ornitz, 1974 - the modulation os sensory input and motor output in autistic children

7/27/2019 Ornitz, 1974 - The Modulation Os Sensory Input and Motor Output in Autistic Children

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to make discriminations in the absence of feedback from moto r responses(Hermelin & O'Connor, 1970), and a faulty modulation of sensory input (Ornitz& Ritvo, 1968a; Bender, 1947; Goldfarb, 1961; Ornitz, 1969; Bergman &Escalona, 1949; Anthony, 1958; Stroh & Buick, 1964).

Autistic children do not show the same preference in the use of the varioussensory modalities as do normal children or nonautistic mentally retarded chil-dren. They have been described as preferring to use proximal receptors (touch,smell, and taste) rather than distal receptors (audition and vision; Goldfarb,1956; Schopler, 1965, 1966). Both autistic and nonautistic children tend torespond to light in preference to sound, but nonautistic children can readily beconditioned to respond preferentially to a sound source, whereas this is notpossible with autistic children (O'Connor, 1971). This apparent dominance ofvisual over auditory stimuli may actually be due to an inability to respond totwo or more stimulus modalities in a complex stimulus presentation. Autisticchildren are overselective in responding to only one component of a stimuluscomplex consisting of, e.g., auditory, visual, and tactile components (Lovaas,Sclareibman, Koegel, & Rehm, 1971; Lovaas & Schreibman, 1971). They alsolimit their attention to only one of two stimulus dimensions in a visual discrimi-nation (Hermelin & O'Connor, 1970). Visual stimulation itself seems less

meaningful to autistic than to nonautistic children in that autistic children showfewer eye movements in response to and spend less time regarding visual displaysthan do nonautistic children (Hermelin & O'Connor, 1970; O'Connor, 1971).While autistic children may have normal or even advanced form perception(Ritvo & Provence, 1953), they make poor use of visual discrimination in learn-ing (O'Connor, 1971; Ottinger, Sweeny, & Lowe, 1965). They seem to bedependent on feedback from their own motor responses toward sensory stimuliin order to make sense out of perceptions (Hermelin & O'Connor, 1970; Frith &

Hermelin, 1969). We will return to this theme after reviewing the symptoms ofinadequate modulation o f both sensory input and motor output.

SYMPTOMS OF INADEQUATE MODULATION OF SENSORY INPUT

The inability to adequately modulate sensory input constitutes a strikingaspect of autistic symptomatology (Ornitz & Ritvo, 1968a; Goldfarb, 1961,1963; Ornitz, 1971; Bergman & Escalona, 1949). All sensory modalities areaffected and the faulty modulation of sensory input may be manifest as either a

lack of responsiveness or an exaggerated reaction to sensory stimuli (Goldfarb,1961, 1963). Both types of abnormal reactivity to sensory stimuli can occur inthe same child (Goldfarb, 1963).

Hyporeactivity to auditory stimuli is apparent in the disregard of bothverbal commands and loud sounds. Sudden sounds which would elicit an impres-sive startle reaction in normal children may elicit no response whatsoever insome autistic children (Anthony, 1958). Visually, the children may ignore newpersons or features in their environment and they may walk into objects as if


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they did not see them. A similar response to tactile s t i m u l i may occur during thefirst two years o f life; objects placed in the hand may be allowed to fall away asif they had no tactile representation. Painful stimuli are often ignored; thechildren may not notice painful bumps, bruises, cuts, or injections.

Contrasting starkly to the hyporeactivi ty to sensory stimuli are markedlyexaggerated reactions to the same stimuli. The children may show both height-ened sensitivity to sensory stimuli and heightened awareness o f sensory stimuli(Goldfarb, 1963).

The unusual sensitivity to sensory stimuli is manifest in many ways. Thechildren may become agitated by the sound of sirens, vacuum cleaners, orbarking dogs and they may cup their hands over their ears in an attempt to shutout both these intense sounds and also mild novel sounds such as the crinkle ofpaper (Goldfarb, 1963; Bergman & Escalona, 1949). Sudden changes in illumina-tion or confrontation with an unexpected object may elicit the same fearfulreactions to visual stimuli. In the tactile modality there may be severe intoler-ance for certain fabrics; the children are often disturbed by wool blankets orclothing and seem to prefer smooth surfaces. During the first year of life theintroduction of the rough-textured table foods may evoke distress. The childrenmay show a marked aversion to the vestibular stimulation induced by rough-

house, antigravity play, or even riding in an elevator.The heightened awareness of sensation is often associated with a

tendency to seek it out and induce it. Some of the mo tor behaviors of autisticchildren seem to provide intense sensory stimulation. The children tend toinduce sounds by scratching surfaces and putting their ears down close to thesurface. They may be distracted by background stimuli of marginal intensity.They may rub, bang, or flick at their ears or grind their teeth, all of whichactivities induce intense auditory input. Visually they regard their own writhing

hand and finger movements or their more vigorous hand-flapping, and theyscrutinize the fine detail o f surfaces. There are also brief episodes of intensestaring. The children may rub surfaces of furniture or fabric in response to freetextural differences. Many of the behaviors of autistic children also suggest thatthey are actively seeking out vestibular and proprioceptive stimulation (Bender,1947, 1956). They whirl themselves around and around, repetitively rock andsway back and forth, or roll their heads from side to side. The repetitive hand-flapping also provides proprioceptive input.

SYMPTOMS OF INADEQUATE MODULATION OF MOTOR OUTPUT

The moto r behaviors of autistic children do not necessarily provide sen-sory input. They are of ten such a predominant part of the syndrome as to meritattention in their own right. To a great extent the strange and bizarre appearanceof autistic children is due to their peculiar mannerisms and motility patterns.The deviant motility may involve the hands, the lower extremities, or the trunk


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and en t i re body. Whi le the manner i sms a re o f t en complex and r i tua l i s t i c andc le a r ly do no t ha ve the a ppe a r a nc e o f e i t he r invo l un t a r y m ov e m e n t s o r s ei zu re

discharge pa t te rn s the y are s te re oty pe d, s t r ik ingly s imi lar in genera l pa t te rn andform in mos t au t i s t i c ch i ld ren , and do no t seem to be en t i re ly vo lun ta ry. Theseve r ity o f th i s a spec t o f the syn dro m e va ri e s m arke d ly f rom o ne au t is t ic ch i ldt o a no t he r. T he de v i a n t m o t i l i ty m a y a ppe a r i n t e r m i t t e n t l y o r i n f r e que n t ly i nsome au t i s t i c ch i ld ren and may occur con t inuous ly in o the rs (Sorosky, Orn i t z ,Brown, & Ri tvo , 1968; Hut t , H ur t , Lee , & Ou ns ted , 1965) .

