Cortical integration of tactile inputs distributed across timescales.

Sensory experiences in the real world cut across timescales from milliseconds to seconds. Emerging evidence suggests that somatosensory processing is sensitive to the temporal structure of the stimuli in the sub-second scale, yet only a few select ranges within this scale have been studied. To process real-world information, the integration of tactile inputs must occur over a much broader temporal range. To address temporal integration across timescales, we studied scalp EEG signals from somatosensory cortex in response to a train of tactile stimuli presented to the fingertips with varying inter-stimulus intervals (ISIs) spanning hundreds of milliseconds to several seconds. We captured the variations in cortical signals as a function of the subsequent ISIs (next interval structure). We tracked cortical tactile processing through its early (<75 ms), intermediate (75 to 150 ms), and late stages (150 to 300 ms). We find that the early and late stages of cortical activity were sensitive to the previous ISI; EEG signals were suppressed with ISIs <500 ms and enhanced with longer ISIs, with this effect persisting even when ISIs were approximately 8 s. The intermediate stage of cortical activity was sensitive to both the previous and the penultimate ISIs. Our findings suggest that the specific somatosensory cortical processing stages integrate temporal structure across timescales to enable complex sensory experiences.