Download Shape of Thought

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CHAPTER
6
Tlte Shape {Thought
single neuron may be rather dumb, but
many subtle ways.
A
it is dumb in
-Francis
Crick
of aspens in oregon is reputed to be the largest single
org".ism on Earth, an underground mass from which over a
hundred thousand tfees tower.It flows over hillsides and along valleys,looking like a mob of distinct, separate tre_es) but combining,
in one network bolder than its sum' an organism that masters
time and space. conquering immobiliry a plant's wofs,t nemesis, it
trqaels.Thetrees work in unison, despite the small sPaces between
them. some trees telegraph their mood and news. under attack,
they send chemical messages to their neighbors, warning-tht-- of
danger so rhey canrally a defense. An individual life with a hundreJtho,rsa.rd |i*br, this vast organism pales beside the billions of
branching neurons in the brain, which are also seParate yet Part of
a single invisible indivisible life.
NJ,rro.r, grow like quaking asPens in the forests of the mind,
sprouting fro* orr. matrix, a hidden grove. Unlike other cells, they
dottt *orr" or divide.They assume branching shapes from pyramid
to star. Best of all, they talk among themselves, eavesdrop, dash off
messages. For that PurPose, they have two kinds of limbs, dendrites
the former to listen, the latter to speak' Dangling from
^rrd "*o^r,
a neuron's pouchy trunk, dendrites hear what neighboring neurons
signal through their axons. Like elegant ladies air-kissing so as not
to muss their makeup, dendrites and axons don't quite touch. The
A
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stand,
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37
38
AN ALCHEMY OF MIND
THE SHAPE OF THOUGHT
contact happens in less than one thousandth
of a second, a spell of
microtime powerful as fate. Some neurons
sprout only a few dendrites, while others send o-u_t many,
creating u hug., i.rt i."t.;urrgt.
that can talk, ultimately, with 100"000
other neurons. Some neurons
broadcast their news, others jusi
gab with each other. some connections are nonstop, others *i"r.a.
Some connections come with
:the genetic suit, others are etched by
experience. If a man tried to
count all those connections, devotingonly
a second ,o
,h. n.rrl
sum would take about 3-million
y*rr. Even if he "u.1,
zul,r..rrty
*r"
reincarnated, but unevolved dus to
chronically U"Jf.ur_", *.t.
talking 42,000 lifetimes.
When shocked, refreshed, or just learning
something neurons
grow new dendritic branches, increasing
thet reach
even more. It's as if a neuron sends
"rriirrfl.r"rr..
gather news. The scours gossip
their reports, a neuron
other neurons, using its
fas.ses -.r_."g.r_to
axon' a fine branching rimb
"rry*h.i. from a few m'lirnei.r, ,o "
merer long. As the axons tip grows,
it senses ir,
g."r"g
cues on which direction to turnsomehow at """iro";;"r,
that nosing ulo.rrra,
connecting, and networking orients
personarity, chisels .f,"r".,.r.
speak an elite pr,cgin neithe, chemical
nor electricar but
..N:"l""r
a iively buz'z that brends th.
i"o, an electroch.-i.a [rrg; thei,
own' To speak, a neuron sends an electrical
"[ the
shudder down
length of its axon in a wave created
from the ebb and flow of
alternating sodium and potassium ions.
A neuron's electricity isn,t
like alamp cord,s, where cu'ent rides
a cloud
.h;;;;. e"a irt
not like a sizzle of arcing electricity.
More like"frolling ,,i.t arr,
back and forth, between you, p"i*,
"
until a spark jumps.
Only
eighty thousandths of a volt, u pjr"
,u.", thro.rgh tfr. iiri.f,.rt nU.r,
at hundreds of miies pe, ho,.rr,
through d;;;:,;;;
.r..0.
Able to fire hundreds of times"nd
a second, one brain cell can rally
a
mob' until whole neurar networks
convey a word kke teacber,a feeling_like jealousy, an event like
a bike ride.
