Cardiovascular and electrodermal responses to simple stimuli in autistic, retarded and normal children

Sensory Gating in Neurodevelopmental Disorders: A Scoping Review

This review aimed to explore the current understanding of sensory gating in neurodevelopmental disorders as a possible transdiagnostic mechanism. We applied methods according to the Joanna Briggs Institute Manual for Evidence Synthesis, following the population, concept, and context scoping review eligibility criteria. Using a comprehensive search strategy in five relevant research databases (Medline, EMBASE, CINAHL, PsychInfo, and Scopus), we searched for relevant peer-reviewed, primary research articles and unpublished data. Two independent reviewers screened the titles and abstracts, full-texts, and completed data extraction. We identified a total of 81 relevant articles and used descriptive analyses to summarize the characteristics and outcomes of all identified studies. Literature regarding sensory gating was most common in autistic populations with relatively fewer studies examining attention-deficit/hyperactivity disorder, tic disorders, and childhood-onset fluency disorder (COFD). The methods to assess sensory gating varied widely both within and between groups and included measures such as habituation, prepulse inhibition, affect-modulated inhibition, medication and other intervention trials. Most consistently, when participants complete questionnaires about their sensory experiences, those who have neurodevelopmental disorders report differences in their sensory gating. Affect-modulated inhibition appears to be discrepant between samples with and without neurodevelopmental disorder diagnoses. Habituation was the most commonly reported phenomenon and many differences in habituation have been found in autistic individuals and individuals with tic disorders whereas concerns with inhibition seemed more common in COFD. Overall, the evidence is inconsistent within and between disorders suggesting there is still much to learn about sensory gating in neurodevelopmental disorders.

A working taxonomy for describing the sensory differences of autism

BACKGROUND

Individuals on the autism spectrum have been long described to process sensory information differently than neurotypical individuals. While much effort has been leveraged towards characterizing and investigating the neurobiology underlying the sensory differences of autism, there has been a notable lack of consistency in the terms being used to describe the nature of those differences.

MAIN BODY

We argue that inconsistent and interchangeable terminology-use when describing the sensory differences of autism has become problematic beyond mere pedantry and inconvenience. We begin by highlighting popular terms that are currently being used to describe the sensory differences of autism (e.g. "sensitivity", "reactivity" and "responsivity") and discuss why poor nomenclature may hamper efforts towards understanding the aetiology of sensory differences in autism. We then provide a solution to poor terminology-use by proposing a hierarchical taxonomy for describing and referring to various sensory features.

CONCLUSION

Inconsistent terminology-use when describing the sensory features of autism has stifled discussion and scientific understanding of the sensory differences of autism. The hierarchical taxonomy proposed was developed to help resolve lack of clarity when discussing the sensory differences of autism and to place future research targets at appropriate levels of analysis.

Autonomic and Electrophysiological Evidence for Reduced Auditory Habituation in Autism

It is estimated that nearly 90% of children on the autism spectrum exhibit sensory atypicalities. What aspects of sensory processing are affected in autism? Although sensory processing can be studied along multiple dimensions, two of the most basic ones involve examining instantaneous sensory responses and how the responses change over time. These correspond to the dimensions of 'sensitivity' and 'habituation'. Results thus far have indicated that autistic individuals do not differ systematically from controls in sensory acuity/sensitivity. However, data from studies of habituation have been equivocal. We have studied habituation in autism using two measures: galvanic skin response (GSR) and magneto-encephalography (MEG). We report data from two independent studies. The first study, was conducted with 13 autistic and 13 age-matched neurotypical young adults and used GSR to assess response to an extended metronomic sequence. The second study involved 24 participants (12 with an ASD diagnosis), different from those in study 1, spanning the pre-adolescent to young adult age range, and used MEG. Both studies reveal consistent patterns of reduced habituation in autistic participants. These results suggest that autism, through mechanisms that are yet to be elucidated, compromises a fundamental aspect of sensory processing, at least in the auditory domain. We discuss the implications for understanding sensory hypersensitivities, a hallmark phenotypic feature of autism, recently proposed theoretical accounts, and potential relevance for early detection of risk for autism.

