Neurobiological correlates of autism: a review of recent research.

This review paper integrates recent structural and functional imaging, postmortem, animal lesion, and neurochemical research about the pathophysiology of autism. An understanding of the neurobiological correlates of autism is becoming increasingly important as more children are diagnosed with the condition and funding for well-targeted interventions increases. Converging evidence suggests that autism involves abnormalities in brain volume, neurotransmitter systems, and neuronal growth. In addition, evidence firmly links autism with abnormalities in the cerebellum, the medial temporal lobe, and the frontal lobe. Potential implications of these findings and suggestions for future research are reviewed.     

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.     

Auditory overselectivity in autistic children

Autistic and normal children were trained to respond to a complex stimulus containing two auditory components. After the discrimination was acquired, the individual components were presented separately, allowing assessment of the extent to which the child's responding was controlled by one or both of the cues. The autistic children, unlike the normal children, provided evidence for stimulus overselectivity in that 6 of 8 autistic subjects responded to only one of the components. These results are consistent with those of previous studies which showed that when autistic children are presented with a complex visual or multiple-modality stimulus, they selectively respond to only one component of the complex. The present results extend the stimulus overselectivity hypothesis to the situation where all of the stimuli occur within the auditory modality. It is suggested that auditory overselectivity may partially account for autistic deficits in speech comprehension.     

Age trends in stimulus overselectivity

Stimulus overselectivity refers to the phenomenon whereby stimulus control over behavior is exerted only by a limited subset of the total number of stimuli present during discrimination learning. It often is displayed by individuals with autistic spectrum disorders or learning disabilities, but is not exclusive to those groups. The present studies investigated the impact of aging on stimulus control and overselectivity. Three age groups--18-22, 47-55, and 70-80 year olds-were studied in two experiments. All participants were trained on a simple discrimination task, randomly assigned to one of two conditions (either with or without a distractor task), and then tested for the emergence of overselectivity (Experiment 1). In Experiment 2 responding controlled by the overselected stimulus elements was reduced by introducing a verbal punisher. In subsequent tests, control of behavior by the previously underselected elements from Experiment 1 was enhanced across the two younger age groups but not the oldest group of participants. The results are discussed in relation to the attention-deficit and overshadowing accounts of overselectivity.     

Stimulus fading and differential reinforcement for the treatment of needle phobia in a youth with autism

Stimulus fading in the form of gradually increased exposure to a fear-evoking stimulus, often combined with differential reinforcement, has been used to treat phobias in children who are otherwise normal and in children with autism. In this investigation, we applied stimulus fading plus differential reinforcement with an adolescent with autism and diabetes whose needle phobia had prevented medical monitoring of his blood glucose levels for over 2 years. Results showed that the treatment was successful in obtaining daily blood samples for measuring glucose levels.     

Reducing stimulus overselectivity in autistic children

It has been repeatedly reported that when presented with a discrimination task involving multiple cues, autistic children, as compared to normal children, tend to respond on the basis of only a restricted portion of the component cues. This phenomenon has been called stimulus overselectivity and has been implicated as a possible basis for some of the pronounced behavioral deficits characteristic of autism. Examination of the results of several previous studies suggests that the overselectivity effect might be reduced with repeated exposure to testing. However, since the previous studies were not designed to test this hypothesis, no conclusions were drawn regarding variables influencing the reduction of the overselectivity phenomenon. The present investigation was therefore conducted to determine if stimulus overselectivity in autistic children is changed as a function of repeated exposure to testing. Nineteen autistic children were trained on a discrimination task with a cue complex composed of two visual cues. After the children reached criterion on the task, they were exposed to a testing phase with probe trials where the cue components were presented singly. The results indicated that 16 of the children initially showed overselectivity and 3 responded to both cues. Of the 16 children who showed overselectivity, 13 decreased their level of overselectivity with continued testing. These results are discussed in relation to variables in the testing procedure itself and to the literature on selective attention.This research was funded by USPHS Research Grants MH11440, MH28210, and MH28231 from the National Institute of Mental Health. The authors wish to acknowledge the assistance of Cathy Hook, Hannelore Wilhelm, and Jon Killion in conducting this research.     

