What’s Going on in There?

What’s Going on in There? Plot Summary

Introduction

Imagine holding a newborn baby and realizing that within that tiny head lies an organ containing 100 billion neurons, each capable of forming up to 10,000 connections with other cells. This incredible structure—the human brain—begins as a simple tube of cells and transforms into the most complex object in the known universe. Yet unlike most organs that come fully formed, the brain develops through a remarkable partnership between genetic instructions and environmental experiences. This dance between nature and nurture shapes not just what we know, but who we become. The science of early brain development has revolutionized our understanding of human potential. We now know that everyday experiences—from the nutrients a fetus receives to the words a toddler hears to the emotional climate of a preschooler's home—literally shape the physical architecture of the developing brain. These early influences establish neural patterns that can last a lifetime, affecting everything from intelligence and emotional regulation to social skills and stress responses. Throughout this book, we'll explore how critical periods in brain development create windows of opportunity, how sensory experiences build the foundation for complex thinking, and how relationships provide the secure base from which young minds can flourish.

Chapter 1: The Dance of Nature and Nurture in Brain Development

The human brain begins its remarkable journey as a simple tube of cells in the embryo. By birth, it contains nearly all the neurons it will ever have—about 100 billion—but these cells have formed only a fraction of their eventual connections. What happens next is one of nature's most extraordinary feats: the brain essentially wires itself through the interplay of genetic instructions and environmental experiences. Genes provide the basic blueprint for brain architecture, guiding neurons to their approximate destinations and establishing the general timeline of development. Different brain regions mature according to genetic timetables, with sensory and motor areas developing earlier than regions responsible for complex thinking and emotional regulation. This sequence reflects evolutionary priorities—a newborn needs to see, hear, and move before needing to solve abstract problems. However, genes alone cannot specify the trillions of precise connections that make each brain unique. This is where experience enters the picture. The developing brain produces an abundance of neural connections—far more than will ultimately survive. During early childhood, these connections undergo a process of competitive selection, where those that are frequently activated through experience are strengthened and preserved, while those that remain inactive are eliminated or "pruned." This "use it or lose it" principle means that the experiences a child has literally shape their brain's physical structure. When a baby sees faces, hears language, feels touch, or experiences any sensory input, specific neural pathways activate and strengthen, becoming more efficient with repeated use. The timing of this experience-dependent development varies across different brain systems, creating what neuroscientists call "critical periods"—specific windows when particular neural circuits are especially receptive to environmental influence. For instance, visual circuits are most malleable during the first year of life, while language circuits remain highly plastic until around age seven. These critical periods explain why certain skills, like learning a second language, are easier to master in childhood than in adulthood. Once these windows close, the brain becomes less malleable, though some degree of plasticity remains throughout life. Understanding this dance between nature and nurture has profound implications for parenting, education, and social policy. It suggests that while we cannot change a child's genetic makeup, we can significantly influence how those genes are expressed by providing experiences that support optimal brain development. The remarkable plasticity of the young brain offers both opportunity and responsibility—opportunity to positively shape development, and responsibility to provide the experiences that allow each child's genetic potential to be fully realized.

Chapter 2: Touch and Motion: Foundational Sensory Experiences

Touch is the first sense to develop in the womb, emerging as early as eight weeks after conception. Long before a baby can see clearly or understand language, they experience the world through tactile sensations. This early development makes touch a foundational sense that profoundly influences brain architecture and sets the stage for cognitive and emotional growth. The skin, our largest organ, contains millions of touch receptors that send signals through the spinal cord to the brain's somatosensory cortex. When a baby feels gentle stroking, firm pressure, or temperature changes, these sensations activate specific neural pathways. With repeated activation, these pathways strengthen, creating more efficient processing networks. Research with premature infants has shown that regular, gentle touch stimulation leads to better weight gain, improved immune function, more mature sleep patterns, and higher scores on developmental tests. These benefits occur partly because touch reduces stress hormones like cortisol while increasing growth hormones and oxytocin, the "bonding hormone" that promotes feelings of trust and attachment. Motion experiences similarly shape the developing brain through the vestibular system—the sensory network responsible for balance and spatial orientation. Located in the inner ear, this system begins functioning around the fifth month of pregnancy, making it one of the most mature sensory systems at birth. When babies are rocked, bounced, or carried, their vestibular systems receive stimulation that strengthens neural connections involved in balance, coordination, and even visual tracking. This explains why infants universally respond positively to rhythmic movement—it provides essential neural stimulation that helps organize their developing brains. The importance of touch and motion becomes starkly evident in cases of severe deprivation. Studies of children raised in understaffed orphanages, where physical contact was minimal and movement restricted, revealed profound developmental delays across multiple domains. Many of these children showed stunted growth, compromised immune systems, and significant cognitive and emotional problems. Remarkably, when these same children were placed in nurturing environments with regular physical contact and freedom of movement, many of their developmental trajectories improved, highlighting the brain's plasticity in response to sensory experiences. For parents and caregivers, this research underscores the value of skin-to-skin contact, infant massage, and physical play. These aren't just pleasant interactions—they're building the neural foundations for emotional regulation, stress management, and cognitive development. In our increasingly digital world, where screen time often replaces physical interaction, ensuring children receive adequate tactile and vestibular stimulation becomes even more essential for healthy brain development.

