Dysfunction In Autism Research Articles

Cortical Dysfunction in Autism

Cerebellar and cortical systems in 26 high-functioning adolescents and young adults with autism were examined and compared to 26 healthy controls at the University of Pittsburgh School of Medicine.

Oculomotor evidence for neocortical systems but not cerebellar dysfunction in autism.

To investigate the functional integrity of cerebellar and frontal systems in autism using oculomotor paradigms. Cerebellar and neocortical systems models of autism have been proposed. Courchesne and colleagues have argued that cognitive deficits such as shifting attention disturbances result from dysfunction of vermal lobules VI and VII. Such a vermal deficit should be associated with dysmetric saccadic eye movements because of the major role these areas play in guiding the motor precision of saccades. In contrast, neocortical models of autism predict intact saccade metrics, but impairments on tasks requiring the higher cognitive control of saccades. A total of 26 rigorously diagnosed nonmentally retarded autistic subjects and 26 matched healthy control subjects were assessed with a visually guided saccade task and two volitional saccade tasks, the oculomotor delayed-response task and the antisaccade task. Metrics and dynamics of the visually guided saccades were normal in autistic subjects, documenting the absence of disturbances in cerebellar vermal lobules VI and VII and in automatic shifts of visual attention. Deficits were demonstrated on both volitional saccade tasks, indicating dysfunction in the circuitry of prefrontal cortex and its connections with the parietal cortex, and associated cognitive impairments in spatial working memory and in the ability to voluntarily suppress context-inappropriate responses. These findings demonstrate intrinsic neocortical, not cerebellar, dysfunction in autism, and parallel deficits in higher order cognitive mechanisms and not in elementary attentional and sensorimotor systems in autism.

Psychophysiological responsiveness to the distress ofothers in children with autism

This study investigates the psychophysiological responsiveness of children with autismand comparison groups to distress cues, threatening and neutral stimuli. 20 children with autism,20 children with moderate learning difficulty and 20 normal developing children were shownslides of these three types of stimuli and their electrodermal responses were recorded. Thechildren with autism showed appropriate electrodermal responses to the distress cues. However,and surprisingly, the children with autism were hyporesponsive to the threatening stimuli. Theresults are interpreted with reference to the violence inhibition mechanism model ( Blair, 1995) and possible frontal lobe dysfunction in autism.

Control of Action and Thought: Normal Development and Dysfunction in Autism: A Research Note

Thirty-six children with autism, 24 children with learning difficulties (matched with the autistic group for sentence comprehension), and 41 normally-developing preschoolers were given two simple tasks: a hand-game requiring inhibitory control, and a delayed-reward situation tapping metacognitive awareness of strategies for coping with the delay period. For both clinical groups, performance on the two tasks was correlated, even when the effect of comprehension level was partialled out. However, no such correlation was observed for the preschoolers, once age was taken into account. The results are discussed in terms of potential links between executive-function and mental-state awareness.

Utilization behaviour in adults with autism: A preliminary investigation

AbstractResearch investigating frontal‐limbic system dysfunction in autism has gained some prominence in recent years, emanating from three main sources; animal studies, investigations of frontal lobe patients and neuropsychological assessment of individuals with autism. It is suggested that some of the repetitive behaviours associated with autism might represent examples of utilization behaviour. Some preliminary data are presented to support this suggestion. The implications of this account are discussed with respect to the links that are frequently made between obsessive‐compulsive disorder, Tourette's syndrome and autism.

Executive Function Abilities in Autism and Tourette Syndrome: An Information Processing Approach

This study used information processing paradigms to provide a detailed examination of executive function abilities in autism. The performance of non-retarded autistic children was compared with that of two matched control groups, one with Tourette Syndrome and the other developmentally normal. Autistic subjects performed as well as controls on tasks requiring global-local processing and inhibition of neutral responses. In contrast to both control groups, however, the autistic sample was significantly impaired on a measure of cognitive flexibility. The performance of children with Tourette Syndrome did not differ from that of normal controls on any task. These results refine our knowledge about executive dysfunction in autism and suggest a new conceptual framework and general method for investigating the cognitive underpinnings of neurodevelopmental disorders.

Medial temporal lobe structures and autism: A review of clinical and experimental findings

Although substantive understanding of brain dysfunction in autism remains meager, clinical evidence as well as animal brain research on the effects of early damage to selective brain system have now yielded enough knowledge that some provisional hypotheses concerning the etiology of autism can be generated. Basically, the underlying premise of this review is that a major dysfunction of the autistic brain resides in neural mechanisms of the structures in the medial temporal lobe, and, perhaps, more specifically the amygdaloid complex. This review begins with a summary of clinical evidence of the involvement of the medial temporal lobe structures in autism. The major behavioral disturbances seen in monkeys that had received neonatal lesions of the medial temporal lobe structures are then described. From this survey it can be seen that distinct patterns of memory losses and socioemotional abnormalities emerge as a result of extent of damage to the medial temporal lobe structures. The potential value of the experimental findings for an understanding of neural dysfunction in autism as well as directions of future research are discussed in the final section of the review.

