The results of this dissertation contribute to the existing literature on neurovascular coupling by suggesting that:
x Simultaneous measurement of neuronal and hemodynamic signals by means of EEG and NIRS represents a powerful tool to study the relationship between direct and indirect neuronal signals in human.
x The resonance phenomenon, a local maximum that appears when the stimulation frequency matches the endogenous alpha-frequency, is not accompanied by an increase in vascular parameters. The scenario depicts a mismatch between the hemodynamic response and dominant electrophysiological signals such as evoked potentials and alpha-power.
x Electrophysiological resting state parameters can provide predictive information for the magnitude of evoked potential, alpha-power and the magnitude of the hemodynamic response upon stimulation.
x Evoked potential and ongoing oscillatory activity in the alpha-range represent no independent electrophysiological signals. The entangled relationship of both signals is manifested in the resonance phenomenon and the relationship of resting alpha-frequency and magnitude of evoked potentials.
x Oscillations in the gamma-range play a pivotal role in visual processing and behavioural performance. The parametrically varied visual stimulus yield to systematic changes in the band only. Faster response times were preceded by a phasic increase in gamma-band activity.
x Higher oscillatory activity represents a neuronal component with a major influence on the hemodynamic signal, irrespective whether the modulatory component origins from external stimulus variation or internal state modulation.
Taken together, the work summarized in this dissertation supports the view that evidence from complementary experiments in humans and animals, as well as the application of concurrent direct electrophysiological based and indirect vascular based methods, can help to elucidate the neurovascular coupling mechanisms. These are of relevance on basic scientific grounds and need to be understood in more detail to fully appreciate the results of neuroimaging techniques relying on the vascular rather than electrophysiological response.
28
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