Some of the mos t cha rac te r i s t i c and s t r ik ing motor behav iors invo lve thehand s (Orn i t z & Ri tvo , 1968a ; S orosky e t a l., 1968 ; Aug & Ables , 19 71;O rn i t z ,1971; R i tvo , Orn i t z , & LaFranch i , 1968; Orn i t z , Brown, Sorosky , Ri tvo , &Diet r ich , 1970) . Th e aut i s tic chi ld m ay hold his han ds in f ron t o f h is eyes andwri the or twis t the f ingers and p a lms. This typ e o f ac t iv i ty of ten m erge s in to arepe t i tive , s t e re o typ ed wiggling o f the f ingers o r the en t i re hand . Th i s hand-f l app ing invo lves a rap id and un t i r ing a l t e rna t ing f l ex ion and ex ten s ion o f thefinge rs o r hands o r an a l t e rna t ing p ro na t ion and sup ina t ion o f the fo rea rm.S im i la r f la p p i ng m o ve m e n t s o f t he l owe r e x t re m i t ie s m a y oc c u r, bu t t he m os ts t rik ing invo lvem ent o f the low er e x t rem i t i e s is toe -wa lk ing (Colbe r t & Koegle r,1958) . Th i s m ay occu r t r ans ien t ly dur ing st a t e s o f exc i t em ent o r whi le the ch i ld

is running in c i rc les. Ho wev er, i t i s of te n the on ly m od e of walking and m aypersis t on occasion in to adolescence .

Dis tu rbances invo lv ing the t runk or en t i re body inc lude s t acca to lung ingand da r t ing m ove m ents , t e rm ina ted by sudden s tops . The ch i ld ren a lso engage ina n unusua l a m oun t o f body - r oc k i ng a nd swa y ing , o f t e n a c c om p a n i e d by he a d -rol ling or head-bang ing. A h is tory o f severe infant i le h ead-ban ging is of te n asso-c ia ted wi th the l a t e r deve lopm ent o f se l f -mu t i la t ion (Green , 1967) . The ch i ld renalso w hiff them selves a rou nd the longi tudina l bo dy axis . In spi te of all th is gross

m oto r ac t iv ity, au t i st ic ch i ld ren a re no t necessa ri ly hyp erac t ive . These ch i ld renare not constant ly in mot ion nor i s there necessar i ly a res t less , i r r i table qual i tyto the i r ac t iv ity. In fac t , t he va r ious behav iors jus t desc r ibed m ay be in t e r rup tedby sudden br i e f ep i sodes o f imm obi l i ty, o f t en a ssoc ia t ed wi th b iza r re pos tu r ingo f the t ru nk or ex t rem i t ie s . Very you ng au t i s ti c ch i ld ren t e nd to a rch the ba cka nd hype r e x t e nd t he ne c k , m a i n t a i n i ng t h i s unc om f o r t a b l e pos i t i on f o r b r i e fpe r iods o f time . S om e or a ll o f these mo t i l i t y pa t t e rns can a t t imes be e l ic i ted b yrap id ly sp inn ing a ch i ld 's top in f ron t o f the pa t i en t .

E X P L A N AT O RY H Y P O T H ES E S

Severa l d i ffe ren t h ypo these s have bee n pu t fo r th to exp la in the re l a tion-sh ip be tw een the d i s tu rbance o f pe rcep t ion and the d i s tu rbance o f m ot i l i t yobserve d in aut i s tic ch i ldren.


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Physiologic Overarousal

A plausible explanation of the apparent tendency toward a specific andpeculiar type of motor discharge which seems to provide and at times to betriggered by sensory input is that autistic children are in a chronic state ofphysiologic overarousal. Hutt et al. (1965) found that autistic children showmore frequent gesturing in more complex environments, suggesting that they arein a more aroused state and therefore more ready to respond to increased stim-ulation. However, investigations that focused on those motor behaviors that arevery specific to the autistic syndrome, e.g., hand-flapping, demonstrated that themotor output persisted through long periods of reduced sensory input (Soroskyet al., 1968) and did not increase significantly in the presence of increasingenvironmental complexity (Omitz et al., 1970; Hermelin & O'Connor, 1970).Furthermore, electroencephalographic studies have not consistently supportedthe notion that autistic children are in a chronic state of hyperarousal. Tworeports of unusuaUy low voltage EEGs suggestive ofhyperarousal (Kolvin et al.,1971; Hutt et al., 1965) were not confirmed in two other studies (Creak &Pampiglione, 1969; Hermelin & O'Connor, 1968) when stimulus conditions werecontrolled. The evidence indicates that excessive motor activity by the autisticchild is not necessarily caused by a chxonic state of physiologic over-arousal.

Insufficient Sensory Stimulation

Since many of the autistic motor behaviors seem to provide sensory input(see above), it seems natural to assume that autistic children have been in or arein a state of sensory deprivation for which they are trying to compensate byself-generated input. Maternal deprivation is a condition which may occur ininstitutionally reared (Provence & Lipton, 1962) or home-reared (Coleman &Provence, 1957) infants and results in severe sensory deprivation during ritecritical early months of life. However, comparison of the clinical syndrome ofchildhood autism with that resulting from maternal deprivation has shown thatthe two conditions are diagnostically distinct and that childhood autism doesnot result from earlier sensory deprivation (Omitz, 1971, 1973). It still remainspossible that autistic children are in a functional state of sensory deprivation,perhaps due to a neurophysiologic dysfunction which results in a tendency to

gate out too much sensory input. This seems unlikely since clinical observationshows that the children react as if they are receiving too much sensory input asoften as too little (Goldfarb, 1963; Bergman & Escalona, 1949; Ornitz, 1973).Although the motor behaviors appear to provide sensory input, a quantitativestudy of the amount of hand-flapping showed that it was not reduced whenautistic children attended to a spinning object. This fmding suggested that the


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ha nd - fl a pp ing wa s no t c om pe nsa t i ng f o r l a c k o f su ffi c ie n t s e nso ry i npu t ( O m i t ze t a l., 1970) . In the same expe r ime nt , howev er, r e s t r ic t ion o f v i sua l inpu t causedone aut i s t ic chi ld to modify his hand-f lapping by brushing his f ingers aga inst h isbod y w i th e a c h ha nd m o ve m e n t , a ppa r e n t l y subs ti tu t ing t a ct il e i npu t f o r t hereduced v i sua l inpu t . Thus , the poss ib i l i ty rema ins open tha t au t i s t i c motorbe ha v io r s m a y p r o v i de senso r y i npu t .

