I only copied the abstract and the conclusion paragraphs so there is lots more at the link.
http://www.cell.com/neuron/fulltext/S0896-6273%2817%2930088-0
Older
adults do not sleep as well as younger adults. Why? What alterations in
sleep quantity and quality occur as we age, and are there functional
consequences? What are the underlying neural mechanisms that explain
age-related sleep disruption? This review tackles these questions.
First, we describe canonical changes in human sleep quantity and quality
in cognitively normal older adults. Second, we explore the underlying
neurobiological mechanisms that may account for these human sleep
alterations. Third, we consider the functional consequences of
age-related sleep disruption, focusing on memory impairment as an
exemplar. We conclude with a discussion of a still-debated question: do
older adults simply need less sleep, or rather, are they unable to
generate the sleep that they still need?
Main Text
Normative
aging is associated with a reduced ability to initiate and maintain
sleep. Moreover, deficits in sleep physiology, including those of
non-rapid eye movement (NREM) sleep and its associated neural
oscillations, are especially prominent in later life. Though sleep
disruption is a common signature of “normal aging”, the underlying
neural mechanisms explaining age-related sleep impairment are only now
being revealed.
This review focuses on physiological
changes associated with normative human aging. First, we characterize
associated alterations in sleep structure and oscillatory activity in
later life. Second, we describe emerging neurobiological mechanisms that
may account for these sleep alterations. Third, we consider
the functional consequences of age-related sleep disruption, focusing on
memory impairment. We conclude with the exploration of a
still-unresolved question: are older adults unable to generate the sleep
that they need or do they simply need sleep less.
S
Sleep Restoration, Aging, and Memory
The
vast majority of studies reporting an association between sleep, aging,
and memory are correlational in nature. However, several studies have
sought to enhance the sleep of older adults, and with it, memory. These
studies are informative in at least two ways. First, they establish a
causal contribution of sleep to memory in the elderly, as has been shown
in young adults. Second, therapeutic interventions that restore sleep
may deliver preventative benefits that reduce the risk and/or severity
of cognitive decline in aging, or mechanisms and/or processes that lead
to mild cognitive impairment or Alzheimer’s disease (Mander et al., 2016a), or body ill-health consequences, such as hypertension or chronic pain (Neikrug and Ancoli-Israel, 2010).
However, it is important to note that these methods have not been
investigated using longitudinal study designs, and thus the longitudinal
utility of such methods remains unknown.
In young
adults, transcranial direct current stimulation (tDCS) in the <1 Hz
slow oscillation frequency range during slow wave sleep increases slow
oscillation power and almost doubles overnight memory retention (Marshall et al., 2006).
In older adults, multiple studies have shown that enhancing the slow
oscillation using tDCS during an afternoon nap leads to a memory
enhancement; one showing heightened SWA in the slow oscillation
frequency range (<1 Hz) and word-pair performance (Westerberg et al., 2015),
and another showing enhanced slow oscillation and fast sleep spindle
EEG power that led to a benefit in a visual memory task (Ladenbauer et al., 2016).
Auditory closed-loop stimulation during slow wave sleep has also been
shown to enhance slow oscillation power and associated
hippocampus-dependent memory consolidation in young adults (Ngo et al., 2013).
Preliminary findings in older adults have reported increased slow
oscillation power during blocks of auditory stimulation that is
associated with enhanced next-day declarative memory recall (Papalambros et al., 2017).
It is of note, however, that some studies implementing varied forms of
brain stimulation have failed to replicate the beneficial enhancement of
sleep physiology and/or memory consolidation (Eggert et al., 2013, Passmann et al., 2016, Sahlem et al., 2015).
Therefore, brain stimulation methods offer potential promise as
intervention tools in the context of aging, but they require further
refinement and demonstration of efficacy and reproducibility before
being realistic options at present.
Pharmacological
methods using classic GABA-targeting hypnotics for selective NREM sleep
enhancement have so far proved less promising in the context of aging
and often fail to trigger any corresponding sleep-dependent memory
benefit in the elderly, sometimes even causing amnestic effects (Feld et al., 2013, Hall-Porter et al., 2014, Mednick et al., 2013, Vienne et al., 2012).
Little is currently known regarding the impact of more contemporary
non-GABA-targeting sleep medications on enhancing sleep and/or cognition
in the elderly populations at risk for dementia.
Overall,
several novel, non-pharmacological approaches are emerging that may
represent candidate methods for sleep restoration in the elderly and,
with such restoration, improvements in those mental and physical
functions that rely on sleep and are causally deficient in the elderly
as a result.
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