Chapter 3: Critical Periods: Windows of Opportunity

Throughout childhood, the brain undergoes a series of remarkable transformations, with different neural circuits developing and refining at different times. These time-sensitive windows of development are known as "critical periods"—specific intervals when particular brain systems are especially receptive to environmental input and vulnerable to disruption. Understanding these critical periods provides crucial insights for optimizing development and addressing potential problems. Critical periods exist because brain development follows a "use it or lose it" principle. During these windows, the brain overproduces synapses—the connections between neurons—creating a dense network of potential pathways. The synapses that receive stimulation are strengthened and preserved, while those that remain inactive are eliminated. This process, called synaptic pruning, is how experience literally shapes the physical architecture of the brain, optimizing neural circuits for the specific environment in which a child is growing up. Different brain systems have different critical periods, reflecting their evolutionary importance and developmental complexity. Sensory systems mature first, with vision, hearing, and touch undergoing their most intensive development during the first year of life. Language circuits remain highly plastic until around age seven, explaining why young children can learn multiple languages with native-like proficiency while adults often struggle to master new languages. The prefrontal cortex, responsible for higher cognitive functions like planning, judgment, and impulse control, has the longest developmental timeline, continuing to mature well into the early twenties. The timing of these critical periods has important practical implications. For instance, congenital cataracts must be treated within the first few months of life to prevent permanent visual impairment. Children with hearing loss benefit most from cochlear implants when they receive them before age three, while the auditory cortex is still highly plastic. And children who experience extreme language deprivation during early childhood may never fully develop normal language abilities, even with intensive later intervention. Environmental enrichment during critical periods can enhance brain development beyond typical expectations. Children exposed to music training before age seven show expanded development of auditory and motor brain regions. Early, high-quality language exposure—with parents who talk, read, and sing to their children—builds stronger language circuits and larger vocabularies. And rich sensory experiences during infancy, from exploring different textures to experiencing varied movements, help optimize sensory processing systems. Fortunately, the brain retains some degree of plasticity throughout life, allowing for recovery and adaptation even after critical periods have closed. Intensive interventions can help children overcome early adversity, though they typically require more effort and produce less complete results than interventions delivered during the critical period itself. This understanding has driven the development of early intervention programs for children with developmental delays, sensory impairments, or exposure to adverse experiences.

Chapter 4: The Olfactory System: Our Most Emotional Sense

The sense of smell, or olfaction, is often overlooked in discussions of brain development, yet it represents one of our most primitive and emotionally powerful sensory systems. Unlike our other senses that require processing through the thalamus before reaching the brain's higher centers, smell information travels directly to the brain's limbic system—the region responsible for emotions and memory. This direct pathway explains why scents can trigger immediate emotional responses and vivid memories in ways that other sensory experiences cannot. The olfactory system begins developing remarkably early, with functional receptors present by the second trimester of pregnancy. This early development allows the fetus to experience the chemical environment of the womb, creating the foundation for smell preferences and recognition that will influence behavior immediately after birth. Amniotic fluid serves as a rich chemical environment, containing molecules from the mother's diet, metabolism, and external environment. When a pregnant woman consumes strongly flavored foods like garlic or spicy dishes, these flavor compounds pass into her bloodstream and eventually into the amniotic fluid, where they can be detected by the developing fetus. This prenatal smell exposure serves several important developmental purposes. It familiarizes the fetus with the chemical environment of its culture and family, creating a sense of olfactory continuity between womb and world. Studies have shown that newborns prefer the scent of their own amniotic fluid over that of other mothers, suggesting they learn and remember their mother's unique chemical signature before birth. This recognition helps the newborn locate the mother's breast after delivery, as amniotic fluid shares many chemical compounds with colostrum and breast milk. The power of smell in early development extends beyond feeding to emotional bonding. When babies nurse while smelling their mother's unique scent, their brains release oxytocin and endorphins, creating neural connections between that particular smell and feelings of security, pleasure, and satisfaction. These early olfactory-emotional associations become templates for future emotional responses, influencing how children process and respond to their environments as they grow. Even in adulthood, certain scents can instantly transport us back to childhood experiences, triggering emotional responses that were established during these early sensitive periods. Given the importance of smell to bonding and emotional security, parents and caregivers should consider the olfactory environment they create for young children. Maintaining consistency in personal scents (like avoiding frequent changes in perfumes or lotions), allowing babies access to items carrying familiar family odors, and being mindful of harsh chemical smells in the home environment can all support healthy olfactory development. These considerations may seem minor compared to more obvious aspects of childcare, but they acknowledge the profound way that smell experiences shape the developing emotional brain.

