Brain scans link myelin with intelligence

**francois** · 10-10-10, 09:23 AM

http://www.technologyreview.com/biomedicine/22333/

New research suggests that the layer of insulation coating neural wiring in the brain plays a critical role in determining intelligence. In addition, the quality of this insulation appears to be largely genetically determined, providing further support for the idea that IQ is partly inherited.

The findings, which result from a detailed study of twins' brains, hint at how ever-improving brain-imaging technology could shed light on some of our most basic characteristics.

"The study answers some very fundamental questions about how the brain expresses intelligence," says Philip Shaw, a child psychiatrist at the National Institute of Mental Health, in Bethesda, MD, who was not involved in the research.

The neural wires that transmit electrical messages from cell to cell in the brain are coated with a fatty layer called myelin. Much like the insulation on an electrical wire, myelin stops current from leaking out of the wire and boosts the speed with which messages travel through the brain--the higher quality the myelin, the faster the messages travel. These myelin-coated tracts make up the brain's white matter, while the bodies of neural cells are called grey matter.

White matter is invisible on most brain scans, but a recently developed variation of magnetic resonance imaging, called diffusion-tensor imaging (DTI), allows scientists to map the complex neural wiring in our brains by measuring the diffusion of water molecules through tissue. Thanks to the fatty myelin coating, water diffuses along the length of neural wires, while in other types of brain tissue it moves in all different directions. Researchers can calculate the direction of fastest diffusion at each point in the brain and then construct a picture of the brain's fiber tracts. A well-organized brain has well-functioning myelin, in which water can be seen clearly moving along specific paths. "Diffusion imaging gives a picture of how intact your brain connections are," says Paul Thompson, a neuroscientist at the University of California, Los Angeles, who lead the study.

Thompson and his colleagues took DTI scans of 92 pairs of fraternal and identical twins. They found a strong correlation between the integrity of the white matter and performance on a standard IQ test. "Going forward, we are certainly going to think of white matter structure as an important contributor of intelligence," says Van Wedeen, a neuroscientist at Massachusetts General Hospital in Boston, who was also not involved in the research. "It also changes how you think about what IQ is measuring," says Wedeen. The research was published last month in the Journal of Neuroscience.

IQ inheritance: By comparing the brain scans of twins, scientists discovered that the quality of the fatty tissue that insulates neural wires is largely inherited. The parietal lobe, which is involved in logic and mathematics, is 85 percent genetically determined, whereas the visual cortex is about 76 percent, and the temporal lobe, which is involved in learning and memory, is only 45 percent genetically determined.

If white matter is linked to both processing speed and IQ, this raises the question: is intelligence merely a function of how fast your brain works? Previous research has linked processing speed to IQ, but the tests used in the study are measures of general intelligence, including verbal skills, math, and logic. "Processing speed plays a big part in how intelligent you are, but it's not the only factor," says Shaw.

The new study is among the first to link a specific neural architecture to IQ in healthy individuals. "Most people have focused on grey matter," says Shaw. "This is good evidence we should be looking at white matter as well." Previous studies using DTI have linked white matter damage to Alzheimer's disease, chronic alcoholism, and traumatic brain injury.

The UCLA researchers took the study a step further by comparing the white matter architecture of identical twins, who share almost all their DNA, and fraternal twins, who share only half. Results showed that the quality of the white matter is highly genetically determined, although the influence of genetics varies by brain area. According to the findings, about 85 percent of the variation in white matter in the parietal lobe, which is involved in mathematics, logic, and visual-spatial skills, can be attributed to genetics. But only about 45 percent of the variation in the temporal lobe, which plays a central role in learning and memory, appears to be inherited.

Thompson and his collaborators also analyzed the twins' DNA, and they are now looking for specific genetic variations that are linked to the quality of the brain's white matter. The researchers have already found a candidate--the gene for a protein called BDNF, which promotes cell growth. "People with one variation have more intact fibers," says Thompson.

The search for the genetic and neuroanatomical basis of intelligence has been controversial, largely because opponents fear it will spawn a deterministic view of abilities and education. "People worry that if something is genetic, they have no power to influence it," says Thompson. "But that's not true at all." For example, both an average runner and a genetically gifted one can benefit from training.

But the debate may be moot since, as Wedeen points out, it is unlikely that an individual brain scan could predict a person's IQ. "The report described aggregate data over number of individuals," he says. "That's not the same as saying we can do a scan and determine a person's intelligence. That may be in the offing, but we don't know that yet."

**francois** · 10-10-10, 09:24 AM

**francois** · 10-11-10, 12:40 PM

Thompson and his colleagues took DTI scans of 92 pairs of fraternal and identical twins. They found a strong correlation between the integrity of the white matter and performance on a standard IQ test. "Going forward, we are certainly going to think of white matter structure as an important contributor of intelligence," says Van Wedeen, a neuroscientist at Massachusetts General Hospital in Boston, who was also not involved in the research. "It also changes how you think about what IQ is measuring," says Wedeen. The research was published last month in the Journal of Neuroscience.

