other minds in the brain

7/21/2019 Other Minds in the Brain

http://slidepdf.com/reader/full/other-minds-in-the-brain 1/20

E L S E V I E R

Cognition 57 (1995) 109-128

O G N I T I O N

Other minds in the brain: a funct ional imaging s tudy

of theory o f m i nd in s tory com preh ens i on

P . C . F l e t c h e r ~ 'c , F . H a p p 6 b , U . F r i t h b ' d '* , S . C . B a k e r ~ ,

R . J . D o l a n ~ c , R . S . J . F r a c k o w i a k ~ , C . D . F r i th ~ 'a '*

Wellcome Department of Cognitive Neurology, Institute of Neurology, 12 Queen Square,

London WCIN 3BG, UK

MRC Cognitive Development Unit, 4 Taviton Street, London WC1H OBT, UK

Royal Free Hospital Medical School, Roland Hil l St, London NW3, UK

~Department of Psychology, University College London, Gower St, London WCIE 6BT, UK

Rec e ived O c tob e r 20 , 1995, f ina l ve rs ion a cce p t ed Augus t 16 , 1995

A b s t r a c t

T h e a b i l i ty o f n o r m a l c h i l d r e n a n d a d u l t s t o a t tr i b u t e i n d e p e n d e n t m e n t a l s t a te s t o

s e l f a n d o t h e r s i n o r d e r t o e x p l a i n a n d p r e d i c t b e h a v i o u r ( t h e o r y o f m i n d ) h a s

b e e n a f o c us o f m u c h r e c e n t r e s e a r c h . A u t i s m i s a b i o l o gi c a l ly b a s e d d i s o r d e r w h i c h

a p p e a r s to b e c h a r a c t e r i s e d b y a s p e c if ic i m p a i r m e n t in th i s m e n t a l i s i n g p r o c e s s .

T h e p r e s e n t p a p e r r e p o r t s a f u n c t i o n a l n e u r o i m a g i n g s t u d y w i t h p o s i t r o n e m i s s i o n

t o m o g r a p h y i n w h i c h w e s t u d i e d b r a i n a c t iv it y in n o r m a l v o l u n t e e r s w h i l e t h e y

p e r f o r m e d s to r y c o m p r e h e n s i o n t a s k s n e c e s s i ta t i ng th e a t t r ib u t i o n o f m e n t a l s ta t e s .

T h e r e s u l ta n t b r a i n a c t iv i ty w a s c o m p a r e d w i t h t h a t m e a s u r e d in t w o c o n t r o l ta s k s :

p h y s i c a l s t o r ie s w h i c h d i d n o t r e q u i r e t h i s m e n t a l a t t r i b u t i o n , a n d p a s s a g e s o f

u n l i n k e d s e n t e n c e s . B o t h s to r y c o n d it io n s , w h e n c o m p a r e d t o th e u n l i n k e d s e n -

t e n c e s , s h o w e d s ig n i fi c a n t ly i n c r e a s e d r e g i o n a l c e r e b r a l b l o o d f l ow i n t h e f o l l o w i n g

r e g i o n s: t h e t e m p o r a l p o l e s b i l a te r a l l y , t h e l e f t s u p e r i o r t e m p o r a l g y r us a n d t h e

p o s t e r i o r c i n g u la t e c o rt e x . C o m p a r i s o n o f t h e t h e o r y o f m i n d s to r ie s w i t h

p h y s i c a l s t o r ie s r e v e a l e d a s p e c i fi c p a t t e r n o f a c t i v a t i o n a s s o c i a t e d w i t h m e n t a l

s t a t e a t t r i b u t i o n : it w a s o n ly th i s ta s k w h i c h p r o d u c e d a c t i v a t i o n i n t h e m e d i a l f ro n t a l

g y r u s o n t h e l e f t ( B r o d m a n n ' s a r e a 8 ) . T h i s c o m p a r i s o n a l s o s h o w e d s i g n i f i c a n t

a c t i v a t i o n i n t h e p o s t e r i o r c i n g u l a t e c o r t e x . T h e s e s u r p r i si n g l y c l e a r - c u t fi n d in g s a r e

d i s c u s s e d i n r e l a t i o n t o p r e v i o u s s t u d i e s o f b r a i n a c t i v a t i o n d u r i n g s t o r y c o m p r e h e n -

s i o n. T h e l o c a l i s a t i o n o f b r a i n r e g i o n s i n v o l v e d in n o r m a l a t t r i b u t i o n o f m e n t a l s t a t e s

a n d c o n t e x t u a l p r o b l e m s o l v i n g is f e a s i b l e a n d m a y h a v e i m p l i c a t i o n s f o r t h e n e u r a l

b a s i s o f a u t i s m .

* A u t h o r s t o w h o m c o r r e s p o n d e n c e s h o u ld b e a d d r e s s e d .

0010-0277/95/$09.50 © 1995 Else vier Science B .V. Al l r ights r eser ved

SSDI 0 0 1 0 - 0 2 7 7 1 9 5 1 0 1 1 6 9 2 - 3



110

P C . F l e t c h e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8

1 . I n t r o d u c t i o n

O u r a b i l it y t o e x p l a in a n d p r e d i c t t h e b e h a v i o u r o f o t h e r s i n te r m s o f th e i r

m e n t a l s ta t e s (b e l i e f s a n d d e s i r e s ) h a s b e e n r e f e r r e d t o a s t h e o r y o f m i n d

( P r e m a c k & W o o d r u f f , 1 97 8) o r m e n t a l i si n g ( F r i t h , M o r t o n , & L e s l i e ,

1 9 91 ). T h i s w a y o f m a k i n g s e n s e o f b e h a v i o u r a p p e a r s t o b e b o t h u s e f u l a n d

u b i q u i t o u s. J u s t a s w e p e r c e i v e c e r t a i n p a t t e r n s o f m o v e m e n t in t e r m s o f

p h y s ic a l c a u s a t i o n ( L e s l ie & K e e b l e , 1 98 7), s o w e c a n n o t h e l p b u t p e r c e i v e

c e r t a i n b e h a v i o u r a l i n te r a c t i o n p a t te r n s in t e r m s o f i n te n t io n ( P r e m a c k

1 99 0; L e s l ie & R o t h , 1 99 3; D a s s e r , U l b a e k , & P r e m a c k , 1 98 9). S o , f o r

e x a m p l e , u n d e r c e r t a i n c o n d i t i o n s a h a n d m o v e m e n t w i l l b e p e r c e i v e d a s a

p o i n t i n g g e s t u r e ( e x p r e s s i n g t h e i n t e n t i o n t o d i r e c t a n o t h e r ' s a t t e n t i o n ) ,

u n d e r o t h e r c o n d i t i o n s a s a w a v e o r a s w i p e a t a f l y .