Chapter 5: How Language Shapes Neural Circuits

Language acquisition represents one of the most remarkable feats of the developing brain. Unlike other skills that must be explicitly taught, language emerges naturally in nearly all children exposed to it. This universal pattern suggests that our brains are specially wired for language learning, with dedicated neural circuits that activate in response to linguistic input. Neuroimaging studies have revealed that language processing primarily occurs in specialized regions of the left hemisphere—particularly Broca's area (involved in speech production) and Wernicke's area (involved in comprehension)—though the right hemisphere also contributes, especially to the emotional aspects of language. The journey toward language begins well before a baby speaks their first word. Even in the womb, fetuses can distinguish their mother's voice from other sounds and show preferences for the rhythmic patterns of their native language. Newborns arrive with an astonishing ability to discriminate between all possible speech sounds used in any human language—a capacity that actually diminishes as they become specialized in their native tongue. By six months, babies begin focusing on the specific sounds of their language environment, and by twelve months, they've largely lost the ability to distinguish between certain foreign phonemes that aren't used in their native language. This specialization process reflects how neural circuits are shaped by experience. Initially, the infant brain contains connections for processing all possible speech sounds. As the baby hears their native language repeatedly, the neural pathways for those particular sounds strengthen, while unused pathways gradually weaken. This "neural pruning" represents a fundamental principle of brain development—connections that are frequently activated become stronger and more efficient, while those that remain inactive are eliminated. In language development, this means the brain becomes optimized for processing the specific language(s) in the child's environment. The quality and quantity of language exposure directly affects how these neural circuits develop. Children who hear more words, in more complex sentences, with more varied vocabulary, develop stronger language networks. Importantly, passive exposure through television or overheard adult conversations provides little benefit; what matters is direct, interactive communication. When adults engage children in conversation, respond to their vocalizations, read to them, and narrate daily activities, they're literally building neural pathways that support language processing and higher-order thinking. Research has identified a critical period for language acquisition that begins to narrow around age seven and continues decreasing through puberty. Children who aren't exposed to language during this window—due to extreme isolation or untreated deafness—never fully develop normal language capabilities, particularly grammar. This explains why young children can learn multiple languages simultaneously with native-like proficiency, while adults typically struggle to achieve the same level of mastery in a new language. The neural circuits for language remain somewhat plastic throughout life, allowing for continued learning, but they never regain the extraordinary receptivity of early childhood.

Chapter 6: Memory Formation in the Growing Brain

Memory is not a single faculty but a collection of distinct systems that develop at different rates in the growing brain. Understanding these developmental trajectories helps explain why children of different ages remember different types of information and why none of us can recall our earliest experiences—a phenomenon known as infantile amnesia. The most basic form of memory, implicit memory, allows infants to learn procedures and associations without conscious awareness. This system depends on primitive brain structures like the cerebellum and basal ganglia that are relatively mature at birth. A three-month-old can learn to kick a mobile to make it move without remembering the mobile itself. Similarly, babies quickly learn to associate certain cues with feeding or comfort, even though they cannot explicitly recall these associations. This implicit memory system explains how infants can recognize familiar faces, voices, and routines long before they can verbally describe these experiences. Explicit memory—the conscious recollection of facts and events—develops more gradually because it relies on the hippocampus and prefrontal cortex, which continue maturing throughout childhood. By eight months, babies can remember the location of a hidden toy for a brief period, demonstrating the emergence of working memory. However, they still struggle with what psychologists call the "A-not-B error"—if they've successfully retrieved a toy from location A several times, they'll continue reaching there even after seeing it moved to location B. This limitation reflects the immaturity of their prefrontal cortex, which is necessary for inhibiting established responses. The autobiographical memory system that creates lasting personal memories requires language and a sense of self, which don't fully develop until around age three. This explains why even the most significant events from the first two years of life—moving to a new home, the birth of a sibling, a hospital stay—typically cannot be explicitly remembered in adulthood. The neural networks necessary for encoding these experiences as personal narratives simply weren't mature enough at the time. As language develops, children begin to organize their experiences into stories, creating the framework for lasting autobiographical memories. Memory capacity increases dramatically throughout childhood due to several brain changes. Myelination—the process of insulating neural pathways with a fatty sheath—accelerates signal transmission, allowing faster processing and retrieval. Synaptic pruning eliminates unused connections while strengthening frequently activated ones, creating more efficient memory networks. The prefrontal cortex continues developing into adolescence, improving children's ability to organize information and use memory strategies like rehearsal and categorization. Parents and educators can support memory development by understanding these developmental patterns. For young children, repetition is crucial—reading the same books, singing the same songs, and maintaining consistent routines helps strengthen neural pathways. As language emerges, discussing experiences helps children organize their memories into coherent narratives. For school-age children, teaching explicit memory strategies like visualization, categorization, and mnemonic devices helps them make the most of their developing memory systems. Throughout childhood, ensuring adequate sleep is essential, as it's during sleep that memories are consolidated and integrated with existing knowledge.