Inadequate Modulation of Sensory lnput

Close ly re l a t ed to the no t ion tha t au t i st ic ch i ld ren m ay excessive ly ga teou t s e nso r y i npu t is the m or e ge ne ra l c on c e p t o f the b r e a k dow n o r f a il ur e t o

deve lop o f the neuroph ys io log ic m echa n i sm s tha t r egu la te the leve l o f sensorybo m ba r dm e n t ( Om i t z , 19 69 ). I n th i s c onc e p t the f a c t t ha t a u t is ti c c h il d re n bo t hund er reac t and ove r reac t to sensory s t imu l i (Go ldfa rb , 1963; Bergman &Esca lona, 1949; Om i tz , 1973 ; A ntho ny , 1958) is t ake n in to acco unt . I t has bee npresen ted in t e rm s o f a de fec tive s t imu lus ba r r i e r o r f il te r ing func t ion (A nth on y,1958; B ergman & Esca lona , 1949) o r a s a bas i c s t a t e o f pe rcep tua l inco ns tanc yre la t ed to an imba lance be tween neurophys io log ic exc i t a t ion and inh ib i t ion(Orn i t z & R i tvo , 1968a , 1968b) . Those wh o have acce p ted these no t ions have

e i the r ignored the s t range m ot i l i t y o f au t is t ic ch i ld ren o r have t rea ted the m ot i l i t yd i st u rba nc e a s a n i nde pe nde n t c onse que nc e o f the po s t d a t e d unc oup l i n g o f e xc i t-a to ry an d inh ib i to ry me chan i sm s (Orn i t z & Ri tvo , 1968a , 1968b) . Th i s fa i lu re tot a ke i n t o a c c ou n t t he poss ib l e i n te r a c t ion o f the m od u l a t i on o f s e nso ry i npu ta nd t he s tr a nge m o t o r o u t pu t wa s a c onse que nc e o f no t pa y i n g su ffi c ie n t a tt e n -t ion to ce r t a in in t e res t ing beh av iora l sequences which can be obse rved c l in i ca lly.In yo un g au t i st ic ch i ld ren i t is a t times obse rved tha t ce r t a in type s o f sensoryinpu t , pa r t i cu la r ly sudden or in t ense aud i to ry s t imul i and v i sua l s t imula t ion w i thsp inn ing ob jec t s , wi l l i nduce exc i t a to ry motor behav ior such a s s t e reo typedrepe t i t ive f l app ing o r osc i l l a t ing o f the ex t remi t i e s . At o the r t imes such s t imul iwill cause t r ans ien t ca ta ton ic -l ike a rre s ts o f mo t ion , o f t e n wi th unusua l pos tu r-ing. These behav ior sequences a re simi la r in fo rm to the sub jec t ive exper i ence o fadu l t sch izophren ics and have been d i scussed in re l a t ion to a pos tu la t ed con t ro lo f bQt h se nso r y i npu t a nd m o t o r ou t pu t by c e n t r a l ve s t i bu l a r m e c ha n i sm s( Or n i tz , 1970 ). T he c onc e p t o f f a il u re o f r e gu la t ion o f bo t h se nso r y i npu t a ndm o t o r o u t p u t d u e t o a d y s f u n c ti o n o f a c o m m o n n e u r o p hy s io l o gi c m e c h a n i s mha s b e e n e l a bo r a t e d i n t e r m s o f t he e f f e c t o f s enso r y i npu t on m o t o r ou t pu t a nd

o f m o t o r ou t p u t on se nso r y i npu t ( Or n it z , 1971 ). T h i s c onc e p t o f c h i ldhoodau t i sm as a d i sorde r o f senso r imo tor in t egra t ion (Orn i t z , 1971) wi ll no w bedeve loped in re la t ion to tw o ty pes o f exp e r im enta l inves tiga t ion .

Disordered Sensorimotor Integration

Tw o convergen t li nes o f invest iga t ion , one c l in i ca l and neurop hys io log ic(Orn i t z , 1969 , 1970 , 1971) , t he o the r psycholog ic (Herm el in & O 'Con no r,


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1 9 7 0 ) , h a v e p o i n t e d t o w a r d a d i s t u r b a n c e o f s e n s o r i m o t o r i n t e g r a t io n i n au t is t icch i ld ren . I wi ll f ir s t cons id e r t he ca re fu l p sycho log ica l exp er im en t s o f He rmel in

& O ' C o n n o r ( 1 9 7 0 ) . I n t h e p r o c e ss o f c o n f i rm i n g t h e d o m i n a n t u s e o f " p ro x i -m a l " r e c e p t o r s s u c h a s t o u c h o v e r " d i s t a l " r e c e p t o r s s u c h a s s o u n d ( G o l d f a r b ,1956 ; Schop le r, 1965 , 1966 ) , t h ey no ted tha t a t ac ti l e s t imu lus , a l i gh t t ug on as t ri n g a r o u n d t h e c h i l d 's a n k l e , w a s a s s o c ia t e d w i t h i n d u c e d m o v e m e n t o f t h ec h i l d 's le g. T h u s , t h e a p p a r e n t d o m i n a n c e o f t h e t a c ti le s e ns e m a y h a v e a c t u a l l yb e e n d u e t o a k in e s t h e t ic s t im u l u s , i .e ., s e n s o r y f e e d b a c k f r o m t h e c h i l d ' s o w nm o t o r r e s po n s e . T h i s w a s c o n f i r m e d i n a s u b s e q u e n t e x p e r i m e n t i n w h i c h i t w a sf o u n d t h a t a u t i s t i c c h i l d r e n w e r e a b l e t o m a k e d i s c r i m i n a t i o n s o n t h e b a s i s o ft h e p o s i t i o n o f a s o u n d a n d li g h t s t im u l u s w h i c h d e t e r m i n e d t h e c h i l d 's m o t o rr e s p o n s e t o r e a c h t h e r e w a r d r a t h e r th a n o n t h e in t e n s i t y - m o d a l i t y c o m b i n a t i o no f t h e s t im u l u s c o m p l e x . T h e a u t i s ti c c h i ld r e n d i s c r im i n a t e d n o t a c c o r d i n g t o ,e .g . , v i sua l cues , bu t t o the i r own hand movemen t s , e .g . , an upward ver sus as t ra i g h t- a h e a d r e a c h . I n a r e la t e d e x p e r i m e n t i t w a s s h o w n t h a t b o t h o l d e ra u t is t ic c h i ld r e n ( 6 t o 1 5 y e a r s o l d ) a n d y o u n g e r n o r m a l c h i l d re n ( 3 t o 5 y e a r so ld ) l ea rned to m ake a pos i t i on d i sc r imin a t ion m ore r ead i ly than a v i sua l d is -c r i m i n a t io n . S i nc e t h e p o s i t i o n d i s c r im i n a t i o n i n v o l v e d t h e l e a rn i n g o f a m o t o rhab i t , i .e . , r each ing in the same d i r ec t ion , t h is r esu lt i nd ica t ed th a t t he d e fec t in

