lateralized brain dysfunction in autism: evidence from the halstead-reitan neuropsychological...

Journal of Autism and Developmental Disorders, Vol. 13, No. 3, 1983

Lateralized Brain Dysfunction in Autism:

Evidence from the Halstead-Reitan

Neuropsychological Battery I

G e r a l d i n e D a w s o n 2

University of North Carolina at Chapel Hill

Selected tests f rom the Halstead-Reitan neuropsychological battery were administered to 10 male individuals who had been diagnosed as autistic in early childhood. Results f rom the battery obtained f rom the autistic group were compared with a group o f retarded persons matched for IQ and with a group o f patients with demonstrable diffuse brain damage. As a group, the autistic subjects showed a pattern o f deficits indicative o f a significantly greater degree o f left hemisphere dysfunction than either comparison group. Furthermore, within-subject comparisons revealed that the autistic group had a significantly greater left than right hemisphere dysfunction, while neither comparison group showed this lateralized pattern.

In recent years, investigators have begun to explore the possible role of brain damage or impairment of brain functions in the syndrome of early infantile autism. The evidence for such a possibility has now accumulated from a number of sources. Conditions suggestive of central nervous system difficulties are more frequently found in autistic children than would

~The cooperation of the autistic persons and their parents is sincerely appreciated. Drs. Martha Perry and Jim Sackett provided helpful feedback on the design and execution of the study, and Dick Holm helped greatly with the analysis of the data. Dr. Eric Trupin provided both the equipment and necessary clinical facilities. Dr. C. G. Matthews's provision of protocols from retarded subjects was critical to the research. Financial support was received from the Gatt- zert Foundation, the Developmental Research Fund at the University of Washington, and a Biomedical Research Grant provided by the Graduate School, University of Washington.

~Address all correspondence to Geraldine Dawson, 268 Davie Hall, Psychology Department, 013A, University of North Carolina, Chapel Hill, North Carolina 27514.

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0162-3257/83/0900-0269503.00/0 �9 1983 Plenum Publishing Corporation

270 Dawson

normally be expected, including an increased incidence of prenatal and perinatal complications (Knobloch & Pasamanick, Note; Lobascher, Kingerlee, & Gubbay, 1970), abnormal electroencephalograms (Creak & Pampiglione, 1969; White, DeMyer, & DeMyer, 1964), "soft signs" on neurological exams (Gubbay, Lobascher, & Kingerlee, 1970; Rutter & Lockyer, 1967), epilepsy (Schain & Yannet, 1960), and vestibular abnormalities (Ornitz, Ritvo, & Panman, 1968). In addition, autistic-like behavior has been associated with CNS viral infection (Chess, 1971), with degenerative disease (Creak, 1961), and with metabolic disturbances (Knobloch & Pasamanick, 1975). While these studies have clearly suggested that autism involves central nervous system dysfunction, the specific nature and cause of this dysfunction remains unclear. Hauser, Delong, and Rosman (1975) reported pneumoencephalographic findings for a group of 18 children with a history of retarded language development, autistic behavior, and no specific diagnosable neurological disease or gross motor dis- order. They found atypical enlargement of the left temporal horn in 15 cases, suggesting a possible hemispheric basis for autism.

Several investigators (Blackstock, 1978; Dawson, 1982; Prior & Bradshaw, 1979; Tanguay, 1976) have pointed out that the specific cognitive and language impairments found in autism involve functions for which the left hemisphere is specialized. In contrast, many autistic children show normal or even superior abilities in right hemisphere functions such as visual-spatial skills and music (Lockyer & Rutter, 1970). Moreover, there is now evidence that many autistic individuals exhibit an atypical pattern of hemispheric specialization, which is characteristic of persons who have sustained early left hemisphere trauma. Prior and Bradshaw (1979), using a dichotic listening task, demonstrated that there was a significant excess of autistic children showing right hemisphere Specialization for verbal stimuli when compared to a normal control group. Dawson (1982) found similar results using electroencephalographic recordings of alpha rhythm asymmetries as a measure of hemispheric dominance during verbal and visual-spatial processing. In contrast to a normal control group, which showed the expected pattern of left hemisphere dominance during language tasks, the majority of the autistic subjects showed greater right hemisphere dominance during both language and spatial tasks.

