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Sat Oct 8 08:16:18 EST 2011


When Samuel Morse established the first commercial telegraph, in 1844, he d=
ramatically changed our expectations about the pace of life. One of the fir=
st telegraph messages came from that year=92s Democratic National Conventio=
n in Baltimore, where the delegates had picked Senator Silas Wright as thei=
r vice presidential nominee. The president of the convention telegraphed Wr=
ight in Washington, D.C., to see if he would accept. Wright immediately wir=
ed back: No. Incredulous that a message could fly almost instantly down a w=
ire, the delegates adjourned and sent a flesh-and-blood committee by train =
to confirm Wright=92s response=97which was, of course, the same. From such =
beginnings came today=92s high-speed, networked society.

Less famously but no less significantly, the telegraph also transformed the=
 way we think about the pace of our inner life. Morse=92s invention debuted=
 just as researchers were starting to make sense of the nervous system, and=
 telegraph wires were an inspiring model of how nerves might work. After al=
l, nerves and telegraph wires were both long strands, and they both used el=
ectricity to transmit signals. Scientists knew that telegraph signals did n=
ot travel instantaneously; in one experiment, it took a set of dots and das=
hes a quarter of a second to travel 900 miles down a telegraph wire. Perhap=
s, the early brain investigators considered, it took time for nerves to sen=
d signals too. And perhaps we could even quantify that time.

The notion that the speed of thought could be measured, just like the densi=
ty of a rock, was shocking. Yet that is exactly what scientists did. In 185=
0 German physiologist Hermann von Helmholtz attached wires to a frog=92s le=
g muscle so that when the muscle contracted it broke a circuit. He found th=
at it took a tenth of a second for a signal to travel down the nerve to the=
 muscle. In another experiment he applied a mild shock to people=92s skin a=
nd had them gesture as soon as they felt it. It took time for signals to tr=
avel down human nerves, too. In fact, Helmholtz discovered it took longer f=
or people to respond to a shock in the toe than to one at the base of the s=
pine because the path to the brain was longer.
Helmholtz=92s results clashed with people=92s gut instinct that they experi=
enced the world as it happened, with no lag between sensation and awareness=
. =93This is altogether a delusion,=94 German physiologist Emil Du Bois-Rey=
mond declared in 1868. =93It appears that =91quick as thought=92 is, after =
all, not so very quick.=94

With their simple tools, Helmholtz and others could manage only crude measu=
res of the speed of thought. Some of them came up with rates that were twic=
e as fast as others. Researchers have been trying to get more precise resul=
ts ever since. Today it is clear why they have had such a hard time. Our ne=
rves operate at many different speeds, reflecting the biological challenges=
 of wiring all the parts of the body together. In some ways evolution has f=
ine-tuned our brains to run like a digital superhighway, but in other ways =
it has left us with a Pony Express.
Thought may not be instantaneous, but it is rapid enough to seem like it is=
 most of the time. The need for speed in the nervous system is not hard to =
understand. Many animals depend on their nerves to sense danger and to esca=
pe from predators; the predators, in turn, depend on their nerves to mount =
a fast attack. But speed also influences us in surprising ways.

In one common experiment for studying the speed of thought, researchers bri=
efly show test subjects a lopsided, upside-down U and then ask them which l=
eg of the figure is longer. It turns out that the subjects=92 reaction time=
s say a lot about their lives in general. People with faster responses tend=
 to score higher on intelligence tests. Some psychologists have argued that=
 a high processing speed in the brain is a vital ingredient for intelligenc=
e. Responses slow down when people suffer certain psychological disorders l=
ike depression. More puzzling, people with sluggish reaction times are more=
 likely to die of incidents like strokes or heart attacks.

High speed is also crucial to the way we perceive the world. Three or four =
times a second, our eyes dart in a new direction, allowing us only about a =
tenth of a second to make sense of what we see in each spot. And we make re=
markably good use of that time. Recently, neuroscientists Michelle Greene a=
nd Aude Oliva of MIT ran an experiment in which they briefly showed people =
a series of landscapes and then asked questions about the scenes. For examp=
le, was there a forest in the picture? Did it look like a hot place? People=
 did well on these tests even when they glimpsed each of the pictures for l=
ess than one tenth of a second.

