TROUBLED DREAMS: Sleep & Memory

Mehrdad Razavi, MD

While sleep disorders are known to negatively affect cardiovascular and metabolic health, their detrimental effect on the brain is just being unraveled. The brain is actually more active during sleep than during wakefulness. All the sensory data gathered during the day need to be sorted out, organized, reactivated and consolidated—and all that occurs during sleep, pushing the “save” button for the preceding day.¹ Sleep exerts powerful effects on molecular, cellular and network mechanisms of plasticity that govern both initial memory encoding (learning) and subsequent long-term memory consolidation, resulting in how our memories are formed and ultimately shaped.²

There is no single system of memory, neither psychological nor anatomical. Our brain uses different neural networks for different types of learning and memory. Declarative memories are those that we can consciously recall, such as facts and names. Procedural memories allow us to perform certain types of actions, such as tying our shoes, driving a car or dancing. Emotional memories are generated by experiences that produce an emotional reaction, such as the first kiss, winning a game or getting into an argument.

Post-learning sleep enhances the consolidation of declarative, procedural and emotional memories.³ Interestingly, different stages of sleep mediate the different types of memory. Slow-wave sleep (SWS) particularly enhances declarative memory, whereas rapid eye movement (REM) sleep supports procedural and emotional memory. While declarative memory profits from rather short sleep periods, procedural memory profits seem more dependent on the amount of sleep.^1–2 Children’s sleep with high amounts of SWS (and even naps) distinctly enhances declarative memories. In contrast, elderly and psychiatric patients with disturbed sleep show impaired sleep-associated consolidation of declarative memories.

Sleep disorders—such as insufficient sleep, insomnia and obstructive sleep apnea (OSA)—are accompanied by impairments of memory, learning, and work and school performance. Moreover, sleep treatments, such as cognitive-behavioral therapy for insomnia (CBT-I) and continuous positive airway pressure (CPAP), could potentially mitigate cognitive impairments and support memory and learning. Recent studies show that OSA is particularly associated with structural changes in the brain, such as brain atrophy, and that treating OSA with CPAP can reverse both memory loss and brain atrophy.⁴ In other words, treating sleep disorders can help our brains get smarter and bigger.

Low blood oxygen pressure seems to be the dominant factor contributing to cognitive deficits in OSA. In the elderly, OSA is associated with age-related cognitive deficits that are absent in elderly patients without OSA.⁵ Other research has linked OSA to a higher likelihood of developing dementia. Future studies need to examine if the inhibition of memory consolidation is tied to the onset of neurodegenerative disease. Conversely, more than half the patients with dementia are likely to have sleep disorders, including insomnia and OSA. Thus, sleep apnea can be a reversible cause of memory loss in dementia. Moreover, treatment of OSA can slow down cognitive decline and reverse brain atrophy.^4,6,7

Healthy sleep is not only important for cognition, but also for healthy mood. Sleep disorders are often accompanied by mood disorders, particularly depression and anxiety. As with cognition, treatment with CPAP and CBT-I can improve depression and anxiety.⁸

The mood and behavioral complications of sleep disorders and their treatment can best be shown in school-age children. OSA in these children is associated with increased risk of ADHD, somatic complaints, oppositional or aggressive behavior, social problems, and other behavioral disorders.⁹ These disorders can be totally reversible after treating children’s OSA with CPAP or surgery.

Medical care of patients with sleep disorders has historically been suboptimal, due to a lack of comprehensive programs, fragmented care and overuse of certain medications, such as hypnotics. Comprehensive sleep centers that offer CPAP desensitization, orofacial myology, oral appliance therapy, surgical options, CBT-I, cognitive rehabilitation and nutritional support can help patients achieve optimal sleep duration and memory retention, along with cardiovascular, cognitive, behavioral and emotional benefits. Fortunately, we do have such comprehensive programs in Marin County.

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Dr. Razavi is a San Rafael sleep-medicine physician with a special interest in memory disorders.
Email: mehrdadrazavi@hotmail.com

References
1.  Stickgold R, “Sleep-dependent memory consolidation,” Nature, 437:1272-78 (2005).
2.  Abel T, et al, “Sleep, plasticity and memory from molecules to whole-brain networks,” Curr Biol, 23:R774-788 (2013).
3.  Diekelmann S, “Whats and whens of sleep-dependent memory consolidation,” Sleep Med Rev, 13:309-321 (2009).
4.  Canessa N, et al, “Obstructive sleep apnea,” Am J Resp Crit Care Med, 183:1419-26 (2011).
5.  Djonlagic I, et al, “Untreated sleep-disordered breathing,” PLoS One, 9:e85918 (2014).
6.  Troussière AC, et al, “Treatment of sleep apnea syndrome decreases cognitive decline in patients with Alzheimer’s disease,” J Neurol Neurosurg Psych, (May 14, 2014).
7.  Cooke JR, et al, “Sustained use of CPAP slows deterioration of cognition, sleep, and mood in patients with Alzheimer’s disease and obstructive sleep apnea,” J Clin Sleep Med, 5:305-309 (2009).
8.  Schwartz DJ, Karatinos G, “For individuals with obstructive sleep apnea, institution of CPAP therapy is associated with an amelioration of symptoms of depression which is sustained long term,” J Clin Sleep Med, 3:631-635 (2007).
9.  Zhao Q, et al, “Association between sleep-disordered breathing and behavior in school-aged children,” J Open Epidemiol, 1:1-9 (2008).