Stop Making Noise! Auditory Sensitivity in Adults with an Autism Spectrum Disorder Diagnosis: Physiological Habituation and Subjective Detection Thresholds

Auditory sensitivities are common among people with autism spectrum disorder diagnoses (ASD). As underlying factors are unknown, we examined whether ASD adults (NASD = 33; NTypically Developing = 31; 25-45 years; IQ > 70): (1) habituated slower to auditory stimuli; (2) had lower auditory detection thresholds; and (3) whether these mechanisms related to self-reported auditory sensitivities. Two auditory stimuli (tone, siren) were repeated, whilst skin conductance responses were recorded to measure habituation. Detection thresholds were measured by stepwise reductions in tone volume. We found no evidence in favor of our hypotheses, but ASD adults did rate the auditory stimuli as more arousing. Based on explorative analyses, we argue that studying the strength of physiological responses to auditory stimuli is needed to understand auditory sensitivities.

A systematic review of physiological reactivity to stimuli in autism

OBJECTIVE

The prevalence of abnormal behavioural responses to a variety of stimuli among individuals with autism has led researchers to examine whether physiological reactivity (PR) is typical in this population. This article reviewed studies assessing PR to sensory, social and emotional, and stressor stimuli in individuals with autism.

METHODS

Systematic searches of electronic databases identified 57 studies that met our inclusion criteria. Studies were analysed to determine: (a) participant characteristics; (b) physiological measures used; (c) PR to sensory, social and emotional or stressor stimuli; (d) the relation between PR and behavioural or psychological variables and (e) baseline physiological activity. A novel measure of methodological quality suitable for use with non-randomized, non-interventional, psychophysiological studies was also developed and applied.

RESULTS

Individuals with autism were found to respond differently than typically developing controls in 78.6%, 66.7% and 71.4% of sensory, social and emotional, and stressor stimulus classes, respectively. However, this extant literature is characterized by variable and inconsistent findings, which do not appear to be accounted for by varying methodological quality, making it difficult to determine what specific factors differentiate individuals with autism who present with atypical PR from those who do not.

CONCLUSIONS

Despite this uncertainty, individual differences in PR are clearly present in autism, suggesting additional research is needed to determine the variables relating to PR among those with ASD and to examine the possible existence of physiological subtype responders in the population.

Physiological responses to social and nonsocial stimuli in neurotypical adults with high and low levels of autistic traits: implications for understanding nonsocial drive in autism spectrum disorders

Researchers have suggested that the two primary cognitive features of autism spectrum disorder (ASD), a drive toward nonsocial processing and a reduced drive toward social processing, may be unrelated to each other in the neurotypical (NT) population and may therefore require separate explanations. Drive toward types of processing may be related to physiological arousal to categories of stimuli, such as social (e.g., faces) or nonsocial (e.g., trains). This study investigated how autistic traits in an NT population might relate to differences in physiological responses to nonsocial compared with social stimuli. NT participants were recruited to examine these differences in those with high vs. low degrees of ASD traits. Forty-six participants (21 male, 25 female) completed the Autism Spectrum Quotient (AQ) to measure ASD traits before viewing a series of 24 images while skin conductance response (SCR) was recorded. Images included six nonsocial, six social, six face-like cartoons, and six nonsocial (relating to participants' personal interests). Analysis revealed that those with a higher AQ had significantly greater SCR arousal to nonsocial stimuli than those with a low AQ, and the higher the AQ, the greater the difference between SCR arousal to nonsocial and social stimuli. This is the first study to identify the relationship between AQ and physiological response to nonsocial stimuli, and a relationship between physiological response to both social and nonsocial stimuli, suggesting that physiological response may underlie the atypical drive toward nonsocial processing seen in ASD, and that at the physiological level at least the social and nonsocial in ASD may be related to one another.

Neuro-immune abnormalities in autism and their relationship with the environment: a variable insult model for autism

Autism spectrum disorder (ASD) is a heterogeneous condition affecting an individual's ability to communicate and socialize and often presents with repetitive movements or behaviors. It tends to be severe with less than 10% achieving independent living with a marked variation in the progression of the condition. To date, the literature supports a multifactorial model with the largest, most detailed twin study demonstrating strong environmental contribution to the development of the condition. Here, we present a brief review of the neurological, immunological, and autonomic abnormalities in ASD focusing on the causative roles of environmental agents and abnormal gut microbiota. We present a working hypothesis attempting to bring together the influence of environment on the abnormal neurological, immunological, and neuroimmunological functions and we explain in brief how such pathophysiology can lead to, and/or exacerbate ASD symptomatology. At present, there is a lack of consistent findings relating to the neurobiology of autism. Whilst we postulate such variable findings may reflect the marked heterogeneity in clinical presentation and as such the variable findings may be of pathophysiological relevance, more research into the neurobiology of autism is necessary before establishing a working hypothesis. Both the literature review and hypothesis presented here explore possible neurobiological explanations with an emphasis of environmental etiologies and are presented with this bias.

