The Human Brain. A Guided Tour

THE HUMAN I]ITAIIN A GuidedTlrtrr

SUSAN GREENIIIIiI,I)

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\tr IT H IN

I

of the United

that every effort should be

awareness

of the benefits

derived from brain research.' \4/e are currently

to be

in the middle

of the 'Decade of the Brain.' A general inlerest in the brain is official. Remote from the rest of the bodv in its own custom-built

THE

H U MAN

BRAIN

B R A IN S

W ITI.' IIN

B R A IN S

casing of skull bone, the brain has a consistency similar to a

the body into the brain. Btrt if t-[re].rrain was the centre for

soft-boiled egg and has no intrinsic moving parts. Thus, it is

thinking, what about the soul?

obviously

not

participate

in

destined to take any physical

strain or

The Greek physician Galen (x.o. a29-199) pointed to a

actions. The

part of the brain that was the least solid, the most ethereal,

Greeks c€rme to the conclusion that this insubstantial and

and clearly discernible to the naked eye. Deep within the brain is a labyrinth of interconnecting cavities, formed

any large-scale mechanical

secretive substance was the perfect site for the soul. Most importantly, soul was immortal: it had nothing to do with

during development in the womb and containing a colour-

thinking.

In fact, all the abilities we now attri.bute to the brain, the Greeks localized in the heart or the lungs (there

less fluid. This insubstantial-seeming fluid bathes the whole of the outer surface of the brain and spinal cord and is

was never total agreement about the precise location). The immortal 'soul' was of course so sacred and elusive t].at the

known as cerebrospinal fluid (CSF). It is often used in the. diagnosis of various neurological problems when sampled

silent, remote grey home provided

from the lower portion

for it by the brain

presented a serious focus with alrnost mystical properties: the Greeks imposed strict taboos against eating the brains of any animal. The soul in this case was quite explicitly a

of the spinal cord in a lumbar

puncture. Norma}ly, however, the CSF is reabsorbed into the blood supply, so that fresh fluid is constantly being produced (about o.2 rnillilitres

per minute in humans) and is

different entit5r from 'consciousness' and the 'mind' and all the other interesting properties that we now associate with

thus constantly circulating.

our individuality

substance, as opposed to ttre sluggish slurry of brain, might have been a good candidate for the substance of the soul. We

and personality.

Such quirky reasoning, where normal mental activities were not associated at all with the brain, changed with a

It is easy to imagine

how

this

mysterious

swirling

great discovery made by Alcmaeon of Croton. Alcmaeon

now know tl at the CSF contains merely salts, sugars, and certain proteins. Far from being the seat of the soui, it has

showed that there were actual connections leading from tle eyes to the brain. Surely, he claimed, this area must be the

even been disparagingly referred to as 'the urine of the brain.' No one, even those who believe in an immortal soul,

seat of thought.

now expects to find it in the brain. The mortal brain, which

This

revolutionary

idea tied

in

with

observations made by two Egyptian anatomists, Herophilus and Erasistlatus, who managed to trace nerves - obviously

everyone regards as obviously

not identified as such at the time - leading from the rest of

of riddles.

responsible

for

all

our

thoughts and feelings, presents in itself the most tantaiizing

THE

HUMAN

BRAIN

B R A IN S

\^/ITH IN

B R A IN S

In this book ure are going to see how far we can progress with

answering

the question: FIow does the brain work? But

this question is far too global and vague to have any meaning of actual

in terms

experiments

or observations.

What

we

need to do instead is to tackle more specific sub-questions that nonetheless

make a contribution

to a final understand-

ing of this secretive mass of tissue in which, essence of our personalities The first

topic

we shall

somehow,

the

is locked away. explore

in this

chapter

is the

j$e

appearance of the brain. Imagine you were looking

physical

at a brain in your hands: what you would be a creamy coloured, wrinkled kilograrn,

be holding

object weighing

on average about 1.3 kilograms.