The present study was designed to assess left and right hemisphere functions in autistic individuals, and to compare these results to a group of nonautistic retarded subjects of similar intellectual ability. Thus, the present study sought to determine whether selective left hemisphere dysfunction is a characteristic that is associated with autism rather than with general mental retardation. Selected measures from the Halstead- Reitan neuropsychological battery (Reitan, 1969) were chosen as a method

Lateralized Brain Dysfunction 271

for assessing brain functioning. This assessment battery included a number of well-standardized behavioral tests that have been demonstrated to be valid for identifying the presence of brain dysfunction in children (e.g., Boll, 1974; Reed, Reitan, & KlCve, 1965; Selz, 1979) and adults (e.g., Kl~ve, 1974; Reitan, 1966; Wheeler & Reitan, 1963). The battery provided information regarding the integrity of hemisphere functioning based on the following measures: (a) levels of performance on cognitive tasks known to be normally mediated by the right or left hemisphere, (b) comparisons of motor and sensory-motor functions on the right and left sides of the body, and (c) comparisons of perceptual ability in auditory, visual, and tactile modalities on the right and left sides of the body.

METHOD

Subjects

Ten male autistic individuals ranging from 9.1 years to 34.0 years of age (mean age = 221.90 months; SD = 105.70 months) participated in the study. The necessity of a large age range arose due to the difficulty in finding autistic subjects who were capable of being tested in a standardized, valid manner and who had an unequivocal diagnosis of autism. Subjects were contacted through the Washington Chapter of the Society for Autistic Children and through the Seattle Public School Special Education Department. One subject lived alone but was supervised by another adult, two lived in group homes, and seven lived at home with their parents. Diagnosis of autism was confirmed by past records of psychological or psychiatric evaluations. Each had been given the diagnosis of early infantile autism by at least two independent clinicians. Furthermore, it was required that each subject's developmental record include behavioral descriptions that fulfilled Rutter's (1971) diagnostic criteria. A description of each subject's birth and early developmental history can be provided by the author. All autistic subjects had some expressive speech. IQ levels for each subject are reported in Table 1.

Data for two comparisons groups were selected from files of individuals who had previously been adminsitered the neuropsychological battery. A group of subjects with a diagnosis of mental retardation was provided by Dr. C. G. Matthews, Neurology Department, University of Wisconsin. Dr. Matthews selected these subjects to match, as closely as possible, the retarded autistic subjects on the basis of sex, age, handedness, and Full Scale IQ score on the Wechsler Intelligence Scale. Seven of the 10

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autistic subjects' Full Scale IQ scores fell in the retarded range. Thus, only these autistic subjects' data were used for comparison with mentally retarded subjects. Dr. Matthews was completely unaware of the hypotheses being tested in the present study and therefore could select an unbiased sample. Subjects were chosen without regard to cause of mental retardation. Three of the 7 subjects were diagnosed as cultural-familial retarded; the other 4 subjects were reported to have general encephalopathy. The caused cited for encephalopathy were postnatal anoxia, postnatal cerebral infection, asphyxia at birth, and postnatal injury.

The second comparison group was selected from the files at the Psychology Testing Laboratory, University Hospital, Seattle, Washington. It was composed of patients who had independent neurological evidence of bilateral or diffuse brain damage by means of electroencephalograms, brain scans, or pneumoencephalograms. On the basis of these diagnostic techniques, these patients showed significant involvement of both hemispheres; damage did not appear to be affecting one hemisphere more than the other. Subjects were chosen without prior knowledge of their performance on the neuropsychological battery. The matching data for the autistic sample and comparison groups are shown in Table 1.