The Interplay between Emotion and Cognition in Autism Spectrum Disorder: Implications for Developmental Theory

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that is clinically defined by abnormalities in reciprocal social and communicative behaviors and an inflexible adherence to routinised patterns of thought and behavior. Laboratory studies repeatedly demonstrate that autistic individuals experience difficulties in recognizing and understanding the emotional expressions of others and naturalistic observations show that they use such expressions infrequently and inappropriately to regulate social exchanges. Dominant theories attribute this facet of the ASD phenotype to abnormalities in a social brain network that mediates social-motivational and social-cognitive processes such as face processing, mental state understanding, and empathy. Such theories imply that only emotion related processes relevant to social cognition are compromised in ASD but accumulating evidence suggests that the disorder may be characterized by more widespread anomalies in the domain of emotions. In this review I summarize the relevant literature and argue that the social-emotional characteristics of ASD may be better understood in terms of a disruption in the domain-general interplay between emotion and cognition. More specifically I will suggest that ASD is the developmental consequence of early emerging anomalies in how emotional responses to the environment modulate a wide range of cognitive processes including those that are relevant to navigating the social world.

The intense world theory - a unifying theory of the neurobiology of autism

Autism covers a wide spectrum of disorders for which there are many views, hypotheses and theories. Here we propose a unifying theory of autism, the Intense World Theory. The proposed neuropathology is hyper-functioning of local neural microcircuits, best characterized by hyper-reactivity and hyper-plasticity. Such hyper-functional microcircuits are speculated to become autonomous and memory trapped leading to the core cognitive consequences of hyper-perception, hyper-attention, hyper-memory and hyper-emotionality. The theory is centered on the neocortex and the amygdala, but could potentially be applied to all brain regions. The severity on each axis depends on the severity of the molecular syndrome expressed in different brain regions, which could uniquely shape the repertoire of symptoms of an autistic child. The progression of the disorder is proposed to be driven by overly strong reactions to experiences that drive the brain to a hyper-preference and overly selective state, which becomes more extreme with each new experience and may be particularly accelerated by emotionally charged experiences and trauma. This may lead to obsessively detailed information processing of fragments of the world and an involuntarily and systematic decoupling of the autist from what becomes a painfully intense world. The autistic is proposed to become trapped in a limited, but highly secure internal world with minimal extremes and surprises. We present the key studies that support this theory of autism, show how this theory can better explain past findings, and how it could resolve apparently conflicting data and interpretations. The theory also makes further predictions from the molecular to the behavioral levels, provides a treatment strategy and presents its own falsifying hypothesis.

Physiological and behavioral differences in sensory processing: a comparison of children with autism spectrum disorder and sensory modulation disorder

A high incidence of sensory processing difficulties exists in children with Autism Spectrum Disorder (ASD) and children with Sensory Modulation Disorder (SMD). This is the first study to directly compare and contrast these clinical disorders. Sympathetic nervous system markers of arousal and reactivity were utilized in a laboratory paradigm that administered a series of sensory challenges across five sensory domains. The Short Sensory Profile, a standardized parent-report measure, provided a measure of sensory-related behaviors. Physiological arousal and sensory reactivity were lower in children with ASD whereas reactivity after each sensory stimulus was higher in SMD, particularly to the first stimulus in each sensory domain. Both clinical groups had significantly more sensory-related behaviors than typically developing children, with contrasting profiles. The ASD group had more taste/smell sensitivity and sensory under-responsivity while the SMD group had more atypical sensory seeking behavior. This study provides preliminary evidence distinguishing sympathetic nervous system functions and sensory-related behaviors in Autism Spectrum Disorder and Sensory Modulation Disorder. Differentiating the physiology and sensory symptoms in clinical groups is essential to the provision of appropriate interventions.

