MEG and EEG polysomnography studies explore the role of K-Complexes and related EEG rhythms in maintaining a sound and safe sleep
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1
University of Patras, Medical School, Physiology, Greece
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2
AAI Scientific Cultural Services Ltd, Cyprus
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3
King Fahad Medical City, Saudi Arabia
MEG and EEG polysomnography studies explore the role of K-Complexes and related EEG rhythms in maintaining a sound and safe sleep
George K. Kostopoulos1 , Lichan Liu2, Vahe Poghosyan2,3, Vassilios Kokkinos1, Andreas Koupparis1, John Zouridis ,Maria Liti1 and Andreas A. Ioannides2
1 Medical School, University of Patras, Greece, gkkostop@upatras.gr,
2Lab. For Human Brain Dynamics, AAI Scientific Cultural Services Ltd, Cyprus
3 MEG Unit, King Fahad Medical City, Riyadh, KSA
The restorative and memory consolidation functions taking place during sleep demand that the brain is unbiased by ongoing environmental and bodily changes. However complete disconnection from the environment makes an animal vulnerable to predators and to homeostatic emergencies. Possibly in response to this challenge, brain mechanisms have been developed which indiscriminately can disrupt processing of sensory inputs: thalamocortical bursting (EEG spindles 11-15 Hz) and cortical down states (hyperpolarization/disfacilitation of cortical neurons lasting >500 ms, underlying the negative wave of EEG frontocentraly prominent K-complexes). However, what is needed is a neuronal mechanism acting as sentinel, i.e. activated by and evaluating sensory stimuli for their salience to the sleeper and in the (usually) negative case promote sleep maintenance through global brain hypersynchronization (1). Taking a decision on the latter without awakening demands unconscious cognitive action with currently unknown neural correlates. To explore them, we have conducted whole night sleep MEG and dense EEG/polysomnography studies in healthy young adults, with emphasis on NREM-1-2 stage of (light) sleep.
The main EEG findings were: Upon coincidence with singular K-complexes, sporadic fast spindles (13-15 Hz maximizing centro-parietaly) invariably stop for the duration of the KC negative wave (2). About 70% of KC were closely followed by spindles starting at the KC positive phase. These spindles were invariably of higher frequency (by about 1 Hz) than the sporadic spindles or even the spindles which the KC interrupted. We found no correlation between the probability that a KC will be closely followed by a spindle and any of all spindles characteristics and the amplitude, duration and wave shape of the preceding KC. Most often, the negative wave of a KC were crowned by a short oscillation in the high theta range (3). This intra-KC-oscillation had two characteristics not shared by KC negative wave: its sequence of 2-4 wavelets had a power maximum relocating antero-posteriorly, while their intervals became shorter, i.e the oscillating frequency increased towards lower alpha. This quick spatio-spectral shift may reflect an arousing process during the KC and play a role in the unconscious cognitive function of sentinel (1). We conclude that spindles, KC and intra-KC-theta-oscillations are dynamically linked, but not necessarily causally - more likely they are grouped by a slower brain process. In consistency with such a role of K-complexes we found that their emergence was more frequent during the ascending slope of NREM stages - when sleep becomes lighter and perhaps more "perceptive" to stimuli, which need not wake us up - on the contrary spindles were more frequent in the descending slope of NREM stage.
Recent, unpublished tomographic analysis of our MEG data during light sleep (NREM stages 1-2) provided candidate spatiotemporal constrains for such a sentinel mechanisms. Upon sleep onset slow wave activity increased frontally and alpha and higher activity decreased subcortically, leading presumably to dampening of brain responsiveness. K-complexes were shown to emerge 1-2 s after distinct focal spectral power changes in pre-frontal cortex and especially in the cingulate extending rostrally from the mid cingulate across specific areas of the rostral and sub-genual anterior cingulate, areas known to be involved in environmental and internal monitoring. These changes were power increases in all frequency bands (delta, theta, alpha, lower and upper sigma) and were further amplified and spread during and immediately after the K-complexes, presumably contributing to sleep maintenance through wide synchronization. Spindles had distinct from K-complexes generation characteristics.
Finally parallel EEG/ECG analysis revealed that K-complexes (but not spindles) exhibit temporal reciprocal relationship to the cardiac cycle: (a) K-complexes incidence slowly increases to almost double in parallel to the ventricular volume curve and (b) There is a short term biphasic fluctuation in heart rate associated with the K-complex. During the hypothesized sentinel function of K-complexes, the autonomic nervous system may therefore be also on guard.
The above provide evidence for a sentinel system assuring our sound and safe sleep. The characteristics of this system can be studied and exploited in the evaluation of insomnias as well as in the design of personalized remote brain monitoring systems as advanced in ARMOR research project - given that K-complexes, spindles and microarousals have been implicated in epileptic ictogenesis
Acknowledgements
This study was supported by the ARMOR EU research project (European Commission under the Seventh Framework Program (FP7/2007-2013) agreement number 287720).
References
References
1. Halász P. The K-complex as a special reactive sleep slow wave - A theoretical update. Sleep Med Rev. 2015 Oct 8;29:34-40.
2. Kokkinos V, Kostopoulos GK. Human non-rapid eye movement stage II sleep spindles are blocked upon spontaneous K-complex coincidence and resume as higher frequency spindles afterwards. J Sleep Res. 2011 Mar;20(1 Pt 1):57-72.
3. Kokkinos V, Koupparis AM, Kostopoulos GK. An intra-K-complex oscillation with independent and labile frequency and topography in NREM sleep. Front Hum Neurosci. 2013 Apr 26;7:163. doi: 10.3389/fnhum.2013.00163. eCollection 2013.
Keywords:
MEG,
EEG,
ECG,
Sleep,
spindles,
K-complex
Conference:
SAN2016 Meeting, Corfu, Greece, 6 Oct - 9 Oct, 2016.
Presentation Type:
Oral Presentation in the Symposium Epilepsy and Sleep
Topic:
Symposium Epilepsy and Sleep
Citation:
Kostopoulos
GK,
Liu
L,
Poghosyan
V,
Kokkinos
V,
Koupparis
AM,
Zouridis
J,
Liti
M and
Ioannides
AA
(2016). MEG and EEG polysomnography studies explore the role of K-Complexes and related EEG rhythms in maintaining a sound and safe sleep.
Conference Abstract:
SAN2016 Meeting.
doi: 10.3389/conf.fnhum.2016.220.00111
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Received:
22 Jul 2016;
Published Online:
01 Aug 2016.
*
Correspondence:
Dr. George K Kostopoulos, University of Patras, Medical School, Physiology, Patra, Achaia, 26500, Greece, gkkostop@med.upatras.gr