The use of historical controls raises the issue of comparability of results obtained from each of the groups.The three groups were tested at different times by different psychometrists. In all cases, however, the psychometrist had received extensive training in standardized administration of the Halstead-Reitan battery. In addition, in all cases, identical norms and cutoff points were used to interpret results.

Procedure

The neuropsychological battery was administered to each autistic subject by a psychometrist who had previously received extensive and specific training in the administration of the battery. The psychometrist was unaware of the hypotheses being tested. Each subject's performance on the battery was judged by the psychometrist to be an accurate reflection of his present level of functioning. Testing required approximately 5 hours with a half-hour lunch break.

Measures

Handedness was assessed by administration of seven unimanual tasks which included writing, throwing a ball, hammering a nail, cutting with a knife, turning a doorknob, using scissors,and erasing.

274 Dawson

Sensory-Motor and Motor Functions. The Finger Oscillation Test and the Tactual Performance Test were used to assess sensory-motor and motor functions on the right and left sides of the body. The Finger Oscillation Test is a measure of finger-tapping speed. The subject is given five consecutive 10-second trials with the index finger of each hand. The hand is held in a constant position in order to require movements of only the finger rather than of the whole hand and arm, The subject is encouraged to tap as fast as he possibly can.

The Tactual Performance Test utilizes a modification of the Sequin- Goddard form board, The subject is blindfolded and is not permitted to see the form board or blocks at any time, thus completing the board by use of touch and kinesthetic feedback only. He first places the blocks into their proper spaces with his preferred hand then repeats the procedure with his nonpreferred hand.

For both of these tests, poor performance relative to norms for one or both hands indicates hemisphere dysfunction contralateral to that side of the body showing such performance deficits. The norms are based on normal and brain-damaged subjects' performances with their preferred and nonpreferred hands. Superior performance is expected from the preferred hand regardless of whether the subject is right- or left-handed.

Sensory-Perceptual Functions. Sensory-perceptual functions were measured using the following tests: sensory irnperception test, tactile finger recognition, fingertip number-writing perception test, and the tactile form recognition test.

The sensory imperception test determines the accuracy with which the subject can perceive bilateral simultaneous sensory stimulation, given that it has been demonstrated that perception of unilateral stimulation on each side is basically intact. Tactile, auditory, and visual modalities are each tested separately. The subject is first stimulated separately on each side of the body. Then, unilateral stimulation is interspersed with trials of bilateral simultaneous stimulation, during which the subject indicates whether he perceives stimulation to be occurring on one or both sides. Patients with known unilateral cerebral lesions will sometimes fail to accurately perceive stimulation contralateral to the damaged hemisphere when bilateral simultaneous stimulation is given.

The tactile finger recognition test assesses the ability of the subject to identify individual fingers on both hands when tactuaUy stimulated on each finger. Four trials are given for each finger and each hand, resulting in a total of 20 trials for each hand. The number of errors for each hand is recorded.

The fingertip number-writing perception test requires the subject to report numbers written on the fingertips of each hand without use of vision

Lateralized Brain Dysfunction 2"/5

(X's and O's can be used). A total of four trials are given for each finger on each hand. The number of errors for each hand is recorded.

The tactile form recognition test requires the subject to identify through touch only, a cross, square, triangle, and circle, which the subject indicates by pointing to the correct shape presented visually (cross-model matching). Four trials for each hand are given. The mean time required to make this judgment and the number of errors are recorded for each hand.

Cognitive Functions. The Wechsler Adult Intelligence Scale (WAIS) or the Wechsler Intelligence Scale for Children-Revised (WlSC-R) was given to each subject. Comparisons of Verbal and Performance IQ scores were made. Significantly lower (>i 15 points) verbal IQ scores were taken as a gross indicator of left hemisphere dysfunction, and significantly lower Performance IQ scores as an indicator of right hemisphere dysfunction.

