The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Dynamic Correlations in Ongoing Neuronal Oscillations in Humans – Perspectives on Brain Function and its Disorders

Simo Monto

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium B at the Aalto University School of Science and Technology (Espoo, Finland) on the 29th of April 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3115-6)   [1184 KB]
Dissertation is also available in print (ISBN 978-952-60-3114-9)


This Thesis is involved with neuronal oscillations in the human brain and their coordination across time, space and frequency. The aim of the Thesis was to quantify correlations in neuronal oscillations over these dimensions, and to elucidate their significance in cognitive processing and brain disorders.

Magnetoencephalographic (MEG) recordings of major depression patients revealed that long-range temporal correlations (LRTC) were decreased, compared to control subjects, in the 5 Hz oscillations in a manner that was dependent on the degree of the disorder. While studying epileptic patients, on the other hand, it was found that the LRTC in neuronal oscillations recorded intracranially with electroencephalography (EEG) were strengthened in the seizure initiation region.

A novel approach to map spatial correlations between cortical regions was developed. The method is based on parcellating the cortex to patches and estimating phase synchrony between all patches. Mapping synchrony from inverse-modelled MEG / EEG data revealed wide-spread phase synchronization during a visual working memory task. Furthermore, the network architectures of task-related synchrony were found to be segregated over frequency.

Cross-frequency interactions were investigated with analyses of nested brain activity in data recorded with full-bandwidth EEG during a somatosensory detection task. According to these data, the phase of ongoing infra-slow fluctuations (ISF), which were discovered in the frequency band of 0.01-0.1 Hz, was correlated with the amplitude of faster > 1 Hz neuronal oscillations. Strikingly, the behavioral detection performance displayed similar dependency on the ISFs as the > 1 Hz neuronal oscillations.

The studies composing this Thesis showed that correlations in neuronal oscillations are functionally related to brain disorders and cognitive processing. Such correlations are suggested to reveal the coordination of neuronal oscillations across time, space and frequency. The results contribute to system-level understanding of brain function.

This thesis consists of an overview and of the following 5 publications:

  1. Klaus Linkenkaer-Hansen, Simo Monto, Heikki Rytsälä, Kirsi Suominen, Erkki Isometsä, and Seppo Kähkönen. 2005. Breakdown of long-range temporal correlations in theta oscillations in patients with major depressive disorder. The Journal of Neuroscience, volume 25, number 44, pages 10131-10137.
  2. Simo Monto, Sampsa Vanhatalo, Mark D. Holmes, and J. Matias Palva. 2007. Epileptogenic neocortical networks are revealed by abnormal temporal dynamics in seizure-free subdural EEG. Cerebral Cortex, volume 17, number 6, pages 1386-1393.
  3. Simo Monto, Satu Palva, Juha Voipio, and J. Matias Palva. 2008. Very slow EEG fluctuations predict the dynamics of stimulus detection and oscillation amplitudes in humans. The Journal of Neuroscience, volume 28, number 33, pages 8268-8272.
  4. Simo Monto, Satu Palva, Shrikanth Kulashekhar, and Matias Palva. 2010. Mapping brain-wide neuronal interactions from MEG / EEG recordings using cortical parcellations. Espoo, Finland: Aalto University School of Science and Technology. 30 pages. Helsinki University of Technology, Department of Biomedical Engineering and Computational Science Publications, Report A14. ISBN 978-952-60-3113-2.
  5. Satu Palva, Simo Monto, and J. Matias Palva. 2010. Graph properties of synchronized cortical networks during visual working memory maintenance. NeuroImage, volume 49, number 4, pages 3257-3268.

Keywords: magnetoencephalography, electroencephalography, human brain, neuronal oscillations, epilepsy, cognition

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Last update 2011-05-26