Stimulus intensity control and personality: A research note

Previous research has suggested that variations in augmenting-reducing, extraversion, and sensation seeking might be explained in terms of a common stimulus intensity control mechanism. However, empirical tests of this hypothesized relationship have produced equivocal findings. The present study attempts to clarify the issue by analyzing scores for extraversion, sensation seeking, and both cortical and questionnaire measures of augmenting-reducing obtained from the same sample of subjects. Apart from a significant positive correlation between the questionnaire index of reducing and sensation seeking, which have not previously been investigated, the results show no evidence of a systematic relationship among the variables.     

The generality of overselectivity in developmentally disabled children

A growing body of research suggests that low Mental Age (MA) autistic and retarded children show a unique stimulus control deficit, one that may cause many or most of their behavioral deficiencies. This problem, stimulus overselectivity, is evidenced when a child responds only to a restricted portion of the stimulus environment when compared with normal children. The purpose of this study was to assess whether this overselectivity is general across situations or whether it is restricted to certain stimulus/task conditions. Eight autistic children, who evidenced overselectivity on a preassessment task, and 8 normal children with similar MA levels participated. All children were trained on 3 tasks to determine if overselectivity varied as a function of different stimulus conditions. Each of the 3 tasks involved training a child to respond to (i.e., touch) a card containing a circle (S +) and to avoid a blank (S ?) card. In each case, the circle comprised a series of dots. The difference between the 3 circles (tasks) was the distance between the successive dots making up each circle. Also, in the minimal separation condition the dots were smaller in size and greater in number than in the larger separation conditions. Of concern was whether autistic children learned about the gestalt (i.e., the circle), which required attention to multiple cues, or whether children would overselect and respond to the dots. The results showed that (1) stimulus overselectivity was found not to be a generalized deficit in autistic subjects; instead, it varied as a function of the stimulus variables; and (2) the stimulus variables manipulated in this study similarly influenced the responding of both normal and autistic children. The implications of these data for a theory of overselectivity are discussed.     

Olfaction in autism spectrum disorders: A systematic review

Olfactory function is a well-known early biomarker for neurodegeneration and neural functioning in the adult population, being supported by a number of brain structures that could be dysfunctioning in neurodegenerative processes. Evidence has suggested that atypical sensory and, particularly, olfactory processing is present in several neurodevelopmental conditions, including autism spectrum disorders (ASDs). In this paper, we present data obtained by a systematic literature review, conducted according to PRISMA guidelines, regarding the possible association between olfaction and ASDs, and analyze them critically in order to evaluate the occurrence of olfactory impairment in ASDs, as well as the possible usefulness of olfactory evaluation in such conditions. The results obtained in this analysis suggested a possible involvement of olfactory impairment in ASDs, underlining the importance of olfactory evaluation in the clinical assessment of ASDs. This assessment could be potentially included as a complementary evaluation in the diagnostic protocol of the condition. Methods for study selection and inclusion criteria were specified in advance and documented in PROSPERO protocol #CRD42014013939.     

Joint attention and children with autism: a review of the literature

Preverbal communication and joint attention have long been of interest to researchers and practitioners. Both attending to social partners and sharing attentional focus between objects or events and others precede the onset of a child's first lexicon. In addition, these prelinguistic acts also appear to have important implications with regard to learning to socialize. The construct of joint attention has been noted as an early developing area prior to the transition to symbolic communication. Thus, the importance of joint attention in typically developing children, and the lack thereof in children with autism, has interested researchers for use in diagnosis and intervention for autism. That is, joint attention has been gaining momentum as an area that not only helps characterize children with autism, but also as a prognostic indicator and a potential intervention goal. In this paper, the status of the literature about initiation of joint attention by young typically developing children and young children with autism was examined. Empirical studies regarding joint attention behaviors, including eye gaze alternation, the use of protodeclaratives and protoimperatives, and studies that investigated joint attention as a predictor of language acquisition were reviewed. Possible areas for future research for children with autism are discussed.     

