When it comes to perception, one of the most remarkable characteristics of the brain is its omnipresent variability: Even to identical sensory stimuli, no neural response is the same. It has been hypothesized that this response variability is induced by fluctuations of the brain’s instantaneous state, yet the underlying dynamics that link such neural states with stimulus-related processes remain poorly understood. Specifically, fluctuations of excitability in sensory regions of the cortex may shape the brain’s response to external stimuli and hence the perception thereof. The current work aimed at characterizing the modulatory role and spatiotemporal organization of cortical excitability in a series of three somatosensory stimulation paradigms in humans, employing electroencephalography (EEG) to examine the interplay between pre-stimulus oscillatory state and short-latency somatosensory evoked potentials, as well as their association with the consciously accessible stimulus percept. Excitability dynamics of the primary somatosensory cortex were found to be (i) temporally structured in a special way (long-range temporal dependencies in line with the concept of criticality), (ii) linked to the behaviorally perceived stimulus intensity already through initial cortical responses, and (iii) organized with spatially confined, somatotopic patterns. Taken together, these findings suggest that fluctuations of cortical excitability reflect the maintenance of a sensitive tradeoff between robustness and flexibility of neural responses to sensory stimuli, enabling the brain to adaptively change the neural encoding of even low-level stimulus features, such as the stimulus’ intensity. Importantly, however, moment-to-moment neural response variability appears not to occur “at random”, that is, in a stochastically independent manner, but to be organized according to specific principles – both in the temporal and spatial domain.