Control of Sleep and Wakefulness in Health and Disease - Progress in Molecular Biology and Translational Science - page 148

that a motor task that increased wake EEG activity in a specific area of the
cortex had a similar increase in slow wave activity in the same area of cortex
during sleep. 77 This implies that, to a certain degree, the amount of activity
occurring in a group of cortical neurons during sleep is due to their activity
during the daytime. It has been hypothesized that the increased activity at
night may be part of a local learning process, with synaptic paring and
enhancement occurring simultaneously. 78 Relatively little is understood
about local networks of sleep, especially the many different anatomical levels
that it might occur (e.g., functional region, cortical column, single neuron).
Pathophysiologically, the loss of coordinated sleep may be best exemplified
by parasomnias such as hypnagogic hallucinations, RBD, and sleep walking.
More work in the coming years may discover more subtle forms of
desynchronized local cortical sleep, which may lead to some of the memory
deficits that occur in a variety of different dementias (e.g., AD, Pick disease).
4. THE ENDOCRINE SYSTEM
In the recent literature, there are a plethora of studies that have exam-
ined the effects of sleep on the output of the endocrine system, especially the
relationship between disrupted sleep and changes in hormones that are crit-
ical to metabolism. 79 While it is well established that many hormones are
directly impacted by sleep, there is less literature examining the potentially
reciprocal relationship of the impact of these hormones on sleep. One of
the most commonly studied hormones is melatonin, most of which is
derived from the pineal gland. Melatonin has a simple, near square-wave
pattern with blood concentrations rising a few hours before habitual sleep
time and falling within an hour or so after habitual wake time. The produc-
tion of melatonin is tightly controlled by the SCN and modulated
by light input such that light acutely suppresses melatonin production
in a ose-dependent manner. 80 In many nonmammalian vertebrates (e.g.,
zebrafish, 81 chicken s 82 ), melatonin is an important regulator of sleep. In
many seasonally breeding mammals, it encodes day length. 83 Its importance
in the regulation of human sleep, however, has been extensively debated.
Exogenous administration of melatonin has mild hypnotic properties mainly
associated with a decrease in sleep latency. 84 The loss of endogenous mel-
atonin, however, secondary to either surgical removal of the pineal or neu-
rologically complete damage to the cervical spinal cord leads to few if any
changes in sleep architecture. 85-87 An acute reduction in melatonin concen-
trations through ocular light exposure is associated with a decrease in