The first feature you would

would

l

just over 1

(See Figure 1-.)

notice is that the strange-looking

object, small enough to be supported in one cupped palm, is made up of distinct

regions of a particular

that fold around each other and interlock

shape and texture according

to discern.

grand scheme that we are only now beginning The brain has the consistency ground

plan that is always

to some

of a raw egg with an overall

the same. There are two clear

ii&* /,,3,{i11' ,*rta$l

halves, called hemispheres, that seem to sit around a kind of thick

stalk (brain stem). Tiris brain stem eventually

clown into

the spinal

tapers

cord. At the back is a cauliflower-

shapod extrusion, a 'little brai.n' (cerebellum) that protrudes prer:ariously behind

the main brain (cerebrum).

If yotr vvere to look at the cerebellum, the srrrface of these hemispheres,

the brain stern, and

you would

see that they

FISURE ' A cross-section of the human brain within the head. Note how the brain is composed of different gross regions easily discernible to the naked eye, and how it is continuous with the spinal cord. (From M. A. England andJ. wakely, A colour Atlas of the Brain and spinal cord, wolfe publishing, 19s1.)

THE

H UM AN

B R A IT.I :

BRAIN

are ali diiTerent in surface texture, as weil as varying slightly in colour

along the cream--pink-brown.

more,

you

if

underside,

turned

it would

the

brain

over

and

be easy to see still

regions again distinguishable

Further-

spectrum. looked

further

at the different

by colour, texture, and shape.

For the most part, each region is duplicated

on either side of

the brain so that you could draw a line down the middle an axis, about which The different

the brain would

ordered anatornical

these boundaries

the stalk-

up by neuroscientists

in an

scheme. One way to think of these brain

regions is as countries

filled ventricle

be syrnmetrical.

regions of ihe brain pile around

like brain stem and are divided

as

distinguished

are very

obvious:

by boundaries. one rnight

Often

be a fluid-

where we saw the soul was once thought

to

vis;iou \tiir$ [haL thet nervous system rvas cord' wilh like an invertecl tr-ee. The trunk was in the spinal the nerves the roots in the brain ancl the branches in the flrst part extending throughout ttre bocly' A little later' in Flourens also of the eighteenth century, Jean-Pierre-Marie the results conclrrcled that the brain was homogeneous' frorn

gland. Malpigiii's

of his rather

experiments'

ghoulish

animals'

variety of laboratory

rather

than

impaired.

selective

With functions

functions

undeniable

selective parts of the brain.

different

name, but we will

example, cerebellum

be gathering

or brain stem) only as we need them.

Rather than a cletailed ciocumentation brain,

our prime

regions

contribute

such labels (for

concern

of the anatomy of the

here is to discover

to the feats of sun'ival

how

in the outside

world as well as to consciousness of that inner world, most private have tantalized

place of thoughts

certain

one's

and feelings. These issues

people since long before the dawning

of the

Decade of the Brain. For some, such as Marcello century,

the brain

functioned

Malpighi

in the seventeenth

homogeneously,

as a huge

logic,

becoming Flourens

could. not be localized

According

has a

on a more

andrnoreoftheirbrainsandobservingtheeffects'Whathe weaker' found. vr.as that all function$ grew progressively

distinct

scheme, each region

removing

methodically

a

employed

\rerysimplerationale:taremoveclifferentpartsofthebrain and see what functiorrs remained' He experimented

lurk, another might be subtly changed in texture or colour. to tkre recognized

Flourens

This scenario of a uniform inspirecl the concept

brain with

of mass action'

specifically decided

that

as such within

no specialist

parts

It is an idea that still

to explain a persists today, in a less extreme form, in order but fairly frequent occurrence: when seeming miraculous a parts of the brain are destroyed, say by stroke' then,after that at }east while, other intact parts appear to take over' so some of the original function is rq'stored' contrast to this idea is tfre view that the brain a highty" can bo divicled into rigid compartments' each with this,-vision specific function' The most famous proponent of In complete

Gall'yras i /as Franz Gall, a cloctor born in Vienna in L758'

I

IO

THE

HUMAN

BRAIN

I

very interested

t,

time,

in the human mind, but he considered

to probe

delicate

B R A IN S

he was probably

GaIl hit upon

Instead,

right.

