Neurobehavioral Processes Shaping Infant Development in the First 6 Postnatal Months and Emerging Differences in Autism Public
Ammar, Zeena (Summer 2023)
Abstract
The first 6 months of life mark a period of immense change in infants. At birth, infants demonstrate a host of reflexive and spontaneous behaviors that allow them to engage with and learn from the world around them. These behaviors not only encourage interactions with their environment, but also with their caregiver, whose responses facilitate later development. As infants age and learn from these interactions, they undergo a shift from these reflexive behaviors to more volitional behaviors as they become more alert and take part in contingent social interactions. Accompanying these behavioral shifts are significant changes in infant brain development. During the first two years of life, the structure of the infant brain is established with increasing gray and white matter volume, cortical thickness, surface area, and synaptogenesis. As the brain is undergoing these changes, it is particularly susceptible to disruptions in development possibly resulting in neurodevelopmental conditions such as autism. Despite the evidence highlighting these first 6 months as a dynamic and critical period of development, few have longitudinally studied this period of development to explore changes in the infant brain and behavior. Understanding development during these first 6 months is vital for understanding the processes underlying typical brain and behavioral development and can provide benchmarks from which to compare atypical trajectories. This thesis aims to fill this gap in early brain and behavior research by developing measures of entrainment during infant-caregiver interactions (Study 1), identifying differences in trajectories of motor development between neurotypical infants and infants later diagnosed with autism (Study 2), and mapping longitudinal developmental trajectories of white matter lateralization (Study 3).
Table of Contents
Table of Contents
INTRODUCTION
Mechanisms of Developmental Change in Early Infancy
Early Brain Development
Autism Spectrum Disorder
References
STUDY 1. Eyeblink Entrainment in Infant-Caregiver Dyads
Abstract
Introduction
Materials and Methods
Table 1.1: Demographics of Participant Sample
Figure 1.1: Infant-Caregiver Live Interaction Equipment Set-up.
Figure 1.2: DeepLabCut Eye Identification and Output.
Results
Figure 1.3: Infant and Caregiver Blink Rates.
Figure 1.4: Time-Locked Infant and Caregiver Eyeblinks During Dyadic Interaction.
Discussion
References
STUDY 2. Differences in Developmental Trajectories of Reflexive and Volitional Grasping in Neurotypical Infants and Infants Later Diagnosed with Autism
Abstract
Introduction
Materials and Methods
Table 2.1: Demographics of Participant Sample.
Figure 2.1 Sampling Distribution and Age of Testing of NT (A) and AUT (B) Infants.
Results
Figure 2.2: Developmental Trajectories and Raw Data of Reflexive Grasping in the First 6 Months of Life in NT (A) and AUT (B) Infants.
Figure 2.3: Developmental Trajectories of Volitional Grasping in NT and AUT and infants.
Table 2.2: Logistic Regression Model Output for Reflexive Grasping
Table 2.3: Logistic Regression Model Output for Volitional Grasping
Discussion
References
STUDY 3. Lateralization of major white matter tracts during infancy is time-varying and tract-specific
Abstract
Introduction
Figure 3.1: Lateralization in FA of Major White Matter Tracts Measured Across Infant Neuroimaging Studies.
Materials and Methods
Table 3.1: Demographics of Participant Sample.
Figure 3.2: Included Scans for All Infant Subjects.
Results
Figure 3.3: Patterns of Time-Varying, Constant, and No Lateralization in FA in Major White Matter Tracts.
Figure 3.4: Tracts with Time-Varying Lateralization Show Significant Change in Rate of Lateralization in FA.
Discussion
References
Supplemental Materials
Supplementary Figure 3.1: Defining Regions of Interest (ROIs) for Delineating Major White Matter Pathways in Infant Brains.
Supplementary Figure 3.2: Delineation of 9 Major White Matter Tracts.
Supplementary Figure 3.3: Trajectories of FA Lateralization in Major White Matter Structures by Infant Sex.
Supplementary Table 3.1: Difference in PC Scores for PC1 and PC2 Between Male and Female Infants.
Supplementary Figure 3.4: Lateralization of Axial Diffusion Measures in Tracts of Interest.
Supplemental Figure 3.5: Lateralization of Radial Diffusion Measures in Tracts of Interest.
Supplemental Figure 3.6: Lateralization of Trace Diffusion Measures in Tracts of Interest.
DISCUSSION
Summary of Research Findings
Implications & Future Directions
Conclusion
References
Acknowledgements
About this Dissertation
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