Spatial representations of touch in infancy and early childhood

The primary aim of this thesis was to examine how infants, and young children, represent touches in space (i.e. with respect to their external environment). Studying infants in the first year of life allows us to map the emergence of the complex processes needed in order to correctly locate touches to the body (and, by extension, the location of the limbs and body parts on which those touches impinge). In a series of seven experiments, I examined the development of the spatial representation of touch. To do this, I explored the development of an external reference frame in which touches are coded, the modulatory effect of changes in posture on the neural representation of a touch and the relationship between vision and touch when locating a stimulus from these sensory modalities in space. To investigate the development of an external reference frame for touch, I used a ‘crossed-hands’ task. This task has been used as a marker of the influence of an external frame of reference for localizing touch and is considered to arise out of conflict (when the hands are crossed) between the anatomical and external frames of reference within which touches can be perceived. Previous research with children had found that this reference frame does not develop until after 5.5-years; I extended this finding by determining that children as young as 4-years are able to locate touches in external co-ordinates. Additionally, in a further study, I found that an external reference frame develops between 4 and 6 months of age. The modulatory role of vision on tactile localization was also investigated. These studies showed that when 4-year-old children are provided with current vision of the hand being touched, this interfered with the benefits of using an external reference frame. However, this interference was limited to when the limbs were in canonical postures. As such, it seems that young children are still refining the ways in which sensory cues to the body help them to locate touches in the world. Considering that early visual experience was implicated in the development of an external frame of reference I also examined the development of an ability to perceive visual and tactile stimuli in a common spatial location. Here, it was found that 6-month-olds demonstrated this ability, with tentative findings suggesting that it may develop even earlier in life (e.g., at 4 months of age). As such, the ability to co-locate tactile and visual stimuli at 6 months is consistent with a role for visual experience in the development of an external frame of reference for touch at this age. Further to this, I examined interactions between vision and touch using a crossmodal cueing event-related potential (ERP) paradigm. In this study, it was found that at 7 months of age visual cues to the hand modulate processing of a subsequent tactile stimulus on that same hand. This provides further evidence of early acquired crossmodal links, but this was the first demonstration of crossmodal attentional cuing effects in infancy. Finally, in a set of two experiments, I investigated how infants (in the first year of life) were able to update the location of a felt touch across changes in arm posture, using an ERP measure. Although these studies demonstrated a null relationship between sensorimotor experience and somatosensory remapping, it was found that only those 8-month-old infants that displayed contralateral reaching behaviours were able to update to the location of a touch across a change in posture. As such, the relationship between sensorimotor experience and somatosensory remapping may not be simple, with other factors (such as brain maturation) also influencing this relationship

Sensitivity to Visual‐Tactile Colocation on the Body Prior to Skilled Reaching in Early Infancy

Two experiments examined perceptual colocation of visual and tactile stimuli in young infants. Experiment 1 compared 4‐ (n = 15) and 6‐month‐old (n = 12) infants’ visual preferences for visual‐tactile stimulus pairs presented across the same or different feet. The 4‐ and 6‐month‐olds showed, respectively, preferences for colocated and noncolocated conditions, demonstrating sensitivity to visual‐tactile colocation on their feet. This extends previous findings of visual‐tactile perceptual colocation on the hands in older infants. Control conditions excluded the possibility that both 6‐ (Experiment 1), and 4‐month‐olds (Experiment 2, n = 12) perceived colocation on the basis of an undifferentiated supramodal coding of spatial distance between stimuli. Bimodal perception of visual‐tactile colocation is available by 4 months of age, that is, prior to the development of skilled reaching

Early Motor Differences in Infants at Elevated Likelihood of Autism Spectrum Disorder and/or Attention Deficit Hyperactivity Disorder

Abstract: We investigated infant’s manual motor behaviour; specifically behaviours crossing the body midline. Infants at elevated likelihood of Autism Spectrum Disorder (ASD) and/or Attention Deficit Hyperactivity Disorder (ADHD) produced fewer manual behaviours that cross the midline compared to infants with a typical likelihood of developing these disorders; however this effect was limited to 10-month-olds and not apparent at age 5 and 14 months. Although, midline crossing did not predict ASD traits, it was related to ADHD traits at 2 years of age. We rule out motor ability and hand dominance as possible explanations for this pattern of behaviour, positing that these results may be a consequence of multisensory integration abilities, and the neurobehavioural shift period, in the first year of life

Early Motor Differences in Infants at Elevated Likelihood of Autism Spectrum Disorder and/or Attention Deficit Hyperactivity Disorder.