I n t h e l i gh t o f i ts a p p a r e n t e v o l u t i o n a r y a d v a n t a g e s , i t is p l a u s i b l e t h a t

m e n t a l i si n g is p e r f o r m e d b y a n in n a t e l y d e t e r m i n e d c o g n it iv e m e c h a n i s m

( L e s l i e , 1 9 8 7 , 1 9 9 4 ; L e s l i e & R o t h , 1 9 9 3 ) . T h e d e v e l o p m e n t a l s e q u e n c e i s

c u l t u r a l l y in v a r i a n t ( A v is & H a r r i s , 1 9 9 1) a n d r e l a t i v e l y in d e p e n d e n t o f t h e

l e v e l o f in t e l l ig e n c e ( N u n e z & R i v i e r e , 1 99 0) , w i th l i tt le i n d i v i d u a l v a r i a t i o n

a n d a s t r i k i n g l y n a r r o w t i m e w i n d o w ( H a p p 6 , 1 9 9 5 ) . A d d i t i o n a l e v i d e n c e

t h a t t h i s a b i l i t y i s b i o l o g i c a l l y b a s e d c o m e s f r o m a c o n s i d e r a t i o n o f a u t i s m

( F r i t h e t a l . , 1 9 91 ). A u t i s m a p p e a r s t o b e c h a r a c t e r i s e d b y a l a c k o f t h e o r y

o f m i n d ( m e n t a l i s i n g ) ( L e s l i e , 1 9 87 ; F r i t h , 1 98 9; B a r o n - C o h e n , T a g e r -

F l u s b e r g , & C o h e n , 1 99 3) . C h i l d r e n a n d a d u l t s w i th a u t is m t y p i c a l l y f a il

f a l se b e l i e f t a s k s ( B a r o n - C o h e n , L e s l ie , & F r i t h , 1 98 5) a n d t h e c o r e s o c ia l

i m p a i r m e n t s s h o w n b y a u ti st ic i n d iv i d u a l s c a n b e r e a d i l y e x p l a i n e d b y a

f a i l ur e t o r e p r e s e n t t h e t h o u g h t s a n d f e e l in g s o f o t h e r s ( F r i th , 1 98 9). W h i l e

m o s t in d i v i d u a l s w i th a u t is m a r e o f lo w I Q , a u t i s m c a n a l s o o c c u r in

c o n j u n c t i o n w i t h n o r m a l o r e v e n s u p e r i o r i n t e l l i g e n c e ( R u m s e y & H a m -

b u r g e r , 1 9 8 8) . T h i s l a t t e r f i nd i n g s ug g e s t s t h a t t h e t h e o r y o f m i n d d e f i c i t is

h i g h l y sp e c i fi c : g e n e t i c o r m e t a b o l i c e f f e c t s m a y d a m a g e t h e b r a i n s u b s t r a t e s

o f m e n t a l i s in g w i t h o u t c o m p r o m i s i n g o t h e r f u n c t i o n s ( F r i t h e t a l . , 1 99 1;

H a p p 6 & F r i t h , 1 9 9 4 ) .

T h e t h e o r y o f m in d a c c o u n t h a s m a d e s u c c e s sf u l p r e d i c t io n s a b o u t r e a l -

l i f e a b i l i t i e s a n d d e f i c i t s . F o r e x a m p l e , c h i l d r e n w i t h a u t i s m c a n u s e g e s t u r e s

t o d i r e c t b e h a v i o u r (e . g ., c o m e h e r e , g o a w a y g e s tu r e s ), b u t n o t t o

a f f e c t i n t e r n a l / m e n t a l s t a te s ( e . g ., g e s t ur e s o f a f f e c t io n o r c o n s o l a t io n )

( A t t w o o d , F r i th , & H e r m e l i n , 1 9 88 ). T h e y c a n a l s o , w h e n t a u g h t , e n g a g e i n

f ix e d s m a l l t a l k , b u t a r e u n a b l e t o c o n d u c t a f l e x ib l e c o n v e r s a t i o n t a k i n g i n to

a c c o u n t t h e i n te r e s t s o f o t h e r s ( F r i t h , H a p p 6 , & S i d d o n s , 1 99 4). T h e

d i s t i n c t i o n b e t w e e n i n t a c t a n d i m p a i r e d a b i l i t i e s i n a u t i s m h a s b e e n d e m o n -

s t r a t e d in m a n y st u d ie s , s o m e o f w h i c h a r e s u m m a r i s e d in T a b l e 1. T h e f in e

c u t s a p p r o a c h , r e f l e c t e d i n t h is t a b l e , s e e m s p a r t i c u l a r l y w e l l s u it e d t o t h e

p o s i t r o n e m i s s io n t o m o g r a p h y ( P E T ) s c a n m e t h o d o f f u n c ti o na l n e u r o i m a g -

i n g i n w h i c h d i f f e r e n t c o g n i t i v e f u n c t i o n s m u s t b e c o n t r a s t e d u s i n g o t h e r w i s e

s i m i l a r t a s k s .



P . C . F l e t c h e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8 111

T a b l e

1

Autist ic assets and defic its as predicted by the

f ine cu~s

t echn ique , be tween tasks which

requ ire menta l i s ing and those which do not

Asse t s De f i c i t s

Order ing b ehavioura l p ic tures

Unders tand ing see

Proto imperat ive po in t

Sabotage

Fa l se photographs

Reco gn is ing happiness and sadness

Objec t occ lus ion

Literal expression

Ordering mental ist ic pictures

(Baron-Cohen , Les l i e , & Fr i th ,

1986)

U n d e r s t a n d in g k n o w

( P e r n e r ,

Fr ith, L es l i e , & Lce kam ,

1989;

Lesl ie & Frith.

1988)

Protodeclarative pointing

( Ba r o n - C o h e n ,

1989)

D e c e p t i o n

(Sodian & Frith,

1992)

False bel iefs

(Les l i e & Tha is s ,

1992;

Leek am & Perner,

1991)

R ecognisin g surprise


Spitz, & Cross, 1993)

In format ion occ lus ion


1992)

M etaphor ica l ex press ion

Happ6 , 1993)

Some ind iv idual s w i t h aut i sm, in par t i c u lar , mor e in t e l l i ge nt adu l t s , do

pass s imple t e s t s o f t he or y o f mind , nor mal ly passe d a t t he age o f 4 ye ar s

( B a r o n - C o h e n , 1 9 8 9 ; B o w l e r , 1 9 92 ; O z o n o f f , P e n n i n g t o n , & R o g e r s , 1 9 9 1 ) ,

but hav e pr ob le ms wi t h me nt a l i s ing a t h ighe r l e v e l s . Re c e nt ly , H app6 t e s t e d

able aut ist ic chi ldren and adult s with a se t of s tor ies requir ing the at tr ibut ion

of c omple x me nt a l s t a t e s ( e .g . , doub le b lu f f , wh i t e l i e , pe r suas ion ) (H app6 ,

1994) . Subje c t s r e ad t he se s t or i e s and answe r e d que s t ions about t he m. In

t he i r answe r s , t he se ab le aut i s t i c ind iv idual s made s t r ik ing e r r or s , mi sunde r -

s t and ing pr ot agon i s t s ' in t e nt ions . T hus , un l ike me nt a l ly hand ic appe d or

young nor mal subje c t s , au t i s t i c subje c t s , e v e n o f nor mal IQ , c onf use d , f or

e x ample , a l i e w i t h a joke , or pe r suas ion wi t h misunde r s t and ing . E r r or s in

me nt a l s t a t e a t t r ibut ion we r e on ly f ound in aut i s t i c subje c t s , and we r e

suf f i c i e n t t o d i sc r iminat e e v e n t hose subje c t s who passe d s t andar d f a l se

be l i e f t asks . B y c ont r as t , au t i s t i c subje c t s had no d i f f i c u l t y in unde r s t and ing

t he phys i c a l e v e nt s in t he s t or i e s , or s t or i e s not inv o lv ing me nt a l s t a t e s .

