non-rhyming words such as " fly " and

" church, " two rhyming words such as " fly " and " eye, " a non-rhyming real word

and a non-word such as " crow " and " treel, " and a rhyming word and non-word

such as " meal " and " treel. "

The boys were asked if the word pairs rhymed or didn't rhyme and if the

pairs contained two real words or one real and one non-word. They responded

by raising a hand to indicate yes or no. In the music test, the boys heard

pairs of notes and raised one hand if they thought the notes were identical

and the other if they believed them to be different.

While the dyslexic boys exhibited nearly five times more brain lactate

activation during a language task that asked them to interpret the sounds of

words, there was no difference in the two groups during the musical tone

test. This means the difference between the dyslexics and the normal

children relates to auditory language and not to nonlinguistic auditory

function, according to s and Berninger.

They also said the findings are important because they shed new light

on brain mechanisms involved with dyslexia at a developmental stage when it

is still amenable to treatment. In addition, the functional differences

between dyslexics and control subjects add evidence that dyslexia is a

brain-based disorder.

" When a child has a brain-based disorder it is treatable, although it

may not be curable, just as diabetes is, " said Berninger. " Dyslexia is a

lifelong condition, but dyslexics may learn to compensate for it later in

life. We know dyslexia is a genetic and neurological disorder. It is not

brain damage. " Dyslexics often have enormous talents in other parts of their

brain and shine in many fields. Einstein was a dyslexic, and so were

inventor Edison and financier Schwab.

" While it is useful to show there are brain differences between

dyslexic and non-dyslexic children, considerably more research is needed to

precisely define the chemical and neurological markers of dyslexia. What we

found is a metabolic marker, but there could be a more fundamental cause. We

need to understand the molecular and neural mechanisms underlying dyslexia, "

she added.

The study, part of a wider UW effort to understand the basis of

dyslexia and develop treatments for it, was funded by the National Institute

of Child Health and Human Development (NICHHD).

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editor: Lenny Schafer east coast editor: , Ph.D.

schafer@... CIJOHN@...

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