Data Analysis

Each subject's test scores on the motor, sensory-motor, sensory- perceptual, and cognitive tests were converted into scaled scores indicating either normal (0), mild impariment (1), moderate impairment (2), or severe impairment (4) based on cutoff points that were previously developed by Finkelstein (1976) for adults and by Selz (1979) for children.Scaling is necessary so that equivalent levels Of impairment can be derived from different types of data (e.g., finger-tapping speed versus number of errors on perceptual tests). Thus, a subject could receive a score indicating right, left, or bilateral dysfunction of varying degrees of severity for the test given. A com- plete description of the cutoff points and how they were derived can be obtained from the author.

RESULTS

For each subject, the scaled scores indicative of left or right hemisphere dysfunction were summed across all tests separately for each hemisphere. The data were then analyzed in terms of the degree of dysfunction, as reflected by the sum of the scores, present in each hemisphere. Table II displays the mean summed scaled scores for each hemisphere for each group.

From here on, the autistic group as a whole, including both retarded and nonretarded autistic subjects (N = 10), will be referred to as the autistic group, whereas the subgroup of retarded autistic subjects (N = 7) will be called the retarded autistic group. T-test comparisons were carried out

276 Dawson

Table II. Degree o f Dysfunct ion Analyzed Separately by Hemisphere

Retarded Matched Bilateral autistic retarded Autistic damage group group group group

( N = 7 ) ( N = 7 ) t a p ( N = 10) ( N = 10) t b p

Right hemisphere .~ 1.14 1.86 .74 n.s. 1.40 3.40 - 2.09 n.s. tr 1.46 1.46 1.58 2.59

Left hemisphere 3.57 1.29 3.55 < .01 ~ 3.20 1.80 2.12 < .025 ~

o 1.40 .95 1.69 1.23

aTtes t for matched pairs. b T test for independent groups.

One-tailed.

between the autistic groups and the two comparison groups. One-tailed t tests were used when the author was predicting a difference of specific direction in the presence of brain dysfunction between the two groups. As can be seen in Table II, the autistic group showed patterns of deficits indicative of a significantly greater degree of left hemisphere dysfunction than the group with bilateral damage, t(18) = 2.12, p < .025. Furthermore, the retarded autistic group exhibited a significantly greater degree of left hemisphere dysfunction than the matched retarded subjects, t(6) = 3.55, p < .01. The retarded autistic group and the matched retarded subjects did not differ significantly in the degree of right hemisphere dysfunction exhibited t(6) = .74, n.s. A comparison of right hemisphere dysfunction exhibited by autistic versus bilaterally damaged subjects also revealed no significant difference, t(18) = - 2.09, n.s. These data thus supported the hypotheses that left hemisphere dysfunction is associated with autism and that this pattern of unilateral dysfunction is not necessarily related to level of intelligence.

Within-group, between-hemispheres comparisons of degree of brain dysfunction provided further support for a link between autism and left hemisphere dysfunction. Using t tests for repeated measures, it was found that the autistic group demonstrated significantly greater left than right hemisphere dysfunction,/(9) = 4.15, p < .005. The retarded group showed no significant difference between the degree of dysfunction evident in the right and that in the left hemisphere t(6) = .79, n.s. Unexpectedly, the bilateral brain-damaged group had significantly greater right than left hemisphere dysfunction t(9) = - 2.26, p < .05.

The intent of this study was to demonstrate that the particular cognitive and language impairments seen in association with autism are related to left hemisphere dysfunction. However, the Halstead-Reitan battery uses


these very measures (cognitive tests of the Wechsler Intelligence Scales) to infer left hemisphere impairment. To avoid this circularity, it was decided to reanalyze the neuropsychological test data deleting the cognitive measures, i.e., relying solely on measures of sensory-motor and perceptual functioning on the right and left sides of the body. Thus, for the next set of comparisons all measures except the congnitive measures were utilized (sensory-motor plus perceptual). The data and comparisons are shown in Table III.