Of t he v ar ious t e s t s v a l idat e d wi t h aut i s t i c subje c t s , H app6 ' s s t or i e s

se e me d be s t su i t e d t o t he c ons t r a in t s o f f unc t iona l imaging . T he y ar e

su i t ab le f or adu l t s and a l l ow sys t e mat i c manipu lat ion o f t he e x t e nt t o wh ic h

t he y r e qu ir e t he c ons ide r at ion o f mot iv at ion and in t e nt ion . T he y may be

pr e se nt e d in wr i t t e n f or m, r e ad ing be ing a c ogn i t i v e f unc t ion whic h has be e n

e x t e ns iv e ly s t ud ie d wi t h PE T . T he y ar e e as i l y adapt e d t o t he c ons t r a in t s o f

sc ann ing t ime r e qu ir e me nt s (one s t or y t ak ing appr ox imat e ly 30 se c onds t o

r e ad) . Unf or t unat e ly , t he c ont r o l s t or i e s use d in t he H app6 s t udy we r e



112

P . C . F l e t c h e r e t a l . / C o g n i t i o n 5 7 I 9 9 5 ) 1 0 9 - 1 2 8

unsuitable for our purposes, since her results showed that they were not

equated for difficulty with the theory of mind stories. Two new types of

control condition were therefore designed for the present study: "physical

stories" and "unlinked sentences".

The physical stories were constructed to parallel the theory of mind

stories in requiring inference beyond the information stated. They both

shared the requirement to integrate information from the constituent

sentences into a story structure, to remember and link events and to infer an

implicit element. However, while both types of stories involved people, the

physical stories did not require or invite consideration of their mental states.

Our aim was that these two conditions should differ only in a requirement

for mentalising and we made sure that our subjects understood this

distinction through practice tasks. Our second control task, "unlinked

sentences", was constructed from sentences taken at random from different

prose passages. This condition contrasts with both story types in not

requiring integration of material into a story structure, and not requiring

inference. However, it required, in common with the other conditions,

reading, attention to sentence meaning, memory and (silent) question

answering.

Our study aimed, then, to locate areas of the brain in which there was

activity specifically associated with the process of mentalising in normal

subjects. Functional brain activation studies of this type provide an alter-

native and promising way of investigating the abnormalities of brain

function that result in autism. In a recent review, Horwitz and Rumsey

(1994) concluded that resting PET scan studies have been inconclusive and

failed to pinpoint any abnormalities specific to the brains of people with

autism. Likewise, reviews of other evidence from neuropathology, neuro-

physiology and neurochemistry demonstrate that even positive findings

(e.g., cerebellar and limbic system abnormalities at the level of neural

density) cannot be interpreted as autism-specific because of lack of adequate

controls and failure to replicate (Bauman & Kemper, 1994). Locating brain

regions implicated in the normal attribution of mental states should help to

isolate putative sites of damage or dysfunction specific to the psycho-

pathology of "mind-blind" autistic people. Before attempting to use func-

tional imaging to localise the pathway at fault in autism, it is first vital to

validate our experimental technique with normal subjects.

2 . M a t e r i a ls a n d m e t h o d s

2 1 Subjects

Six right-handed male volunteers (age range 24-65 years; average 38

years) took part in this study, which was approved by the Hammersmith

Hospital Ethics Committee and the Administration of Radioactive Sub-



P . C . F l e t c h e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8

113

s ta n c e s A d v i s o r y C o m m i t t e e ( A R S A C ) . A l l s u b je c t s g a v e w r i tt e n , in f o r m e d

c o n s e n t . A l l s u b j e c t s w e r e f it , h e a l t h y a n d f r e e o f a n y si gn if ic a n t p r e v i o u s o r

c u r r e n t m e d i c a l , p s y c h i a t r ic o r n e u r o l o g i c a l i l ln e ss .

2.2. Positron emission tomography scanning

S c a n s o f r e g i o na l c e r e b r a l b l o o d f l ow ( r C B F ) w e r e o b t a i n e d u s in g a C T I

m o d e l 9 5 3 B - P E T s c a n n e r ( C T I , I n c . , K n ox v il l e , U S A ) w i t h c o ll im a t i ng

s e p t a r e t r a c t e d . S u b j e c t s r e c e i v e d a 20 - se c o n d i n t r a v e n o u s b o l us o f H 2150 a t

a c o n c e n t r a t i o n o f 5 5 m B q m l - l a n d a f l ow r a t e o f 10 m l m i n ~ t h r o u g h a

f o r e - a r m c a n n u la . T w e l v e d y n a m i c P E T s ca n s w e r e c o l l e c te d , e a c h o v e r a

p e r i o d o f 2 .5 m i n u t e s , b e g i n n i n g 0 .5 m i n u t e s b e f o r e t h e d e l i v e r y o f t h e

b o l u s . T h e i n t e g r a t e d r a d i o a c t iv i ty c o u n ts a c c u m u l a t e d o v e r t h e a c q u i si ti on

p e r i o d w e r e u s e d a s a n in d e x o f r C B F . S u b j e c t s w e r e s c a n n e d i n a q u ie t ,

d a r k e n e d r o o m . T h e r e w a s a 1 0 -m i nu te g a p b e t w e e n e a c h s c a n.

2.3. Tasks

T h r e e ty p e s o f p a s s a g e w e r e p r e s e n t e d : t h e o r y o f m i n d s t or i e s ( T O M S ) ,

p h y s i c a l s t o r ie s ( P S ) a n d u n l i n k e d s e n t e n c e s ( U S ) . E x a m p l e s o f t h e s e

a r e g iv e n in t h e A p p e n d i x .

T h i s m a t e r i a l w a s v a l i d a t e d w i th 6 0 n o r m a l s u b j e c t s o f a s im i l a r a g e

( 1 6 - 5 5 y e a r s ) a n d e d u c a t i o n a l l e v e l a s o u r P E T s c a n v o lu n t e e r s . S u b j e c t s

w e r e g iv e n e x a m p l e s o f t h e t h r e e t y p e s o f s to r y a t th e b e g i n n i ng o f th e

s e s si on . T h e s t o r ie s a n d u n c o n n e c t e d s e n t e n c e s w e r e t h e n p r e s e n t e d , o n e

p e r p a g e , in r a n d o m o r d e r . S u b j e c t s w e r e i n s t r u c t e d to r e a d e a c h p a s s a g e

s i le n t l y a n d t u r n o v e r t h e p a g e a s s o o n a s t h e y f i ni sh e d . P a g e t u r n i n g w a s t h e

s ig n a l f or th e e x p e r i m e n t e r t o st op t im i ng . T h e n e x t p a g e p o s e d a q u e s t i o n

a b o u t t h e s t o r y w h i c h t h e s u b j e c t h a d t o a n s w e r .