Evidence for executive dysfunction in autism

A group of young people with autism (ranging in ability from high functioning to moderately learning disabled), and ability-matched control groups of (i) non-autistic individuals with moderate learning disabilities, and (ii) normally developing children, were presented with two tests of executive function: the Intra-dimensional/Extra-dimensional set-shifting task and the Tower of London planning task. These tests were graded in difficulty and included internal control measures. On each task, the autistic group was differentially impaired with respect to both control groups. Moreover, this impairment was specific to the stages of each task which placed greatest demands upon executive control. This evidence for executive dysfunction in autism is discussed in the context of Norman and Shallice's ( Centre for Human Information Processing Technical Report 99, 1980) “Supervisory Attentional System” model of frontal function.

Recent Research in Autism

Recent research in three areas is reviewed. Advances in diagnosis and classification will likely lead to convergence between the American and international definitions of autism and related disorders, which should facilitate research of these conditions. Studies of psychological process have focused on understanding the nature of social dysfunction in autism. In the area of neurobiologic research, much interest has centered on the possible role of genetic mechanisms in the pathogenesis of autism.

Pragmatic Language Dysfunction in Autism: “Competence” or “Performance”?

The purpose of this investigation was to determine whether pragmatic language difficulties in referential communication could be ameliorated by application of a brief, but directive, prompt and subsequently whether improved performance would generalize to a similar situation employing novel stimuli. Ten high functioning autistic adolescents and young adults were matched for age, sex, and language skill to normally developing subjects, and presented with a barrier game referential communication task. Significantly improved performance occurred following administration of the prompt and was maintained in the generalization condition. Maintained improved performance was interpreted as indicative of a difficulty in initial spontaneous application of available skills (ie. a performance problem) rather than a specific developmental skill deficit (ie. a competence problem).

Autism: Its Primary Psychological and Neurological Deficit

Autism is a perplexing condition because of its unique presenting signs and high degree of variability. Evidence is presented that the basic underlying information processing disorder is a dysfunction of the appreciation of the emotional significance of incoming stimuli and attaching motivational value to the stimuli. It is proposed that this dysfunction occurs when the amygdaloid nucleus and/or its connections are disrupted, resulting in the variability of the presentation of this syndrome among individuals. Herpes simplex encephalitis sometimes results in signs of autism. The virus has a predilection to attack specific areas of the brain, which provides information on the probable underlying neurological dysfunction in autism.

Left-hemisphere dysfunction in autism: What are we measuring?

This study sought to investigate the left hemisphere deficit hypothesis regarding autism. A group of 15 autistic youngsters between the ages of 8 and 13 years was compared with a group of 15 mentally retarded youngsters matched for age and IQ on a set of measures presumed to be sensitive to neuropsychological dysfunction. The results suggested that this sample of autistic youngsters is best characterized by bilateral neuropsychological involvement, affecting left-hemisphere functioning predominantly but not exclusively. The findings of this and other such studies seem to be somewhat determined by the varied samples and assessments employed in the research. The practice of selecting tests which presumably tap left or right cerebral functions is highly inferential, and warrants concern, particularly when assessing complex cognitive functioning in autistic individuals.

Left-hemisphere dysfunction in autism: What are we measuring?

This study sought to investigate the left hemisphere deficit hypothesis regarding autism. A group of 15 autistic youngsters between the ages of 8 and 13 years was compared with a group of 15 mentally retarded youngsters matched for age and IQ on a set of measures presumed to be sensitive to neuropsychological dysfunction. The results suggested that this sample of autistic youngsters is best characterized by bilateral neuropsychological involvement, affecting left-hemisphere functioning predominantly but not exclusively. The findings of this and other such studies seem to be somewhat determined by the varied samples and assessments employed in the research. The practice of selecting tests which presumably tap left or right cerebral functions is highly inferential, and warrants concern, particularly when assessing complex cognitive functioning in autistic individuals.

Facial perception in autism.

Disturbances in gaze and patterns of facial interaction are prominent aspects of social dysfunction in autism; the nature of this disturbance has up to the present been unclear. This study examined the ability of autistic subjects to use the human face as a source of information. Autistic and age- and MA-matched retarded control subjects assembled a series of puzzles displaying photographs of human faces; puzzles differed in complexity, familiarity of the faces and configuration (normal vs scrambled faces). Significant effects of all three factors, but not of diagnostic group, were observed. The autistic subjects did not exhibit specific deficits in perception of faces.

Brain-stem dysfunction in autism. Results of vestibular stimulation.

Responses to vestibular stimulation can, under well-controlled experimental conditions, provide a measure of brain-stem function. Autistic children had significantly longer time constants during the primary nystagmus response and significantly fewer beats during the secondary response than normal children when stimulated with constant angular acceleration in complete darkness. These findings could not be attributed to gross differences in arousal, to developmental retardation, to associated clinical conditions, or to either the influence of vision or habituation. Rather, they are suggestive of a neurophysiologic dysfunction, perhaps involving the brain stem, and may be an expression of the process that underlies those autistic behaviors that suggest faulty modulation of sensory input and motor output. Brain-stem centers modulate both general sensory input and motor excitation and may play a role in the elaboration of the more complex adaptive and motivated behaviors that are also disturbed in autism.

