Hemisphere functioning and motor imitation in autistic persons

Previous research has found that a high proportion of autistic individuals exhibit an atypical pattern of hemispheric specialization suggestive of impaired left hemisphere functioning: namely, right hemisphere dominance for both verbal and visual-spatial processing. Studies of brain-damaged persons have suggested that the left hemisphere is specialized for the use of nonverbal gesture. Since a major characteristic of autism is an impairment in the use of gesture, it was predicted that autistic persons would also show atypical hemispheric specialization for motor imitation. To test this hypothesis, hemispheric activation was measured using EEG recordings of alpha rhythm in autistic and matched normal control subjects during four motor imitation tasks. Autistic subjects showed significantly greater right hemisphere activation during the imitation tasks, than normal subjects. This pattern was particularly evident in younger autistic subjects and during oral, rather than manual, imitation tasks.     

Atypical speech lateralization in adults with developmental coordination disorder demonstrated using functional transcranial Doppler ultrasound

Research using clinical populations to explore the relationship between hemispheric speech lateralization and handedness has focused on individuals with speech and language disorders, such as dyslexia or specific language impairment (SLI). Such work reveals atypical patterns of cerebral lateralization and handedness in these groups compared to controls. There are few studies that examine this relationship in people with motor coordination impairments but without speech or reading deficits, which is a surprising omission given the prevalence of theories suggesting a common neural network underlying both functions. We use an emerging imaging technique in cognitive neuroscience; functional transcranial Doppler (fTCD) ultrasound, to assess whether individuals with developmental coordination disorder (DCD) display reduced left‐hemisphere lateralization for speech production compared to control participants. Twelve adult control participants and 12 adults with DCD, but no other developmental/cognitive impairments, performed a word‐generation task whilst undergoing fTCD imaging to establish a hemispheric lateralization index for speech production. All participants also completed an electronic peg‐moving task to determine hand skill. As predicted, the DCD group showed a significantly reduced left lateralization pattern for the speech production task compared to controls. Performance on the motor skill task showed a clear preference for the dominant hand across both groups; however, the DCD group mean movement times were significantly higher for the non‐dominant hand. This is the first study of its kind to assess hand skill and speech lateralization in DCD. The results reveal a reduced leftwards asymmetry for speech and a slower motor performance. This fits alongside previous work showing atypical cerebral lateralization in DCD for other cognitive processes (e.g., executive function and short‐term memory) and thus speaks to debates on theories of the links between motor control and language production.     

Neuropsychological analysis of a case of crossed dysphasia verified at postmortem

A case is reported of crossed dysphasia in a right-handed monolingual patient, where neuropathological verification of the unilateral site of the lesion was obtained within a year of detailed neuropsychological assessment. The patient's pattern of language impairment was characterized by agrammatic speech and relatively preserved naming ability. In addition, the patient had good repetition, poor comprehension, and marked impairment on visuospatial tasks. Neuropathological investigations showed a large area of infarction affecting cortex, white matter, and subcortical structures in the right hemisphere. The possibility is discussed of a distinction between two types of crossed dysphasia with either dissociated or simultaneous language and visuospatial deficits due to reversed representation of hemispheric specific functions or transfer of most cognitive functions to the right hemisphere.     

Hemispheric asymmetries in the visual evoked potentials to temporal frequency: preliminary evidence

Steady-state evoked potentials were recorded in eight adult subjects from occipital and temporal leads of both hemispheres to investigate the effect of temporal frequency on the hemispheric specialization for basic visual information. A 3 cycles deg-1 grating was phase-reversed at different temporal frequencies (from 4 to 18 Hz), and the frequency spectrum of evoked potentials was computed by means of a fast Fourier transform program. Significant results were obtained for the component at twice the temporal frequency of stimulation. Occipital evoked potentials did not show hemispheric asymmetry, whereas temporal evoked potentials showed an interaction between hemisphere and temporal frequency: right and left hemispheres were respectively prominent for low (4 and 6 Hz) and for high (8-18 Hz) temporal frequencies. The results are discussed in the context of current research on hemispheric specialization for basic spatiotemporal parameters of visual information processing.     

