What are the parts of the brain associated with sleep?

A summary of the neurological basis of sleep, the parts of the brain that are activated during sleep.

It is clear that sleep is a very important process for the life of living beings, but... Which areas of the brain are involved in the act of sleeping? What relationships between them allow the occurrence of each sleep phase?

In this article we will describe how is the process of sleep, which phases constitute it, as well as which regions of the brain is involved, is activated or inhibited in each phase, that is to say, which areas are linked to the neural control of sleep.

Definition and phases of sleep

The dream is a state produced by a decrease of the conscience that allows the rest both corporal and cerebral.. There is a decrease in brain activity generated by fatigue. Sleep is a basic, vital need, being fundamental a good functioning and regulation of the different regions involved in this process so that the living being is in an optimal state and can stay alive.

In the waking state, the electrical activity of the brain is desynchronized with fast frequency waves called Beta waves. When the subject is at rest, relaxed, the waves become a little slower, giving rise to Alpha waves.

During sleep, two main stages can be distinguishedNREM or slow-wave sleep, and REM sleep, also called paradoxical sleep because the waves increase their frequency again, generating Beta waves in the same way as in wakefulness.

In REM sleep, apart from the increase in the frequency of brain activity, there is also an increase in eye movements, desynchronizations and a decrease in Muscle tone.

NREM sleep is necessary for the brain to rest and recover from the activity produced during wakefulness; on the other hand, REM sleep will be linked above all to learning processes, consolidating the information obtained during the day.

The parts of the brain linked to sleep: organic basis of the act of sleeping.

At first it was believed that sleep acted as a passive process produced by sensory interference, lack of stimulation. But the neuropsychologist Giuseppe Moruzzi proved that the mesencephalic reticular formation, located in the brainstem, has the function of generating wakefulness; for its part, the medulla oblongata is responsible for inhibiting the anterior structure, allowing rest.

Thus, this scientist was able to affirm, given the inhibitory function of the medulla oblongata, that sleep is an active process.

• Related article, "Do all animals sleep?"

Areas of the brain involved in NREM sleep.

As we have already noted, in this phase of sleep there is a decrease in brain activity, allowing the brain to rest and recover.

The function of the ventrolateral preoptic area, located in the hypothalamus, has been found to be particularly important for the sleep process.located in the lateral hypothalamus, a brain region mainly related to endocrine function, with hormones. It was proved in different experiments with animals that the lesion or destruction of this area causes total insomnia, difficulty to sleep, on the contrary, its stimulation generates drowsiness and somnolence.

The neurotransmitter GABA, a messenger involved in the decrease of brain activity, is projected from the ventrolateral preoptic area to the tuberomammillary nucleus, also located in the hypothalamus, to the dorsal pons located in the brainstem, to the raphe nucleus located in the brainstem and responsible for the production of serotonin, and to the locus coeruleus, also located in the brainstem and linked to the production of the neurotransmitter norepinephrine. These projections inhibition of these areas..

As we have pointed out at the beginning, the ventrolateral preoptic area is related to decreased arousal and therefore to sleep; this fact is reaffirmed by the inhibitory function it produces to the aforementioned areas of the hypothalamus and brainstem. It has also been proven that these regions would be related to cerebral and behavioral activation.

Similarly, the existence of a reciprocal inhibition circuit called "flip-flop oscillator" has also been the existence of a reciprocal inhibition circuit called "flip-flop oscillator" has also been observed, in this circuit there is alternating inhibition of the ventrolateral preoptic area and the projecting regions of the trunk and hypothalamus.In this circuit there is an alternating inhibition of the ventrolateral preoptic area and of the projecting regions of the brainstem and hypothalamus, which means that the activation of one will provoke the deactivation of the other, so that both cannot be found functioning, allowing alternating periods of sleep and wakefulness.

On the other hand, it has been noted that this circuit does not always work well and can lead to imbalances and decompensation. imbalances and decompensations can occur, giving rise to sleep-wakefulness disorders such as narcolepsy, cataplexy (cataplexy) and sleep-wakefulness disorders.cataplexy (loss of muscle tone), sleep paralysis and hypnagogic hallucinations.

Similarly, it has been shown that the hypocretinergic neurons of the lateral hypothalamus (i.e., the neurons that secrete hypocretin) are responsible for regulating and stabilizing the alternating sleep-wake circuit, the flip-flop oscillator, making it stay on and thus allowing the individual or animal to remain awake or awake.

It has also been shown that the action of adenosinea substance that appears after cortical activity, on the basal forebrain (mainly related to cognitive functions such as attention and learning), produces inhibition or deactivation of this, thus allowing the onset of sleep.

On the other hand, adenosine can also act by deactivating the hypocretinergic neurons of the lateral hypothalamus, linked to the waking state, as we have seen.

Areas of the brain involved in REM sleep.

As we mentioned in the first sections, the activity or brain waves during REM sleep are similar to those of wakefulness, showing a high electrical frequency observed with the electroencephalogram technique..

A characteristic and distinctive sign of the REM phase is the appearance of PGO (protrusion-geniculate-occipital) waves, thus signaling that the individual is in REM. PGO waves are large, brief electrical waves that initiate in the pons and travel to the lateral geniculate nuclei and subsequently to the occipital lobe, specifically the primary visual cortex.

The region with the greatest involvement in the REM floor is the dorsolateral pons, which is formed by neurons of the dorsolateral geniculate nuclei.which is formed by cholinergic neurons, producers of the neurotransmitter acetylcholine. This region is inhibited by the aforementioned raphe nuclei and locus coeruleus, through the projection of noradrenaline and serotonin respectively, thus allowing and appearing NREM sleep or wakefulness.

Similarly, it has been observed that the peribrachial area, located in the pons, which is constituted by the pedunculopontine and laterodorsal tegmental nucleus, together with the superior intermediate superior reticular nucleus, are formed by cholinergic neurons producing acetylcholine, which as we have said, one of its functions is to control REM sleep.

Thus, depending on the region where the cholinergic neurons project, they will give rise to or allow different functions of the REM sleep phase.The following are some of the most important aspects: projections to the thalamus (one of the main regions of information passage in the brain) and to the basal forebrain allow cortical activation and desynchronization, and connections with the lateral geniculate nucleus allow or are related to PGO waves.

It has also been considered that projections to the tectum of the midbrain, located in the brainstem, control rapid eye movementsand the link with the lateral preoptic area could be related to penile erection during sleep.

Finally, connections with neurons in the magnocellular nucleus of the medulla oblongata, also located in the brainstem, allow it to inhibit motor neurons in the spinal cord, thus producing muscle atonia, loss of muscle tone, typical of REM sleep.

Areas involved in brain activation

It is also interesting to know which areas of the brain are related to arousal, since they will be important and will participate in the neural control of sleep.

The main region involved with brain activity is the ascending reticular activating system, also known as SARA.also known as SARA. This is constituted by neurons of the upper part of the brainstem, the hypothalamus and the basal forebrain. These pathways connect the thalamus and the cerebral cortex, allowing them to transmit and respond correctly to sensory inputs.

If a lesion or damage occurs in this system, an alteration and decrease in consciousness will appear. Thus, an optimal functioning of the SARA will result in a correct state of wakefulness, not allowing states of relaxation or sleep.