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Trial Lecture – time and place
See Trial Lecture.
Adjudication committee
- First opponent: Professor Bjørn Ebdrup, University of Copenhagen, Denmark
- Second opponent: Senior Lecturer Predrag Petrovic, Karolinska Institutet, Sweden
- Third member and chair of the evaluation committee: Professor II Agnieszka Butwicka, University of Oslo
Chair of the Defence
Professor Randi Ulberg, University of Oslo
Principal Supervisor
Researcher Kjetil Nordbø Jørgensen, University of Oslo
Summary
Psychotic disorders are severe conditions that often involve changes in perception, such as visual and auditory hallucinations. Previous research has suggested that the brain regions responsible for processing visual and auditory information may function differently in these disorders. However, it is unclear why these functional changes occur.
The main aim of this thesis was to investigate how brain function and brain structure are related in the visual and the auditory cortices, both in healthy individuals and in people with psychotic disorders. Brain function was measured using electroencephalography (EEG), specifically event related potentials (ERPs), which capture the brain’s electrical responses to external sensory stimuli. Brain structure was assessed using magnetic resonance imaging (MRI) to provide information about cortical surface area, thickness, and myelination.
In this thesis, I focused specifically on examining both the function and the structural characteristics of the visual and auditory cortices, in order to better understand how alterations in these regions may be linked to psychotic disorders.
The study included healthy control participants as well as individuals diagnosed with schizophrenia spectrum disorders or bipolar disorder.
In healthy individuals, the results showed a positive relationship between the strength (amplitude) of the P100 component of the visual evoked potential (VEP) - an EEG measure reflecting function in the visual cortex - and the surface area of the visual cortex. In other words, a larger visual cortical surface area was associated with a stronger neural response to visual stimuli.
Among individuals with schizophrenia spectrum disorders, a lower amplitude of the N100 component of the auditory evoked potential (AEP) - an EEG measure reflecting activity in the auditory cortex - was associated with a thinner auditory cortex. This association was particularly evident in individuals who had experienced auditory hallucinations. These findings suggest that structural and functional changes in the auditory cortex may be linked and could reflect a shared neural mechanism related to auditory hallucinations.
The results also indicated that biological sex may play a role in how psychotic disorders affect brain function. Males with schizophrenia spectrum disorders showed lower N100 amplitudes compared to healthy males, whereas no comparable differences were observed among women. This highlights the importance of considering biological sex in neurobiological research and may help why illness trajectory and treatment response often differ between men and women.
Measures of myelin in the auditory cortex did not explain the observed correlations between reduced auditory function (lower N100 amplitude) and thinner auditory cortex in individuals with schizophrenia spectrum disorders.
The findings show a clear link between brain structure and function in the visual cortex of healthy individuals and in the auditory cortex of individuals with schizophrenia spectrum disorders. They highlight the importance of studying basic sensory processes to better understand psychotic symptoms, as early sensory alterations may form part of the neurobiological basis of these disorders. The results also emphasize the need to consider biological sex in future research. Greater insight into these mechanisms may ultimately contribute to improved diagnostics and more targeted, effective treatments for psychotic disorders.
Additional information
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