State and trait characteristics of anterior insula time-varying functional connectivity.

The human anterior insula (aINS) is a topographically organized brain region, in which ventral portions contribute to socio-emotional function through limbic and autonomic connections, whereas the dorsal aINS contributes to cognitive processes through frontal and parietal connections. Open questions remain, however, regarding how aINS connectivity varies over time. We implemented a novel approach combining seed-to-whole-brain sliding-window functional connectivity MRI and k-means clustering to assess time-varying functional connectivity of aINS subregions. We studied three independent large samples of healthy participants and longitudinal datasets to assess inter- and intra-subject stability, and related aINS time-varying functional connectivity profiles to dispositional empathy. We identified four robust aINS time-varying functional connectivity modes that displayed both "state" and "trait" characteristics: while modes featuring connectivity to sensory regions were modulated by eye closure, modes featuring connectivity to higher cognitive and emotional processing regions were stable over time and related to empathy measures

Untersuchung der neuronalen Aktivität mit der Magnetresonanzspektroskopie: Die Rolle der inhibitorischen und exzitatorischen Neurotransmitter in der Gehirndynamik auf Systemebene

This thesis investigates the role of most abundant inhibitory and excitatory neurotransmitters – GABA and glutamate – in the visual system. The combination of two methods: magnetic resonance spectroscopy (MRS) and functional magnetic resonance imaging (fMRI), allowed to relate the levels of neurotransmitters with the neuronal activity. Furthermore, we studied the effects of transcranial magnetic stimulation (TMS) on the GABA- and glutamatergic neurotransmission and the fMRI.Diese Dissertation untersucht die Rolle der wichtigsten inhibitorischen und exzitatorischen Neurotransmitter - GABA und Glutamat - im visuellen System. Die Kombination zweier Methoden: Magnetresonanzspektroskopie (MRS) und funktionell Magnetresonanztomographie (fMRT), erlaubte es, die Neurotransmitterlevel mit der neuronalen Aktivität zu verknüpfen. Darüber hinaus untersuchten wir die Auswirkungen der transkraniellen Magnetstimulation auf die Neurotransmission, sowie auf das fMRT

Opposite Dynamics of GABA and Glutamate Levels in the Occipital Cortex during Visual Processing

Magnetic resonance spectroscopy (MRS) measures the two most common inhibitory and excitatory neurotransmitters, GABA and glutamate, in the human brain. However, the role of MRS-derived GABA and glutamate signals in relation to system-level neural signaling and behavior is not fully understood. In this study, we investigated levels of GABA and glutamate in the visual cortex of healthy human participants (both genders) in three functional states with increasing visual input. Compared with a baseline state of eyes closed, GABA levels decreased after opening the eyes in darkness and Glx levels remained stable during eyes open but increased with visual stimulation. In relevant states, GABA and Glx correlated with amplitude of fMRI signal fluctuations. Furthermore, visual discriminatory performance correlated with the level of GABA, but not Glx. Our study suggests that differences in brain states can be detected through the contrasting dynamics of GABA and Glx, which has implications in interpreting MRS measurements.Othe

State and trait characteristics of anterior insula time-varying functional connectivity.

The human anterior insula (aINS) is a topographically organized brain region, in which ventral portions contribute to socio-emotional function through limbic and autonomic connections, whereas the dorsal aINS contributes to cognitive processes through frontal and parietal connections. Open questions remain, however, regarding how aINS connectivity varies over time. We implemented a novel approach combining seed-to-whole-brain sliding-window functional connectivity MRI and k-means clustering to assess time-varying functional connectivity of aINS subregions. We studied three independent large samples of healthy participants and longitudinal datasets to assess inter- and intra-subject stability, and related aINS time-varying functional connectivity profiles to dispositional empathy. We identified four robust aINS time-varying functional connectivity modes that displayed both "state" and "trait" characteristics: while modes featuring connectivity to sensory regions were modulated by eye closure, modes featuring connectivity to higher cognitive and emotional processing regions were stable over time and related to empathy measures