T h e t h e o r y o f m i n d t e x ts w e r e r e a d sl ig h t ly , b u t s ig n if ic a n t l y, f a s t e r

( m e a n 2 5 s e c o n d s , SD 7 . 9 ) t h a n t h e p h y s i c a l t e x t s ( m e a n 3 0 s e c o n d s , SD

9 . 5 ) a n d t h e u n l i n k e d s e n t e n c e s ( m e a n 2 8 s e c o n d s ,

SD

9 . 1 ) . T h e a n s w e r s t o

t h e q u e s t i o n s w e r e s c o r e d a s 0 f o r w r o n g , 1 f o r i m p l i c it l y o r p a r t i a l l y c o r r e c t ,

2 f o r e l a b o r a t e a n d e x p l ic i tl y c o r r e c t . F o r th e u n c o n n e c t e d s e n t e n c e s , t h e

a n s w e r s w e r e s c o r e d e i th e r 0 f o r i n c o r r e c t o r 2 f o r c o r r e c t , a s t h e r e w a s n o

i n t e r m e d i a t e p o s si b il i t y. T h e r e w a s t h u s a m a x i m u m o f 16 f o r e a c h

c o n d i t i on . T h e r e su l t s s h o w e d t h a t t h e r e w e r e n o d i f fe r e n c e s b e t w e e n t h e

t h r e e c o n d i t io n s in a c c u r a c y o f a n s w e r s . M e a n s c o r e s w e r e : T o M S 1 2. 9

SD

1 . 9 ) , P S 1 2 . 8 SD 2 ) , U S 1 2 . 2 SD 2 .8 ) . W e t h e r e f o r e c o n s id e r e d t h e t h r e e

t a s k s t o b e o f e q u a l d i f fi c u l ty . I m p o r t a n t l y , f o r th e l o gi c o f su b t r a c t i o n w h i c h

u n d e r l i e s t h e e x p e r i m e n t a l d e s i gn , th e t a s k w h i c h h a d t h e e x t r a r e q u i r e m e n t

o f m e n t a l i s i n g w a s t h e f a s t e s t r a t h e r t h a n t h e s l o w e s t.

D u r i n g s c a n n in g , t h e p a s s a ge s w e r e p r e s e n t e d o n t h e s c r e e n o f a

M a c i n to s h L C I I p e r s o n a l c o m p u t e r s u sp e n d e d o n a c r a d l e a p p r o x im a t e l y 2

f e e t f r o m t h e s u b j e c t s. P r i o r to sc a n n i ng , t h e e x p e r i m e n t e r a s c e r t a i n e d t h a t



114

P . C . F l e t c h e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 5

t h e s u b j e c t c o u l d r e a d t h e m c o m f o r t a b l y . T h e s u b j e c t w a s a s k e d t o r e a d t h e

p a s s a g e s il e n tl y , o n c e a t h i s o w n p a c e . H a v i n g d o n e t h i s, h e t o u c h e d t h e

s c r e e n w i th h i s r ig h t h a n d . T h i s c a u s e d t h e p a s s a g e t o b e r e p l a c e d b y a

q u e s t i o n w h i c h h e w a s i n s t r u c t e d t o a n s w e r s i l e n t l y . H a v i n g d o n e t h i s , h e

t o u c h e d t h e s c r e e n a g a in a n d a s e c o n d p a s sa g e o f p r o s e a p p e a r e d w h i c h in

t u r n w a s f o l l o w e d b y a qu e s t io n . T h e t o t a l ti m e t a k e n t o r e a d a p a s s a g e a n d

a n s w e r i ts q u e s t io n w a s r e c o r d e d f o r e a c h o f t h e t w o p a s sa g e s s e e n d u r i n g

t h e s c a n . A f t e r t h e s c a n h a d f i n is h e d , t h e s u b j e c t ' s a n s w e r s f o r t h e t w o

p a s s a g e s w e r e r e c o r d e d .

A t t h e b e g i n n i n g o f t h e s e s s io n , s u b j e c t s w e r e b r i e f e d a b o u t t h e t y p e s o f

p r o b l e m t o b e s o l ve d a n d g iv e n sh o r t e x a m p l e s . I t w a s e x p l a i n e d t h a t , i n

T o M S s t o r ie s , i t w a s v it a l t o c o n s i d e r t h e t h o u g h t s a n d f e e l i n gs o f t h e

c h a r a c t e r s , w h i l e , i n t h e o t h e r p a s s a g e s ( P S a n d U S ) , t h i s w a s n o t o n l y

i r r e l e v a n t b u t u n d e s i r a b l e . I n t h e n o n - s to r y c o n d i t io n ( U S ) , t h e y w e r e a s k e d

n o t t o tr y to m a k e c o h e r e n t s e n se o f th e p a s s a g e . P r i o r to e a c h s c a n ,

s u b j e c t s w e r e t o l d w h i c h t y p e o f p a s s a g e t h e y w o u l d s e e . W it h in a n y s c a n ,

t w o p a s s a g e s o f t h e s a m e t y p e w e r e p r e s e n t e d . T h e o r d e r o f t a sk s w a s

c o u n t e r b a l a n c e d r a t h e r t h a n r a n d o m i se d in o r d e r t o a v o id v a r ia b l e o r d e r

a r t e f a c t s d u e t o t h e s m a l l n u m b e r o f s u b je c t s s tu d i e d . E a c h o f t h e t h r e e

t a sk s w a s a d m i n i s te r e d f o u r ti m e s o v e r t h e c o u r s e o f t h e 12 s c a ns in a n A B C

c o u n t e r b a l a n c e d d e s ig n .

W e p r e d i c t e d t h a t a c o m p a r i s o n o f t h o se s c a n s in w h i c h t h e s u b j e c t

p e r f o r m e d a T o M S t a s k w i th t h o se i n w h i c h h e p e r f o r m e d a U S t a s k w o u l d

i d e n t i f y b r a i n a r e a s i n v o l v e d in u n d e r s t a n d i n g a s to r y w h i c h r e q u i r e d

a t t r i b u t i o n o f m e n t a l s ta t e s . S i m i l a r l y , c o m p a r i s o n o f P S w i th U S s c a n s

w o u l d s h o w a r e a s e n g a g e d b y p r o c e s si n g a s to r y th a t d i d n o t i n vo l v e

a t t r ib u t i o n o f m e n t a l s t a te s . F i n a l ly , c o m p a r i s o n o f t h e T o M S a n d P S w o u l d

i s o la t e t h o s e a r e a s u n i q u e l y i n v o l v e d in th e a t t r i b u t i o n o f m e n t a l s t a t e s .

2 4 Da ta analysis

E a c h r e c o n s t r u c t e d r C B F s c a n , c o ns is ti ng o f 31 p r i m a r y t r a n s v e r s e p l a n e s ,

w a s i n t e r p o l a t e d t o 4 3 p l a n e s t o r e n d e r t h e v o x e l s a p p r o x i m a t e l y c u b ic .