On Spatial Frequencies and Cerebral Hemispheres: Some Remarks from the Electrophysiological and Neuropsychological Points of View

The spatial frequency hypothesis on hemispheric specialization gave rise to contradictory experimental results, commented on in Brain and Cognition by Christman (1989) and Peterzell (1991). The question is discussed through a review of the electrophysiological and neuropsychological research on hemispheric asymmetry of spatial frequency processing. The general hypothesis of the hemispheric specialization for this basic visual information appears to be supported by recent works on evoked potentials by gratings and checkerboards. However, an interaction between the cerebral hemisphere, spatial frequency, and temporal frequency was found more than a sharp dichotomy between low (right hemisphere) and high spatial frequencies (left hemisphere), as indeed it was proposed by the spatial frequency hypothesis. Other relevant physical parameters in generating the hemispheric asymmetry were found to be the contrast and the visual field size. The neuropsychological research on brain-injured patients has given some further evidence of the hemispheric asymmetry in spatial frequency processing. In conclusion, it is argued that the major merit of the spatial frequency hypothesis was in the attempt to investigate the hemispheric specialization of lower and higher levels of visual information processing from the perspective of a unified computational conception of visual perception.     

Hemispheric differences in the perception of words and faces in deaf and hearing children

The purpose of this study was to investigate hemispheric functional asymmetry in 18 normal hearing children and 18 congenitally deaf children aged 13-14 years. The task was identification of a visual stimulus (3-letter word or photograph of a face) presented in either the left or right visual field. The children responded by pointing to the target stimulus on a response card which contained four different words or three different faces. The percentage of errors for presentations to the two visual fields were analysed to determine hemispheric dominance. The pattern of hemispheric differences for the hearing children was consistent with that from previous investigations. The results for the deaf children differed from those of the normals. In word perception we observed a right hemisphere advantage and in the face recognition a lack of hemispheric differences. These results point to a lack of auditory experiences which is affecting the functional organization of the two hemispheres. It is suggested that the necessity to make use of visuo-spatial information in the process of communication causes right hemisphere dominance in verbal tasks. This may influence the perception of other visuo-spatial stimuli which may yield a lack of hemispheric asymmetry in face recognition.     

Cerebral lateralization in individuals diagnosed as autistic in early childhood

Early infantile autism was found to be associated with an atypical pattern of cerebral lateralization. Based on EEG measures of hemispheric activation during cognitive processing, it was found that 7 of the 10 autistic individuals tested showed a pattern of hemispheric specialization rarely seen in the normal population; namely, a “reversal” in lateralization reflective of a lack of left-hemisphere specialization for linguistic functions. Furthermore, the autistic individuals' pattern of cognitive strengths and weakness is suggestive of a selective impairment of the left cerebral hemisphere.     

Stimulus overselectivity in autistic,trainable mentally retarded,and non-handicapped children: Comparative research controlling chronological (rather than mental) age

Much of the comparative research on stimulus overselectivity has been flawed by either failure to control for chronological age and language ability of the subjects or reliance on the controversial technique of matching on mental age. The present study investigated the prevalence of overselectivity in autistic, trainable mentally retarded, and non-handicapped children demonstrating some expressive speech. The ages of the children were between 6 years-6 months and 9 years-3 months. Thus, chronological age and language ability were controlled, rather than allowed to vary unsystematically. Results indicated no significant differences between the autistic and TMR samples, but significant differences between the handicapped samples and the non-handicapped group. Some, but not all, of the handicapped children displayed overselectivity.     

Abnormalities of visual evoked potentials by checkerboards in children with specific reading disability

Visual evoked potentials by checkerboards of varying check sizes were recorded in the two hemispheres of 16 specific reading disabled and 8 normal children. In most of the disabled subjects a gross hemisphere asymmetry was assessed, while in the control group the usual evoked potential symmetry was observed. In some disabled subjects the evoked potentials had a larger amplitude in the right hemisphere, while in others the amplitude was larger in the left hemisphere. In a small subgroup the evoked potentials were symmetrical, but they had a smaller amplitude than in the control subjects. The results, giving evidence of a dysfunction in basic visual processing, are discussed in the context of current literature on clinical subgroups and the interhemispheric relationship in the dyslexic syndrome.     

Cerebral lateralization for speech in deaf and normal children

The cerebral lateralization pattern for speech production in normal hearing and congenitally deaf children was studied using the dual-task paradigm. Performance under the verbal task conditions showed predicted left hemispheric dominance for speech production in the normal hearing children. No developmental trends in asymmetry were found, suggesting that speech lateralization is present in normal 3-year-old children. These data support the developmental invariance hypothesis of cerebral organization. Deaf children showed more symmetrical patterns of cerebral control for speech production. No developmental trends in functional brain organization were observed among prepubescent deaf children.     