the skulls of the

the theory that if he studied

I

He developed

t,

characters of those people, then perhaps he could identify

I I I I I I I

up were the most easy feature to detect: the bumps

t I \'

up with

dead and then saw how these matched

physical

trait

with

corresponded

that

the alleged a

aspects of

certain

character. The aspects of the brain tl at Gail chose to match on the

concluded

that

were

there

character traits. These purported

different

twenty-seven

blocks of person-

building

ality actually

turned

out to be rather sophisticated

of the human

mind:

instinct

and friendship,

attachment

offspring,

oneself and one's property, instinct

defensive

ing

of

to steal, pride and

individual.

nremory

for people, sense of words,

sense of the spoken

The nagging

were

small

and still

a specific

a physical

displaced they

by the bumps

were

pushed

particular

pattern

somewhat

primitive

to pierce

of perforations readout

Caspar Spurzheim,

|ohann the

upward

r and sarcasm, poetic irnit

umdfrllt' ,nfim-''"

God and religion, e different

spirit, sense of

talent, goodness, faculty

of

steadfastness.

qualities

- which

were

eventually

mental

each

state might let alone

on the skull.

the procedure

'the

study

at the brain,

on objective measurements,

true science - as such it rapidly

with

a new

The

character.

of the mind,'

and its underlying

became

paper.

one of Gall's colleagues, coined

a new way of looking

Phrenologv

through

of an individual's

Greek terrn pftrenology,

describe

pins were

in the paper thus gave a

captured

popular

basis for morality,

philosophy.

to It

and because it

it had all the lr:stre of a

present people with a more 'scientific'

wisclom, depth of thought and metaphysical

in

on the surface of the skull so that

rolationship

comparative

the

question

infrastructure,

times.

sense of mechanics,

or large

unanswerable

worcl, sense of colour, sense of tonal relations, sense of the of numbers,

where

of hat. When placed on the skull, movable

relied

and

- a

The apparatus that Gall used to make his enalyses was a

relations,

of things

for exarnple, banality

one as remote from brain tissue as a bump

facts, sense of spatial

memory

lumps

ever be associated with

offered

circumspection

the

B R A IN S

to greater or lesser degrees, accord-

was not even raised of how

foresight,

vanity,

to include,

were localized

to whether

and

authority,

of

instinct

for cruelty, cleverness,

feoling of possessiveness and inclination love

features

love for one's

of reproduction,

to thirty-two

map of the surface of the head was produced,

kind

surface of the skull. Gall

expanded

functions

the brain.

more subtle way of studying

seemingly

another,

quite

of the

the techniques

Given

surgically.

it too

W ITH l N

of the

because it seemed

to

approach as well as

something

measured and did not entail difficult

the spirit

that

could

be

and abstract ideas, like

soul. Seen as a secular, objective system, stripped

of any

need for bli.nd faith,

to the

phrenology

catered

superbly

tl

:,+19!&r:r,.!il

I7

THE

H U M At.!

growing

B i,-.i r' 1.;

f!R,AIN

number

of people disaffected

at tirat time with

the

church.

appeal. 'I'he problslrr lvas .roiirl)ounded wlien, a i.;w yoars later, another

Anotller of making

physician,

advantage was, of course, tl:at it was a new way

covered a different

large amounts

that Wernicke

of money: phrenology

books, and models all started to proliferate.

pamphlets,

Indeed phrenol-

ogy became an integral

:3

'. . : !-?-;i

different

dis-

Carl Wernicke,

the Austrian

In the patients

type of speech problem.

In this case the patient,

The only problem

in

zodiac, so in the last century

Words are jumtrled together in an incoherent sequence and

would

have a tiny,

personalized

handle. But eventually tive endeavour

phrenology

this fascinating,

painless, and lucra-

was to run into trouble.

In 1861, in France, the neuroanatomist Paul Broca examined man could words,

bust on the

and anthropologist

pronounce

any other

hence he was ref'erred to as 'Tan', even though

real name was Leborgne.

his

Tan earned his place in history

because six days after the examination

he had the misfor-

is t}.at the speech is often gibberish.

no apparent mean-

with

fr-equently new words are invented ing at all. The discovery

a man who was unable to speak. This

only say 'tan': he couldn't

aphasia

words perfectly.

unlike

Tan, could articulate

canes, for example,

of yet another

associated with, but linked that the problem

shows

area of the brain,

was not

for phrenology

of a single

speech

centre

functions.

brain. It turned

on the skull as an index of brain function,

completely

out that the area of the brain damaged was

different

some phrenology in the lower

from tllat predicted

by phrenology.

