Dokument: The Invariable Variability of Alpha Oscillations: Alterations in Power and Peak Frequency
| Titel: | The Invariable Variability of Alpha Oscillations: Alterations in Power and Peak Frequency |
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=73659 |
| URN (NBN): | urn:nbn:de:hbz:061-20260622-133824-9 |
| Kollektion: | Dissertationen |
| Sprache: | Englisch |
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation |
| Medientyp: | Text |
| Autor: | Balaji, Vaishali [Autor] |
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| Beitragende: | PD Dr. Lange, Joachim [Gutachter] Prof. Dr. Zimmermann, Eckart [Gutachter] |
| Dewey Dezimal-Klassifikation: | 600 Technik, Medizin, angewandte Wissenschaften » 610 Medizin und Gesundheit |
| Beschreibung: | Alpha oscillations are a defining feature of the brain’s rhythmic activity. Although they were initially dismissed as an idle rhythm, a growing body of evidence indicates that they play an essential role in perception and cognition. Given their functional relevance, the alpha rhythm is unlikely to be static; rather, both its strength and speed are dynamically adjusted. In this thesis, I aimed to elucidate the extent of their flexibility by actively modulating the amplitude of alpha oscillations using weak electrical stimulation in Study 1, and by characterising spontaneous variability in alpha dynamics in Study 2.
In Study 1, we modulated oscillatory alpha activity in the right somatosensory cortex using short trains of transcranial alternating current stimulation (tACS). During simultaneous magnetoencephalography (MEG) recordings, participants received intermittent tACS or no stimulation, which served as a control. Stimulation was administered in 10 s and 30 s trains at an individually-adapted stimulation frequency (ISF), selected to approximate each participant’s alpha peak frequency (APF) at rest. We observed elevations in oscillatory power following tACS relative to control, most prominently around the ISF, with additional effects extending into the beta range. These effects were distributed bilaterally across somatosensory and frontal regions. Notably, 10 s trains produced a greater increase in power than 30 s trains, demonstrating that even very brief periods of tACS can robustly modulate alpha-band activity. Study 2 was motivated by a key limitation identified in Study 1, namely the difficulty of aligning ISF with each participant’s endogenous APF. Using resting-state MEG data from the control sessions of Study 1, we characterised spontaneous fluctuations in APF at a fine temporal scale across the cortex. We found that variability in APF increases systematically along the posterior-to-anterior cortical axis, from occipital to frontal regions. Comparisons with amplitude-matched simulated data confirmed that this gradient could not be explained by measurement noise alone. Across cortical regions, APFs exhibited poor temporal reliability, suggesting that APF reflects a transient state rather than a stable trait. In Study 1, we demonstrated that alpha power can be modulated through brief bouts of electrical stimulation, whereas in Study 2, we showed that alpha frequency fluctuates substantially even in the absence of external modulation. Overall, this work contributes to a broader understanding of alpha oscillations, highlighting that variability is a fundamental characteristic of their dynamics, rather than mere noise. |
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz |
| Fachbereich / Einrichtung: | Medizinische Fakultät » Institute » Institut für Medizinische Psychologie Mathematisch- Naturwissenschaftliche Fakultät |
| Dokument erstellt am: | 22.06.2026 |
| Dateien geändert am: | 22.06.2026 |
| Promotionsantrag am: | 12.02.2026 |
| Datum der Promotion: | 19.05.2026 |
