Summary
Tactile experiences in the real world are rich in texture and temporal patterns. While the role of texture in driving somatosensory cortical activity is well established, there is emerging evidence that somatosensory activity is sensitive to tactile temporal statistics (i.e., the time intervals that separate stimuli in trains of successive tactile pulses). Cortical processing of tactile pulses may be shaped by preceding pulses, but this influence will vary with inter-stimulus intervals. It is possible that tactile information lingers only briefly in primary somatosensory cortex and will influence processing of the next pulse only at short intervals; in secondary somatosensory cortex it lingers longer, allowing it to shape the processing of even multiple successive pulses over more prolonged intervals. Here we recorded scalp EEG signals from somatosensory cortex in response to a train of tactile pulses presented to the fingertips with varying inter-stimulus intervals spanning 100 to 10,000 ms. We traced cortical tactile processing through its early (<75 ms), intermediate (75 to 150 ms) and late stages (150 to 300 ms). The early and late stages of somatosensory activity were similarly shaped by the preceding pulse; this influence declined with increasing inter-stimulus interval. The intermediate stage of somatosensory activity was sensitive to both the previous and the penultimate pulses, a sensitivity that was again modulated by their temporal dynamics. Our findings suggest that somatosensory cortex integrates complex temporal patterns during its intermediary processing stages, allowing previous and even penultimate stimuli to modulate ongoing processing of current stimuli.
Competing Interest Statement
A.G. is a co-founder and chairman of QuantActions AG, and is an advisor for Axite B.V. W.W. and K.R.R. had no conflicts to disclose.