On

busts, the centre for }anguage is localized

part of the left eye socket, whereas

in Tan,s

problem

Irrespective

of how

of the absurdity

a cohesive behaviour,

thought is translated into a physical

was a simple one-to-one mapping

of the left-hand side of the brain. Henceforth tJ'is part of the

product -

brain became knornrn as Broca's orea.

single, small region. In retrospect

observations

unequivocal

such as these, phrenology

clinical

started to lose its

is not valid.

a complex

function

of measuring

brain bumps

there is still the

skill,

sensation,

event somewhere

brain, and vice versa. The phrenologists

brain, the damaged area was a small region toward the front

Because it did not match up with

of location,

Bumps on the skull clearly do not represent different

tune to die, thereby giving Broca the chance to examine his

even a

observations

raised the even deeper issue that, irrespective even the concept

clearly

aspect of, speech,

to a different

of the speech centre: Wernicke's

mislocation

thought

or

in the

that there

of the complete finished

such as language - with

a

it is easy to see that they centres

of memorY,

ernotion, and so forth still persists in folklore

views of the

were

wrong,

II

I

part of many people's lives. Just as today items ranging from mugs to jewellery bear signs of the walking

I rl

.studied, there was damage to a completely

part of the brain.

tVernicke's

|

although

the

idea

of

l;

r;

It

1l

it F T

t

T

t t

.4

THE

HUMAN

BRAIN

B R A IN S

brain. But if chunks and directly

of the brain are not rnerely passively

corresponcling

to chunks of the outside wcrld,

or chunks

of our behavioural

what kind

of alternative

the brain

most primitive ing functions hs'ce

Abnorrnal now

then

(i.835-j.9j.1),

a British

neurolo-

as organized into a hierarchy.

that were increasingly

more sophisticated,

in humans.

The

rnovements

be interpreted

resulting

from

as an unleashing

lnvoluntary

rnovements

inlluencos.

similarly,

and even sociology. brain

damage could

of lower

functions,

from their normal restraining sigmund

and

This idea was to have

for neurology, psychiatry,

of the bumps

higher

Freud was able to refer to

psychiatric

or

Paul

Maclean

viewed

the

in

the

brain

more advanced'old mammalian.'

The

also be interpreted

havlng escaped from a 'higher' controlling Alttrough llrovides

Hughlings-|ackson's

an interesting

llsychiatry,

and

even

force.

spinal

framework trehaviour,

nssrrrnption rnade by the phrenologists

the old mammalian

behaviour, rnamrnalian

region

but

this

time

reptilian,'

brain,

which

interconnecting

brain

the

corresp-

behaviour.

was constituted

middle

brain-level

system, which

particularly brain

for instinctive

was the

controlled

area for rational

in the outer layer

from

from

a

emotional the new pro-

ttrought

of ttre brain.

derived

By

structures

aggression and sex. Finally,

is kno'r,vn as the cortex,

This

outer

the Latin

for

fcrr neurology,

'bark,' sirrce it covers the outer surface of the brain as does

the

the bark on a tree.

erroneous

lurks here also. The

Maclean

r:orrr;opt of a lrierarchy implies something must be at the top,

maintained

llrnl tlrero rnust be some ultimate

condition

controller.

Maclean

and the most sophisticated

reptilian

cord), was responsible

cesses housed

idea is appealing in that it

common crowd

as

by

onded to the brain stem (tlle central stalk arising from the

as the limbic

mob could

the

the function-

1.95Os. Again,

of hierarchy,

mammalian,'

known

lorrr of an ungoverned

a physical

brain within

of three tiors: the most 'prirnitive

composed

'ne'w

1-94Os and

as a kind

of

behav-

have

in

ing of gross brain regions to each other was developed

series

brain, the anarchic

not

attempt at a scherne for interrelating