We investigated infant's manual motor behaviour; specifically behaviours crossing the body midline. Infants at elevated likelihood of Autism Spectrum Disorder (ASD) and/or Attention Deficit Hyperactivity Disorder (ADHD) produced fewer manual behaviours that cross the midline compared to infants with a typical likelihood of developing these disorders; however this effect was limited to 10-month-olds and not apparent at age 5 and 14 months. Although, midline crossing did not predict ASD traits, it was related to ADHD traits at 2 years of age. We rule out motor ability and hand dominance as possible explanations for this pattern of behaviour, positing that these results may be a consequence of multisensory integration abilities, and the neurobehavioural shift period, in the first year of life

Early differences in auditory processing relate to Autism Spectrum Disorder traits in infants with Neurofibromatosis Type I.

BackgroundSensory modulation difficulties are common in children with conditions such as Autism Spectrum Disorder (ASD) and could contribute to other social and non-social symptoms. Positing a causal role for sensory processing differences requires observing atypical sensory reactivity prior to the emergence of other symptoms, which can be achieved through prospective studies.MethodsIn this longitudinal study, we examined auditory repetition suppression and change detection at 5 and 10 months in infants with and without Neurofibromatosis Type 1 (NF1), a condition associated with higher likelihood of developing ASD.ResultsIn typically developing infants, suppression to vowel repetition and enhanced responses to vowel/pitch change decreased with age over posterior regions, becoming more frontally specific; age-related change was diminished in the NF1 group. Whilst both groups detected changes in vowel and pitch, the NF1 group were largely slower to show a differentiated neural response. Auditory responses did not relate to later language, but were related to later ASD traits.ConclusionsThese findings represent the first demonstration of atypical brain responses to sounds in infants with NF1 and suggest they may relate to the likelihood of later ASD

Behavioural Measures of Infant Activity but Not Attention Associate with Later Preschool ADHD Traits.

Mapping infant neurocognitive differences that precede later ADHD-related behaviours is critical for designing early interventions. In this study, we investigated (1) group differences in a battery of measures assessing aspects of attention and activity level in infants with and without a family history of ADHD or related conditions (ASD), and (2) longitudinal associations between the infant measures and preschool ADHD traits at 3 years. Participants (N = 151) were infants with or without an elevated likelihood for ADHD (due to a family history of ADHD and/or ASD). A multi-method assessment protocol was used to assess infant attention and activity level at 10 months of age that included behavioural, cognitive, physiological and neural measures. Preschool ADHD traits were measured at 3 years of age using the Child Behaviour Checklist (CBCL) and the Child Behaviour Questionnaire (CBQ). Across a broad range of measures, we found no significant group differences in attention or activity level at 10 months between infants with and without a family history of ADHD or ASD. However, parent and observer ratings of infant activity level at 10 months were positively associated with later preschool ADHD traits at 3 years. Observable behavioural differences in activity level (but not attention) may be apparent from infancy in children who later develop elevated preschool ADHD traits

Increased cortical reactivity to repeated tones at 8 months in infants with later ASD.

Dysregulation of cortical excitation/inhibition (E/I) has been proposed as a neuropathological mechanism underlying core symptoms of autism spectrum disorder (ASD). Determining whether dysregulated E/I could contribute to the emergence of behavioural symptoms of ASD requires evidence from human infants prior to diagnosis. In this prospective longitudinal study, we examine differences in neural responses to auditory repetition in infants later diagnosed with ASD. Eight-month-old infants with (high-risk: n = 116) and without (low-risk: n = 27) an older sibling with ASD were tested in a non-linguistic auditory oddball paradigm. Relative to high-risk infants with typical development (n = 44), infants with later ASD (n = 14) showed reduced repetition suppression of 40-60 Hz evoked gamma and significantly greater 10-20 Hz inter-trial coherence (ITC) for repeated tones. Reduced repetition suppression of cortical gamma and increased phase-locking to repeated tones are consistent with cortical hyper-reactivity, which could in turn reflect disturbed E/I balance. Across the whole high-risk sample, a combined index of cortical reactivity (cortical gamma amplitude and ITC) was dimensionally associated with reduced growth in language skills between 8 months and 3 years, as well as elevated levels of parent-rated social communication symptoms at 3 years. Our data show that cortical 'hyper-reactivity' may precede the onset of behavioural traits of ASD in development, potentially affecting experience-dependent specialisation of the developing brain