We are able to understand the world so quickly because of some clever speed=
 boosters built into our eyes. Tim Gollisch of the Max Planck Institute of =
Neurobiology in Germany recently discovered evidence of one of these. He ex=
tracted retinal tissue from amphibians and exposed the living tissue to a s=
eries of simple geometric patterns. Then he recorded how the nerve cells fi=
red in response. He noticed that each neuron started firing a little earlie=
r or a little later, depending on which picture he showed. The shifts were =
distinctive enough that he could predict a shape just by looking at the tim=
ing of the neural reaction. Although this test involved amphibians, Gollisc=
h proposes that the results would hold true for human brains as well. They =
might not wait for all the signals from the retina to arrive before they be=
gin building a representation of the world. They might get a head start wit=
h the very first bits of information.
Using a fast code helps speed up thought, but to a large extent the brain=
=97like a telegraph network=97really depends on efficient pathways. Impulse=
s from the retinas, for instance, have to travel up the optic nerve to the =
thalamus, which relays the signals to the visual cortex in the back of the =
brain. Then they ripple forward to other brain centers, where we use the vi=
sual information to make decisions and take actions. One way to hasten that=
 journey is to use fast wiring. In 1854 physicist William Thomson showed th=
at the wider a telegraph wire, the faster its signal and the farther the si=
gnal could travel. That same principle applies to nerves. The fattest axons=
, such as Betz cells in the brain, are 200 times thicker than the thinnest =
ones.

Another way to speed up wires is to insulate them, and again the same goes =
for neurons. Some neurons are wrapped in an insulating material known as my=
elin. In the heavily myelinated neurons running down the spine, signals can=
 travel up to 180 miles an hour. In neurons that lack myelin, signals trave=
l just over half a mile an hour. Nerve fibers that carry pain are among the=
 slowest. Pain can take many seconds to reach the brain, explaining why som=
etimes we seem to react to a stubbed toe in slow motion.

In principle, our thoughts could race far more efficiently if all the axons=
 in our brains were thick. But the human brain has at least a quarter of a =
million miles of wiring=97more than enough to reach from Earth to the moon=
=97and is already packed tight. Sam Wang, a Princeton University neuroscien=
tist, calculated how big our brain would be if it were built with thick axo=
ns. =93Making an entire brain out of them would create heads so large that =
we couldn=92t fit through doorways,=94 he concluded. Such a brain would als=
o consume a tremendous amount of energy.

Given the constraints of biology and physics, our brains appear to have evo=
lved to run very efficiently. For instance, neurons in the brain tend to be=
 joined together into small networks, which are then linked to one another =
by relatively few long-range connections. This kind of network needs less w=
iring than other arrangements, and therefore shortens the distance signals =
need to travel.
In some ways evolution has fine-tuned our brains to run like a digital supe=
rhighway. In other ways it has left us with a Pony Express.
Our brains also speed up through practice. Rene Marois, a neuro=ACscientist=
 at Vanderbilt University, measured this effect by having people perform a =
basic multitasking test: They had to identify which of two possible faces a=
ppeared on a computer screen while responding to one of two possible sounds=
. In just two weeks of training (encompassing eight to twelve practice sess=
ions), the test-takers were able to do both tasks in rapid succession almos=
t as quickly as doing either one on its own. With practice, Marois speculat=
es, the neurons in the brain=92s bottleneck regions, primarily in the prefr=
ontal cortex, require fewer signals and less time to produce the right resp=
onse.
Sometimes our brains actually need to slow down, however. In the retina, th=
e neurons near the center are much shorter than the ones at the edges, and =
yet somehow all of the signals manage to reach the next layer of neurons in=
 the retina at the same time. One way the body may do this is by holding ba=
ck certain nerve signals=97for instance, by putting less myelin on the rele=
vant axons. Another possible way to make nerve impulses travel more slowly =
involves growing longer axons, so that signals have a greater distance to t=
ravel.

In fact, reducing the speed of thought in just the right places is crucial =
to the fundamentals of consciousness. Our moment-to-moment awareness of our=
 inner selves and the outer world depends on the thalamus, a region near th=
e core of the brain, which sends out pacemaker-like signals to the brain=92=
s outer layers. Even though some of the axons reaching out from the thalamu=
s are short and some are long, their signals arrive throughout all parts of=
 the brain at the same time=97a good thing, since otherwise we would not be=
 able to think straight.

So when Helmholtz recognized that thought moves at a finite rate, faster th=
an a bird but slower than sound, he missed a fundamental difference between=
 the brain and a telegraph. In our heads, speed is not always the most impo=
rtant thing. Sometimes what really matters is timing.

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(E)MOTION FREQUENCY deceleration research archive 2011

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