Results showed that, even when the cognitive measure is removed, the retarded autistic subjects exhibited significantly greater left hemisphere dysfunction than matched retarded subjects. However, in this comparison, the autistic subjects no longer showed left-sided dysfunction to a greater degree than individuals with bilateral damage.

Within-group, between-hemispheres comparisons were then carried out using t tests for repeated measures. On the basis only of measures of perceptual and sensory-motor functions on the right and left sides of the body, the autistic group again exhibited significantly greater left than right hemisphere dysfunction, t(9) = - 1.83, p < .05, whereas neither the retarded group nor the bilaterally damaged comparison group showed a predomin- ance of right or left hemisphere dysfunction, t(6) = .42, and t(9) = 1.03, n.s., respectively.

In Table IV, results of analyses on sensory-motor (Finger-Tapping and T.P.T.) versus perceptual (Sensory Imperception, Finger Recognition, Fingertip Writing, T.F.R.) measures are presented separately. A consistent pattern of greater left hemisphere dysfunction was found for sensory- motor and perceptual tests for the autistic group and retarded autistic subgroup. The reverse pattern, i.e., greater right hemisphere impairment, was found in the matched retarded group and the bilateral damage group. When

Table III. Degree o f Dysfunct ion in Each Hemisphere Based on Sensory-Motor and Perceptual Tests

Retarded Matched Bilateral autistic retarded Autistic damage group group group group

( N = 7) ( N = 7) t ~ p ( iV= 10) ( N = 10) f ' p

Right hemisphere X 1.00

Left hemisphere .~ 2.57

1.57 - 57 n.s. 1.30 2.40 - .91 n.s.

1.28 2.22 < .05 c 2.30 1.40 .81 n.s.

aTtes t for matched pairs. b T test for independent groups. c One-tailed.

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each of these neuropsychological measures was analyzed separately, a significant group difference was found only for the Finger-Tapping measure, with retarded autistic subjects showing significantly greater left hemisphere dysfunction than matched retarded subjects, t = 1.95, p < .05. A similar trend was found for the Tactual Performance Test measures, t -- 1.66, p < �9 10. As is true of brain-damaged populations, errors on the perceptual tests were relatively rare; such that a statistical comparison on any given test was not very meaningful. However, even when subjects' performances on the perceptual tests were combined, significant differences were not found. Thus, it appears that the motor tests were more sensitive for detecting lateralized dysfunction.

Patterns of Cognitive Abilities

Cognitive Abilities. It was predicted that the autistic subjects would show differential levels of ability on cognitive tasks known to be mediated by the right and left hemispheres. Reitan (1964) has used the Verbal and Performance IQ scores f rom the Wechsler Intelligence Scale as measures of left and right hemisphere functioning, respectively. However, these IQ scores are based on the number of subtests that are not necessarily mediated primarily by the right or left hemisphere. Therefore, in addition to the IQ scores, two verbal and two visual-spatial subtests f rom the Wechsler scale were chosen as representing tasks most likely to be mediated by either the left or the right hemisphere. These tasks were verbal comprehension and vocabulary (left) and block design and object assembly (right). The scaled scores on these subtests can range f rom 0 to 20. The mean score based on Wechsler's normative data is equal to 10, with a standard deviation of 3. Figure 1 shows the mean IQ scores for each group. Significantly higher Per- formance than Verbal IQ scores were found for both the autistic group, t(9) = 5.08, p < .001, and the retarded autistic subsample, t(6) = 4.68, p < .005. Significant differences between Performance and Verbal IQ were not found for the mentally retarded, t(6) = .95, n.s. and the bilaterally damaged, t(9) = 1.41, n.s., groups.

Figure 2 shows the mean subtest scores for the two language (left hemisphere) tasks and the visual-spatial (right hemisphere) tasks, for the autistic, retarded, and bilaterally damaged groups. While the autistic group as a whole performed at or near the normal level on the visual-spatial tasks, their mean performance on the language tasks was severely impaired. Moreover, five o f the autistic subjects' scores on the right-hemisphere-mediated tests fell in the high average to gifted performance range. This pattern of differential ability on these tasks was not evident in the comparison groups.