Hemispheric function and linguistic skill in the deaf

The nature of hemispheric processing in the prelingually deaf was examined in a picture-letter matching task. It was hypothesized that linguistic competence in the deaf would be associated with normal or near-normal laterality (i.e., a left hemisphere advantage for analytic linguistic tasks). Subjects were shown a simple picture of a common object (e.g., lamp), followed by brief unilateral presentation of a manually signed or orthographic letter, and they had to indicate as quickly as possible whether the letter was present in the spelling of the object's label. While hearing subjects showed a marked left hemisphere advantage, no such superiority was found for either a linguistically skilled or unskilled group of deaf students. In the skilled group, however, there was a suggestion of a right hemisphere advantage for manually signed letters. It was concluded that while hemispheric asymmetry of function does not develop normally in the deaf, the absence of this normal pattern does not preclude the development of the analytic skills needed to deal with the structure of language.     

Hemispheric Asymmetry in Transient Visual Evoked Potentials Induced by the Spatial Factor of the Stimulation

In order to enhance the effect of spatial frequency on the hemispheric asymmetry of visual evoked potentials (VEP), the response amplitudes to ON-OFF modulated gratings were compared with the responses to pattern reversal stimulation. Sinusoidal gratings of different spatial frequencies were presented to six righthanders. VEPs were recorded from temporal leads on each hemisphere. In the left hemisphere, the amplitude was constant for the two modes of presentation and independent of spatial frequency. In the right hemisphere, the response amplitude was larger to the ONSET stage of ON-OFF stimulation than to reversal and presented the characteristic spatial frequency tuning curve. This asymmetry is assumed to reflect a difference in sensitivity of the two hemispheres to the spatiotemporal characteristics of the stimulus. The relevance of these findings is discussed in relation to the other hemispheric specialization models.     

Language learning disabilities: integrating research approaches

Developmental language learning impairments affect 10 to 20% of children and increase their risk of later literacy problems (dyslexia) and psychiatric disorders. Both oral- and written-language impairments have been linked to slow neural processing, which is hypothesized to interfere with the perception of speech sounds that are characterized by rapid acoustic changes. Research into the etiology of language learning impairments not only has led to improved diagnostic and intervention strategies, but also has raised fundamental questions about the neurobiological basis of speech, language, and reading, as well as hemispheric lateralization.     

The effect of congenital deafness on cerebral asymmetry in the perception of emotional and non-emotional faces.

Functional hemispheric specialization in recognizing faces expressing emotions was investigated in 18 normal hearing and 18 congenitally deaf children aged 13-14 years. Three kinds of faces were presented: happy, to express positive emotions, sad, to express negative emotions, and neutral. The subjects' task was to recognize the test face exposed for 20 msec in the left or right visual field. The subjects answered by pointing at the exposed stimulus on the response card that contained three different faces. The errors committed in expositions of faces in the left and right visual field were analyzed. In the control group the right hemisphere dominated in case of sad and neutral faces. There were no significant differences in recognition of happy faces. The differentiated hemispheric organization pattern in normal hearing persons supports the hypothesis of different processing of positive and negative emotions expressed by faces. The observed hemispheric asymmetry was a result of two factors: (1) processing of faces as complex patterns requiring visuo-spatial analysis, and (2) processing of emotions contained in them. Functional hemispheric asymmetry was not observed in the group of deaf children for any kind of emotion expressed in the presented faces. The results suggest that lack of auditory experience influences the organization of functional hemispheric specialization. It can be supposed that in deaf children, the analysis of information contained in emotional faces takes place in both hemispheres.     

Are there different patterns of cerebral asymmetry between dyslexic subtypes?

The purpose of this research has been to analyze the cerebral asymmetry in dyslexic children and, specifically for demonstrating whether there are different patterns of cerebral asymmetry among subtypes of dyslexia. We used a sample of 89 dyslexic children divided into subtypes obtained from the Jimenez and Ramirez (2002) study. The dual-task method was used to assess hemispheric specialization. The data were compared with that obtained from a control group of normal readers of same age (CA; N= 37) and with a younger reading level control group (RL; N= 40). We found that in the dyslexic group, similarly to the younger reading level group, a high percentage of children showed convergence in the left hemisphere of both linguistic and spatial functions. This pattern was also found in the RL control group. On the other hand, we did not find different patterns of cerebral asymmetry between dyslexic subtypes.     