,,,
4 Every New Yearts Eve, serected students in the Ithaca
college
dorms leave their room lights
o., o. ofr, _irrdo* rfrrJ*
a
creare huge glowing numlrals.
"p.",
At midnight, on
s
"r'onffilltff"JJTT:I
;;,"tli;**
j:
39
their lights on or off to change the numbers. From miles away, people watch and understand. Worlds within worlds, systems within
systems, our neural networks combine to organize, integrate, and
encode every kiss, hissy fit, prank, and prayer"
How important are the brain salts? One spring day,after strolling
along a meandering pathway for only forty minutes in Morikami
Japanese Gardens in Delray Beach, Florida,I suffered severe heat
exhaustion: spine-crumbling weakness, crabbiness, panting, chills. My
conscious mind was an empty cutlery drawer. V\/ood can warp and
skull ache; mybrain seemed alldownstairs. Higher thought-ideas,
creating-floated beyond reach. Although I could understand and
answer people in basic ways, I seemed to move in a slow, staggering
blur. I felt irritable. Speech was too exhausting to initiate. Suffering
from dehydration, my brain struggied with its electrical signals and I
felt logy The idea of food sickened me. I dozed between naps and
woke craving sleep. My bodywas in drought and its delicate salt balance out of whack Two days, a hospital visit, and many liters of water
and Gatorade later,I felt normal again. But it brought home to me
the brute power and fragile equilibrium of potassium, sodium, magnesium, and other salts essential to the brain's electricity. Without
water, they cant dissolve, and it doesnt take much to disturb them
a water loss of only zbout 2 percent will do.
Brain cells communicate by sort of shaking hands at hundreds of
billions of minute contact points Called syna?ses (Greek for "clasp
together"), slender channels between neurons. At land's end there's
a terminal, where a neuron talks to its neighbor by releasing special
molecules, more than a hundred different neurotransmitters, that can
drift across the tiny gap and bind to receptors on the other side. The
molecules are sometimes pictured as keys, the receptors as locks.
When all household keys become electronic,I suppose our antique
analogy of a lock-and-key fit will change, but for the moment it's
still a sexy image: one shape perfecdy machined to fit inside another.*
*Plumbers and engineers call connecting parts male and ltmale. Years ago, planning
station hookup, Russian and American scientists garhered to discuss the logisheard from one ofthem that a lengthy source ofdisagreement was that neither
country wanted to be the female part!
a space
tics.
I
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AN ALCHEMY OF MIND
CHAPTER
7
Traditionalloclsandkeysareriltbendablebutimperviousmetalonly
in films.that
can pick. We've seen the image so many times
i[uln,
unplr"rl"d by a uniquely designed soft
angles and etrrys, which is
key. We like cr-eating solid objects with
*iry *. find the surealist dieamtime of Salvador Dalit melting
membranes'
po.k", watch so arresting'. But on the surface of cell
'r.."p,orc
keywith the same
sit like uniquely shaped soft iocks' A soft
chemitransmitter
that key may be a
,fr^p. ."" oPen the L.k,
it,s hard to imagine a soft 10ck
Inner
Space
. . . life is tolerable only by the degree of rnystification we
endow it with.
""i
-E.
caloralook-alikedrugusedtofoolthereceptor.It'sstillbreaking
jangle a.ITF" set of
and entering, minus tte villains. We long to
the image: the receptors are onloff switches
chemical k |.. Ct
"nge
the key is a car key that
that activate the next"cell. Cha"ge the image:
starts or turns off the engine'
mob, each
one molecule wont"do. It takes a perfectly timed
ions
binding to its receptor. When the door opens' potassium
an-electrical
rush out and sodium ions rush in, again creating
which Passes along the
charge, this time in the receiving neuron'
sparks'
infor"mation by releasing u ch"mital to lrs neighbor'-whrc!
of
environs
wholeand so on, until the message zooms among
underlies everyneurons. This one Process (synaptic transmission)
and
thing the brain dois, nit oi o"t ttttowledge' motivilyirims'
puts it: "Ultimately all
desires. ,Frs The Dana Guide to Brain Heakh
feelings-can be boiled
that we are-all our memories, hopes, and
the membrane wall
down to the banal transfer of a few ions across
of brain cells." Hold that thought like a doubioon'
M. Cioran,
A Short History of Decay
f mpossible as it sounds, we have more brain cell connections than
I th.t. are stars in the universe.The visible universe, I mean, since
96 percent of the measurable universe is invisible, to us at least.
