Noradrenergic and cholinergic modulation of sleep and dreams

The study of consciousness and conscious experiences during sleep, such as
dreaming, have long fascinated humankind, yet the precise neural mechanisms
behind these experiences remain unclear. Understanding these mechanisms by
researching brain activity and the neuromodulatory systems during sleep could
provide new insights and treatments for sleep disorders and broaden our
understanding of consciousness. These results could provide potential
applications for conditions involving abnormal mental activity during sleep,
such as recurring nightmares, parasomnias (i.e. abnormal dream-related
behaviors), epic dreaming disorder (i.e. excessive and exhausting dreams), and
paradoxical insomnia (i.e. feeling awake during sleep and experiencing
persistent ruminations), which affect about 5% of the population and
significantly impair sleep quality. Additionally, studying conscious
experiences during sleep can shed light on related phenomena like
hallucinations and delusions in psychiatric disorders such as schizophrenia, as
both involve the brain generating experiences without external stimuli.

Conscious experiences during sleep (i.e. dreaming) can occur in both rapid eye
movement (REM) sleep and non-rapid eye movement (NREM) sleep, each
characterized by distinct EEG patterns. A neural signature of dreaming shared
by both REM and NREM sleep, is local activation of posterior brain regions,
named the *posterior hot zone*. Furthermore, dreaming seems closely related to
two types of brain waves, which will be referred to here as type I and type II
potentials. Specifically, a dream was particularly likely to be reported when
in NREM sleep, a high amplitude and widespread frontocentral slow wave (i.e.,
type I potential) appeared in the EEG recording shortly before the awakening,
and when, at the same time slow waves in the posterior hot zone of the brain
(i.e., type II potentials) were particularly small. However, it remains unknown
which neurophysiological processes underlie this neural signature of dreaming,
and how the contents of dreams are generated.

Type I potentials may be associated with noradrenergic activity stemming from
the locus coeruleus (LC). Animal studies indicate that LC neurons discharge
intermittently, synchronized with sleep spindles and slow-wave up-states,
suggesting that the LC could drive cortical activity during NREM sleep slow
waves. In humans, functional magnetic resonance imaging (MRI) has shown
activation in the pons, including the LC, during high-amplitude slow waves in
NREM sleep, potentially corresponding to spontaneous type I slow waves, as well
as during sound-evoked K-complexes. Furthermore, the cortical regions where
type I slow waves originate from, such as the posterior medial parietal cortex
and the sensorimotor cortex, also have the highest concentrations of
noradrenaline, while the occipital cortex, typically spared by type I slow
waves, has the lowest levels of cortical noradrenaline. During wakefulness
brain waves similar to type I potentials (i.e. vertex potentials) are observed
in response to unexpected sensory stimuli. These results suggest that
noradrenergic activity (i.e. LC activation) in the absence of sensory
stimulation may underlie spontaneous type I potentials in NREM sleep.

Slow waves can also occur during REM sleep, although with a smaller amplitude
compared to NREM sleep. Similar to NREM sleep, REM sleep features two types of
slow waves: sawtooth waves and medio-occipital slow waves. Sawtooth waves,
which are considered a type I potential, share several characteristics with
ponto-geniculo-occipital (PGO) waves, originally identified in cats. Both
sawtooth and PGO waves last between 60-360ms, appear at the NREM-REM sleep
transition several seconds before the first rapid eye movement, occur in
bursts, are activating, and are often, but not always, associated with trains
of rapid eye movements. One of the few studies documenting potential PGO-wave
equivalents in humans with intracranial recordings described indeed the
presence of a concomitant sawtooth waves in the scalp EEG, supporting the
analogy between sawtooth and PGO waves. Animal studies have demonstrated that
the aminergic system inhibits PGO waves, while cholinergic stimulation triggers
PGO wave bursts. This suggests that cholinergic transmission may also be
responsible for generating sawtooth waves (type I potentials) during REM sleep
in humans.

The associations between the noradrenergic and cholinergic systems and type I
potentials and their association with conscious experiences (i.e. dreaming)
have not been explored in humans. In this study, we therefore aim to examine
the relationship between type I potentials to arousal systems and dreaming
through pharmacological modulation n of the noradrenergic and cholinergic
neuromodulatory systems. This study will contribute to our understanding of the
neurophysiological processes of dreams and how dreams are generated in the
brain.

The overarching objectives of this proposal are: 1) To evaluate the effect of
noradrenergic modulation on type I potentials in wakefulness (vertex
potentials), and NREM sleep (vertex sharp waves, K-complexes) and on dreaming
in NREM sleep; 2) To evaluate the effect of cholinergic modulation on type I
potentials (sawtooth waves) and dream features in REM sleep.

Specifically, we hypothesize that:
1. compared to placebo, the amplification of noradrenergic modulation induced
by atomoxetine will increase the amplitude of evoked and spontaneous type I
potentials (vertex wave in wakefulness, vertex sharp waves and K-complexes in
NREM sleep) but will not substantially affect type II slow waves. It will
result in an increase in the incidence of dream reports in NREM sleep.