r e s p o n d i n g t o s e n s o r y c u e s a n d t h e n e e d f o r k i n e s t h e ti c f e e d b a c k f r o m m o t o rresponses in the o lde r au t i s t ic ch i ld ren r ep resen ted a dev e lopm en ta l d i s tu rbance .T h u s t h e " m a t u r a t i o n a l l a g " w h i c h h a s b e e n o b s e r v e d b o t h c li n ic a ll y ( B e n d e r &F r e e d m a n , 1 9 5 2 ) a n d i n e x p e r i m e n t a l s le ep s t u d ie s ( O r n i t z , 1 9 7 2 ) o f a u t is t icch i ld ren is a l so m an i fes t i n t he n eed o f t he im m atu re o rgan i sm to r eceive feed -back f rom se l f -genera t ed mo to r r esponses in o rder t o l ea rn . In a f ina l se r i es o fe x p e r im e n t s H e r m e l in & O ' C o n n o r ( 1 9 7 0 ) a n d F r i th a n d H e r m e l i n ( 1 9 6 9 ) u s e db o t h a t r a c k i n g a n d a c a r d - a r r a n g e m e n t t a s k t o s h o w t h a t a u t i s t i c c h i l d r e n

lea rned th ro ug h cues tha t were p r imar i ly m an ipu la t ive , i .e . , i nvo lv ing m o t o rfeedback , and benef i t ed l i t t l e f rom add i t iona l v i sua l i n fo rmat ion . Thus au t i s t i cc h i ld r e n " s e e m t o r e ly m o r e o n p e r c e p t u a l a c t i v i ty th a n o n p e r c e p t u a l a n a l y s is , "a t e n d e n c y t h a t i s a l s o s e e n i n v e r y y o u n g n o r m a l c h i l d r e n a n d t h e r e f o r e r e p r e -sen t s , i n pa r t , a deve lopmen ta l de l ay.

H O W D O E S T H E A U T I S T IC C H I L D M A K E S E N S E O U T O F S E N S AT I O N ?

C a n t h e i m p a i r e d a b i li ty o f a u t is t ic c h i ld r e n t o u s e s e n s o ry i n p u t t o m a k ep e r c e p t u a l d i s c ri m i n a t io n s i n t h e a b s e n c e o f f e e d b a c k f r o m t h e i r o w n m o t o rr e s p o n se s ( H e r m e l i n & O ' C o n n o r, 1 9 7 0 ) h e l p u s t o u n d e r s t a n d t h e s i g ni fi c an c eo f the i r s t r ange m o t i l i t y pa t t e rn s , e .g ., hand - f l app ing ? I have sugges t ed tha t t heb i z a r r e a n d r e p e t i t i v e m o t o r o u t p u t m a y a c t u a l l y b e a c o m p e n s a t o r y a c t i v i t yw h ich he lp s the au t i s ti c ch i ld to m ake sense ou t o f sensa t ion (Orn i t z , 1973 ) .Th i s no t ion fo l lows f rom c l in i cal obse rv a t ions w h ich para ll e l t he ca re fu l exper i -m e n t a l w o r k o f H e r m e l i n & O ' C o n n o r. I n t h e t a s k -o r i e n te d e x p e r i m e n t s , t h e


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au t i s t i c ch i ld ren u t i l i zed e i the r manipu la t ion o r pos i t ion ing o f the i r ex t remi t i e sto m ake d i sc rimina t ions . In the i r spon taneo us ac t iv i ty au t is t ic ch i ld ren a recont inuaUy spir ting, twir l ing, f licking, tappin g, o r rubb ing objec ts . Fu r th erm ore ,they repet i t ive ly f lap , wri the , wiggle , or osc i l la te the i r ext remi t ies whi le regard-ing them in ten t ly. Ana logous to the exper imenta l l ea rn ing s i tua t ions , cou ldau t i st ic ch i ld ren in the i r spon tane ous "p lay " be ge t ting the sense o f ob jec t s inthe i r env i ronment , i nc lud ing the i r own bodies and the i r pa r t s , t h rough k ines-the t i c ( sen sor im otor ) f eedb ack in li eu o f norm al pe rcep tua l p rocesses?

O B S E RVA T I O N S O F M O T O R IN H IB IT IO N I N R E S P O N S E

T O S E N S O RY S T I M U L AT I O N

Ind i rec t su ppo r t fo r th i s c lin ical in fe rence c om es f ro m c lin ica l neuro phy s-io log ic stud ies o f se nsor im otor d ysfun c t ion in au t i s t ic ch i ld ren . In these s tud iest he r e sponse o f the oc u l om o t o r sy s t e m t o s e nso ry st i m u l a t i on du r ing bo t hwakefu lness and s leep i s p resen ted a s a poss ib le m ode l o f mo re gene ra l senso-r i m o t o r f u nc t ion .

Experimental Findings

I n t he a l er t no r m a l sub j e c t t he oc u l om o t o r r e sponse ( nys t a gm us ) t oves t ibu la r s t imula t ion o f the hor i zon ta l semic i rcu la r cana ls (p rov ided b y acce ler-a t ion in a ro ta t ing chai r ) i s consis tent ly suppressed when opt ic f ixa t ion i spe rm i t ted (Wen dt , 19 51; Collins , 1 968) . Studies of ny stag m us in figure ska ters(Coll ins, 1966 ) a nd baUet dance rs (Dix & H oo d, 19 69) s t rongly suggest tha t thesuppress ion o f ves tibu la r ly induced nys tagm us by o p t i c f ixa t ion is an adap t ive

response which serves to prev ent the disor ienta t ion , s tagger ing, and loss ofba lance which w ould o the rwise occur. Th i s suggests th a t the m od ula t io n o f theoc u lo m oto r ou t pu t no t on ly fac il it a te s the s t ab i l i ty o f the pe r iphe ra l v i sion bu ta l so in some way in f luences the p rocess ing o f in t ense sensory inpu t f rom theves t ibu la r sys t em so a s to m od i fy and im prove the en t i re o rgan i smic re sponse .Three s tud ies o f ves t ibu la r nys tagm us in au t i st i c ch ild ren have shown tha t w henvi sua l f ixa t ion is p e rm i t t ed , the suppress ion o f nys tag m us is s ign if i can t ly g rea te rin au t i s ti c ch i ld ren than in age -matched norm al ch ild ren (Po l l ack & Kr iege r,1958; Colbe r t , Koeg le r, & Markham , 1959; Ri tvo , O m i tz , Ev ia ta r, M arkham ,Br own , & Ma son, 1969 ). Re c e n t l y c om p l e t e d s t ud ie s i n ou r l a bo r a t o r y ( Om i t z ,Brown, M ason , & Putnam , 1974a , 1974b) have a l so shown tha t ves t ibu la rnys tagm us i s m ore seve re ly suppressed by au t i s ti c ch i ld ren than by norm alch i ld ren no t o n ly w hen ocu la r f txa t ion is pe rm i t t ed b u t a lso wh en the re t ina iss t imula ted b y l igh t while f ixa t ion i s p rec luded . T here fo re excess ive damp ing o fthe ocu lomotor re sponse to ves t ibu la r s t imula t ion in a l e r t au t i s t i c ch i ld ren i sde pe nde n t on a t le a st t wo m e c ha n i sm s , one t ha t is oc u l om o t o r a nd doe s u t il iz e


