Public defence in Systems Neuroscience, M.Psych. Heidi Ala-Salomäki

Title of the thesis: Reliable MEG metrics of cortical language function

Doctoral student: Heidi Ala-Salomäki
Opponent: Associate Professor Vitória Piai, Radboud University, Donders Centre for Cognition, Netherlands
Custos: Professor Riitta Salmelin, Aalto University School of Science, Department of Neuroscience and Biomedical Engineering

Language production, as a critical function for humans, is widely studied across different brain imaging metrics. MEG (magnetoencephalography) is a direct measure of the activity of neural populations and it provides information on brain processing at high time resolution. MEG evoked responses represent time-locked changes of brain activation at a certain brain location. Whereas, the processing performed by groups of connected brain regions can be studied by quantifying MEG oscillatory activity and functional connectivity. Understanding language production in brain requires a cohesion of a wide variety of findings, highlighting the reliability of the findings. However, currently, little is known about the reliable brain features related to language production, or about factors affecting reliability. This thesis aimed to diminish this gap by using different MEG metrics: evoked responses, modulation of oscillatory activity, and functional connectivity. A further aim was to define factors affecting reliability, as well as to study reliability at the level of individual participants.

The findings of this thesis illustrated that different MEG metrics provide complementary information on reliable brain features related to language production: The reliable evoked activations were highly left-lateralized and occurred near the Sylvian fissure. In contrast, the reliable oscillatory activity and functional connectivity were highlighted in bilateral motor regions. This thesis also illustrated that the beta oscillatory activity in motor regions was reliably detectable during language production task and also during resting state. To summarize, the findings of this thesis provide high spatiotemporal and complementary information on reliable brain features for language production.

What should be done in future studies investigating reliability of brain imaging findings? This thesis proposes that studying the link between the brain’s functional and structural properties and reliability can offer insight into the reliable functional features of the brain. In addition, it is important to consider the validity and behavioral relevance of the brain imaging findings. Moreover, this thesis made a successful effort to advance towards examining individuality when studying reliability. These are critical steps, especially in the sense of finding associations between brain signals and behavioral phenotypes for clinical purposes. 

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/ 

Doctoral theses at the School of Science: https://aaltodoc.aalto.fi/handle/123456789/52