Regional differences in cortical electroencephalogram (EEG) slow wave activity and interhemispheric EEG asymmetry in the fur seal

UCLA & VA GLAHS, Sepulveda, CA, USA Utrish Dolphinarium Ltd, Moscow, Russia Severtsov Institute of Ecology and Evolution, Moscow, Russia South Federal University, Rostov-on-Don, Russia.
Journal of Sleep Research (Impact Factor: 3.35). 06/2012; 21(6). DOI: 10.1111/j.1365-2869.2012.01023.x
Source: PubMed


Slow wave sleep (SWS) in the northern fur seal (Callorhinus ursinus) is characterized by a highly expressed interhemispheric electroencephalogram (EEG) asymmetry, called 'unihemispheric' or 'asymmetrical' SWS. The aim of this study was to examine the regional differences in slow wave activity (SWA; power in the range of 1.2-4.0 Hz) within one hemisphere and differences in the degree of interhemispheric EEG asymmetry within this species. Three seals were implanted with 10 EEG electrodes, positioned bilaterally (five in each hemisphere) over the frontal, occipital and parietal cortex. The expression of interhemispheric SWA asymmetry between symmetrical monopolar recordings was estimated based on the asymmetry index [AI = (L-R)/(L+R), where L and R are the power in the left and right hemispheres, respectively]. Our findings indicate an anterior-posterior gradient in SWA during asymmetrical SWS in fur seals, which is opposite to that described for other mammals, including humans, with a larger SWA recorded in the parietal and occipital cortex. Interhemispheric EEG asymmetry in fur seals was recorded across the entire dorsal cerebral cortex, including sensory (visual and somatosensory), motor and associative (parietal or suprasylvian) cortical areas. The expression of asymmetry was greatest in occipital-lateral and parietal derivations and smallest in frontal-medial derivations. Regardless of regional differences in SWA, the majority (90%) of SWS episodes with interhemispheric EEG asymmetry meet the criteria for 'unihemispheric SWS' (one hemisphere is asleep while the other is awake). The remaining episodes can be described as episodes of bilateral SWS with a local activation in one cerebral hemisphere.

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    • "The local, use-dependent facet of sleep regulation had been suggested about 20 years ago, and since then it has received substantial experimental support (Krueger and Obal 1993; Krueger et al. 2008). The most appealing evidence for the local occurrence of sleep has been obtained from marine mammals, such as dolphins and seals, which exhibit unihemispheric slow wave activity while in water (Lyamin et al. 2012; Mukhametov et al. 1977). Such asymmetries appear to be homeostatically regulated, as manifested in a unilateral increase of SWA after selective suppression confined to one hemisphere (Oleksenko et al. 1992). "
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