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Modulation o f Sensory Input and M otor Output 205

ocu la r fLxa t ion , and ano the r tha t i s ocu losensory and does no t u t i l i ze ocu la rfLxation. Thu s the suppress ion o f p os t ro ta to ry nys tagm us in au t i s t ic ch i ld ren doesno t depe nd on ly on the occ ur renc e o f ocu la r fLxation. Ins t ead , a m ore pe rvasivein te rac t ion o f the v i sua l sys t em an d the ves t ibu la r sys t em i s invo lved . Fur the r-m ore , i t no w seems l e ss l ike ly tha t the g rea te r suppress ion o f ves t ibu la rny stagm us in the prese nce o f ocu lar fLxat ion in aut i st ic chi ldren rep resents al ea rned re sponse . Au t i st i c ch i ld ren p rob ab ly a re no t r eac t ing to the ves t ibu la rs t imulus b y f ixa t ing in the sense tha t th is reac t ion oc curs in f igure ska ters(Coll ins , 1966 ) and ba l l e t dance rs (D ix & Hood , 1969) . The p resen t f ind ings a rem or e c om pa t i b l e w i t h t he hy po t he s i s t ha t i n t he p r e se nc e o f v isual st i m u l a t ion(e i the r ligh t o r a f ixa t ion p o in t ) the excess ive dam ping o f the re sponse to ves ti -bu la r inpu t re f lec t s a bas ic neuroph ys io log ic dysfu nc t ion .

A s im i l ar phe n om e no n ha s be e n de m ons t r a t e d i n a sm a ll g r oup o f s le e p ingau t i st i c ch i ld ren who showed a d am ping of the phas ic ocu la r ac t iv i ty o f REMsleep in re sponse to ves tibu la r s t imula t ion (Orn i t z , Fo rsy the , & de l a Pc?m, 1973a ,1973b) . In these ex per im ent s a v e ry mi ld s inuso ida l osc il la t ion was app l i ed to aspec ia l bed in which the ch i ld ren s l ep t th roughout the n igh t . Quant i t a t ive mea-sures o f the dura t ion and organ iza t ion o f the rap id -ey e -m ove m ent burs t s signifi-can t ly inc reased dur ing the course o f the n igh t in the n orm al ch i ld ren in re -

sponse to the ves t ibu la r s t imula t ion and showed no re sponse dur ing the courseof the n igh t in the au t i s t i c ch i ld ren . The induced changes can be in t e rpre ted a sm ani fes t a t ions o f a spec i fi c e ffec t on the phas ic o cu la r ac t iv i ty o f REM s leeps ince no changes in the p e rcen t o f REM s leep t ime o r the noc turn a l s leep cyc leoccur red . S ince i t i s know n tha t the re is an enha nced ac t iv i ty o f the v i sua lsys tem ( inc reased neuron a l d i scha rge in the occ ip i ta l cor t ex and the l a t e ra lge n i c u la t e nuc le i) sync h r onous wi t h t he e ye - m ove m e n t bu r s ts (B i zz i, 1966b ) ,th i s r e l a t ive ly de f i c i en t ocu lomotor re sponse to ves t ibu la r s t imula t ion dur ing

RE M s le e p a t t he t i m e o f e ndoge nous oc u l o se nso ry s t im u l a t ion m a y t e n t a t ive l ybe a t t r ibu ted to de fec t s in the same pa thw ays which a re invo lved in the de f i c i en tves t ibu la r nys tagm us re sponse in the p resence o f v i sua l inpu t in the waking s t a t e .

Clinical, Observations

Before indu lg ing in specu la t ions a s to which neura l pa thways migh t beinvolved, i t is necessary to re turn br ie f ly to c l in ica l obse rva t ion s o f aut i s t ic

c h i ld r e n i n o r de r t o d oc um e n t t he sugge st ion t ha t t he de fi c ie n t oc u l om o t o rresponse to combined ves t ibu la r and v i sua l sensory s t imula t ion i s a mode l o f am or e ge ne r a l s e nso r i m o t o r dys f unc t i on . A t t e n t i on ha s a l r e a dy be e n d i r e c t e d t othe h yp erm ot f l i ty o f au t i st i c ch ild ren in conn ec t ion w i th the sugges t ion tha tt h e y a r e c om pr e he nd i ng t he i r e nv i r onm e n t t h r ough se nso r i m o t o r f e e dba c k ( se eabove) . How ever, t he de f i c i en t ves t ibu la r ly in i t ia t ed oc u lo m oto r re sponses in thepresence o f v i sua l sensory inpu t a re mo re c lose ly re l a ted to an o th e r a spec t o f thec lin ic al s y n d r o m e - t he hy pom ot i l i t y o f au t is ti c c h il dr en . T he se c h il d re n f r e-


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q u e n t l y r e s p o n d t o v i su a l, a u d i t o r y , o r p a i n f u l s t im u l i w i t h a h y p o a c t i v e st a rt ler e s p o n s e , c a t a t o n i c a rr e st s o f m o t i o n , o r ge n e ra l l a c k o fe m o t i o n a l r eac t ion . In

genera l , a r educed mo to r r esponse to senso ry s t imu la t ion i s a s ign i f i can t a spec to f a u t is t ic s y m p t o m a t o l o g y : A u t i s t i c ch i l d re n o f t e n " u n d e r- r e a c t " t o v is u al ,a u d i t o r y, o r p a i n f u l s t im u l i . M i n i m a l m o t o r a n d e m o t i o n a l r e s p o n s e s ar e c h a r a c-t er is ti c s y m p t o m s o f a u ti sm .