S u b s e q u e n t l y , t h e t o ta l s e t o f s c a n s w a s r e a l i g n e d s o t h a t a l l 1 2 s c a n s o f e a c h

s u b j e c t w e r e i n r e g i s t e r ( A I R s o f tw a r e ) ( W o o d s , C h e r r y , & M a z z i ot a ,

1 9 92 ). T h e d a t a w e r e s u b s e q u e n t l y t r a n s f o r m e d i nt o a s t a n d a r d s t e r e o t a c t i c

s p a c e ( T a l a i r a c h & T o u r n o u x , 1 9 8 8; F r i s t o n e t a l ., 1 9 8 9) . S u c h tr a n s f o r m a -

t i o n o f th e s c a n s a l l o w s f o r p i x e l - b y - p i x e l a v e r a g i n g o f d a t a a c r o s s s u b j e c t s i n

t h e s t a n d a r d s p a c e . A G a u s s ia n f i lt e r ( fu l l w i d t h a t h a l f m a x i m u m 2 0 m m )

w a s a p p l i e d a t t h i s s t a g e t o s m o o t h e a c h i m a g e i n o r d e r t o a c c o m m o d a t e

i n te r - s u b j e c t d i ff e r e n c e s i n gy r a l a n d f u n c ti o na l a n a t o m y a n d t o su p p r e s s

h i g h - f r e q u e n c y n o is e .

D i f fe r e n c e s in gl o b a l a c t i vi ty w i th i n a n d b e t w e e n s u b je c t s w e r e r e m o v e d

b y a n a l y s is o f c o v a r i a n c e ( W i l d t & A h t o l a , 1 9 78 ) g e n e r a t i n g a c o n d i t i o n -

s p e c if ic a d j u s te d m e a n r C B F v a l u e ( n o r m a l i s e d t o 50 m l d l- ~ m i n - ~ ) a n d a n



P . C . F l e t ch e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8

115

associated adjusted error variance. This allowed comparison of the means

across all sets of conditions using the t statistic. The resulting set of t values

constitutes a statistical parametric map (SPM(t)) (Friston, Frith, Liddle, &

Frackowiak, 1991). Only pixels showing a change significant at the level of

p <.001 were se lected since this level of significance has been found to

protect adequately against false positives with our equipment (Bailey, Jones,

Friston, Colebatch, & Frackowiak, 1991). In fact, the majority of activations

seen in this study would survive a planewise correction for multiple non-

independent comparisons at p < .05 (Z score threshold approximately 3.8).

Image analysis was performed using SPM software (MRC Cyclotron,

London, UK (Frackowiak & Friston, 1994) on a SPARC 1 workstation (Sun

Microsystems Inc., Surrey, UK) using an interactive image analysis software

package (ANALYZE, Biodynamic Research Unit, Mayo Clinic, USA

(Robb & Hanson, 1991). Calculations and image matrix manipulations were

performed in PRO MATLAB (Mathworks Inc., New York).

3 . R e s u l t s

3 1 Task per formance

The times taken to perform the tasks are summarised in Table 2. Subject's

responses to each of the questions were collected in the interval before the

next scan. Across all of the theory of mind stories, the subjects answered

satisfactorily referring to the mental states of the characters, indicating that

they were engaging in mentalising in order to make sense of the stories.

Reference was made to a mental state (in each case, to a desire of a

character in the story) in only three of the 48 instances when subjects were

presented with a "physical" story. As in the theory of mind task, per-

formance was at an extremely high level: in the former task, all questions

were answered correctly; in the latter, 47/48 answers were correct.

On average, subjects gave 5.3 out of 8 correct answers on the unlinked

sentences task (total 31.8/48). No mental state terms were used by subjects

in giving these answers.

Table 2

Performance times

Task Mean

S D

Range Errors

Theory of 34 11.3 21-49 ().[)

mind stories

Physical 35.3 8.3 23-44 0.2

stories

Unlin ked 32.7 6.4 23-39 2.7

sentences



116 P.C . Fle tcher e t a l . / C ogn i t ion 57 199 .5 ) 109 - 128

3 2 P E T results

3 2 1 To MS versus US tasks

T h i s c o m p a r i s o n s h o w e d t h a t f o u r s e p a r a t e r e g i o n s w e r e a c t i v a te d b y th e

t h e o r y o f m i n d s to r i e s t o a s ig n i f ic a n t ly g r e a t e r e x t e n t t h a n w h e n t h e

s u b j e c t s r e a d a p a s s a g e o f un l in k e d s e n t e n c e s . T h e a c t i v a t e d r e g i o n s w e r e

t h e t e m p o r a l p o l e s b i la t e r a l l y , t h e le f t s u p e r i o r t e m p o r a l g y r u s , t h e p o s t e r i o r

c i n g u l a t e c o r t e x a n d t h e l e f t m e d i a l f r o n t a l g y r u s ( se e F i g . l ) .

3 2 2 PS versus US

T h i s c o m p a r i s o n s h o w e d t h r e e o f t h e a r e a s o f a c t i v a t io n f o u n d i n th e

T o M S v e r s u s U S c o m p a r i s o n , n a m e l y t h e t e m p o r a l p o l e s b i l a te r a l ly , t h e l e f t

z z g [ t t : 1 : : o F o n ~ 1

J - J q

1 0 4

v F ( - : ~ , . , ~ 5 , ( - :

6 S

- r , - .

? , d

J ~ ; 4 -

6 4

t r + ~ - - ] ~ s , . ,, . e t - s ~

Fig. 1 . Sta t is t ica l param et r ic map s (SPM s) of the compa rison of the theory of mind task wi th

the unl inked sentences t ask . (A fur ther Gaussian f il t e r (8 mm ful l w idth a t ha l f maximum) w as

app l ied a t the stage of computat ion o f sta t is t ica l param et r ic map s to increase the signal- to-noise

ra t io in the da ta se t) . View s are sh ow n f rom the r ight ( labe l led sagi tt a l ) , beh ind ( cor ona l )

and above ( t ransv erse ) . Act ivat ions signi ficant (a t p < .001) are show n in the t empora l poles

bi la te ra l ly (1) , the poster ior c ingula te cor tex (2) , the lef t super ior t empora l gyrus (3) and the

left medial frontal gyrus (4).



P.C. F le tcher e t a l . Cog n i t ion 57 199 .5 ) 109 -12 8 117

s u p e r i o r t e m p o r a l g y r u s a n d t h e p o s t e r i o r c in g u l a te c o r t e x . S t r ik i n gl y , th e r e

w a s n o a c t iv a t i o n o f t h e l e f t m e d i a l f r o n t a l g y r u s ( s e e F i g. 2 ) .

3 2 3 ToM S versus PS

T h i s c o m p a r i s o n s h o w e d a c t iv a t io n in th e l e f t m e d i a l f r o n ta l g y r u s ,

p r e d o m i n a n t l y B r o d m a n n ' s a r e a 8 , e x t e n d i n g p o s t e r i o r l y i nt o a r e a 9 a n d th e

a n t e r i o r c i n g u l a t e c o r t e x . T h e r e w a s a d d i t i o n a l a c t i v a t i o n i n t h e p o s t e r i o r

c i n g u l a t e c o r t e x a n d i n f e r i o r p a r i e t a l l o b e o n t h e r i g h t ( s e e F i g . 3 ) .