280 Dawson

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Individual Patterns

The above analyses have provided evidence for the presence of left hemisphere dysfunction in autistic persons. Moreover, this pattern of pre- dominant left hemisphere dysfunction was not found in the retarded and brain-damaged comparison groups. Eight of the 10 autistic subjects showed greater left than right hemisphere dysfunction. Neither of the comparison groups showed a similar pattern: Only 2 of the 7 retarded subjects and 2 of the 10 subjects with bilateral damage had greater left than right hemisphere dysfunction. Using Fisher's exact test, it was found that the frequency of subjects with greater left hemisphere dysfunction was significantly higher in the retarded autistic group (N = 7) than in the matched retarded group (p < .05), and in the autistic group as a whole (N = 10) than in the bilateral damage group (p < .05). However, closer examination of the data from individual autistic subjects revealed that not all autistic subjects showed unilateral left hemisphere dysfunction. On the basis of the combined cognitive, perceptual, and sensory-motor tests, 5 autistic subjects exhibited im-


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pairment of the left hemisphere accompanied by relatively little or no impairment of the right hemisphere, and 5 subjects showed either mild but equal involvment of both hemispheres or significant involvement of both hemispheres with left-sided dsyfunction predominating.

Relationships with Age and IQ

It was of interest whether differences in age and intellectual functioning in the autistic subjects were related to the more direct measures of cerebral functioning, namely, measures of perceptual and sensory-motor functioning on the right and left sides of the body. Although the sample size is too small to draw any firm conclusions, a number of questions could be addressed. First, it was of interest whether older subjects differed in their patterns of brain dysfunction from younger subjects. Dividing the subjects into two groups of five (13 years and below defined the younger group), it was found that younger were more likely than older subjects to exhibit left hemisphere dysfunction, in 8 of the 10 cases examined (binomial probability = .043). Four of the five younger subjects exhibited left hemisphere impairment, whereas only one of the five older subjects did so. This relationship did not hold for right hemisphere dysfunction; older and younger subjects were equally likely to exhibit right hemisphere dysfunction.

The second question was whether individuals exhibiting unilateral, left-sided dysfunction as reflected on the perceptual and sensory-motor tests differed from those showing bilateral involvement in terms of their level of

282 Dawson

Table V. Performance of Individual Subjects: IQ and Other Neuro- psychological Measures

Left Right hemisphere hemisphere

Subject Age(years) functioning a functioning a FSIQ VIQ PIQ

1 9 Severe Normal 52 45 70 2 9 Severe Mild 55 45 74 3 12 Severe Severe 60 49 77 4 13 Severe Normal 53 45 71 5 13 Mild Normal 40 45 46 6 18 Mild Mild 72 59 93 7 22 Severe Severe 59 57 65 8 19 Mild Mild 92 93 93 9 31 Normal Mild 95 88 103

10 34 Mild Mild 113 115 110

aBased on measures of perceptual and sensory-motor functioning on the right and left sides of the body:

Normal = Performance on neuropsychological tests within normal range.

Mild = Only mild impairment exhibited (based on norms) and never on more than two of the six tests given.

Severe = Impairments on any given test falls into moderate to severe range of dysfunction.

language ability, visual-spatial ability, or general intellectual ability. Prior and Bradshaw (1979) have suggested that the substantial variability in eventual language acquisition of autistic individuals may be related to the integrity of hemispheric functioning. Presumably, if in some individuals the right hemisphere is intact, compensation for left-sided impairment may be possible to some extent. With the present data, it is possible to determine whether poor language ability is associated with bilateral cerebral dysfunction, as reflected in impaired sensory-motor and/or perceptual functions on the right and left sides of the body.