S E N S O R I M O T O R I N C O N S TA N C Y

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

s e n s o r y s ti m u l i. T h i s u n p r e d i c t a b i l i ty o r i n c o n s t a n c y o f b e h a v i o r i n r e s p o n s e t os t i m u l a t i o n h a d e a rl ie r b e e n r e f e r re d t o a s a s t at e o f p e r c e p t u a l i n c o n s t a n c y i nau t i st i c ch i ld ren (Orn i t z & Ri tvo , 1968a , 1968b ) . In the con tex t o f bo th the c lin ica la n d e x p e r i m e n t a l d a t a u n d e r c o n s i d e r a t io n , t h i s a s p e c t o f au t is t ic b e h a v i o r isb e t t e r d e s c ri b e d a s a s t at e o f s e n s o r i m o t o r i n c o n s t a n c y. R e t u r n i n g t o t h e e x p e r i-m e n t a l d a t a , w e fr e d t h a t t h is f a c e t o f t h e c l in i ca l m a t e r i a l - t h e c o m b i n a t i o n o fh y p e r r ea c t iv e a n d h y p o r e a c t i v e m o t o r r e sp o n se s t o s e n so r y s t i m u l a t i o n - a ls ohas a pa ra l l e l i n t he ocu lomoto r r esponse to ves t ibu la r s t imu la t ion . Grea te rwi th in - sub jec t t r ia l - to - t ri a l va r i ab i l it y o f t he nys t ag rnus du ra t ion in r esponse toca lo r i c ves t ibu la r s t imu la t ion has been demons t ra t ed in au t i s t i c t han in no rmalch i ld ren un der co nd i t ion s o f v i sua l i npu t (Co lbe r t e t al., 1 959 ) . R ece n t ly w eh a v e o b t a i n e d a si m il ar r es u lt f o r t h e n y s t a g m u s re s p o n s e t o a n a b r u p t b r a k i n gdece le ra t ion (O rn i t z e t al ., 19 74b) . In da rkness the s lope o f nys t agm usf r e q u e n c y a s a f u n c t i o n o f p o s t r o t a t o r y t i m e is s ig n i fi c a nt ly m o r e v a ri ab le ina u t is t ic c h i ld r e n t h a n i n n o r m a l c h i l d re n . T h u s u n d e r c o n d i t i o n s o f n o v is u alinpu t t he t im e cou rse o f t he r esponse o f an au ti s t ic ch i ld to ves t ibu la r i npu t isa l so le s s p red ic t ab le f rom t ri a l t o t r i a l t han is t he r esponse o f a no rm al ch i ld .B o t h i n h i b i te d a n d e x a g g e r a te d m o t o r r e s p on s e s t o s e n s o r y s t im u l i a r e t y p i c a lo f au t i s t i c ch i ld ren . Thus i t i s no t su rp r i s ing tha t , i n nys t agmus s tud ies con -d u c t e d b o t h w i t h v i su a l i n p u t a n d i n d a rk n e s s , t h e v a r i a ti o n o f r e s p o n se s o f t h esame sub jec t i s g rea t e r in au t i s t i c t ha n in no rm al ch i ld ren .

T H E IM P O RTA N C E O F T H E C E N T R A L C O N N E C T IO N S O F T H EV E S T I B U L A R S Y ST EM

I n t h e p r e c e d i n g d i s c u s s io n t h e d e v i a n t o c u l o m o t o r re s p o n s e s t o v e s ti b u lo -s e n s o ry s t i m u l a t i o n h a v e b e e n u s e d a s a n e x p e r i m e n t a l m o d e l f o r t h e m o r egenera l i zed senso r imo to r dys func t ion obse rved c l in i ca l ly in au t i s t i c ch i ld ren .T h e r e is e v i d e n c e, h o w e v e r, t h a t t h e c e n t ra l c o n n e c t i o n s o f th e v e s t i b u la r s y s t e mp l a y a s i g n if ic a n t r o le i n t h e m u t u a l r e g u l a t io n o f s e n s o r y in p u t a n d m o t o ro u t p u t i n n o r m a l d e v e l o p m e n t . T h i s r o le w il l n o w b e d is c u ss e d a s a b a c k g r o u n d


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t h r oug h e xc i t a t ion o f f u s i m o t o r ne u r ons by s t i m u l a t i on o f ve s ti bu la r c om po-nents o f the e igh th crania l nerve (Die te-Spi ff , Carli , & Po m pe iano , 1967) . Info r-

m a t i on f r om t he c on t r a c t ing sp ind le s m a y be f e d ba c k i n t o t he c e n t r a l ne r voussys t e m a nd poss ib l y pa r t a ke i n t he a d j u s t m e n t o f s enso r y pe r c e p t i on ( E l d re d ,1960) , s ince musc le a ffe ren t s p ro jec t to sensory cor t ex (Gardner & Mor in ,1953 ). A t t he s a m e t i m e t ha t sp ina l m o t on e u r o ns a re e x c i t e d by s t im u l a t ion o fthe ves t ibu la r com po nen t s o f the e igh th c ran ia l ne rve , the ves t ibu la r sys t emac t ive ly inh ib it s segm enta l a ffe ren t inpu t to these mo tone uro ns , th e reb yp r e ve n ti ng " i n s t a b i l i t i e s . . . wh i c h m i gh t oc c u r w he n som a t i c s e nso ry vo l le y se l ic i ted dur ing m ove m ents are fed ba ck in to the sp ina l cord a nd in te rac t w i th thed i scha rg ing m oto ne uro ns " (Co ok e t a l., 1968) . A l so , r e sponses to e igh th c ran ia lne rve s t im ula t ion recorded in the me dia l long i tud ina l f a sc icu lus a re depresseddu r ing pha si c e xc i t a t i on a c c om pa ny i ng the e ye - m ove m e n t bu r s ts o f RE M s l ee pand dur ing o r i en t ing reac t ions to a rous ing s t imul i (Lenz i , Pompe iano , & Sa toh ,1968) . As the m edia l longi tudina l fasc iculus carr ies f ibers o f the m edia l vest i -bu la r nuc leus to m oton euro ns , a depress ion o f the in f luence o f ves t ibu la r inpu ton m o t o r ou t pu t oc c u r s j u s t a t t he t i m e o f i n te r na ll y ge ne r a t e d e xc i t a t ion du r ingbo t h RE M s l ee p a nd e x t e m a U y induc e d e xc i t a t ion du ri ng wa k i ng .

In add i t ion to these descend ing e ffec t s up on the mo du la t ion o f sensa t ion ,mot i l i t y, and sensor imotor in t egra t ion , low- in tens i ty s t imula t ion o f the ves t i -bu la r ne rve re su l ts in a scend ing ac t iv i ty, evok ing s low w ave po ten t i a l s f rom theorbi ta l surface o f the fe l ine cerebra l cor te x (Megir ian & Manning, 1967) . Slowwave po ten t i a l s in th i s same a rea have a lso been evo ked by som atosen sory,visua l, and aud i tory s t im ula t ion , whi le e lec t r ica l s t im ula t io n o f th is a rea affec tssp ina l m oto ne uro n exc i t ab i l ity. S tud ies o f s ingle neuron s a lso dem ons t ra t e theconvergence o f ves t ibu la r r e sponses wi th re sponses in o the r sensory moda l i t i e sth ro ug ho ut the c or t ex an d in the la t e ra l gen icu la t e nuc leus (Ko rnhu ber & da