Linger with that thought a moment, picturing the infinities of
space-a carbon-paper night struck through with countless stars.
Then picture the microscopic hubbub in one brain' A typical
brain contains about 100 billion neurons, consumes a quarter of the
body's oxygen, and spends most of the body's calories, though it
onlyweighs about tfuee pounds. A ten-watt lightbulb uses the same
amount of electrical energy. In a dot of brain no larger than a single grain of sand, 100,000 neurons go about their work at a billion
synapses. In the cerebral cortex alone, 30 billion neurons meet at 60
trillion synapses a billionth of an inch wide. Only a tiny lightningbolt-like apostrophe, and a space essential as the gap between
neurons, stands between impossible and I'm possible.
To cross or not to cross. Sometimes it takes more than one signal to rouse an idle mind, so the brain nags itse[ sending the same
signal over and over. Getting a neuron's attention isrlt easy-what
if itt a false alarm? Better to doze a while until the nagging cant be
ignored. S omething like p e r s u as i o n frnally happens. The neuron gets
excited, joins in, spreads the word. A tribe of neurotransmitters
4t
42
rNNER
AN ALCHEMY OF MIND
sPAcE
43
GABA recePtors' the inhibitory ones' and neurons can become so
inhibited you feel dozY.
our sense of self thrives in those minute spaces, convergence
serve as go-betweens.I picture rush hour on the jammed streets of
Manhattan, where cars, trucks, limos, taxis, buses, and people con*
verge, hoping not to collide, whiie death-defring bicycle messengers weave at speed amid the traffic, sailing through the narrows
between truck and car, shifting hips and shoulders to balance as they
the
zones wher e pvzzlesbecome pictures and concepts' We haunt
tiny intersections throughout the brain where traffic
sialf colides, or drives across. The space between two neurons'
synapses,
swerve, one-handed, carrying a parcel under an arm. Sometimes
they skim metal or bruise a shin, creating chaos for others, but sti11
meet to
called a synaptic junction, provides a narrows where they
the air between
send and receive news.It is a small liquid sPace, as is
they continue at speed, hell-bent for their destination-a single
doorway on a tall dendritic building. Once a message arrives, anything or nothing can happen. However enthusiastic, an invitation
to join a friend at a nudist camp might not excite you. By disposition, you might not even consider it.
Like hidden Caribbean resorts, synapses can favor excitement or
inhibition. Francis Crick puts it charmingly in The Astonishing
Hypothais: "It is important to realize that what one neuron tells
another neuron is simply how much it is excited." Life is commotion. Four fifths of the neurons in the neocortex favor excitement.
The neurotransmitter glutamate feeds that excitement; a small
molecule called GABA feeds inhibition. Glutamate and GABA are
the speed demons, on call for quick responses to colossal amounts
of information. Some slower neurotransmitters include serotonin,
norepinephrine, and dopamine, which star in treatments for depression. All sorts of molecules-amino acids, peptides, hormones, and
even gases (like nitric oxide)-serve as special messengers. What
happens really depends more on the mood of the receptor than the
willingness of the messenger. The same messenger can be exciting
at one doorway and inhibiting at another, causing wildly di{ferent
outcomes.
I often marvel at how pills no larger than a hummingbird's eye
can produce such dramatic results in a big mammal. Because what
happens at the synapses is mainly chemical, not electrical, tiny molecules such as antidepressants and sedatives can insinuate their way
in and reshape events. My mother, for example, used to take Valium on occasion to calm her nerves, and it always made her sleepy.
That's because Valium belongs to a family of drugs that bind with
junctwo whispering lovers, yet so much life happens there- Each
the
tion is aL^r^i full of tommerce, intrigue, and possibility' In
vital
the
brain, every.thing depends on almost nothing, a lively space'
channel between neurons.