Table V displays the data for individual subjects on the following measures: Age, Full Scale IQ (FSIQ), Verbal IQ (reflective of left hemisphere functioning), PIQ (reflective of right hemisphere functioning), and degree of impairment found for the right and left hemispheres based on perceptual and sensory-motor functioning on the right and left sides of the body.

It was found that obtaining a Full Scale IQ in the nonretarded range ( i> 70) was associated with superior left hemisphere functioning (either normal or only mild dysfunction of left hemisphere). This relationship was found for 9 of the 10 subjects (binomial probability = .009). Full Scale IQ was not found to be related to the integrity of the right hemisphere. Similar results were found with respect to Verbal IQ (VIQ). For 8 of the 10 subjects, VIQ in the nonretarded range was associated with better left hemisphere

Laleralized Brain Dysfunction 283

Table VI. Relationship Between Hemisphere Functioning a and Cognitive Abilities (number of subjects correctly classified)

Left Binominal Right Binomial Variable hemisphere probability hemisphere probability

Age 8/10 .043 5/10 .246 FISQ 9/10 .009 6/10 .205 VIQ 8/10 .043 5/10 .246 PIO 5/10 .246 8/10 .043

aBased on perceptual and sensory-motor functions on the right and left sides of the body.

functioning (p = .043), whereas no consistent relationship was found between right hemisphere integrity and VIQ. However, Performance IQ (PIQ) was found to be related to right hemisphere functioning. In 8 of the 10 cases, obtaining a PIQ in the nonretarded range was associated with superior right hemisphere functioning (i,e., normal or mild dysfunction). No consistent relationship was found between PIQ and the integrity of left hemisphere functioning. These results are summarized in Table VI.

DISCUSSION

This report provides further evidence for a link between early infantile autism and left hemisphere dysfunction. On the basis of sensory-motor, perceptual, and cognitive measures from the Halstead-Reitan neuropsychological battery, autistic subjects showed a pattern of deficits indicative of a significantly greater left than right hemisphere dysfunction, a pattern that was not found in either the mentally retarded comparison group or the group of subjects with demonstrable diffuse brain damage. Compared with either group, autistic subjects showed significantly greater left hemisphere dysfunction but did not differ significantly in the degree of right hemisphere dysfunction exhibited. The results were additionally confirmed utilizing only comparisons of sensory-motor and perceptual functions on the right and left sides of the body, which can be considered more direct measures of right and left hemisphere functioning than the cognitive measures.

As reported in earlier studies (e.g., Lockyer & Rutter, 1970), autistic subjects do show a striking pattern of cognitive strengths and weaknesses that is consistent with selective left hemisphere dysfunction. In contrast to the retarded subjects, autistic subjects, as a group, had significantly higher Performance IQ scores than Verbal IQ scores, which is not necessarily surprising in light of the severe language impairment that is characteristic of the syndrome. More impressive was the finding that on subtests that have

284 Dawson

been traditionally associated with the right hemisphere (block design and object assembly), the autistic group functioned at normal levels, with 5 of the 10 subjects scoring in the high average to gifted performance range. Such findings appear to rule out the possibility of global brain damage as a basis for autism.

These findings in conjunction with previous studies point to early or congenital left hemisphere dysfunction as one factor in the explanation for autism. The left hemisphere has been shown to be normally involved with language and other aspects of symbolic functioning. Moreover, studies of both brain-damaged patients (Kimura, 1977) and normal children and adults (Dawson, Note 2) have found the left hemisphere to be involved in nonverbal motor imitation and the use of gesture, another commonly noted deficit of autistic children.

