The dark side of the alpha rhythm: fMRI evidence for induced alpha modulation during complete darkness

Authors

  • Eti Ben-Simon,

    1. Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
    2. Functional Brain Center, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center, Tel- Aviv, Israel
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  • Ilana Podlipsky,

    1. Functional Brain Center, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center, Tel- Aviv, Israel
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  • Hadas Okon-Singer,

    1. Functional Brain Center, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center, Tel- Aviv, Israel
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  • Michal Gruberger,

    1. Functional Brain Center, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center, Tel- Aviv, Israel
    2. Department of Computer Science, Tel Aviv University, Tel Aviv, Israel
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  • Dean Cvetkovic,

    1. School of Electrical and Computer Engineering, RMIT University, Melbourne, Australia
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  • Nathan Intrator,

    1. Department of Computer Science, Tel Aviv University, Tel Aviv, Israel
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  • Talma Hendler

    Corresponding author
    1. Functional Brain Center, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center, Tel- Aviv, Israel
    2. School of Psychological Sciences, Tel Aviv University, Tel Aviv, Israel
    • Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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Correspondence: Professor T. Hendler, as above.

E-mail: talma@tasmc.health.gov.il

Abstract

The unique role of the EEG alpha rhythm in different states of cortical activity is still debated. The main theories regarding alpha function posit either sensory processing or attention allocation as the main processes governing its modulation. Closing and opening eyes, a well-known manipulation of the alpha rhythm, could be regarded as attention allocation from inward to outward focus though during light is also accompanied by visual change. To disentangle the effects of attention allocation and sensory visual input on alpha modulation, 14 healthy subjects were asked to open and close their eyes during conditions of light and of complete darkness while simultaneous recordings of EEG and fMRI were acquired. Thus, during complete darkness the eyes-open condition is not related to visual input but only to attention allocation, allowing direct examination of its role in alpha modulation. A data-driven ridge regression classifier was applied to the EEG data in order to ascertain the contribution of the alpha rhythm to eyes-open/eyes-closed inference in both lighting conditions. Classifier results revealed significant alpha contribution during both light and dark conditions, suggesting that alpha rhythm modulation is closely linked to the change in the direction of attention regardless of the presence of visual sensory input. Furthermore, fMRI activation maps derived from an alpha modulation time-course during the complete darkness condition exhibited a right frontal cortical network associated with attention allocation. These findings support the importance of top-down processes such as attention allocation to alpha rhythm modulation, possibly as a prerequisite to its known bottom-up processing of sensory input.

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