The bolded part is pretty interesting, I think. So the strength and speed of connections have an important relationship to IQ.

The oligodendrocyte, which is a type of glial cell, is what wraps the myelin around the axon in the CNS. Although Einstein's brain was of normal size, it's been suggested that he had a higher than average proportion of glial cells to nerve cells. Perhaps these extra glial cells were oligodendrocytes and helped keep his axons well myelinated.

This is an interesting way to think about intelligence. There are many different IQ correlates, but one of them always struck me as peculiar--reaction speed. People with higher IQs have higher reaction speed, from say, visual impetus, to physical reaction. Perhaps this is why. Faster interneural speeds cause faster reaction times as well as quicker thinking/higher intelligence.

Of course, intelligence is a global process--something that arises out of cooperation of large portions of the brain. Perhaps the relationship of IQ and quality of myelination isn't caused so much by the speed of the enabled transmissions, but the reliability. When an axon is poorly myelinated, the electrical message is more like a wave; when the axon is well myelinated, the message is more like a saltation--it's more like a digital message, which is less susceptible to attenuation and noise.

Think about when you watch a football game when it's snowing. It looks like a blizzard, but really, it only looks that way because of the zoom of the camera. It's only dusting, but you really are looking at a lot of snow by virtue of the fact that you're viewing the field from a long distance.

The brain is a big network of connections, so a little attenuation there, and a little noise there, makes a big difference as messages travel, because you're going a long distance. Therefore, the better insulated the channels are, the better the overall communication of the network.

**GeoffP** · 10-11-10, 01:25 PM

Yeah, poor sheathing = attenuated signal = lower functional cognition.

**WillNever** · 10-11-10, 01:36 PM

Adults who have MS progressively lose myelination in their brains yet they do not lose intelligence.

**francois** · 10-11-10, 03:11 PM

Originally Posted by WillNever

Adults who have MS progressively lose myelination in their brains yet they do not lose intelligence.

General intelligence
People with MS sometimes say they feel "dumber." The good news is that general intelligence is usually not affected in MS. However, individual functions that make up general intelligence, such as memory, reasoning, or perceptual skills, can be affected or slowed temporarily during a relapse or more permanently over the course of the disease. So, a person's intelligence quotient (IQ), which is a composite score made up of individual subtest scores on all these functions, can become lower over time.

Read more: http://www.dummies.com/how-to/conten...#ixzz125FYFJck

That's kind of confusing to me. Cognitive functions like memory and reasoning can decline, but intelligence stays same? Another thing confusing is that she mentions general intelligence explicitly--but that's something that IQ tests specifically try to hone in on--and IQ is something that is known to become lower over time with MS. Makes sense, what can you really achieve without memory?

**GeoffP** · 10-11-10, 03:13 PM

You don't (presumably) lose stored info, but you can't transmit into motor function and the use or recall of that information. Functional intelligence declines.

**WillNever** · 10-11-10, 03:30 PM

Halt. Do either of you actually have any firsthand experience with patients with MS? I have cared for many. Their intelligence is unchanged. If you didn't know about their illness, you would not be able to distinguish MS patients from non MS patients through intelligence or even memory. You would only notice the difference in motor function.

According to my medical PDA that I use in the hospital, perceptual deficits may occur but they result from lesions on the optic nerve and represent the same demyelinating neuropathy that affects all parts of the body. Mentally, only their attention span is shortened and they may be depressed.

**GeoffP** · 10-11-10, 03:43 PM

Originally Posted by WillNever

Halt. Do either of you actually have any firsthand experience with patients with MS?

As the OP says, it's a factor. I'm not referring specifically to MS patients, myself, but to general cognition; this neuropathy might occur in any neurological disorder. Francois mentions that elements of cognition may be affected.

**WillNever** · 10-11-10, 03:45 PM

Anything is remotely possible geoff, but any intellectual deficit that occurs is insignificant enough that you wouldn't perceive it from communicating with MS patients.

**GeoffP** · 10-11-10, 03:50 PM

Possibly not, but I'm not discussing that group specifically.

**visceral_instinct** · 10-12-10, 10:16 AM

Originally Posted by francois

This is an interesting way to think about intelligence. There are many different IQ correlates, but one of them always struck me as peculiar--reaction speed. People with higher IQs have higher reaction speed, from say, visual impetus, to physical reaction. Perhaps this is why. Faster interneural speeds cause faster reaction times as well as quicker thinking/higher intelligence.

That's odd because I tested as gifted, but I have the crappiest reaction time. ?