Chapter 7: Emotional Security and Cognitive Development

The brain is not just a thinking organ but also an emotional one, with neural circuits dedicated to processing feelings, relationships, and social information. These emotional systems develop in close interaction with cognitive systems, creating a foundation where feelings of security and connection actually enhance learning and intellectual growth. Understanding this relationship challenges the false dichotomy between emotional nurturing and cognitive stimulation, revealing how deeply intertwined they are in the developing brain. At birth, the limbic system—including structures like the amygdala, hippocampus, and cingulate cortex—is already functioning, allowing newborns to experience basic emotions and form attachments. However, the prefrontal regions that regulate these emotional responses mature much more gradually, continuing to develop well into adolescence. This developmental sequence explains why young children experience emotions intensely but have limited ability to control them. A toddler's tantrum reflects not willful misbehavior but an immature brain in which emotional triggers operate without adequate regulatory systems. Attachment—the emotional bond between infant and caregiver—plays a crucial role in shaping both emotional and cognitive development. When caregivers consistently respond to an infant's needs with sensitivity and warmth, they help establish healthy patterns of neural activity in the limbic system. These secure attachment relationships create what psychologists call a "secure base" from which children can explore their environment. Knowing they have a reliable emotional haven to return to, securely attached children show greater confidence in exploring, taking risks, and engaging with challenging material—all behaviors that promote cognitive development. The biological mechanism behind this connection involves stress hormones like cortisol. When children feel chronically unsafe or unsupported, their bodies maintain elevated cortisol levels, which actually inhibit activity in the hippocampus—a brain structure crucial for learning and memory. Conversely, secure relationships buffer stress responses, keeping cortisol at levels that optimize rather than impair brain function. This explains why children learn better in emotionally supportive environments and why chronic stress or trauma can interfere with cognitive development even when educational resources are available. Beyond stress regulation, responsive caregiving directly stimulates cognitive growth through social interaction. When adults engage in "serve and return" interactions—responding to a child's babbling, gestures, or questions with appropriate language and attention—they're not just building emotional connections but also creating the neural foundations for language, problem-solving, and social understanding. These back-and-forth exchanges stimulate the growth of neural connections across multiple brain regions, integrating emotional and cognitive networks. For parents and educators, this research suggests that emotional support isn't just a nice addition to cognitive stimulation but an essential foundation for it. Creating environments where children feel secure, valued, and understood doesn't distract from academic learning—it enables it. Similarly, addressing emotional and behavioral problems isn't separate from educational intervention but an integral part of supporting cognitive development. By recognizing how deeply emotional security influences brain function, we can create more effective approaches to fostering both emotional well-being and intellectual growth in developing children.

Summary

The developing brain represents one of nature's most remarkable achievements—a self-organizing system that builds itself through the dynamic interplay of genetic instructions and environmental experiences. From the earliest prenatal stages through adolescence, specific windows of opportunity open when particular neural circuits are especially receptive to environmental influence. During these critical periods, everyday experiences—from the nutrients a fetus receives to the words a toddler hears to the emotional climate of a preschooler's home—literally shape the physical architecture of the brain, establishing patterns that can last a lifetime. This scientific understanding of brain development carries profound implications for how we approach parenting, education, and social policy. It suggests that investing in early childhood—through prenatal care, family support, quality childcare, and preschool education—yields returns far greater than interventions later in life. It highlights the importance of addressing not just cognitive stimulation but also nutrition, emotional security, and sensory experiences. And perhaps most importantly, it offers hope. While respecting the role of genetics and individual differences, the science of brain development affirms that thoughtful, informed caregiving can significantly enhance children's developmental trajectories, helping each child move closer to their full potential. How might our society change if we truly designed our parenting practices, educational systems, and public policies around this understanding of the brain's remarkable plasticity and vulnerability during the early years?

About Author

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Lise Eliot

Lise Eliot is a mother of three, and the Associate Professor of Neuroscience at The Chicago Medical School of Rosalind Franklin University. She is the author of What’s Going On In There? How the Brain and Mind Develop in the First Five Years of Life.

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