I n o r d e r t o a s c e r t a i n th a t t h e r e w a s n o s u b t h r e s h o l d a c t i va t io n o f t h e l e f t

m e d i a l f r o n t a l g y r us i n a s s o c i a t io n w i t h th e P S ta s k , w e r e - e x a m i n e d t h is

c o m p a r i s o n a t a l o w e r th r e s h o l d ( p < .0 5 n o t c o r r e c t e d f o r m u l ti p l e

c o m p a r i s o n s ) . N o a c t i v a t io n w a s se e n r e l a t i v e t o t h e U S t a s k . W e a l s o

e x a m i n e d r C B F e q u i v a l e n ts f o r t h e p i x e l o f m a x i m a l a c t iv a t io n . A g a i n ,

t h e r e w a s n o e v i d e n c e o f a n y a c t iv a t i o n in th i s r e g i o n i n th e P S t a s k

( r C B F = 5 4 . 4 m l d l ' m in ~ a s c o m p a r e d t o 5 4 . 4 m l d l ' r a in ~ f o r t h e U S

1 r l ¢

s a g l t t l 3 1 c O F C I F , G t

- 7 , )

~ 3,_ ~4

- r ' . '

v 'P 12: v ', , , l/ .~

0

61¢

t r - o r - s v e r - s e

F i g . 2 . S P M s p r e s e n t e d a s f o r F i g. l s h o w i n g a c t i v a t i o n s i n t h e c o m p a r i s o n o f t h e p h y s i c a l s t o r y

w i t h t h e u n l i n k e d s e n t e n c e s . H e r e a c t i va t i on s a r e s e e n i n t h e t e m p o r a l p o l e s b i l a te r a l l y (1 ) , t h e

p o s t e r i o r c i n g u l a t e c o r t e x ( 2 ) a n d t h e l e f t s u p e r i o r t e m p o r a l g y r u s ( 3 ) , b u t n o t t h e l e f t m e d i a l

f r o n t a l g y r u s .



118

P.C. Fletcher et al. Cognition 57 1995) 109-128

s a g [ t t a l

]l

0 , 0

0 4 V I

V P C , / ~ . C

o i i i i i

C O K - i r l r l ]

/ " . . " . . ..

. I : [ Z : I q l l l , - , , , i :

. . . .~ . . i ~ . ~ - j

7 . . . ... i

0

Fig. 3. SPM show ing a di rec t compar ison be twee n the theory of mind and the physica l t ask .

Th e m ain area of di fference betw een the tw o types of story is the lef t med ia l fronta l region (1) ,

w i th a sma l l d i f ference in ac t ivation in the a nter ior (2) and p oster ior c ingula te cor tex (3) .

t a s k a n d 5 5 . 3 m l d l ~ m m ~ f o r t h e T o M S t a s k ) . T h e r e s u l t s a r e s u m m a r i s e d

i n T a b l e 3 .

3.2.4. US versus TOMS + PS)

T h i s c o m p a r i s o n , i n d i c a t i n g b r a in a r e a s m o r e a c t i v e d u r i n g th e u n l i n k e d

s e n t e n c e s t a sk , s h o w e d a c t i v a t io n o f t h e p r e f r o n t a l c o r t e x , p r e d o m i n a n t l y o n

t h e r ig h t , a n d p o s t e r i o r p a r ie t a l a r e a s , n o t a b l y t h e p r e c u n e u s ( B r o d m a n n ' s

a r e a 7 ) . R e s u l ts a r e s u m m a r i s e d in T a b l e 4 .

4 . D i s c u s s i o n

O u r e x p e r i m e n t a l l o w s u s t o m a k e t h e su r p r i s in g i n fe r e n c e t h a t t h e

a t t r i b u t i o n o f m e n t a l s t a t e s is p a r t i c u l a r l y a s s o c i a t e d w i th t h e f u n c t i o n o f a

h i g h l y c i r c u m s c r i b e d b r a i n sy s te m .

W e h a v e u s e d a n e x p e r i m e n t t h a t i n v o l v e s r e a d i n g a n d u n d e r s t a n d i n g

p r o s e p a s s a g e s , s o m e o f w h i c h i n v o l v e d t h e a t t r i b u t io n o f m e n t a l s t a t e s

w h i l e o t h e r s r e q u i r e d o n l y a l o gi c a l u n d e r s t a n d i n g o f t h e s e n s e o f t h e s t o r y



P.C. Fle tcher e t a l . / C ogni t ion 57 (1995) 109 -128

119

Fig. 4 . The l ef t media l f ronta l act ivat ion (from the ToMS vs . PS compar ison) has been

s upe r imp os ed on to a magne t ic r e s onance image r ende r ed in to s t anda r d s t c r eo t ac t i c s pace in

o r de r to g ive an ind i ca t ion o f t he a r ea o f a c t iv i ty to b r a in s l r uc tu r e . In o r de r to f ac i l i t a t e

s upe r imp os i t ion o f t he ac t iva t ion , a d i ff e r en t ana l ys is o f t he comp ar is on w as mad e in wh i ch a

s eco nda r y s mooth ing f il te r was no t us ed . T he pu r p os e o f t h i s figur e i s s imp l y to he l p ana tomica l

o r i en t a t ion to r e ade r s unfami l i a r w i t h SPM pr es en t a t ions in F igs . 1 -3 .

w i t h o u t r e f e r e n c e t o t h e m e n t a l s t a t e s o f t h e c h a r a c t e r s . I d e n t i f i c a t io n o f

a r e a s c o n c e r n e d w i t h t h e p r o c e s s i n g o f s to r ie s w a s p o s s ib l e b e c a u s e w e u s e d

a c o n t r o l t a s k w h i c h c o n s i s t e d o f i n d i v id u a l l y m e a n i n g f u l b u t o v e r a l l

u n c o n n e c t e d s e n t e n c e s .

T h e r e w e r e t h r e e a r e a s c o m m o n w i th t h e m e n t a l i s in g a n d n o n - m e n t a l i s i n g

s t o r y t a s k s : t h e t e m p o r a l p o l e s b i l a t e r a l l y , t h e l e f t s u p e r i o r t e m p o r a l g y r u s

a n d t h e p o s t e r i o r c i n g u la t e c o r t e x . U n i q u e l y a c t i v a t e d in t h e t h e o r y o f m i n d

t a s k w a s t h e m e d i a l f r o n t a l g y m s , t o g e t h e r w i th a p o r t i o n o f t h e p o s t e r i o r

c i n g u l a t e g y r u s . A l l t h e a r e a s w h e r e w e f o u n d s ig n i f ic a n t a c t i v a t i o n h a v e

s h o w n a c t i v a t i o n in p r e v i o u s P E T s t ud i e s i nv o l v in g v e r b a l m e m o r y , l a n -

g u a g e a n d s t o r y c o m p r e h e n s i o n ( se e b e l o w ) .

O n l y t h e m e n t a l s t a te s t o r i e s , i n c o n t r a s t t o b o t h c o n t r o l t a s k s , c a u s e d

a c t i v a t i o n i n t h e

l e ft m e d i a l f r o n t a l g y r u s ( B r o d m a n n s a r e a 8 ) .