Throughout nature' space can be a powerful essential' Consider
How can a
fireflies, tiinkli.tg like nomadic stars on summer nights'
on and
firefly recognize ia, o*n mate with so many glows flicking
couple
ofn iUi*i"[ two chemicals to create a cold green light' ea-ch
calling first'
flashes u .J.r., code during courtship, with the male
invites him
then waiting for his partnei's reply, a come-hither that
down to mate. But their password is an absence' not a Presence'
How long she delays before flashing is what the male decodes'
Al"r, ,ori" larger f.-"1", (known as femrries fatales) lure their
the male to
neighbor's matJby mimicking their code, and then eat
females
abslrb a tonic thatwards off hungrybirds and spiders. And
in the
prefer males with longer flashes' But that's another chapter
of life on Eartf,, which is storied with precious hollows and
"rr."1,
channels.
The power of a real and present emptiness is what I'm thinking
of two neurons'
o[, the minute space that thrives between thr: banks
fillff
(selecssRls
of that sPace
Some populur arrtid"pr.ssants expioit the power
ing it with the neuroiransmitter serotonin. Known
as
ti'ie serotonin reuptake inhibitors), ZoIoft,Prozac' and their kin
at the
work by "inhibiting the reuptake'" I picture that happening
northern
they're
eye,
coastline of wvo J.trrtri"r. In my mind's
European port cities during the Renaissance, with a river flowing
b.t*..r, them, across which cargo must Sail. A ttansmitter chem-
$t,
)
,NNER
AN ALCHEMY OF MIND
44
ical like serotonin waits in warehouses on the east coast, and at a signal the boats are loaded and they cross the river. At the other side,
locals rejoice at the sight of such riches. At that point the serotonin's
job is finished. shippers carry it backto the original shore,where it's
once again stofed in warehouses, to await another order to cross.
At tiillions of synaptic juncl-ions, crossing molecules carry news,
even if the news is that there's nothing new to report. The same old
rigmarole is worth reporting' too. To do something is to act, but so
isioing nothing; u.iit g and not acting are both choices, even if
one thinks not acting is not choosing.
A common myth about the brain is that it's as unyieiding as a
steel vault. But whenever we learn something, the brain mints
new connections or enlivens old ones along familiar pathways' One
famous exampie: brain imaging shows that expert violinists develop
more motor lortex for the busy left hand than for the right. Neuroscientists like to say that the brain rs plastic, a curiously inorganic
if fashionable word tirat takes us back to the h"yd^y of plastic in the
The
Lg50s, when it entered everyday life as a moldable wonder.
brain bends, learns, effloresces, adapts' When we learn something'
we grow new synaPtic connections. Neuron trees grow new twigs
aloig their borr.h"r, while some of the branches themselves
b..o"-. stronger. Our brain can rewire itself. We do it all the time
ice-skating or learn surgery or pick up knitting'
when we
-"rt.,
Otherwise, how could we have survived the Ice Age, when, among
other useful things, we invented the needle? Much of the brain's
wiring takes place after birth.The ultimate immigrant, abrain traveh [!ht, gaihering notions when it arrives. The destination is
childf,ood] u *orlJ that begins in the family, where what a child
child
hears, sees, and feels partly designs the growing brain"'The
"My
poem
his
in
is father of the *"n,"!Villiam Wordsworth writes
Heart Leaps lJp," and to some extent thatt true. We arrive in this
world clothed in the loose fabric of a self, which then tailors itself
to the world it finds.
As the developing brain blooms and prunes connections, it has
to decide which onei to fix permanently in place and which to dissolve. Preserving what's useful and killing the rest, it chooses-
spAc'
+l
How does it know what's usefirl? Whatever we use most. Hence the
populariry of bad habits. Breaking them feels iike splitting welded
steel, and in a sense it is. The (Jse it or loseir axiom has a dark side.