Anxiety disorders in persons with developmental disabilities: empirically informed diagnosis and treatment. Reviews literature on anxiety disorders in DD population with practical take-home messages for the clinician

Anxiety disorders are common in individuals with developmental disabilities (DDs), although they may not be diagnosed and treated as often as they are in patients without DDs. Patients with mental retardation, autism, and other pervasive developmental disorders may exhibit comorbid anxiety disorders, such as generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), phobias, and other anxiety symptoms at much higher rates than in the general population, but identification of these comorbid anxiety disorders may be made more difficult by the presence of the DD and concurrent difficulties with communication, other behavior problems, the lack of standardized assessments specific to diagnosing patients with DDs and psychiatric comorbidities, and the need for greater collateral sources of assessment information. In addition, systematic study of the treatment of anxiety in patients with DD is limited to a relatively small number of empirical studies done specifically in these patients along with case reports and theoretical reviews on the extension and modification of more well-studied treatments used for anxiety in patients without DDs. The present article reviews the literature on the prevalence, features, assessment and diagnosis of anxiety disorders in individuals with DDs, and also reviews empirical studies of pharmacological and psychological treatment of patients with comorbid anxiety and DD and summarizes the findings. Recommendations are made to guide treatment and further research in this area.

Age and novelty: Event-related brain potentials and autonomic activity

Our aim was to study age-related differences in the habituation of orienting reaction by using novel visual stimuli. We intended to fill a gap in habituation research by recording both autonomic and ERP components of orienting to visual stimuli in the same sample and in highly related paradigms. We report data showing that in young subjects repetition of visual novels yielded fast habituation of both skin conductance responses and ERP components (P3(novel), N2b) whereas elderly people displayed no sign of habituation. However, cardiac deceleration--thought conventionally to be part of the orienting reaction--did not habituate in either group. Overall, most of our results harmonize with those obtained by using auditory stimuli; therefore we conclude that there is no significant modality specificity in age-related deterioration of habituation processes.

Skin Conductance Responses to Another Person’s Gaze in Children with Autism

The effects of another person's gaze on physiological arousal were investigated by measuring skin conductance responses (SCR). Twelve able children with autism and 12 control children were shown face stimuli with straight gaze (eye contact) or averted gaze on a computer monitor. In children with autism, the responses to straight gaze were stronger than responses to averted gaze, whereas there was no difference in the responses to these gaze conditions in normally developing children. Thus, these results showed that eye gaze elicited differential pattern of SCR in normally developing children and in children with autism. It is possible that the enhanced arousal to eye contact may contribute to the abnormal gaze behaviour frequently reported in the context of autism.

Arousal and Activation in a Continuous Performance Task

Abstract: The concepts of arousal and activation have had a confused history in Psychophysiology, and there is no widely accepted consensus on their usefulness in the field. This study aimed to explore whether these concepts could be separated in terms of their effects on the phasic Orienting Response (OR) and behavioral performance. We defined arousal at a particular time to be the energetic state at that time, reflected in electrodermal activity and measured by skin conductance level. Task-related activation was defined as the change in arousal from a resting baseline to the task situation. A continuous performance task was used with normal children. The magnitude of the mean phasic OR elicited by target stimuli was dependent on arousal, but not on task-related activation. Two performance measures (mean reaction time and number of errors) improved with increasing activation, but not with arousal. These data suggest the value of conceptualizing arousal and activation as separable aspects of the energetics of physiological and behavioral responding in future studies of attention, cognition, and emotion.

Efficacy of sensory and motor interventions for children with autism

Idiosyncratic responses to sensory stimuli and unusual motor patterns have been reported clinically in young children with autism. The etiology of these behavioral features is the subject of much speculation. Myriad sensory- and motor-based interventions have evolved for use with children with autism to address such issues; however, much controversy exists about the efficacy of such therapies. This review paper summarizes the sensory and motor difficulties often manifested in autism, and evaluates the scientific basis of various sensory and motor interventions used with this population. Implications for education and further research are described.

Physiological and cognitive correlates of child abuse

OBJECTIVE

To compare the physiological responses of abused children to different stimuli with responses of children in a reference group and to correlate the physiological responses with intellectual and personality functioning.

