Rhythmic Fluctuations in Tactile Attention

There is increasing evidence that sensory information in the visual and auditory domains is processed not in a continuous but in a rather rhythmically fluctuating fashion, reflecting underlying oscillations in neural excitability. So far, little is known about whether a similar mechanism is also implemented in the somatosensory modality, which, given its importance for monitoring and protecting our bodily integrity, might sample sensory input differently. Here, we investigated (1) whether tactile detection performance fluctuates over time at the speed of somatosensory alpha- and beta-band oscillations and (2) whether attention samples two simultaneously monitored body parts at different time points, similar to previous demonstrations in the visual and auditory domains. Thirty-one human participants (female and male) performed a behavioral dense-sampling experiment, consisting of a tactile cuing task, in which they responded to tactile vibrations at detection threshold presented to the left or right index fingers. In line with our hypotheses, we observed temporal fluctuations in both hit rates and response times, at a speed of 8-16 Hz, consistent with electrophysiological alpha- and beta-band oscillations commonly observed over somatosensory areas. Further, hit rate fluctuations exhibited phase differences at ~13 Hz between the left and right hands, suggesting that somatosensory spatial attention samples cued and uncued locations at different points in time. Overall, along with recent work, which identified markers of attentional sampling also beyond sensory processing, our study provides novel evidence that cyclical information processing and alternating sampling of simultaneously attended entities might be a general mechanism in the brain.