T h i s r e s u l t

c l o s e l y r e s e m b l e s t h a t o f M a z o y e r e t a l . ( 1 99 3 ) i n w h i c h l i s t e n i ng to s t o r ie s

p r o d u c e d , in a d d i t i o n to t e m p o r a l p o l e a n d s u p e r i o r t e m p o r a l a c t iv a t io n ( se e



120

P C . F l e t ch e r e t a l. / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8

T a b l e 3

I n c r e a s e s i n b r a i n a c t i v i t y a s s o c i a t e d w i t h s t o r y c o m p r e h e n s i o n

R e g i o n C o o r d i n a t e s a

x y z

Z v a l u e

T h e o r y o f m i n d s t or i es

v s . u n l i n k e d s e n t e n c e s

L . m e d i a l f r o n t a l g y r u s - 1 2 , 42 40 4 . 8

( B A 8 )

L . t e m p o r a l p o l e ( B A 3 8 ) - 4 4 , 2 0, - 1 6 4 . 9

R . t e m p o r a l p o l e ( B A 3 8 ) 4 4 , 1 8, - 1 6 5 . 3

R . p o s t e r i o r c i n g u l a t e 4 , - 6 4 , 1 2 4 . 8

c o r t e x ( B A 2 3 / 3 1 )

L . s u p e r i o r t e m p o r a l - 4 4 , - 5 8 2 0 4 . 2

g y r u s ( B A 2 2 / 3 9 )

P h y s i c a l s t o r i e s v s .

u n l i n k e d s e n te n c e s

L . t e m p o r a l p o l e ( B A 3 8 )

R . t e m p o r a l p o l e ( B A 3 8 )

L . p o s t e r i o r c i n g u la t e

c o r t e x ( B A 2 3 / 3 1 )

L . s u p e r i o r te m p o r a l

g y r u s ( B A 2 2 / 3 9 )

- 4 0 , 1 6 , - 1 2 4 . 7

4 4 , 1 6 , - 1 6 4 . 3

- 2 , - 6 2 8 4 .8

- 4 2 , - 6 4 , 1 6 3 .6

T h e o r y o f m i n d s t or i es

v s . p h y s i c a l s t o r i e s

L . m e d i a l f r o n t a l g y r u s - 1 2 , 3 6 , 3 6 4 . 1

( B A 8 )

R . p o s t e r i o r c i n g u l a t e 6 , 5 6 , 1 6 3 . 6

( B A 2 3 / 3 1 )

A n t e r i o r c i n g u l a t e ( B A 3 2 ) 0 , 3 8 , 2 4 3 . 7

R . i n f e r i o r p a r i e t a l ( B A 4 0 ) 4 2 , - 5 0 , 2 4 3 . 5

C o o r d i n a t e s a r e g i v e n w i th r e f e r e n c e t o a s t a n d a r d s t e r e o t a c t ic s p a c e ( T a l a i r a c h & T o u r n o u x ,

1988).

T a b l e 4

D e c r e a s e s i n b r a i n a c t iv i ty a s s oc i a te d w i t h s t o r y c o m p r e h e n s i o n

R e g i o n C o o r d i n a t e s Z v a l u e

x y z

U n l i n k e d s e n t e n c e s v s .

s to r ie s

R . m i d d l e f r o n t a l g y r u s 3 6 , 3 0 , 2 8 6 . 6

( B A 4 6 )

L . m i d d l e f r o n t a l g y r u s - 3 2 , 5 0 , 2 0 3 . 9

( B A 1 0)

R . p r e c u n e u s ( B A 3 1 / 7 ) 8 , - 7 4 , 3 6 4 .1

L . p r e c u n e u s ( B A 3 1 / 7 ) - 1 4 , - 6 6 , 3 6 4 . 2

A n t e r i o r c i n g u l a t e 0 , 1 6 , 40 4 . 7

c o r t e x ( B A 3 2 )



P . C . F l e tc h e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8

121

below), activation in an area referred to as the left superior prefrontal

region corresponding to Brodmann's area 8. Although the authors were not

specifically concerned with the content of the stories used, subsequent

inspection of their materials showed that both test stories involved complex

social interaction (e.g., competition, deception, intrigue), and necessitated

the attribution of higher-order mental states to the story characters (Mehler,

personal communication),

One previous study in which functional brain imaging was used to

investigate theory of mind has recently been reported (Baron-Cohen et al.,

1994). Targeting the orbitofrontal regions, this study used a different task

(discriminating words which described mental states from those which did

not), a different, less sensitive methodology (single-proton emission com-

puter tomography: SPECT) and a more limited type of image analysis (a

"regions of interest" approach applied to the frontal cortex), This study

found different activation patterns relating to the orbitofrontal regions only.

In our study, we found no significant differences in activity in this region.

Instead, our data pinpointed the medial dorsal region of the left frontal

cortex as being critically involved in mentalising.

Functions of the medial frontal region in humans have not been well

documented. It has been regarded as a transitional region between the

premotor area and the dorsal prefrontal cortex (Brodmann's areas 6 and

9/46 respectively). It has widespread cortical connections including parietal

(Petrides & Pandya, 1984), temporal polar (Moran. Mufson, & Mesulam,

1987), occipital and anterior cingulate cortex (Pandya, Van Hoesen &

Mesulam, 1981). Lesions to the region produce deficits in conditional

learning in monkeys (Petrides, 1982) and humans (Petrides, 1990). A recent

functional imaging study showed activation of this region in association with

a conditional associative learning task. In this task, the correct response

(pointing to one symbol from a choice of eight) was dependent upon the

colour of a stripe at the top of the display (Petrides, Alivisatos, Evans, &

Meyer, 1993). One possible, but tenuous, explanation for the occurrence of

medial frontal activation in our theory of mind tasks and the conditional

task of Petrides is that the tasks share the need for integration of

information in the light of other stimuli. For instance, in our example story

(see Appendix), the policeman's request for the burglar to stop, in the

context of the story, has very different implications from its usual meaning.

Interestingly, a claim for a connection between conditional reasoning and

theory of mind skills has been made (Frye, Zelazo, & Palfai, 1994).

In the direct comparison between the ToMS and PS tasks, two additional

areas were identified: anterior cingulate and inferior parietal cortex. How-

ever, since these areas did not appear in the comparisons of the ToMS tasks

with the US task, we cannot assume that they have a specific association

with mentalising abilities.

Bilateral activation of the temporal poles the anterior-most part of the

temporal lobes, corresponding to Brodmann's area 38, was a significant



P.C. Fletcher et al . / Cognition 57 1995) 10 9-128

123

wind, 1965; Hart & Gordon, 1990): Hart and Gordon, noting three patients

with semantic comprehension deficits associated with lesions to the region,

suggest that the anterior part of this area is concerned with "higher level

elaboration" of auditory and visual information and the posterior superior

part with "integration of this information with language". In several

functional imaging studies, this region has shown activation notably in

lexico-semantic processing (Peterson, Fox, Posner, Mintun & Raichle, 1989:

Ddmonet et al., 1992). Our own finding of superior temporal activation in

both story conditions compared to unlinked sentences indicates a role in a

higher level of language processing, that is, cohesion across sentence

boundaries.

