All of the disorders described above can have their onset during childhood, adolescence, or adulthood. Some often begin early in life (lots of adolescents develop anxiety disorders or depression), and in fact, half of all disorders begin by age 14, and three-quarters by age 24 (Kessler, Berglund, et al., 2005). But neurodevelopmental disorders always, by definition, begin in childhood or adolescence, and if they don’t, you are never going to have them. These include autism spectrum disorder, attention-deficit/hyperactivity disorder, intellectual disability (formerly called mental retardation), learning disorders, communication disorders, and motor skill disorders, in addition to many others. The first two are among the most common and well known, so we will review them briefly here.

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Marco is a 4-year-old only child. Although his mother stays home with him all day and tries to play with him and talk with him, he still has not spoken a single word and he shows little interest in trying. He spends much of his time playing with his toy trains, sometimes sitting for hours staring at spinning train wheels or pushing a single train back and forth, seeming completely in his own world, uninterested in playing with anyone else. Marco’s parents have become concerned about Marco’s apparent inability to speak, disinterest in others, and development of some peculiar mannerisms, such as flapping his arms repeatedly for no apparent reason.

Autism spectrum disorder (ASD) is a condition beginning in early childhood in which a person shows persistent communication deficits as well as restricted and repetitive patterns of behaviors, interests, or activities. In DSM–5, ASD is considered a single disorder that includes autistic disorder, Asperger’s disorder, childhood disintegrative disorder, and pervasive developmental disorder not otherwise specified.

The true rate of ASD is difficult to pinpoint. Estimates from the 1960s indicated that autism was fairly rare, occurring in 4 per 10,000 children, but current estimates range as high as 60 per 10,000 children (Newschaffer et al., 2007). It is unclear whether this increased rate is due to increased awareness and recognition of ASD, better screening and diagnostic tools, or to some other factor. Boys have higher rates of ASD than girls by a ratio of about 4:1.

One current model suggests that ASD can be understood as an impaired capacity for empathizing, knowing the mental states of others, combined with a superior ability for systematizing, understanding the rules that organize the structure and function of objects (Baron-Cohen & Belmonte, 2005). Consistent with this model, brain imaging studies show that people with autism have comparatively decreased activity in regions associated with understanding the minds of others and greater activation in regions related to basic object perception (Sigman, Spence, & Wang, 2006). At the same time, some people with ASD have remarkable abilities to perceive or remember details, or to master symbol systems such as mathematics or music (Happé & Vital, 2009).

Although many people with ASD experience impairments throughout their lives that prevent them from having relationships and holding down a job, many go on to very successful careers. The renowned behavioral scientist and author Temple Grandin (2006) was diagnosed with autism at age 3, started learning to talk late, and then suffered teasing for odd habits and “nerdy” behavior. Fortunately, she developed ways to cope and found a niche through her special talent—the ability to understand animal behavior (Sacks, 1996). She is now a professor, author, and the central character in an HBO movie based on her life. Temple Grandin’s story lets us know that there are happy endings. Overall, those diagnosed with ASD as children have highly variable trajectories, with some achieving normal or better-than-normal functioning and others struggling with the profound disorder. Autism is a childhood disorder that in adulthood can turn out many ways (see the Hot Science box).

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Chances are you have had the experience of being distracted during a lecture or while reading one of your other textbooks. We all have trouble focusing from time to time. Far beyond normal distraction, attention-deficit/hyperactivity disorder (ADHD) is a persistent pattern of severe problems with inattention and/or hyperactivity or impulsiveness that cause significant impairments in functioning. This is quite different from occasional mind wandering or bursts of activity. Meeting criteria for ADHD requires that a child have multiple symptoms of inattention (e.g., persistent problems with sustained attention, organization, memory, following instructions), hyperactivity–impulsiveness (e.g., persistent difficulties with remaining still, waiting for a turn, interrupting others), or both. Most children experience some of these behaviors at some point, but to meet criteria for ADHD, a child has to have many of these behaviors for at least 6 months in at least two settings (e.g., home and school) to the point where these behaviors impair the child’s ability to perform at school or get along at home. Approximately 10% of boys and 4% of girls meet criteria for ADHD (Polzanczyk et al., 2007).

For a long time, ADHD was thought of as a disorder that affects only children and adolescents and that people “age out” of the disorder. However, we now know that in many instances, this disorder persists into adulthood. The same symptoms are used to diagnose both children and adults (e.g., children with ADHD may struggle with attention and concentration in the classroom, whereas adults may experience the same problems in meetings). Approximately 4% of adults meet criteria for ADHD, and adults with this disorder are more likely to be male, divorced, and unemployed—and most did not receive any treatment for their ADHD (Kessler, Adler, et al., 2006).

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Because ADHD, like most disorders, is defined by the presence of a wide range of symptoms, it is unlikely that it emerges from one single cause or dysfunction. The exact cause of ADHD is not known, but some studies suggest a strong genetic influence (Faraone et al., 2005). Brain imaging studies suggest that those with ADHD have smaller brain volumes (Castellanos et al., 2002) as well as structural and functional abnormalities in brain networks associated with attention and behavioral inhibition (Makris et al., 2009). The good news is that current drug treatments for ADHD are effective and appear to decrease the risk of later psychological and academic problems (Biederman et al., 2009).