Fonseca , 1964) .S t imula t ion o f the e igh th c ran ia l ne rve augm ents the an t id rom ic re sponse

in the op t i c t r ac t to l a t e ra l gen icu la te s t imu la t ion , sugges ting p resyn ap t i c inh ib i-t ion o f v i sua l inpu t (M arch ia fava & Po m pe iano , 1966) . The same presy nap t i cinh ib i tion occur r ing dur ing the rap id eye mo vem ents o f REM s leep has beende m ons t r a t e d by : ( 1 ) a ugm e n t a t ion o f t he op t i c t ra c t a n t i d r om i c r e sponse a ndr e duc t i on o f the op t ic t r a c t o r t hod r om i c r e sponse to e le c tr ic a l st i m u l a t ion o f thela te ra l gen icu la te and the op t i c t r ac t ; and (2 ) reduc t ion o f f l ash evoked re sponses

in the la te ra l genicula te and in the visua 1 co r tex (Bizz i , 1966a) . T he pa thw ay forth i s ves t ibu la r ly induced inh ib i t ion o f v i sua l inpu t is th rou gh the me dia l anddescend ing ves t ibu la r nuc le i which ac t iva te the spon taneo us neurona l ac t iv ity o fthe l a t e ra l gen icu la te nuc leus dur ing the eye m ov em en t burs t s o f REM s leep(Morr i son & Pompe iano , 1966) . I t has a l so been sugges ted tha t s ince na tu ra ll abyr in th ine s t imula t ion induces eye movement , ves t ibu la f ly induced inh ib i t ionof v i sua l inpu t a t t he l a t e ra l gen icu la t e l eve l migh t con t ro l the s t rong re t ina l


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bar rage acc om pa nyin g po s t ro ta t io na l n ys tagm us e l ic i t ed in f igh t (March ia fava &Pom pe i a no , 1966 ) .

T H E I N F L U E N C E O F T H E C E N T R A L N E R V O U S S Y S TE M O N T H EV E S T I B U L A R S Y S T E M

T hus v e s t i bu l a r i np u t s e e m s t o i n t e r a c t w i t h a nd m a y m o du l a t e bo t h o t he rf o r m s o f a f f e r e n t i npu t a nd m o t o r e x c i t a b il it y a t sp ina l, subc o rt ic a l , a nd c o r t ic a lleve ls . A cen t ra l dy sfunc t ion o f th i s ves t ibu la r con t ro l o f sensory inp u t -m oto rou t pu t i n t e r a c t ion c ou l d e xp l a i n m uc h o f the s e nso r i m o t o r dys f unc t i onob serve d c l in ica l ly in au t i s tic ch i ldren.

T he e xpe r i m e n t a l obse r va t i ons r e l e va n t t o ve s t i bu l a r dys f u nc t i o n ha vede m ons t r a t e d : ( 1 ) a r e duc e d o c u l o m o t o r r e spo nse (nys t a gm u s ) t o ve s t ibu l a rs t imu la t ion in the p resence o f exo geno us v i sua l inpu t in the waking au t i st icc h il d; a nd ( 2 ) a r e duc e d oc u l om o t o r r e sponse (r a p id e y e m ove m e n t bu r st s ) t oves t ibu la r s t imula t ion in the p resence o f endogenous v i sua l s t imula t ion in thes leep ing au t i s ti c ch i ld . Thus o ur a t t en t ion m us t no w tu rn to cons ide ra t ion o fthose cen t ra l ne rvous sys tem mechan i sms which can in f luence the ves t ibu la rsy s t e m a nd t hus m od i f y i ts e f f e c t on se nso r i m o t o r in t e r ac t ions . Ju s t a s t heves t ibu la r nuc le i e ffec t sens or im otor in t egra t ion a t sp ina l, m idbra in , and cor t i ca ll eve ls (see abo ve) so do these reg ions b o t h fac i li t a te and inh ib i t t he ves t ibu la rsy s t e m ( Ma r kha m , 1972 ) , t he r e b y c om pl e t ing a f e e dba c k l oop wi th b r oa di m p l i c a t ions f o r s e nso r i m o t o r c on t r o l . T he f i na l c o m m on pa t hw a y o f t h isdescend ing con t ro l ove r the ves t ibu la r nuc le i may be an e ffe ren t ves t ibu la rsys tem wh ich m odi f i e s the im pac t o f ves t ibu la r s timul i a t t he l evel o f the pe -r iphe ra l r ecep tors (Sa la , 19 65) . S ince the ex per im enta l d a ta have been in the

d i rec t ion o f a reduced nys tagm us in re sponse to ves t ibu la r s t imula t ion o f au t is t icch i ld ren , the con t inu ing d i scuss ion will focus on those neura l pa thw ays whichinh ib i t t he re sponse o f the v es t ibu la r sys t em. The ves t ibu la r nuc le i a ffec tsensor imotor in t egra t ion a t sp ina l , midbra in , and cor t i ca l l eve l s . At the samet ime , these reg ions bo th fac i li ta t e and re s tra in the ves t ibu la r sys t em , com ple t inga f e e dba c k loop v i ta l t o s e nso r i m o t o r c on t r o l .

S ince a ll sub jec t s were s tud ied wi th eye s op en in a non s leepy s t a t e o fr e l a xe d a t t e n t i on , t he ba sa l e x pe r i m e n t a l c ond i t i ons f a c i l i t a t e d t he p r o duc t i on

o f nys t a gm us i n bo t h t he no r m a l a nd a u t i s t i c c h i l d r e n ( se e T j e m s t r 6m , 1973 ) .Only the exper imenta l va r i ab les , ocu lomotor (v i sua l fLxa t ion) and ocu losensory(d i ffuse ligh t) s t imula t ion , inh ib i t ed the nys tagm us; and bo th fo rm s of v isua ls t imula t ion induced a s ign i f ican t ly g rea te r degree o f inh ib i t ion in the au t i s ti cchi ldren (O rni tz e t a l ., 1974a , 1974 b) . Severa l possible pa thw ay s could beinvo lved in th i s ty pe o f excessive inh ib i t ion . A t the cor t i ca l l evel exp e r im enta lab la t ions o f e i the r occ ip i t a l lobes o r f ron ta l lobe a reas 4 and 6 enha nced