2. compared to placebo, the attenuation of noradrenergic modulation induced by
clonidine will decrease the amplitude of evoked and spontaneous type I
potentials (vertex wave in wakefulness, vertex sharp waves and K-complexes in
NREM sleep) but will not substantially affect type II slow waves. It will
result in a decrease in the incidence of dream reports in NREM sleep.

3. compared to placebo, the amplification of cholinergic modulation induced by
donepezil/ galantamine will increase the amplitude of sawtooth waves but will
leave other slow waves of REM sleep unaffected. It will induce an accentuation
of dream-like features (vividness, perceptual aspects of dreams). This study
will not examine a reduction in cholinergic transmission because REM sleep is
expected to be too strongly inhibited by anticholinergics, even at low doses.

Secondary, the association between type I potentials and dreaming under
different drug conditions and physiological arousal (i.e. heart rate,
respiration, skin conductance and pulse wave amplitude), physical arousal (i.e.
electromyographic (EMG)) and subjective arousal (i.e. sleepiness/alertness
(Karolinska Sleepiness Scale - KSS; Pre-Sleep Arousal Scale) and subjective
estimation of sleep quality and quantity) will be examined. This will allow us
to further explore the association between type I potentials, dreaming and the
arousal system.

Dit is een dubbelblinde, placebogecontroleerde, gerandomiseerde cross-over
studie met vier middelen. Deelnemers krijgen eenmalig een enkele dosis van 40
mg atomoxetine (een selectieve noradrenaline heropname remmer die de
extracellulaire noradrenaline verhoogt), 0.05 mg clonidine (een α2-noradrenerge
auto-receptoragonist die de LC-activiteit remt en daarmee de afgifte van
noradrenaline remt in de cortex), 5 mg donepezil (een selectieve
cholinesteraseremmer die centrale cholinerge transmissie bevordert), of placebo
in pseudo-gerandomiseerde volgorde, op verschillende onderzoekavonden 2 uur
voor het slapen gaan. Er zitten ongeveer 2 weken tussen de afspraken om er
zeker van te zijn dat de betreffende middelen het lichaam hebben verlaten
voordat een nieuwe middel wordt ingenomen. Elke deelnemer (cluster) wordt
willekeurig toegewezen aan een van de vier reeksen, volgens een Latin Square
Design, zodat elk middel één keer aan elk ander middel voorafgaat. Tijdens de
overnachting worden door geluiden geïnduceerde type I-hersenpotentialen
geregistreerd en tussen de middelen vergeleken. Tijdens de overnachting worden
de deelnemers ook op verschillende tijdstippen van de nacht wakker gemaakt en
gevraagd naar hun dromen en de kenmerken van de dromen.

N/A

None of the procedures included in this study are considered to be therapeutic
or diagnostic. In this respect, the study offers no direct benefits to the
subjects.

No serious side effects from the single doses of atomoxetine, clonidine and
donepezil/ are expected. Considering the extensive exclusion criteria, the
recruitment of healthy young participants, screening procedure, and constant
monitoring of the participants the chances of side-effects are minimal.
However, if participants experience side effects of the medication during the
study such as headache, diarrhea, nausea, dizziness, sedation, low blood
pressure upon standing, dry mouth, decreased appetite, insomnia, increase in
blood pressure/increased heart rate, the experiment will not be continued until
the participant feels better. If participants need medical assistance for any
reason, there is always at least one person present at the institute who can
provide first aid, including resuscitation. If necessary, the researcher
approaches this person and calls an ambulance. In addition, the research takes
place next to the Amsterdam UMC, so help is in close proximity.

Rarely, skin irritation and allergic reactions to the electrode gel or the
material of the net can occur. In case a subject presents an allergic reaction
to the electrode gel or the material of the net, the experiment will be
discontinued. According to the severity of the reaction, the participant will
either be monitored, encouraged to contact the general practitioner or referred
to the first aid.

Fatigue and sleepiness the next day will likely occur due to sleep
fragmentation (by multiple awakenings/interviews on mental activity). Sleep
restriction could impair someone*s ability to drive or safely perform other
potentially dangerous tasks. For this reason, participants will be advised not
to drive or participate in other potentially dangerous tasks the day after the
study nights.

Sleep restriction or deprivation might trigger a manic/hypomanic episode or
seizures in vulnerable persons. For this reason, people with a known history of
bipolar or manic/hypomanic episodes or of seizures will not be able to
participate. However, some people may still have this risk and not know about
it. If investigators observe any unusual behavior or manifestations, medical
care will be sought.

Sleep reduction or deprivation may trigger or aggravate a migraine headache in
susceptible people. Subjects with a history of migraine may choose not to
participate in the experiments. If they do participate, they are instructed to
inform the investigators if they begin to experience a headache. They will be
able to stop the experiment and take their usual headache medications, if this
medication does not interact with the study medication. They may stay in the
lab to sleep and or return home.

There are no risks associated with auditory stimulation. Auditory stimuli will
be delivered at a volume that are compatible with sleep and thus safe for human
hearing.