It is noteworthy that not all autistic subjects in the present study exhibited unilateral dysfunction on the neuropsychological battery. The fact that half of the sample had predominantly left-sided dysfunction with little or no right hemisphere involvement suggests that autism, in some cases, exists concurrently with intact right hemisphere functioning. However, our data suggest that many autistic children may have bilateral involvement. It was of particular interest whether, in the present sample, these two groups differed significantly in intellectual ability, language skills, or visual spatial ability. Previous authors (Prior & Bradshaw, 1979) have suggested that a poorer prognosis for language acquisition may exist for children with bilateral rather than unilateral dysfunction. It is reasoned that right hemisphere compensation may occur in cases of selective left hemisphere dysfunction. Our data do not support such a theory. Intellectual ability, as reflected by Full Scale IQ, and language skills, as reflected by Verbal IQ, were related to the integrity of the left hemisphere, and independent of accompanying right hemisphere functioning. Perfor- mance IQ, on the other hand, was found to be related to right, but not left, hemisphere functioning (based on perceptual and sensory-motor skills on the right and left sides of the body). At this point, our data suggest that fight hemisphere integrity is not related to the level of language acquisition. However, these data are limited for a number of reasons. The sample size is quite small and the range of language ability seen in the present sample is from moderate to superior; no cases of mute children are included, due to the requirements of the study. Second, the measures of hemisphere functioning are quite limited. The measures of perceptual and sensory-motor functioning assess particular areas of the brain, particularly the primary projection areas and sensory-motor cortex. The more relevant areas for language functioning, such as the temporoparietal association area, are not assessed by these measures. Dichotic listening techniques, as


well as direct measures of electroencephalographic activity during linguistic processing, may be more appropriate measures of right and left hemisphere language processing.

Another question that warrants further research is whether the autistic child's unique manner o f processing visual and auditory information (see Hermelin, 1972) is related to an underlying atypical neural organization that predisposes them to right hemisphere processing. Dawson (1982) and Prior and Bradshaw (1979) found that many autistic individuals favor the right hemisphere for both verbal and nonverbal processing. Are these individuals more likely to use information-processing strategies that are characteristic of the right hemisphere? Answers to these questions could eventually be relevant in developing therapy methods for autistic children.

Future research involving both neurophysiological and behavioral measures and autistic individuals of varying age and severity of symptoms may allow us to distinguish meaningful subgroups of autistic persons that differ in the degree and type of neuropathology. A recent study by Fein, Skoff, and Mirsky (1981), which demonstrated a specific relationship between brain stem pathology and affective and attentional problems in autistic children, has taken a step in the direction. This study also underscores the fact that left hemisphere impairment in autistic individuals can be accompanied by dysfunction in other areas of the brain, at cortical as well as subcortical levels.

REFERENCE NOTES

1. Knobloch, H., & Pasamanick, B. Etiologic factors in "'early infantile autism'" and "'childhood schizophrenia." Presented at the 10th International Congress of Pediatrics, Lisbon, September 1962.

2. Dawson, G. Left hemisphere specialization for facial and manual imitation in children and adults. Paper presented at the American Psychological Association meeting, Los Angeles, 1981.

REFERENCES

Blackstock, E. G. Cerebral asymmetry and the development of infantile autism. Journal of Autism and Childhood Schizophrenia, 1978, 8, 339-353.

Bolt, T. J. Behavioral correlates of cerebral damage in children 9-14. In R. M. Reitan & L. A. Davison (Eds.), Clinical neuropsychology: Current status and applications. Wash- ington, D.C.: Winston, 1974.

Chess, W. Autism in children with congenital rubella. Journal of Autism and Childhood Schizophrenia, 1971, 1, 33-47.

Creak, M. Schizophrenic sydrome in childhood: Progress report of a working party. Cerebral Palsy Bulletin, 1961, 3, 501-503.

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Creak, M., & Pampiglione, G. Clinical and EEG studies on a group of 35 psychotic children. Developmental Medicine and Child Neurology, 1969, 11,218-227.

Dawson, G. Cerebral lateralization in individuals diagnosed as autism in early childhood. Brain and Language, 1982, 15, 353-368.

Fein, D., Skoff, B., & Mirsky, A. F. Clinical correlates of brain dysfunction in autistic children. Journal of Autism and Developmental Disorders, 1981, 11, 303-315.

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lateralized brain dysfunction in autism: evidence from the halstead-reitan neuropsychological...

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