METHOD

Abused children were compared with a reference group on two batteries of tests that were administered on separate days. In one session, children were shown slides with emotional or cognitive content while heart rate, pulse height, skin conductance, electromyography, and skin temperature were measured. In the other session, intellectual and personality functioning was measured using the WISC-R, Quick Neurological Screening Test, and the Junior Eysenck personality inventory.

RESULTS

Abused children had smaller changes in pulse height in the first two stimulus conditions presented ("No Signal" and "Math"), but their electrodermal responses were lower throughout all stimulus conditions. Abused children also had higher introversion and lower Verbal and Full Scale IQ scores. Verbal and Full Scale IQ scores were inversely related to the severity of abuse that had been experienced. When these variables were used in a discriminant function analysis, children were assigned to the correct group 86% of the time.

CONCLUSION

These findings support a model that describes the effects of abuse as delaying cognitive development and inhibiting physiological responsiveness to the environment.

Unimodal and crossmodal reactivity in autism: presence of auditory evoked responses and effect of the repetition of auditory stimuli

Using auditory evoked responses, this work compares the reactivities to unimodal and crossmodal stimuli and the main neurocognitive functions most often disturbed in autism. With the aim of testing the hypothesis that the deficit in the ability to form crossmodal associations in autism is linked to a cognitive abnormality, auditory evoked responses to simple and to crossmodal (auditivo-visual) stimuli were recorded in 30 autistic children and compared with those of 30 normal and 30 mentally retarded children. Relationships between electrophysiological reactivity and neurocognitive functions showed that the cognitive deficit in the ability to maintain crossmodal associations is preceded by a more elementary perceptive abnormality in autistic children.

Abnormal electrodermal reactivity to novel visual stimuli in autistic children

Skin conductance responses and eye-fixation behavior to visual stimuli were measured in high-functioning autistic children, normal children, children with externalizing disorders, and children with internalizing disorders. Novelty, complexity, and subjective significance of the stimuli were manipulated. Autistic children were electrodermally hyporesponsive to novel stimuli. In all groups, manipulation of stimulus complexity only influenced fixation time. Manipulation of subjective significance influenced fixation time as well as skin conductance response in all groups. In the autistic group, adding subjective significance to a stimulus changed electrodermal nonresponders into responders, indicating that nonresponsiveness or hyporesponsiveness in autistic children does not imply a loss of (novel) stimulus detection, filtering, or orientation reaction capability, per se.

Applied orienting response research: some examples

The development of orienting response (OR) theory has not been accompanied by many applications of the concept--most research still appears to be lab-based and "pure," rather than "applied." We present some examples from our own work in which the OR perspective has been applied in a wider context. These cover the exploration of processing deficits in autistic children, aspects of the "repression" of anxiety in elite athletes, and the locus of alcohol effects. Such applications of the OR concept in real-life situations seem a logical and, indeed, necessary step in the evolution of this area of psychophysiology.

Coding of stimulus parameters in autistic, retarded, and normal children: evidence for a two-factor theory of autism

Phasic changes in respiratory period, electrodermal activity, and the vasoconstrictive peripheral pulse amplitude response, were examined in matched groups of autistic, retarded, and normal children using repeated presentation of simple visual and auditory stimuli of differing magnitudes. Analysis of response magnitudes as a function of group membership, trials, stimulus magnitude, and age, indicated both similarities and differences between the autistic and control groups. The autistic group differed from the control groups in its failure to show response habituation to repeatedly presented stimuli. However, data indicated that autistic children coded stimulus magnitude similarly to controls, suggesting that the failure to adequately process stimulus novelty does not reflect a general processing failure. Autistic children also exhibited relative hyperreactivity in all measures. Age effects showed this to be interpretable as reflecting developmental delay. These two differences support a recent two-factor theory of autism.

A comparison of phasic cardiac responses derived from the electrocardiogram and the peripheral pulse

In recent years, psychophysiologists have increasingly used the peripheral pulse as a more convenient source of cardiac information than the electrocardiogram. We explored some of the measurement problems associated with this choice by comparing estimates, produced by both data sources, of the cardiac response evoked by innocuous visual stimuli. The most important difference is that pulse transit time results in the immediately-prestimulus beat of a significant proportion of pulse-derived responses being mislabelled as the following beat, shifting the entire apparent response by one beat. This reduces correlations between the data streams, and has implications for the adequate measurement of evoked cardiac responses.