1692 AMYGDALA DYSFUNCTION IN AUTISM

The anatomic site responsible for infantile autism is unknown. Based upon converging neuropsychological/neuropathological evidence that the temporal lobe may be the primary site of dysfunction in autism, we have adapted discrimination and memory tasks that distinguish amygdalar from hippocampal damage in monkeys (Murray/Mishk in l982). This neuropsychological paradigm was applied to 18 autistic subjects matched very closely to 18 Down's syndrome (DS) controls on the basis of age, sex and scores on the Raven Progressive Matrices. A subject was considered autistic when he/she achieved a score within 1 SD of the mean for the autistic subgroup of a 2,000 subject standardization sample (Autism Behavior Checklist, ABC). On a delayed nonmatching-to-sample task (DNMTS) cross-modal scores correlated with ABC body and object use (r= -0.42, p<0.05) and cross-modal with ABC social and self-help skills (r= -.45, p < 0.05). These correlation scales contain several items in common with the Kluver-Bucy syndrome, a neurobehavioral abnormality in animals and humans associated with damage to the amygdala. On the visual DNMTS, a significant group x task interaction was found (F= 6.68, DF= 2, 34, p < .01) indicating that DS performed better than autistics. Impairment of the visual DNMTS in monkeys results from lesions in both the amygdala and the hippocampus. There were no significant differences observed between the two groups on the spatial location tasks reflective of the hippocampal lesions alone. Taken together, these results suggest a disportionate functional impairment of the amygdala in autism.

Conceptual problem-solving in highly verbal, nonretarded autistic men.

Nine highly verbal, nonretarded men, ages 18 to 39, with clearly documented childhood diagnoses of infantile autism were studied with the Wisconsin Card Sorting Test, a measure of conceptual problem solving sensitive to frontal system dysfunction, and with a measure of social-adaptive functioning. Their performances were compared with 10 controls matched for age, sex, education, and IQ, as well as with published norms for various groups of brain-damaged patients. Significant deficits in the formulation of rules and significant perseverative tendencies were documented in the autistic sample. No significant correlation between these deficits and social-adaptive deficits was seen. These findings were discussed with respect to the heterogeneity of the autistic disorder and Damasio's hypothesis concerning frontal-subcortical dysfunction in autism.

Lateralized brain dysfunction in autism: evidence from the Halstead-Reitan neuropsychological battery.

Selected tests from the Halstead-Reitan neuropsychological battery were administered to 10 male individuals who had been diagnosed as autistic in early childhood. Results from the battery obtained from the autistic group were compared with a group of retarded persons matched for IQ and with a group of patients with demonstrable diffuse brain damage. As a group, the autistic subjects showed a pattern of deficits indicative of a significantly greater degree of 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.

Autistic children's hand preferences: Results from an epidemiological study of infantile autism

Twenty-six autistic children, constituting a total population sample of children diagnosed in accordance with Rutter's criteria as suffering from infantile autism, were assessed with regard to handedness and certain associated factors. They were compared with 52 age-, sex-, and IQ-matched controls. Sixty-two percent of the autistic children were non-right-handed compared with 37% of the controls. Left-handedness in autism was associated with an abundance of delayed echolalia. Heredity for left-handedness in some cases, and assumed brain damage and immature patterns of lateralization in others, were considered the cause of non-right-handedness in the autistic children. Computed tomographic (CT) brain scans and other neurobiological examinations did not provide evidence indicating clear-cut unilateral left hemisphere dysfunction in autism. Rather, a slight trend in the opposite direction (i.e., an association with right hemisphere dysfunction) was seen in the left-handed autistic children. The result points toward the need for further studies of handedness in autism.

The functional neuroanatomy of infantile autism.

Infantile autism is a behavioral syndrome consisting of specific disturbances of social relating and communication, language, response to objects, sensory sensitivity and motility. The uniqueness of this syndrome suggests one underlying pathophysiologic mechanism, although multiple etiologies, which could activate or replicate such a mechanism, have been demonstrated. Review of considerable experimental evidence and clinical observation suggests that the symptomatology of autism, including the disturbances of social relating and communication, can best be explained as a disorder of sensory modulation. This in turn suggests a neurophysiologic mechanism consisting of dysfunction of a cascading series of neurophysiologic levels or interacting neuronal loops in the brainstem and diencephalon which subserve modulation of sensory input. Some of those same systems modulate motor output in response to sensory input, and their dysfunction may release the abnormal perseverative motility of infantile autism. Other experimental evidence and clinical observations stress the language deficits of autism and implicate dysfunction of cortical structures. Brainstem and diencephalic centers project rostrally to telencephalic structures and these, in turn, modify brainstem and diencephalic function. Theories of rostrally and caudally directed sequences of pathoneurophysiologic contributions to the system dysfunction in autism are compared. It is concluded that the symptoms of autism can best be explained in terms of dysfunction of brainstem and related diencephalic behavioral systems and their elaboration and refinement by selected higher neural structures.