Pre-sleep jolts: myoclonic jerks

Why does this sensation of falling into a void occur, which awakens us abruptly?

It's three o'clock at night. You wake up abruptly, practically jumping out of bed, with the sensation of falling off an eight-storey building.. You notice how your viscera are still reacting with some panic.

Your partner wakes you up at three in the morning, slightly surprised and annoyed. He tells you that you have kicked him several times in your sleep. These two small fragments reflect the existence of a phenomenon that occurs with great frequency in most of the population: the realization of small sudden and involuntary movements during sleep.

These movements are called nocturnal myoclonic jerks.

What is myoclonus?

Myoclonic spasms refer to a series of abrupt, brief, totally involuntary muscle contractions that cause a displacement of the body or a part of it. They are usually caused by sudden muscle contractions or muscle relaxation..

Although this type of spasm can be found in some disorders such as epilepsy, there are also so-called benign myoclonus spasms. These are generally not considered pathological, being considered normal in people without associated pathology. In fact, a phenomenon as common as hiccups would be considered normal in people with no associated pathology, such a common phenomenon as hiccups would be a valid example of benign myoclonus spasm..

These spasms can appear both in the waking state and during sleep, with the present article focusing on the latter.

Nocturnal myoclonic spasms

Although the general definition of myoclonus reflects the type of phenomenon being discussed, those occurring during sleep have a peculiarity: as with hypnagogic and hypnopompic hallucinations, they occur in a state of altered consciousness: sleep or the transition between sleep and wakefulness. The myaclonic spasms would be in this case a type of parasomniaThese are episodic phenomena or disorders that occur during sleep and are characterized by the presence of vegetative or motor symptoms.

It is a generally non-pathological phenomenon with a high prevalence in the population. It is estimated that about 70% of the population has presented at some time a myaclonic spasm during sleep. during sleep. However, if the symptoms occur repeatedly and constantly, it would be advisable to seek medical advice, because if they occur persistently it could indicate the presence of a disorder.

It should be taken into account that it is possible to confuse this type of alteration, which is not dangerous, with an epileptic seizure. In this aspect, one of the few ways to differentiate them is by means of electroencephalogram, since myoclonic jerks are not the same type of alterations that are visualized in cases of epilepsy.

Neurological causes of myoclonic jerks during sleep

The reason for the occurrence of these spasms during sleep has a neuroscientific explanation.

The occurrence of nocturnal myoclonus spasms is due to the presence of an incoordination, the maintenance at the same time of the activity, of two specific cerebral areas. Specifically, the reticular formation or reticular activation system (SAR) and the ventrolateral preoptic nucleus.

Reticular activation system

This system located in the brainstem is the main system in charge of keeping us alive, as it is the brain system that directs unconscious processes such as breathing, digestion or Heart rate. Apart from these physiological processes, it is also involved in maintaining alertness and focusing attention, maintaining wakefulness.

Ventrolateral preoptic nucleus

The ventrolateral preoptic nucleus can be found in the anterior hypothalamus, near and in contact with the occipital lobe. This nucleus is responsible for "turning off consciousness" by inducing the sleep state, as well as for protecting the organism during sleep by provoking the body paralysis that prevents us from moving and damaging ourselves during deep sleep.

When do myoclonic jerks occur?

In order to understand the appearance of spasms, it must be taken into account that although during sleep its functioning is reduced, the SAR does not cease to function (as this would lead to the death of the affected person).

Thus, this system still presents a certain activation that can sometimes come into contradiction with the functioning during sleep of the ventrolateral preoptic nucleus that causes us to sleep.

This contradiction, the cause of which is still unknown, can partially provoke motor reactions typical of wakefulness during sleep.. In other words, it is the origin of myoclonic spasms during sleep.

Types of nocturnal myoclonus

Myoclonic jerks during sleep are not uniform and homogeneous. are not uniform and homogeneous, but rather there are three basic types.

The first type is found in repetitive movements during sleep. Similar to the typical movements of epileptic seizures, these movements appear during non-paradoxical sleep and are repetitive movements of short duration. Although treatment is not usually required, very severe forms can be treated pharmacologically.

A second type of myoclonic spasm presenting during sleep is nocturnal jerking or startle myoclonus. The most obvious example of this type of spasm is the typical movement made upon awakening from a dream in which we have the sensation of falling down.. They usually occur in superficial sleep, i.e. in the first two phases of sleep, causing the awakening of the sufferer with some abruptness. They are usually massive shaking of the whole body, especially the lower extremities.

Finally, some spasms can be found at the moment of transition between wakefulness and sleep. This type of myoclonus, classified as nonspecific, acts on the muscles of the face and extremities.

Bibliographical references:

• Ferber, R. & Kryger, M. (1995). Principles and Practice of Sleep Medicine in the Child. W.B.Saunders Company.

• Besag, F.M.C. (1995). Myoclonus and Infantile Spasms. In: Robertson MM, Eapen V, eds. Movement and allied disorders in childhood. Chichester: John Wiley and Sons, Ltd.; p. 149-76.

• Fejerman, N.; Medina, C.S. & Caraballo, R.N. (1997). Paroxysmal disorders and non-epileptic episodic symptoms. In: Fejerman N, Fernández-Álvarez E, eds. Pediatric Neurology. 2nd ed. Madrid: Editorial Médica Panamericana S.A.; p. 584- 99.

• Fernández-Álvarez, E. & Aicardi, J. (2001). Movement disorders in childhood. London: Mac Keith Press.

• Morairty, S.; Rainnie, D.; McCarley, R. & Greene, R. (2004). Disinhibition of ventrolateral preoptic area sleep-active neurons by adenosine: a new mechanism for sleep promotion. Neuroscience; 123: 451-7

• Svorad, D. (1957). «Reticular activating system of brain stem and animal hypnosis». Science 125 (3239): 156-156.