Behave in a certain way often enough-whether it's using chopsticks, bickering, being afraid of heights, or avoiding intimacy-and
th.e brain gets really good at it. One can master unfortunate skills
that are hard to forget. Great for knowing how to protect oneself,
balance a bike, or drive a car. Not great when it comes to deferise
mechanisms still in use long after the threat that created them has
vanished. The reason psychotherapy takes time is that the brain has
to be retrained at the level of the synapses. One paradox at the heart
of all living things is their ability to.change while remaining the
same. Our minds remain reasonably stable and effective for an
entire lifetime, despite all the daily stresses they encounter. And yet
they can bend and adapt and revise themselves when necessary.
Like stars in the universe, neurons dont occupy all of the brain,
most of which is water. And neurons dont act alone. Though
they are litde-known players in the drama of the mind, 90 percent
of the brain's cells are spidery glia (Greek for "glue"). A varied crowd
of cells with manyjobs, from cook to bodyguard, they're dominated
by star-shap ed astrocytes, which unfurl long arms and reach right
into synapses, altering events. Without glia, neurons would be
nothing. On their own, neurons can't feed or sheathe themselves,
avoid saboteurs, make themselves understood.
For some while, these glial ce1ls were regarded mainly as filler, the
gummy sludge holding neurons in place. But now they're taken
more seriously, not just as the neurons' servants but possibly their
handlers. A tightly packed corps, they nourish the neurons with lactate (manufactured from glucose in the blood). To protect neurons,
they can flatten capillaries with the palmlike ends of their tendril
arms and thus hold toxins atbay outside the brain.They can clean
up spilis of glutamate, the vital neurotransmitter that's nonetheless
poisonous in excess (it's implicated in stroke and Alzheimer's, for
example, and contributes to the headache from MSG in Chinese
cuisine).
r
But glia are also manipulative cells that can converse among
+6
AN ALCHEMY OF MIND
themselves, listen to neurons, voice their own concerns, and
ulti-
CHAPTER
mately influence what nerrrons say. They may prompt neurons to
create more synapses, rou$e sleepy neurons and put them to work,
and order neurons to streryyhen or weaken their best contacts. They
may be vital to memory and learning. Glia with many faces and jobs
touch neurons, profoundly altering their fate. Coexisting, as they
must, both neurons and glia are dependable, dependent, full of talk
and back tailq central to the brain's social fabric and perpetual hum.
Attention
8
Please
Steep thyselfin a bowl of summertime.
Minor poems
-Virgil,
takes.
,l:
local
".tr*a kick airport, its wheels spring back
r.A\ i,l]ll;,et
lrke a horse giving
over a hurdle, and then
even faster on polished air.
whiie that
it .li_b,
drama stears my attention,
the airport, the wooden bench my bottom
sits on, ,h" h,rrrg.,
rto-""h, tfr. tirrkly miat* of
lone goldfinch, and the rest of liie recede.
ffr""gi, ;""p.r","r. "f
become eyes and a mental notepad.
f,m engrossed in the jet,s
climb not because I need that memory
to survive, but because novi:
Before the brain ."r,;,rdg. what,s i-porturrt,
:1,y lveting.
ii rrr,r*
identify the nera4 srrange, different. I riro*
about il"rr"r, trt trrt
mini-jet, a pocket rocket, I havent seen before.
The scene might be only a momentary distraction
on a dozy
morning, aforgettabre frutter. or watching
the jet take off might
feed me a fact that srinks into memory,
lii.. ,rri, ."",-*;;r"".
its wheels, it speeds up and i..orrr., more
_r:llacts
steerable.
pangs making radio wheeze in my
Wleel-s muddy the smooth flo#of air.
So do birds,legs. Witt o,rt
such clutter, the wind pours like satin
above and freneath the
wings, designed with a
curye to speed the airflow, .;;;i;;;""._
1op
uum on top that lifts the
prane up, As the jet becomes ,lJ.t.r,
it
races faster, steadier, and higher.*
*Bird
winp work differently: tinywindows in
letting air through only on th. upst
oke.
47
each wing open and crose
as theyflap,
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