In a very recent Journal of Neuroscience, a handful of experts in sleep research are once again localizing the neuroanatomical origins of various electrophysiological waveforms characteristic of specific stated of sleep and wakefulness as well as re-assigning these specific states of sleep and wakefulness to specific functions. For example, slow wave activity (name implies the type of waveform) are directly associated with sleepiness and high pressure to sleep across wakefulness as well as serving as markers of deep, restorative sleep and the extent of recovery from sleep loss. Within the past six months, I have also discussed the neuroanatomical origin of sleep spindles, which are present during a lighter stage of sleep in humans (stage 2), as well as their influences of learning, memory, and cortical development. Unlike slow waves, the frequency (think Hertz) of spindles is much faster, ranging from 12-15 Hz.
In this particular original research paper, it was found that slower spindles and faster spindles originate from different cortical areas, with the former arising from frontal areas and the latter from centroparietal areas. An inverse relationship between time spent in deep, restorative sleep where slow waves are the dominant waveforms and the number of sleep spindles was also observed.
The beauty of this study, in my opinion, was not the results, but rather the experimental design and electrode technology that were implemented. As background, this study is an extension of a previous study that showed rapid and dynamic changes in neuronal and slow wave activity during deep, restorative sleep, the specific neuroanatomical origins of these slow waves, and the neuronal consequences of when sleep intrudes into wakefulness, such as during sleep deprivation (Nir et al. 2011; Regional Slow Waves and Sleep Spindles in Human Sleep; Neuron). This was achieved by placing numerous small, deep recording electrodes in many cortical and subcortical brain areas in patients undergoing preclinical surgery for pharmacologically resistant epilepsy (a supplemental, basic experiment as part of a more clinically-relevant study). The design of the recording electrode as well as the extensive array of brain areas in which the electrodes were placed can be found on page 2 of the paper. More importantly, this study, like its predecessor, is revolutionizing what we know about the origins of electrophysiological waveforms characteristic of particular states of sleep and wakefulness as well as how neurons behave during such states. Really cool and inspiring work, indeed.
Andrillon, T., Nir, Y., Staba, R., Ferrarelli, F., Cirelli, C., Tononi, G., & Fried, I. (2011). Sleep Spindles in Humans: Insights from Intracranial EEG and Unit Recordings Journal of Neuroscience, 31 (49), 17821-17834 DOI: 10.1523/JNEUROSCI.2604-11.2011