Professor Cheong Eunji’s Research Team Finds Clues for Sleeprhythm generation
"Sleep spindles are generated in the absence of T-type calcium channel- mediated low-threshold burst firing of thalamocortical neurons"
Sleep is characterized by the altered consciousness, relatively inhibited sensory activity, and inhibition of nearly all voluntary muscles in animals. Although the functions of sleep are still unresolved, a great effort has been made to understand the brain mechanisms that control sleep and wakefulness. An understanding of these mechanisms is of enormous importance to our daily life. Sleeping tablets are among the most widely prescribed medicines, and disturbances in sleep are associated with a wide range of medical and psychiatric conditions.
Sleep is defined in the sleep laboratory, in both humans and animals, by recording the electrical field activity of large groups of cortical neurons and muscle cells, represented as electroencephalogram (EEG) and electromyogram (EMG). According to the electrical activity in EEG and EMG, sleep is composed of REM (rapid eye movement) sleep and non-REM sleep. Sleep spindle is one of major rhythmic brain waves that appear in EEG during nREM sleep. A surge of interest in sleep spindles sparked in the past years in the context of sleep’s implication in learning and memory formation. Sleep spindle consists of characteristic waxing-and-waning EEG pattern, grouped into 7-14 Hz oscillations that last for 1 to 3 seconds and recur once every 5 to 10 seconds in the thalamus and the cortex in humans and experimental animals.
Our study suggested a neural mechanism how the sleep spindles are generated. The significance of our study is in that it addresses the most fundamental issues in sleep spindle generation. This existing theory that low-threshold burst firing mediated by T-type calcium channels in thalamocortical neurons is essential for the sleep spindles has been accepted as a dogma and appear as a fact in many literatures. Here we showed that T-type channels in thalamocortical neurons are not required for sleep spindles. Therefore, the current view on the essential role of T-type channels in all kind of thalamocortical oscillations is not valid. We believe that our study will advance the current knowledge on sleep and vigilance control into another level of understanding.