Concordance of MEG and fMRI patterns in adolescents during verb generation

In this study we focused on direct comparison between the spatial distributions of activation detected by functional magnetic resonance imaging (fMRI) and localization of sources detected by magnetoencephalography (MEG) during identical language tasks. We examined the spatial concordance between MEG and fMRI results in 16 adolescents performing a three-phase verb generation task that involves repeating the auditorily presented concrete noun and generating verbs either overtly or covertly in response to the auditorily presented noun. MEG analysis was completed using a synthetic aperture magnetometry (SAM) technique, while the fMRI data were analyzed using the general linear model approach with random-effects. To quantify the agreement between the two modalities, we implemented voxel-wise concordance correlation coefficient (CCC) and identified the left inferior frontal gyrus and the bilateral motor cortex with high CCC values. At the group level, MEG and fMRI data showed spatial convergence in the left inferior frontal gyrus for covert or overt generation versus overt repetition, and the bilateral motor cortex when overt generation versus covert generation. These findings demonstrate the utility of the CCC as a quantitative measure of spatial convergence between two neuroimaging techniques

Examining phonological processing in the healthy and damaged brain

In this thesis I explore the neural signature of different types of speech sound processing, in the healthy brain and after damage through stroke. The first two Experiments applied a newly developed fMRI language paradigm in healthy controls to study phonological retrieval from speech, orthography and semantics. This showed that there are at least two types of phonological processing that can be dissociated on a neuronal level. Bilateral superior temporal gyri were associated with processing auditory (phonological) representations of speech, consistent with the notion of input to phonology. In contrast, left putamen and precentral cortex/pars opercularis were associated with pre-articulatory activity, and thus with outputs from phonology. The validation of the results in a separate, larger sample increased confidence that these findings are robust rather than false positives. Experiment 3 was concerned with examining the role of a “key player” in phonological processing, which revealed that different parts of the supramarginal gyrus differ in their response profile during a set of language tasks. This is in accordance with cytoarchitectural and connectivity studies demonstrating the structural variability of the region, and has implications for prior imaging studies considering the supramarginal gyrus as a uniform entity in the phonological network. The final experiment revealed that the loss of supramarginal gyrus through stroke has inconsistent effects on language abilities, possibly due to other brain regions or white matter tracts that were damaged in some patients but not in others. It also showed that additional brain regions were recruited in patients compared to controls, which might reflect compensatory brain activation that supports recovery. Taken together, this work proposes a new way of interpreting phonological effects, in particular within the supramarginal gyrus, and new insights into how the brain supports phonological processing after stroke-induced damage

Functional Magnetic Resonance Imaging

"Functional Magnetic Resonance Imaging - Advanced Neuroimaging Applications" is a concise book on applied methods of fMRI used in assessment of cognitive functions in brain and neuropsychological evaluation using motor-sensory activities, language, orthographic disabilities in children. The book will serve the purpose of applied neuropsychological evaluation methods in neuropsychological research projects, as well as relatively experienced psychologists and neuroscientists. Chapters are arranged in the order of basic concepts of fMRI and physiological basis of fMRI after event-related stimulus in first two chapters followed by new concepts of fMRI applied in constraint-induced movement therapy; reliability analysis; refractory SMA epilepsy; consciousness states; rule-guided behavioral analysis; orthographic frequency neighbor analysis for phonological activation; and quantitative multimodal spectroscopic fMRI to evaluate different neuropsychological states

The Affective Amygdala : towards a better understanding of adolescent depressive and anxiety disorders

This thesis aimed to investigate the neurobiological mechanisms of adolescent onset depression and anxiety disorders. A longitudinal fMRI study design was used that included both task related brain activation and resting state functional connectivity. All participants were scanned three times in a six-month period. In between scan sessions the adolescents from the clinical group received treatment as usual. Adolescents from the control group were scanned within the same time interval but did not receive treatment. During a scan session several MRI parameters were collected including task based fMRI (emotional face processing task) and resting state fMRI. We also administered several questionnaires about derpession and anxiety symptomatology. It was demonstrated that adolescents with depressive and anxiety disorders show differentiating patterns of amygdala reactivity and connectivity compared to a healthy control group. Furthermore, using a dimensional approach and taking individual differences in self-reported depression and anxiety symptoms into account highlighted the role of self-reported anxiety symptoms in amygdala reactivity during emotional faces processing. These findings indicate that the amygdala indeed is an important region involved in emotional face processing and that focusing on this region can provide further insights in the development and persistence of depressive and anxiety disorders in adolescents.Pathways through Adolescenc

Absolute quantification of oxygen metabolism in the human brain using FMRI

To produce energy and maintain healthy function the brain requires a steady supply of oxygen which if interrupted results in impaired function and tissue damage. Oxygen metabolism is therefore presented as a desirable physiological function to measure as it is closely linked with brain tissue function and health. Recently an MRI method was introduced capable of measuring absolute oxygen metabolism in the brain. The technique is based on using both hypercapnic and hyperoxic respiratory challenges to calibrate the blood oxygen level dependent (BOLD) functional MRI (FMRI) signal. The aim of this thesis is to further develop this promising technique, referred to here as dual calibrated FMRI (dcFMRI), proving its suitability for application in further studies of oxygen metabolism in the brain. Initially, in this thesis, the role of oxygen metabolism in energy production, brain function and disease is discussed. To motivate the development of dcFMRI a review of current measurement techniques is presented followed by an introduction to the basic MRI concepts underpinning the dcFMRI approach. The dcFMRI technique is then described in detail. The optimal ASL acquisition available in our centre for application in the dcFMRI measurement was experimentally investigated, allowing a dcFMRI protocol to be implemented. A comparison of dcFMRI respiratory designs, for detecting regional changes in oxygen metabolism, was made and the within and between session repeatability of these measurements were assessed. In order to make the technique more clinically feasible, reductions in acquisition time were assessed using a retrospective analytical approach. The ability of dcFMRI to detect global flow related changes in oxygen metabolism was demonstrated and a novel dcFMRI approach was implemented. This availed of an R2' based measure to replace the hypercapnic respiratory challenge in the dcFMRI protocol. Potential areas for future work and further application of the dcFMRI technique are then considered