Sleep studies may have diagnostic purposes for diseases such as epilepsy, sleep apnea, narcolepsy, insomnia and so on. This study can also be used for scientific purposes, such as studying the role of sleep in memory consolidation, studying dreams and their functions, studying consciousness, and so on.
The quintessential tool for the study of sleep is the recording of electroencephalography (EEG). This tool allows recording the electrical activity generated by the brain, but also by the eyes and muscles of the neck and chin, being a noisy signal in this case. Electrodes that are placed on the scalp surface and connected to signal conditioning and amplification equipment are used to record before the information is sent to a computer.
For more information on the neurophysiological basis of the EEG and its registration, visit the following links:
Sleep labs
For both clinical diagnostic and scientific sleep studies, the equipment is used to record brain electrical activity (EEG), muscle activity (EMG), eye movement (EOG), heart activity (ECG), movement of the body or legs, snoring, respiratory flow, among others.
Sleep studies are usually conducted day and night, depending on the type of information you wish to collect. During the day, individuals/volunteers should take a nap of about 120 minutes and at night it usually takes all night. For this, they are summoned to the sleep lab and upon arrival, the electrodes are placed on the head and other sensors, trying to ensure that they are not disconnected during the study. Finally, they will sleep for the allotted time.
Sleep labs generally have rooms similar to each person in your home: with a bed, bedside table, lamp, décor, and so on. The goal is for volunteers to feel as comfortable as possible. Near the rooms, there is a room where the technicians and researchers who carry out the studies remain. There, they receive and monitor signals acquired by equipment connected to study participants.
While this is the most common way of conducting studies, the global trend today is to begin studying at participants' homes. They only go to the lab to put their electrodes on, but then go to their homes to sleep. Portable and easy-to-use types of equipment are used for this. Take, for example, EEG for Android.
Registered Signals
From the EEG signal, with the help of other recorded signals, it is possible to determine the different states of consciousness that the patient or volunteer will go through during the study.
These different states of consciousness include the waking state when we are awake and the sleep state that can be classified as non-REM and REM sleep. The REM comes from Portuguese Rapid Eye Movement = Rapid Eye Movement because at this stage there are periods when lateral eye movement is observed. The Non-REM state is subdivided into three types: NREM1, NREM2, and NREM3.
The electrical activity of the brain during the NREM and REM stages is very different, as are different neurochemical and physiological variables in the rest of the body. At each stage, there are characteristic rhythms, characterized by their frequency, amplitude, and periodicity (figure below).
One result of the study is the sleep profile or hypnogram (Figure below) which briefly shows how different states of consciousness evolved throughout the study. Note that the profile has a cyclic form, in which the different states are given consecutively. Each cycle that involves NREM-REM takes about 90 minutes and is usually between 3 and 5 per night.
In future posts, we will develop in detail the features and functions of the NREM and REM stages.
References
Kryger, M., Roth, T., & Dement, W. C. (2014). Principles and Practice of Sleep Medicine. Igarss 2014. https://doi.org/10.1007/s13398-014-0173-7.2
Buzsáki, G. (2006). Rhythms of the brain. Rhythms of the Brain. https://doi.org/10.1093/acprof:oso/9780195301069.001.0001
Rasch, B., & Born, J. (2013). About Sleep’s Role in Memory. Psychological Reviews, 93(2), 681–766. https://doi.org/10.1152/Physrev.00032.2012
Matthew Walker. (2017) Why We Sleep: The New Science of Sleep and Dreams. Penguin UK.
The content published here is the exclusive responsibility of the authors.