Introduction to Abnormal Child and Adolescent Psychology. Robert Weis

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СКАЧАТЬ mother toward the pups (e.g., licking, grooming) caused this portion of the gene to unwind from the histone, allowing it to be expressed. When these pups reached adulthood, they were better able to cope with stress than rats whose mothers were less nurturing. Subsequent research showed that these epigenetic changes affected the care these rats gave to their own offspring, thus passing on this stress response to the next generation (Masterpasqua, 2009).

      Researchers are only beginning to understand how epigenetics might help explain the development of disorders in children. In one recent study, researchers examined the caregiving behaviors of depressed and nondepressed mothers. As we might expect, depressed mothers expressed more negative emotions toward their infants than nondepressed mothers. Moreover, the infants of depressed mothers showed different epigenetic structures than the infants of nondepressed mothers, suggesting that these early caregiving experiences might affect children’s epigenetic activity. Longitudinal research is needed to determine whether these epigenetic changes, brought on by early experience, might affect children’s subsequent behavior (Moore, 2015).

      Other research has begun to examine the epigenetic structure of children with existing behavior problems. In one of the largest studies so far, researchers examined children and adolescents referred to mental health clinics because of disruptive behavior. The researchers found that children’s stress hormones and their severity of behavior problems were associated with changes in their epigenetic structure, specifically, structures associated with the expression of the cortisol receptor gene. This finding is interesting because cortisol is the body’s main stress hormone; furthermore, the cortisol receptor gene plays a role in regulating the body’s stress response. Epigenetic changes to the expression of this gene might underlie some of the problems shown by these youths (Dadds, Moul, Hawes, Mendoza Diaz, & Brennan, 2016).

      We are only beginning to appreciate how behavioral epigenetics can help us understand the emergence of childhood disorders. Perhaps equally as important, research might someday be helpful in developing medications that can affect epigenetic structures, genetic expression, and risk for mental health problems (Nigg, 2016b).

       Review

       According to the diathesis–stress model, children must have both (1) a genetic risk and (2) an environmental stressor to develop a disorder. The model helps explain multifinality, that is, the tendency of children with similar genes or experiences to have different outcomes.

       The gene–environment correlation model assumes that our genes and environments are related. There are three types of gene–environment correlations: passive, evocative, and active. Their relative importance changes across development.

       Epigenetic structures (e.g., methyl tags and histones) can turn genes “on” or “off.” These structures, which are not part of children’s genotype, can be altered by environmental experiences and passed down from one generation to the next.

      How Does the Brain Change Across Development?

      Scientific advances have given us increasingly more detailed pictures of the brain and nervous system from infancy through adolescence. Studies examining children over time have yielded several principles of brain development (Roberts, 2020).

       1. The brain consists of 100 billion neurons.

      A neuron is a nerve cell that is typically very narrow and very long. Most neurons are small. You could place 50 neurons side by side within the period that ends this sentence. Neurons vary from 1 millimeter to more than 1 meter in length. Neurons are also very numerous; if you counted each neuron in your brain, one neuron per second, it would take you more than 3,000 years to finish.

      The structure of a neuron can tell us something about its function. The center of most neurons contains the cell body. Its main purpose is to perform metabolic functions for the cell, that is, to keep the cell alive. The neuron also has dendrites, fingerlike appendages that receive information from either outside stimuli (e.g., light, pressure) or other neurons. Finally, the neuron has a longer axon, which relays information from the dendrites and cell body to the terminal endings of the neuron. Neurons relay information electrically, by controlling the positively and negatively charged particles that are allowed to enter the cell. Information is conducted down the axon in a manner analogous to electricity flowing down a wire. Mammalian axons are wrapped in a fatty substance called myelin (produced by Schwann cells), which increases conduction and speeds the electrical impulse (Image 2.5).

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      2. Neurons communicate using chemical messengers.

      Each neuron typically forms many connections with other neurons, forming a complex neural network. Although information travels within neurons electrically, it travels between neurons chemically. When an impulse reaches the end of an axon, it triggers the release of a chemical messenger called a neurotransmitter. The neurotransmitter is released into the synapse, a small cleft between neurons. In the synapse, neurotransmitters can be detected by other neurons, causing them to change their electrical charge. Sufficient stimulation by neurotransmitters can cause other nerve cells to become active, thus sending the impulse to the next neuron.

      Neurotransmitters have different functions. Some are excitatory—that is, they increase the positive charge of neurons, making them more likely to become active. For example, dopamine is an excitatory neurotransmitter that is important for attention and concentration. Insufficient dopamine in certain brain regions is associated with ADHD. Other neurotransmitters are inhibitory—that is, they increase the negative charge of neurons, making them less likely to become active. For example, gamma aminobutyric acid (GABA) is an inhibitory neurotransmitter. Alcohol causes an increase in GABA, slowing reaction time, judgment, and decision-making. Most psychotropic medications and drugs affect behavior by enhancing or attenuating the effects of neurotransmitters.

      3. The brain is organized from the bottom up.

      Evolutionarily older areas of the brain develop first, followed by more complex, higher-order brain regions. For example, the brain stem consists of the medulla, pons, and midbrain and is largely responsible for basic metabolic functions such as heart rate, respiration, and arousal. It is developed at birth and is necessary to keep us alive (Ganzel & Morris, 2016).

      Similarly, the cerebellum is a brain region located near the back of the brain; it is chiefly responsible for balance and coordinated motor activity. It develops rapidly during the first year of life. Interestingly, the cerebellum undergoes a second round of maturation during early adolescence. Researchers believe the cerebellum plays a role in mental gracefulness and efficiency in addition to adroitness in physical movement. Maturation of the cerebellum during adolescence might explain the increased physical gracefulness exhibited by older adolescents as well as a general increase in mental efficiency across development.

      Just above the brainstem, in the center of the brain, are two important regions that also mature relatively early. The basal ganglia are located between the brainstem and the higher-level cortical regions. The basal ganglia perform many important functions. One of their primary roles is to help control movement. Another function is to filter incoming information from the senses and relay this information to other brain regions where it can be processed. The basal ganglia have also been implicated in the regulation of attention and emotions. Researchers believe that structural changes in the basal ganglia during childhood and adolescence might account for children’s СКАЧАТЬ