Activation of the

p o s t e r i o r c i n g u l a t e c o r t e x ,

Brodmann's area 23/31, was

also common to both story conditions when compared to unlinked sen-

tences. This activation was significantly greater in the theory of mind stories

than in the physical ones. The posterior cingulate gyrus is a region with

widespread cortical connections, notably to the prefrontal and medial

temporal regions, the inferior parietal lobe and the superior temporal sulcus

(Pandya et al., 1981). Human studies have linked the area with memory

function (Valenstein et al., 1987; Rudge & Warrington, 1991) . Further

evidence for this role has come from functional imaging work (Grasby et al.,

1993) and one recent study has suggested that this area is preferentially

involved during the encoding stage of episodic memory (Shallice et al.,

1994). It seems unlikely, prima facie, that a role in memory could account

for the posterior cingulate activation in this study since, if anything, the

control condition (unlinked sentences) is likely to place a greater load on

memory function than either of the story conditions. However, the more

coherent nature of the material presented in the story tasks may mean that

the subject is more likely to try to encode relevant material on-line in order

to maintain the cohesion of the narrative, and incorporate new information

into the accumulating story structure. By contrast, in the unlinked sentences

condition, material encountered early in the passage should not affect

encoding of later material and subjects would be unable to predict which

pieces of information should be memorised for question answering. Anothe r

explanation for the finding is the suggested involvement of this area in visual

processes (Rudge & Warrington, 1991). If the presentation of the stories

(whether mentalising or non-mentalising) leads to more visual imagery than

unlinked sentences, then we might expect to see increased activity in

posterior cingulate cortex. However, both of these suggestions are post hoc

attempts to explain this activation.

We will not comment on the relative activations in the

u n l i n k e d s e n t e n c e s

task except to say that the areas seen (bilateral frontal and posterior

parietal/precuneus) have all been previously implicated in PET studies of

memory (Grasby et al., 1993). Recently, it has been claimed that right

frontal and precuneus activity are especially important at the retrieval stage

(Shallice et al., 1994) . The necessity, during the US task , of recalling



124 P . C . F l e t ch e r e t a l . / C o g n i t i o n 5 7 1 9 9 5 ) 1 0 9 - 1 2 8

disparate sentences rather than retaining the overall sense of the story could

perhaps explain this finding. However, this, again, is a post hoc suggestion

which the study was not designed to address.

To summarise, we have used PET to examine the neural correlates of an

important facet of cognitive function: the ability to attribute mental states.

We identified a circumscribed brain system the medial frontal gyrus on the

left. Two directions for further research are clear. We need to replicate these

findings with further groups of volunteers, particularly through tasks which

engage theory of mind in different ways (e.g., silent animation rather than

stories). Secondly, the paradigms can be applied to autistic (or Asperger's

syndrome) subjects in future studies. In this way, we may be able to shed

light on the physiological basis of the normal ability to attribute mental

states, and on the brain pathways implicated in the autistic disorders.

Appendix: examples of materia ls

Theory o f mind s tor i es

A burglar who has just robbed a shop is making his getaway. As he is

running home, a policeman on his beat sees him drop his glove. He doesn't

know the man is a burglar, he just wants to tell him he dropped his glove.

But when the policeman shouts out to the burglar, " Hey , you Stop ", the

burglar turns round, see the policeman and gives himself up. He puts his

hands up and admits that he did the break-in at the local shop.

Sub ject touches screen story disappears question appears:

Q: Why did the burglar do this?

Sub ject internally answers quest ion and touches screen whe reupon seco nd

story appears:

During the war, the Red army capture a member of the Blue army. They

want him to tell them where his armies' tanks are. They know that they are

either by the sea or in the mountains. They know that the prisoner will not

want to tell them, he will want to save his army, and so he will certainly lie

to them. The prisoner is very brave and very clever, he will not let them find

his tanks. The tanks are really in the mountains. Now when the other side

ask him where his tanks are he says, "They are in the mountains."

Q: Why did the prisoner say that?



P.C. Fletcher et al . / Cognition 57 1995) 10 9-12 8

125

P h y s i c a l s t o r i e s

A b u r g l a r i s a b o u t t o b r e a k i n t o a j e w e l l e r s ' s h o p . H e s k i l fu l ly p i c k s t h e

l o c k o n t h e s h o p d o o r . C a r e f u l l y h e c r a w l s t in d e r t h e e l e c t r o n ic d e t e c t o r

b e a m . I f h e b r e a k s t h is b e a m it w i ll se t o ff t h e a l a r m . Q u i e t l y h e o p e n s t h e

d o o r o f th e s t o r e - r o o m a n d s e e s t h e g e m s g li tt e r in g . A s h e r e a c h e s o u t ,

h o w e v e r , h e s t e p s on s o m e t h i n g s of t. H e h e a r s a sc r e e c h a n d s o m e t h i n g

s m a l l a n d f u r r y r u n s o u t p a st h i m , t ow a r d s t h e s h o p d o o r . I m m e d i a t e l y th e

a l a r m s o u n d s .

Q : W h y d i d t h e a l a r m g o o f f ?

T w o e n e m y p o w e r s h a v e b e e n a t w a r f o r a v e r y l on g t im e . E a c h a r m y h a s

w o n s e v e r a l b a t t le s , b u t n o w t h e o u t c o m e c o u l d g o e i t h e r w a y . T h e f o r c e s

a r e e q u a l ly m a t c h e d . H o w e v e r , t h e B l u e a r m y i s s t r o n ge r t h a n t h e Y e l lo w

a r m y i n f o o t so l d i e r s a n d a r t il l e r y . B u t t h e Y e l l o w a r m y i s s t r o n g e r t h a n t h e

B l u e a r m y i n a ir p o w e r . O n t h e d a y o f th e f in a l b a t t l e , w h i c h w i l l d e c i d e t h e

o u t c o m e o f t h e w a r , t h e r e i s h e a v y f o g o v e r t h e m o u n t a i n s w h e r e t h e

f i gh t i n g is a b o u t t o o c c u r . L o w q y i n g c l o u d s h a n g a b o v e t h e s o l d i e r s. B y th e

e n d o f t h e d a y t h e B l u e a r m y h a v e w o n .

Q: W h y d i d t h e B l u e a r m y w i n ?

U n l i n k e d s e n t e n c e s

T h e f o u r b r o t h e r s s t o o d a s i d e t o m a k e r o o m f o r t h e i r s is te r , S t e l l a . J il l

r e p e a t e d t h e e x p e r i m e n t , s e ve r a l tim e s . T h e n a m e o f t h e a i r p o r t h a d

c h a n g e d . L o u i s e u n c o r k e d a l it tl e b o t t l e o f o il . T h e t w o c h i l d r e n h a d t o

a b a n d o n t h e i r d a i l y w a l k . S h e t o o k a s u it e in a g r a n d h o t e l . I t w a s a l r e a d y

t w e n t y y e a r s s i n c e t h e o p e r a t i o n .

Q : D i d t h e c h i l d r e n t a k e t h e i r w a l k ?

O n e d a y U n c l e S i m o n c a m e t o vis it A l e x . T h e f ir st p a r t o f t h e p e r -

f o r m a n c e h a d c o m e t o a n e n d . H e p u t a w a y th e l e t t e r a n d s tu c k h is h a n d s i n

h i s p o c k e t . S h e w a s s t i l l h o l d i n g h e r u m b r e l l a . T h e c a t s r a i l b a c k t o t h e b o y .

F l o r a c a m e i n to t h e m i d d l e o f t h e s q u a r e . T h e l it t le i sl a n d h a d a h i gh r o c k y

s h o r e l i n e .

Q : D i d F l o r a g o t o t h e s q u a r e ?

Acknowledgement

T h i s w o r k w a s c a r r ie d o u t a t t h e M R C C y c l o t ro n U n i t , H a m m e r s m i t h

H o s p i t a l . W e a r e e x t r e m e l y g r a t e f u l f o r t h e u s e o f th e s e f a c i l it ie s .



126

P.C. Fletcher et al. / Cognition 57 1995) 109-128

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