Precursors to a theory of mind in infancy: perspectives for research on autism

There is ample evidence for a conceptual deficit in normally developing 3-year-olds' and autistic children's understanding of the mind. Recent research using nonverbal tasks has challenged this view since even 15-month-old infants appear to base their action predictions on a representation of the agent's beliefs (Onishi & Baillargeon, 2005). Our own findings from looking-time experiments indicate, however, that 16-month-olds' action predictions depend on behavioural and situational cues, rather than on a person's access to information. Further research is reviewed that indicates that 14-month-olds understand what another person can and cannot see, and that 18-month-olds predict a person's action from what she previously saw, when supported by behavioural cues. These findings support a constructivist view of a gradual understanding of conditions for knowing during the second year. The relevance of such findings for research on autism is discussed.     

Current directions in research on autism

One of the most active areas of current research in the field of developmental disorders is autism. Since the NIH State of the Science conference, held in 1995 (Bristol et al. [1996] J. Autism Dev. Disorders 26:121-154), funding opportunities for comprehensive research programs addressing genetic, neurobiological, and behavioral aspects of this complex disorder have grown exponentially. Although we are far from having a complete understanding of the causes and deficits that define autism, significant progress has been made over the past few years. In this review, we summarize recent developments across a number of different areas of research in the field of autism, including diagnosis; defining the phenotypic features in individuals with autism; genetic bases; and neurobiological deficits.     

Visuo‐spatial abilities in autism: A review

Individuals with autism show various signs of heightened abilities in visuo‐spatial functioning. First, it is long‐established that they excel on embedded figures and block design tests relative to comparison participants. Second, some evidence suggests that processing global features is affected by inappropriate processing of the constituent elements of a stimulus. Third, they are more accurate than comparison participants in judging the shape of a slanted circle in a context in which ambient visual cues are eliminated. This suggests that their perception of the shape is less influenced by prior knowledge. Fourth, they are fast at searching for feature and conjunctive targets in a visual array. Contrary to earlier reports, however, they are susceptible to visual illusions. Also, they do show evidence of utilising prior knowledge when pairing a colour with an atypically coloured target. Accordingly, we conclude that there is something distinctive about autistic visuo‐spatial functioning, but not necessarily in ways that are predicted by the ‘weak central coherence’ hypothesis. Copyright © 2004 John Wiley & Sons, Ltd.     

Cognitive abilities and disabilities in infantile autism: A review

The literature on various aspects of learning and performance in autistic children is reviewed and interpreted as indicating very little that is specific to autism. Inadequate and inconsistent methodology precludes generalizations concerning the nature of the disorder. It is suggested that future research should be particularly concerned with controlling for developmental influences on performance, and with investigation of the higher functioning autistic children who are less governed by retardation factors. The current evidence is considered to support a hypothesis concerning abnormal hemisphere functioning in this group of children.     

Kleptomania: a review of the research.

Research on kleptomania is limited. Earlier views and recent reports of treatment are reviewed in this article. More study is needed to delineate this impulse-control disorder.     

Hardiness: a review of theory and research.

Although a large body of research on hardiness (a personality construct with dimensions of commitment, control, and challenge) has accumulated, several fundamental issues remain unresolved. Although there are several hardiness scales, the properties of these scales have not been compared. There is debate as to whether hardiness is one or several characteristics. Research studying the pathways through which hardiness exerts its effects has not been comprehensively evaluated. Whereas critics have argued that hardiness does not buffer stress, others have suggested that hardiness buffers for working adults, for males, and in prospective analyses. There is also growing concern that hardiness is related to neuroticism. A review of the literature supports the following conclusions: The Dispositional Resilience Scale (DRS) has several advantages over alternative scales; DRS items form three factors that are consistent with hardiness theory; hardiness dimensions generally show low to moderate intercorrelations; the most common way of categorizing subjects as high or low in hardiness is not consistent with hardiness theory; hardiness does not buffer stress, and it does not buffer stress for working adults, for males, or in prospective analyses; both old and new hardiness scales inadvertently measure neuroticism. Recommendations for future research are provided.