The neurobiology of sleep
Philip N. Murphy in The Routledge International Handbook of Psychobiology, 2018
As sleep deepens, two electrical phenomena (sleep spindles and K-complexes) begin to appear periodically, and constitute the first neurophysiological break-point in brain function before a second continuum is reached. Both phenomena are specific markers of the NREM-2 sleep stage. Firstly, sleep spindles are short bursts of fast activity mainly in the sigma band (i.e., between 12 and 15 Hz). However, theta waves still predominate during NREM-2. Spindles mainly occur in central areas, with the greatest density observed near the supplementary motor area in the frontal lobes. These features are thought to reflect communication between the frontal lobe and the thalamus (Steriade & McCarley, 2005). The spindles’ frequencies measured on the scalp are close to those recorded in the thalamus, and the neurons of the reticular thalamic nucleus have been identified as the spindles’ pacemakers (Wang & Rinzel, 1993). When spindles occur, sensory inputs cannot be relayed to the cortex because the thalamocortical neurons are hyperpolarized – reducing their responsiveness to peripheral stimulation. Spindles thus have a “gating” function for information moving from the thalamus to the cortex. The second electrical phenomenon is the K-complex – a brief, high-voltage peak that occurs either spontaneously or in response to external stimuli. The greatest density of K-complexes is observed at the vertex and in front of the medial line. The complexes might be generated by the Brodmann areas 6 and 9. Furthermore, it has been suggested that K-complexes might help to maintain the NREM-2 sleep state by suppressing cortical arousal (Colrain, 2005). Examples of sleep spindles and K-complexes are depicted in Figure 24.1.
Scoring of Data in Adults
Ravi Gupta, S. R. Pandi Perumal, Ahmed S. BaHammam in Clinical Atlas of Polysomnography, 2018
K complexes are large waves that appear distinct from the background activity with initial negative followed by positive deflection having the duration of at least 0.5 seconds and seen with maximum amplitude in frontal leads (Figure 13.9). An epoch having either sleep spindle or K complex in first half is scored as N2. If an epoch shows these waveforms in second half, then subsequent epoch should be scored as N2, unless it confirms waveforms depicting any other sleep-wake stage (Figure 13.10). Any K complex associated with arousal is not considered as K complex (Figure 13.11).
Anesthesia and the Patient with Epilepsy
Stanley R. Resor, Henn Kutt in The Medical Treatment of Epilepsy, 2020
High-dose intravenous fentanyl (SO to 100 pg/kg) has been used extensively for cardiac anesthesia because of its ability to produce a high degree of hemodynamic stability. The effects of such large doses upon the EEG in patients undergoing cardiac surgery has been examined by a variety of authors who report that the consistent EEG changes are produced (67). The EEG appearance is predominantly one of depression and is quite similar to that seen during the normal progression of sleep, though K-complexes are not seen.
Targeted Memory Reactivation During Sleep, But Not Wake, Enhances Sensorimotor Skill Performance: A Pilot Study
Published in Journal of Motor Behavior, 2018
Brian P. Johnson, Steven M. Scharf, Kelly P. Westlake
Both Sleep+NoTMR and Sleep+TMR groups underwent standard polysomnographic observation throughout the night of sleep. The Sleep+TMR group received TMR throughout the first and second cycles of SWS as done previously with behavioral performance success, and to decrease the likelihood of participants being awoken that might accompany other stages of sleep with lower waking thresholds (Hauner, Howard, Zelano, & Gottfried, 2013). Delivery of TMR during SWS involved the use of a speaker placed 30 cm from the edge of the bed. The decibel level was increased in 5-dB increments starting from 0 dB until a k-complex was visually apparent on the electroencephalographic recording, which are known to be elicited during the presentation of external stimuli during sleep (Coenen, 2010; Forget, Morin, & Bastien, 2011). Session two began ∼20 min after waking.
EEG coherence and power spectra during REM sleep related to melatonin intake in mild-to-moderate Alzheimer’s disease: a pilot study
Published in International Journal of Neuroscience, 2023
Manuel Alejandro Cruz-Aguilar, Ignacio Ramírez-Salado, Marisela Hernández-González, Miguel Angel Guevara, Ana Paula Rivera-García
In humans, sleep is divided into rapid eye movement (REM) and non-rapid eye movement (No-REM) stages. No-REM sleep is associated with a synchronized EEG pattern in which sleep spindles, K complexes, and high-voltage low-wave activity can be recorded over the entire cortical surface. As No-REM sleep deepens, slow-wave oscillations appear in EEGs and muscle tone is low but not abolished [11]. Compared to the wakefulness state, in No-REM sleep levels of acetylcholine and monoamines are reduced, while the level of GABA increases [12–16]. During REM sleep, muscle activity is strongly suppressed and sleep EEGs show low amplitude, fast activity, and sporadic τ activity, which in humans oscillates between 4-7 Hz. This EEG band plays a role in the consolidation of memory, spatial memory, spatial learning, and emotional memories in the hippocampus, amygdala and prefrontal cortex [17]. Several studies using magnetoencephalography and intracranial electroencephalography in humans have indicated that the hippocampus has a basal frequency of τ oscillations which have been linked to memory and spatial learning [18]. Likewise, the τ coherence between the hippocampus and amygdala is related to the presence of ponto-geniculo-occipital waves and the processing of emotional memory in the hippocampus during REM sleep [17]. Scarpelli et al. [19] showed that τ oscillations in the final minutes of REM sleep predict the retrieval of the memory of subsequent sleep.
Metabolism of megestrol acetate in vitro and the role of oxidative metabolites
Published in Xenobiotica, 2018
Larry House, Michael J. Seminerio, Snezana Mirkov, Jacqueline Ramirez, Maxwell Skor, Joseph R. Sachleben, Masis Isikbay, Hari Singhal, Geoffrey L. Greene, Donald Vander Griend, Suzanne D. Conzen, Mark J. Ratain
To determine sites of metabolic change to MA, NMR spectroscopy was employed. NMR spectra were acquired on a Bruker Avance III HD NMR spectrometer (Billerica, MA) operating at a proton frequency of 600.13 MHz utilizing a 5 mm inverse triple resonance gradient probe tuned to 1H, 13C and 15N. All samples were dissolved in 0.5 ml d-chloroform containing 0.03% (v/v) tetramethylsilane (TMS) (Aldrich, St. Louis, MO) and spectra were acquired at 25 °C. A series of one dimensional regular proton spectroscopy (1H 1D), homonuclear correlation spectroscopy (COSY), nuclear overhauser enhancement spectroscopy (NOESY), total correlation spectroscopy (TOCSY) and heteronuclear single quantum correlation (1H,13C HSQC) spectra were acquired. Typical 1H 90° times were 7.5 μs and the recycle delay was 1 s. In the 1H 1 D spectra, 16 k complex points were acquired over a spectral width of 10 parts per million (ppm) with a resulting acquisition time of 2.7 s. In the 2 D spectra, 1k complex points were typically taken over 10 ppm in the directly detected dimension (acquisition time 170 ms), while in the indirectly detected dimension 128 complex points were acquired with a 10 ppm spectral width for 1H in the COSY, NOESY and TOCSY spectra and 100 ppm for the 13C spectral width in 1H, 13C HSQC.