Neural correlates of conscious and unconscious somatosensory processing

Every day there are somatosensory stimuli on our skin that we perceive one moment and the next not, despite their unchanged physical presence (e.g., insects, wind, clothing). Yet, which are the physiological determinants and neural correlates that accompany external stimuli to enter consciousness or not? To address this question and inform theories of consciousness, this dissertation presents three empirical studies that used weak electrical finger-nerve stimulation which led - despite being physically identical - to subjective experiences of stimulus presence and absence. The first two studies investigated the interaction of tactile conscious perception with two dominant body rhythms: the cardiac and respiratory cycle. The third study investigated the configuration of neural networks being involved in this near-threshold phenomenon. Tactile conscious perception changed over the course of the cardiac cycle (increased detection during diastole) and respiration was tuned such that stimuli occurred more likely during late inspiration / early expiration, resulting in increased detection during early expiration. On the neural level, conscious perception was accompanied by global broadcasting of sensory content across the brain without substantial reconfiguration of the whole-brain functional network in terms of graph metrics. The cardiac cycle effect on conscious tactile perception is a result of cognitive processes which model and predict our body’s internal state to inform perception and guide behavior (e.g., tuning respiration). This perceptual integration of interoceptive and exteroceptive 'beliefs' is also an explanation for widely distributed brain activity differences without whole-brain functional network changes when a tactile stimulus is perceived