The brain is a complex structure that allows us to do all of the wonderful things humans do. After conception and around 3 weeks of development, we start to form our brain and nervous system. Children are born with billions of brain cells that transmit information to their bodies. Neurons are a type of brain cell that sends signals to the nervous system. Genetics and epigenetics play a big role in early brain formation and determine how many neurons a child starts off with and their arrangement within the brain (Graham & Forstadt, 2011). The experiences and interactions a child has determines whether the connections between neurons, or synapses, are strengthened or weakened. If neurons are like wires then we can think of synapses as electrical signals that connect the wires and help relay information.

At least one million new neural connections are made every second, more than at any other time in life (Zero to Three, 2023). The brain goes through a rapid development during the first three years of life where certain brain connections reach their peak. At birth, the number of synapses per neuron is 2,500, but by age two or three, it’s about 15,000 per neuron (Graham & Forstadt, 2011). These peaks are known as sensitive periods of development. Vision, for example, exists when a child is born but the neuron connections peak at intensity at around 8 months. Early visual stimulation causes the neurons and synapses associated with vision to grow and get stronger during this age. This is around the time when we notice infants becoming more aware of the world around them.

Synaptic pruning refers to the process by which the brain eliminates certain neural connections and strengthens others. This process helps the brain become more efficient and helps the child thrive in their respective environments. Once our brain has completed its overall growth in adulthood, we will lose around 40 percent of these connections due to synaptic pruning (Webb et al., 2001). The phrase “use it or lose it” is applicable when it comes to how the brain is wired. Connections that are used often will become permanent within the brain while connections that are not used will not fully develop.

It is important to note that although there are sensitive periods of brain development, scientists have learned that the brain is highly “plastic” throughout our lives. Brain plasticity, or neuroplasticity, “is a process that involves adaptive structural and functional changes to the brain” (Puderbaugh & Emmady, 2022). This process means that the brain can continue to grow and rewire itself even when exposed to adverse experiences or trauma. This is especially true during childhood when the brain is more plastic.

The brain experiences two types of neuroplasticity. The first is called experience-expectant plasticity in which stimuli from the environment guide normal brain development, especially during sensitive periods. This type of plasticity occurs mostly during early postnatal development. An infant who experiences being held by their caregivers, seeing different faces or objects, or hearing spoken language will generate experience-expectant plasticity.

The second type of neuroplasticity is experience-dependent plasticity in which the brain is remodeled due to unique or unexpected experiences. This type of plasticity can occur during or outside of sensitive periods of development, in childhood or adulthood. Learning a new skill such as playing an instrument or a specific sport would guide experience-dependent learning. This is also the type of plasticity that responds to stress or trauma within a child’s environment.

All young children experience stress to some degree such as when they’re hungry, get hurt, or attempt something new. This type of stress is considered normal and healthy when combined with adequate parental response. Scientists have researched the impact of stress in childhood and what they have learned is that chronic or toxic stress is damaging to the developing brain. Toxic stress is stress that results in “excessive or prolonged activation of stress response systems in the body and brain” (Center on the Developing Child, 2015). Toxic stress damages neural connections in the prefrontal cortex and hippocampus regions (see Figure 5.1). These regions are responsible for a variety of processes such as problem solving, attention, and memory.

Chronic stress causes the brain to produce cortisol, known as the stress hormone. Babies who are exposed to high levels of cortisol can experience disruptions to their learning and may exhibit behavior problems and even health issues later in life. Luckily, there are protective factors that can mediate the impact of stress on the brain and body. Researchers noted that responsive parenting can protect young children from the negative impact of stress (Asok et al 2013).

Figure 5.1. Persistent stress changes brain architecture. Credit: Center on the Developing Child.

We know that genes, experiences, and environmental stressors impact a child’s growing brain but what about exposure to technology? The use of technology in everyday life is new within the span of human existence. Screen time, or a person’s use of electronic devices with a screen such as a phone, laptop, or television, has become a regular part of American society and the impact on a child’s development continues to be studied. Many educators we work with have expressed concern over the use of screen time, especially in the aftermath of the COVID-19 pandemic with social restrictions and increases in remote learning. A report by Common Sense media states that infants and toddlers spend an average of 49 minutes to 2 hours and 30 minutes on screen media daily and that usage increases for boys as well as lower income children (Rideout & Robb, 2020).

The World Health Organization recommends that children under the age of 1 get zero sedentary screen time and that children ages 1-3 get one hour or less of sedentary screen time per day (WHO, 2019). As we can see, young children are getting much more than the recommended amount of screen time. So why should we care? How does this impact a child’s brain development? A recent study on a sample of 47 children showed that increased screen time was associated with underdeveloped or disorganized white brain matter (Hutton et al, 2019). This is a significant finding given that white matter supports the formation of executive functions, language, and literacy skills. While the sample size of this study was small, it suggests the importance of studying how screen time impacts a child’s brain, especially during this crucial time of development.