Master thesis : Clarifying the Neuronal and Neurovascular Properties of the fMRI Global Signal Amplitude During Mind-Blanking Reports

Abstract

Mind-blanking, a state where individuals report an absence of thought, has been associated with slow-wave electroencephalogram (EEG) activity and increased functional magnetic resonance imaging (fMRI) global signal amplitude (GSA). However, the specific contributions to GSA during this state remain unclear. The objective of this study is to identify and clarify the specific components of the fMRI global signal during mind-blanking. Understanding how these components contribute to the phenomenon can shed light on the underlying neural and physiological mechanisms driving this state. We analysed the data collected from the simultaneous EEG–fMRI. Participants performed the Sustained Attention to Response Task and were asked to report their mental state and level of alertness throughout the experiment. We extracted fMRI GSA, EEG oscillatory amplitudes, and heart rate variability derived from electrocardiogram (ECG) from these data. Then, linear mixed-effects models were used to examine how these measures relate to GSA across mind-blanking, mind-wandering, and on-task conditions.

Our findings showed that when individuals reported mind-blanking episodes, the global signal amplitude was significantly negatively linked to delta and theta EEG activity, and moderately positively linked to physiological factors, particularly heart rate variability. Across all states, GSA correlated positively with theta and negatively with alpha oscillations. In summary, the observed increase in the global signal amplitude appears to be primarily driven by physiological changes, which can provide insights that mind blanking is not a purely neuronal process and can be associated with increased heart rate activity as well.