Correlations between glucose metabolic rates in brain regions of healthy male adults at rest and during language stimulation

This study examines the effect of different behavioral conditions on patterns of correlation between regional cerebral metabolic rates for glucose. Cerebral glucose metabolism was determined with positron emission tomography and (11C)-deoxyglucose in 29 normal subjects between the ages of 23 and 55. Seventeen subjects were studied in an unstimulated (resting) condition and 12 subjects during a phoneme monitoring language stimulation. Partial correlation coefficients, controlling for whole brain glucose metabolism, were calculated for pairs of metabolic rates in 14 cortical and 2 subcortical regions. Both stimulated and unstimulated subjects showed statistically significant correlations between left and right hemisphere homologs. The stimulated subjects also showed significant within-hemisphere correlations between left but not right hemisphere regions. These included left perisylvian regions classically associated with language functions (left inferior frontal, left superior temporal and left transverse temporal cortical regions) as well as other regions. Significant correlations between left regions and a right superior temporal region were also found. In general, these findings show a pattern of cross-hemisphere symmetry at rest and of hemisphere asymmetry during stimulation. Moreover, the asymmetry observed during stimulation appears to be superimposed upon a pattern of cross-hemisphere symmetry similar to that observed in the unstimulated state.     

Auditory event-related potential probes and behavioral measures of aphasia

This study examined the relationship between an auditory event-related potential probe technique measure of differential hemispheric processing and traditional tests of aphasia in aphasic patients. Subjects were 10 aphasic and 10 normal adult males. The results of the electrophysiological measures indicated that the aphasic subjects responded differently from the normal group particularly when the task required processing of verbal information. During the verbal task the aphasic group showed higher amplitude right hemisphere responses as compared to left. The normal group showed little hemispheric task related asymmetries. The pattern of electrical asymmetry in the aphasic group seems to be an indicator of severity as measured by traditional aphasia examinations.     

ASYMMETRY IN MOUTH OPENING DURING DIFFERENT SPEECH TASKS

When a normal subject is speaking, the right side of the mouth typically opens more widely or moves over a greater total distance. This asymmetry is most consistent during purely verbal word list generation and verbal recall tasks, less consistent when emotional expression and/or visual imagery is involved, and reversed during smiling. Aphasic patients also show the right bias during word lists, repetition, and conversation, but not during serial speech, singing and smiling. Since observable mouth asymmetry is presumed to result from hemispheric asymmetry in motor control, these observations confirm the major role of a left hemisphere control system for pure verbal expression and provide evidence for involvement of the right hemisphere in mouth motor control during emotional and prosodic expression or visual imagery. Therapeutic possibilities are also suggested.     

Cerebral specialization for speech production in persons with Down syndrome.

The study of cerebral specialization in persons with Down syndrome (DS) has revealed an anomalous pattern of organization. Specifically, dichotic listening studies (e.g., Elliott & Weeks, 1993) have suggested a left ear/right hemisphere dominance for speech perception for persons with DS. In the current investigation, the cerebral dominance for speech production was examined using the mouth asymmetry technique. In right-handed, nonhandicapped subjects, mouth asymmetry methodology has shown that during speech, the right side of the mouth opens sooner and to a larger degree then the left side (Graves, Goodglass, & Landis, 1982). The phenomenon of right mouth asymmetry (RMA) is believed to reflect the direct access that the musculature on the right side of the face has to the left hemisphere's speech production systems. This direct access may facilitate the transfer of innervatory patterns to the muscles on the right side of the face. In the present study, the lateralization for speech production was investigated in 10 right-handed participants with DS and 10 nonhandicapped subjects. A RMA at the initiation and end of speech production occurred for subjects in both groups. Surprisingly, the degree of asymmetry between groups did not differ, suggesting that the lateralization of speech production is similar for persons with and persons without DS. These results support the biological dissociation model (Elliott, Weeks, & Elliott, 1987), which holds that persons with DS display a unique dissociation between speech perception (right hemisphere) and speech production (left hemisphere).     

Intonation and Emotion in Autistic Spectrum Disorders

The classic picture of an autistic individual includes an impoverished ability to interpret or express emotion. The prosody of spoken language in autistic children is thought to lack emotional content. In this study, the verbal intonation of children with autism was examined and compared to that of children with Asperger Syndrome (AS) and normal controls (ctrl). Utterances elicited by repetition and by spontaneous story completion were analyzed by quantifying phonetic features (pitch, amplitude, and length) and comparing them to subjective ratings of produced emotion (happy, sad or angry). Since the most consistent phonetic correlate of these emotional targets has been demonstrated to be pitch range, speakers with autistic spectrum disorders were expected to have decreased pitch range; however in the repetition task, autistic subjects actually had a larger pitch range than the other groups. Other measures of intonation including amplitude, duration, and location of pitch peak revealed defects that are more complex than predicted. In spontaneous speech, autistic subjects performed more poorly on both phonetic targets and subjective ratings than ctrls, and AS subjects fell between autistics and normals.