Anyone who has ever pulled an all-nighter knows that sleep is essential to brain functioning. Without adequate sleep, our cognitive performance deteriorates drastically, with difficulty concentrating and paying attention, and a diminished working memory (Higgins and George, 2007). I was struck by how these effects resemble a common disorder I see in my pediatric psychiatric clinical placement: Attention Deficit Disorder with Hyperactivity, or ADHD. To be diagnosed with ADHD, a patient must present with “a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development” (APA, 2013, p. 59). Symptoms include difficulty holding attention, forgetfulness, distractibility, trouble organizing, and trouble following through on tasks. Sound familiar? These are all consequences of insufficient sleep. These similarities, combined with the fact that children require more sleep than adults (Higgins and George, 2007), led me to turn to the literature to see what the experts say about this topic.
Corkum, Tannock, and Moldofsky (1998) found that an estimated 25% to 50% of children and adolescents with ADHD present with sleep problems, particularly in initiating and maintaining sleep. Owens (2005) reports that, “Estimates of parent-reported sleep problems in schoolage populations range from 11% of 4 to 12 year olds to 37% of elementary school-age children, making sleep issues also one of the most common complaints in pediatric practice” (p. 312). In fact, sleep disturbances used to be a key diagnostic feature of ADHD, though it has been removed in newer versions of the DSM (APA, 2013).
So which comes first? Does poor sleep lead to ADHD, or is there an element of the pathophysiology of ADHD that leads to poor sleep? Some hypothesize that sleep disturbance in children with ADHD might stem from the hyperactivity component, or that kids can’t settle down at night because of their excess energy (O’Brien et al., 2003). But other researchers say that there may be something else going on involving circadian rhythms. Indeed, sleep deficits can manifest as hyperactivity and impulsivity in children (as opposed to lethargy and sluggishness in adults), and treating sleep issues can often resolve symptoms of ADHD in children (Shur-Fen Gau, 2006).
To help parse this out, let’s first look at the areas of the brain involved in attention and hyperactivity, and how sleep impacts the functioning of these regions. Higgins and George (2007) explain that the three main areas of the brain involved in ADHD are the prefrontal cortex, the striatum, and the cerebellum. Studies show through brain imaging that patients with ADHD have decreased prefrontal gray matter, along with a smaller cerebellum and posterior parietal cortex (Durston et al., 2005; Monuteaux et al., 2008; Shaw et al., 2007). There is also evidence suggesting that there may be a connection between ADHD and specific regions of the thalamus that are specifically related to working memory and behavioral inhibition (Owens, 2005). To understand what this means in terms of behavior, it’s important to know what these areas of the brain control. The prefrontal cortex is responsible for helping us to organize our thoughts and emotions, and to make complex decisions. Lesions in this area can result in poor planning and impulsivity – a key component of ADHD. The striatum is part of the basal ganglia, a region of the brain involved in coordinating movement. The cerebellum is also involved in controlling movement, and together with the striatum is implicated in some of the hyperactivity symptoms that patients with ADHD exhibit.
So what is the overlap between the psychopathology of ADHD and the symptoms common to insufficient sleep? We all know that sleep is essential to proper functioning, but there is much dispute as to exactly why we need to sleep. Higgins and George (2007) outline the most prominent theories for us, including theories that say it’s important for our development, which is supported by the fact that infants need much more sleep than older adults. Other theories say that we need sleep because this is when our brains our able to grow new neurons and consolidate memories. Others say that it’s simple conservation of energy, and other, newer studies suggest that it’s a time for us to flush out toxins (http://www.washingtonpost.com/national/health-science/brains-flush-toxic-waste-in-sleep-including-alzheimers-linked-protein-study-of-mice-finds/2013/10/19/9af49e40-377a-11e3-8a0e-4e2cf80831fc_story.html).
But how does sleep affect those areas of the brain implicated in ADHD? The evidence clearly shows that a lack of sleep impacts functions attributed to the frontal cortex, including attention and working memory (Fallone, Owens & Dean, 2002). The thalamus, or the relay station of the brain that I mentioned above, also plays a key role in regulating non-REM sleep (Owens, 2005). There is also an overlap in neurotransmitter disruptions between ADHD and sleep disturbances, specifically in the noradrenergic and dopaminergic systems (Owens, 2005). Others studies suggest a broader disturbance involving circadian rhythms, specifically that an alteration in the CLOCK gene, or the gene that helps to regulate our sleep-wake cycle, has been found in patients with ADHD (Kissling et al., 2008). One study looked at the sleep cycles of 34 children with ADHD and 34 controls, and found that all of the children with ADHD showed a decrease in delta sleep, or that deep sleep we need to feel fully rested. Taken as a whole, this evidence has led to one possible theory that suggests that ADHD might be related to hypoarousal instead of hyperarousal, which may explain why treatment with stimulants is first line (Owens, 2005).
To answer my initial question that asked which comes first, sleep disturbance or ADHD, Owens (2005) has the most complete answer:
…the relationship between sleep problems and ADHD is essentially bidirectional and may be manifested in several ways: sleep problems may mimic ADHD symptomatology, may exacerbate underlying ADHD symptoms, may be themselves associated with or exacerbated by ADHD, and psychotropic medications used to treat ADHD may result in sleep problems. (p. 312)
There is no one answer, and much more to be done in this area of study, but the current research suggests that an important overlap exists between sleep and ADHD symptomatology. As clinicians, we need to be careful investigators into our patients’ habits surrounding sleep, and make sure that we are looking at and treating the whole person and not simply the symptoms that are present in our offices.
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