Technologies of sleep research

Abstract

Sleep is investigated in many different ways, many different species and under many different circumstances. Modern sleep research is a multidisciplinary venture. Therefore, this review cannot give a complete overview of all techniques used in sleep research and sleep medicine. What it will try to do is to give an overview of widely applied techniques and exciting new developments. Electroencephalography has been the backbone of sleep research and sleep medicine since its first application in the 1930s. The electroencephalogram is still used but now combined with many different techniques monitoring body and brain temperature, changes in brain and blood chemistry, or changes in brain functioning. Animal research has been very important for progress in sleep research and sleep medicine. It provides opportunities to investigate the sleeping brain in ways not possible in healthy volunteers. Progress in genomics has brought new insights in sleep regulation, the best example being the discovery of hypocretin/orexin deficiency as the cause of narcolepsy. Gene manipulation holds great promise for the future since it is possible not only to investigate the functions of different genes under normal conditions, but also to mimic human pathology in much greater detail.

Figure 1

(a) Example of multiunit activity oscilloscope traces recorded from the suprachiasmatic nucleus, with three examples of above-threshold (horizontal line in a) spikes enlarged in (b). Textbook theory says that the shape of an action potential within a single neuron is always the same. Therefore, the shape of the spikes is sampled, and discrimination between the three occurs on the basis of amplitude of the up- and downward swing of the signal or, if necessary, on the entire shape of the recorded spikes. The spike marked with ‘+’ is sufficiently different from the other two, and it can be concluded that the three spikes are produced by at least two different neurons. The shape of a single spike can be followed over time, and the activity of a single neuron can be documented in different vigilance states.

Figure 2

(a) Schematic representation of the position of the cannula when extracting cerebrospinal fluid (CSF) from the cisterna magna to analyse hypocretin content. (b) The schedule shows the original order of sampling (black dots) over 3 days. (c) Simultaneous recording of drinking activity enabled precise localization of sample time in each individual animal, which results in the circadian pattern of hypocretin in the CSF [8].