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nystag m us to th e side o f the lesion, indicat ing a release from co rt ical inhib i t ion(Wycis & Spiegel , 1953). Also st imu lat ion o f cort i fugal f ibers in the cerebral

peduncles and internal capsule inhibi ted vest ibular nystagmus (Scheibel ,M arkham, & K oegler, 1961) . T he cerebel lum has a lso b een impl icated in inhibi -tor y c on tro l over ves t ibular afferen ts f rom bo th the o to l i th sys tem (Llings &Pre cht , 1972 ) an d the sem icircular canals (B ake r, Prech t , & Llinfis, 1972 ). Cere-bel lar inhibi t ion of ves t ibular nys tagmus is par t icular ly re levant to the exper i -mental Finding of increased suppression of nystagmus during visual f ixat ion inaut is tic chi ldren , s ince s t imulat ion o f the cerebel lar ro of nuclei induce center ingof the eyes and com ple te inh ib it ion o f nys tagmus in the ca t (Wol fe, 1969).Several s tudies have suggested that the efferent vest ibular system may receiveimpulses direc t ly from brain-stem regions. A lterat ions in the DC rest ing po tent ialof one labyrin th af te r e lect r ical s t imulat ion o f the re t icular subs tance or calor ics t imulat ion of the o ther labyrin th in precol l icular ly decerebrated and decere-bel la ted preparat ions sugges ted a bulbo pon t ine re t icular orig in o f the effere ntves t ibular sys tem (Sala , 1965) . This sys tem has inhibi tory com pon ents w hich areprob ably located in par t wi th in and betw een the ves tibular nuclei and wo rkthrou gh a chol inergic mech anism (Pom peiano , 1972) . Scheibel e t a l . (19 61 ) w ereable to consis tent ly inhibi t ves t ibular nys tagmus by s t imulat ing the brain s tem

ret icular core , a l though they point ou t that the suppress ion of nys tagmu s ampli-tude was associated w i th a ve ry great increase in nys tagm us frequ enc y; the la terobservat ion sugges ts that an exci ta tory effect may be associated wi th themanifes t inhibi t ion o f the ves t ibulo-ocular ref lex arc . M arkham (197 2) has d is -cussed the co m plex pathways by w hich two specif ic midbrain centers mayinhibi t the ve s t ibulo-oc ulom otor arc: the m echanism b y w hich the nucleus ofDarkschew itsch inhibit s ves t ibular ly induced e ye m ovem ents is unclear (Scheibelet al. , 1961 ) while s t im ulat ion o f the interst i tial nucleus o f Cajal inhibi ts type -I

vest ibular cel ls of the horizontal semicircular canals (Markham, Precht , &Shimazu, 1966) . Another midbrain inhibi tory c i rcui t may take i t s or ig in insupranuc lear oc u lom otor cen te rs . Observa tion o f f requenc y mo dula t ion in theves t ibular nerve in re la t ion to ves t ibular ly induce d eye m ovem ents dem onst ra tedthe possib le exis tence of ves tibular afferen t m odu lat ion by o cu lom oto r impulsesm ediated b y ef feren t f ibers (Dichgans , Schm idt , & Wist, 1972) . These impulsesmay also be the source of monophasic wave act ivi ty in the lateral geniculatenuclei (LG N ), since m onoph asic waves recorded in b oth LG N and visual cor tex

are p receded by mono phas ic w aves in the ocu lom otor nuc le i (Cos t in &H afem ann, 1970) . To nic re tinal inhibi t ion o f the ves t ibulo-ocular ref lex arc byre tina l s t imula tion (Markham, 1972) can be in fe rred f rom the enhance me nt o fpost ro ta t ional nys tagm us fo l lowing lesions of the LG N (Spiegel & Scala , 1945)or th e supe rior qu adrigeminal bodies (Spiegel & Scala, 1946). Final ly, l ight-evoke d discharges f ro m the LG N m ay be enha nced or depressed by labyrin th ines t imulat ion (Papaioannou , 1973) . Thus , a co m plex brain stem ci rcui t ry m ayinvolve the mu tual regulat ion of v isuosensory input ( re t ina , L GN , super ior col-


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Modulation of Sensory Input and Motor Output 211

liculus), oculomotor output (oculomotor nuclei, vestibular nuclei), and vesti-bular input (labyrinth, vestibular nuclei). Dysfunction of such a system could be

the neurophysiologic basis of the excessive inhibition of postrotatory nystagmusin autistic children which was found in the presence of retinal stimulation(Ornitz et al., 1974a, 1974b).

S U M M A R Y A N D C O N C LU S IO N S

This paper explores the possible pathophysiologic mechanisms whichmight underlie the unusual motili ty disturbances which occur in autistic chil-dren. The strange motili ty patterns of autistic children are characterized by bothhypomotility and hypermotility and cannot readily be explained by eitherpostulated states of overarousal or insufficient sensory stimulation. This dys-function of the modulation of motor output is in some way related to the faultymodulation o f sensory input, which is also a significant feature o f the autisticsyndrome because the children frequently show underreactive or overreactivemotor responses to sensory stimuli. Psychologic experiments have revealed thatautistic children learn through manipulation and position cues rather than

through normal perceptual processes. It is therefore suggested that the sponta-neous spinning and flicking of objects, the flapping and oscillating of theirextremities, and the whirling and rocking of their bodies may be the autisticchildren's way of making sense out of the sensations in their environment,including their own bodies and their parts, through kinesthetic (sensorimotor)feedback. Clinical neurophysiologic studies of the oculomotor response to vesti-bulosensory stimulation in the presence of visuosensory stimulation have demon-strated that there is a significantly greater inhibition of pos tro tato ry nystagmus

in autistic children than there is in normal children. During sleep the vestibularlymediated phasic eye movement bursts of REM sleep are also diminished inautistic children in response to vestibular stimulation. These experimentaldemonstrat ions of a deficient oculomotor response to vestibular or vestibular-and-visual stimulation parallel clinical observations of the hypomotility also seenin response to sensory stimulation. While the oculomotor responses to vesti-bulosensory stimulation serve as an experimental model for the more generalizedsensorimotor dysfunction observed in autistic children, there is reason to suspect

that a dysfunction of the central vestibular system might be fundamental to thisfacet of the autistic syndrome. Review o f the neurophysiology of the vestibularsystem reveals that the vestibular nuclei either directly modulate or transmitmodulating influences over motor o utput at the time of sensory input and oversensory input at the time of motor output. While cortical centers may inhibitvestibular function, the experimental findings of depressed oculomotor responseto vestibular stimulation in the presence of either visual fixation or visuosensorystimulation are more compatible with a dysfunction o f cerebellar or brain-stem


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2 1 2 O r n i t z

i n f l u e n c e . To c o n c l u d e , a d y s f u n c t i o n o f a c o m p l e x c i r c u it r y in v o l v i n g t h e

c e n t ra l c o n n e c t i o n s o f t h e v e s t i b u la r sy s t e m w i th t h e c e r e b e l l u m a n d t h e b r a i n

s t e m m a y b e r e s p o n s ib l e f o r t h e s tr a n ge s e n s o r i m o t o r b e h a v i o r o b s e rv e d i na u t i s t ic c h i l d r e n . T h i s p o s t u l a t e d d y s f u n c t i o n o f s u b c o r t i c a l n e u r a l m e c h a n i s m s

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

d r e n l e a rn a b o u t t h e i r e n v i r o n m e n t a n d d e v e l o p t h e i r b o d y i m a g e , s in c e c l i n ic a l

s t ud i e s p o i n t t o w a r d a s t ro n g m o t o r c o m p o n e n t t o t h e i r p e r c e p t u a l p r o ce s s e s .

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