Technical Research on Sleep

Animal Studies

Electrical stimulation of the thalamus initiates sleep behaviour in cats. When the appropriate electrical current is applied the cat will circle their chosen resting place, yawn and stretch their limbs before curling up and going to sleep.

The process can be reversed and sleeping cats (and other animals) can be woken up by electrical stimulation of the brainstem, in particular a region of the brainstem known as the ascending reticular formation.

Pharmacological studies have suggested that some specific groups of nerve cells containing serotonin and others that contain norepinephrine play a role in the regulation of sleep.

Serotonin carrying neurons are found in a series of nuclei called the Raphe nuclei that are scattered along the ventral region of the brainstem.. If these neurons are depleted of their serotonin the affected animal of person is unable to sleep.

Once again, reversing the process, sleep can be restored if a precursor of serotonin (called 5-hydro-xytryptophan) is administered. Noradrenergic neurons are located beneath the cerebellum in an area of the brain called the locus caruleus. If these neurons are depleted of their norepinephrine (by a metabolic inhibitor) the affected animals are able to enter a type of delta wave sleep, but do not have the associated REM sleep patterns which would be anticipated with normal sleep.

Human Studies

In humans it appears norepinephrine has potent and long-lasting ionic effects on cortical and thalamic neurons.

Together with the actions of the other neuromodulatory neurotransmitters (acetylcholine, histamine, serotonin) these effects facilitate the switch of these neurons from a state of rhythmic oscillation and low excitability during drowsiness and slow wave sleep to a state of increased excitability and responsiveness during periods of waking, attentiveness and cognition.

It would appear that the sleep-wakefulness cycle is a complex chemical process involving the controlled release of a chemical cocktail which lowers activity in the brainstem, this in turn lessens cortical activity and results in sleep. Subsequent activity in the noradrenergic neurons give rise to REM episodes.