Altered theta-beta ratio in infancy associates with family history of ADHD and later ADHD-relevant temperamental traits.

Funder: European Federation of Pharmaceutical Industries and Associations; Id: http://dx.doi.org/10.13039/100013322Funder: Autistica; Id: http://dx.doi.org/10.13039/100011706Funder: Simons Foundation Autism Research Initiative; Id: http://dx.doi.org/10.13039/100014370Funder: Autism Speaks; Id: http://dx.doi.org/10.13039/100000073BACKGROUND: Uncovering the neural mechanisms that underlie symptoms of attention deficit hyperactivity disorder (ADHD) requires studying brain development prior to the emergence of behavioural difficulties. One new approach to this is prospective studies of infants with an elevated likelihood of developing ADHD. METHODS: We used a prospective design to examine an oscillatory electroencephalography profile that has been widely studied in both children and adults with ADHD - the balance between lower and higher frequencies operationalised as the theta-beta ratio (TBR). In the present study, we examined TBR in 136 10-month-old infants (72 male and 64 female) with/without an elevated likelihood of developing ADHD and/or a comparison disorder (Autism Spectrum Disorder; ASD). RESULTS: Infants with a first-degree relative with ADHD demonstrated lower TBR than infants without a first-degree relative with ADHD. Further, lower TBR at 10 months was positively associated with temperament dimensions conceptually related to ADHD at 2 years. TBR was not altered in infants with a family history of ASD. CONCLUSIONS: This is the first demonstration that alterations in TBR are present prior to behavioural symptoms of ADHD. However, these alterations manifest differently than those sometimes observed in older children with an ADHD diagnosis. Importantly, altered TBR was not seen in infants at elevated likelihood of developing ASD, suggesting a degree of specificity to ADHD. Taken together, these findings demonstrate that there are brain changes associated with a family history of ADHD observable in the first year of life

Look duration at the face as a developmental endophenotype: elucidating pathways to autism and ADHD.

Identifying developmental endophenotypes on the pathway between genetics and behavior is critical to uncovering the mechanisms underlying neurodevelopmental conditions. In this proof-of-principle study, we explored whether early disruptions in visual attention are a unique or shared candidate endophenotype of autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). We calculated the duration of the longest look (i.e., peak look) to faces in an array-based eye-tracking task for 335 14-month-old infants with and without first-degree relatives with ASD and/or ADHD. We leveraged parent-report and genotype data available for a proportion of these infants to evaluate the relation of looking behavior to familial (n = 285) and genetic liability (using polygenic scores, n = 185) as well as ASD and ADHD-relevant temperament traits at 2 years of age (shyness and inhibitory control, respectively, n = 272) and ASD and ADHD clinical traits at 6 years of age (n = 94).Results showed that longer peak looks at the face were associated with elevated polygenic scores for ADHD (β = 0.078, p = .023), but not ASD (β = 0.002, p = .944), and with elevated ADHD traits in mid-childhood (F(1,88) = 6.401, p = .013, $\eta _p^2$=0.068; ASD: F (1,88) = 3.218, p = .076), but not in toddlerhood (ps > 0.2). This pattern of results did not emerge when considering mean peak look duration across face and nonface stimuli. Thus, alterations in attention to faces during spontaneous visual exploration may be more consistent with a developmental endophenotype of ADHD than ASD. Our work shows that dissecting paths to neurodevelopmental conditions requires longitudinal data incorporating polygenic contribution, early neurocognitive function, and clinical phenotypic variation