I could be just one outlier, though.

Or it could be those tests mean absolutely jack shit. I certainly don't feel that I'm exceptionally smart.

**GeoffP** · 10-12-10, 10:40 AM

Correlation between reaction time and "functional intelligence" is less than unity.

**francois** · 10-14-10, 09:30 PM

http://www.psychologicalscience.org/...ction_time.pdf

This is a study that finds a relationship between IQ and reaction speed. The correlations were .49 and .31 with choice and simple reaction time, respectively. That's definitely significant. They find that both are related to longevity: those with higher IQs live longer. But reaction speed was an even better predictor of longevity than IQ.

There were several hypothese, but the one that the author seemed to prefer is that IQ is a reflection of "suboptimal integrity of one's physiology." That would make sense to some extent, since it's known that IQ also relates with body symmetry, which is an indicator of the stability of one's development. He suggests this because it doesn't matter when the IQ test is administered--whether it's when the person is a child or in late age--it's a valuable predictor.

On the other hand, it could represent--and this is just my own musing--the body using whatever genetic variation it had to focus on making the brain strong, and causing the person to live a longer time, rather than say develop early and have many babies. Both are viable strategies. I think it's called r/K selection theory.

**WillNever** · 10-15-10, 07:02 AM

Has that study and its results been reproduced anywhere?

**visceral_instinct** · 10-15-10, 08:57 AM

Originally Posted by francois

http://www.psychologicalscience.org/...ction_time.pdf

This is a study that finds a relationship between IQ and reaction speed. The correlations were .49 and .31 with choice and simple reaction time, respectively. That's definitely significant. They find that both are related to longevity: those with higher IQs live longer. But reaction speed was an even better predictor of longevity than IQ.

There were several hypothese, but the one that the author seemed to prefer is that IQ is a reflection of "suboptimal integrity of one's physiology." That would make sense to some extent, since it's known that IQ also relates with body symmetry, which is an indicator of the stability of one's development. He suggests this because it doesn't matter when the IQ test is administered--whether it's when the person is a child or in late age--it's a valuable predictor.

On the other hand, it could represent--and this is just my own musing--the body using whatever genetic variation it had to focus on making the brain strong, and causing the person to live a longer time, rather than say develop early and have many babies. Both are viable strategies. I think it's called r/K selection theory.

That is another weird one.

I have asymmetrical cheekbones, more strength in my left side, and I have one eye that looks kinda Asian.

And I'm supposedly gifted.

**francois** · 10-15-10, 09:22 AM

Originally Posted by visceral_instinct

That is another weird one.

I have asymmetrical cheekbones, more strength in my left side, and I have one eye that looks kinda Asian.

And I'm supposedly gifted.

It's not so strange. Scientists likely have a different way of measuring symmetry than simple eye shot. And of course, if you truly are a mutant (jk), then that's just one person and can't speak for much in general trends.

**visceral_instinct** · 10-15-10, 11:17 AM

Originally Posted by francois

It's not so strange. Scientists likely have a different way of measuring symmetry than simple eye shot. And of course, if you truly are a mutant (jk), then that's just one person and can't speak for much in general trends.

Oh I know, but any way you measure symmetry...I am asymmetric. So I'll guess that as you said, I'm simply not a member of the general trend.

**iceaura** · 10-15-10, 12:21 PM

Adults who have MS progressively lose myelination in their brains yet they do not lose intelligence.

I thought they lost myelination in their motor neurons and other axons that are vulnerable to a haywire immune system?

The internal neurons of the brain are not vulnerable to that kind of immune system dysfunction.

**WillNever** · 10-15-10, 01:35 PM

That isn't correct ice. Sensory neurons are affected as well. That is why a lot of MS patients have numbness, tingling, parathesia. Cranial nerve II (the optic nerve) is purely sensory, and that is also affected.

Here's an excerpt from my medical PDA:

"MS is a chronic, progressive degenerative disease that affects the myelin sheath of the white matter of the brain and spinal cord. Each year 25,000 people are newly diagnosed with MS. The disease affects quality rather than duration of life. In MS, nerve impulses are conducted between the brain and spinal cord along neurons protected by the myelin sheath, which is a highly conductive fatty material. When plaques form on the myelin sheath, causing inflammation and eventual demyelination, nerve transmission becomes erratic. Areas commonly involved are the optic nerves, cerebrum, and cervical spinal cord."

MS seems to affect pathways from the brain to the spinal cord or along the cranial nerves mainly, according to the above. To what degree the internal structure of the brain is affected seems elusive, but according to what francois has shown us, their learning appears to be affected in a minute way. However, I think that is probably due to the higher rates of depression that often accompanies MS patients (depression is correlated with decreased mental functioning). If you ever met MS patients, their minds appear entirely unaffected.