Brain encoding of naturalistic, continuous, and unpredictable tactile events

Abstract

AbstractStudies employing EEG to measure somatosensory responses have been typically optimized to compute event-related potentials in response to discrete events (ERPs). However, tactile interactions involve continuous processing of non-stationary inputs that change in location, duration, and intensity. To fill this gap, this study aims to demonstrate the possibility of measuring the neural tracking of continuous and unpredictable tactile information. Twenty-seven young adults (females = 15) were continuously and passively stimulated with a random series of gentle brushes on single fingers of each hand, which were covered from view. Thus, tactile stimulations were unique for each participant, and fingers were stimulated. An encoding model measured the degree of synchronization between brain activity and continuous tactile input, generating a temporal response function (TRF). Brain topographies associated with the encoding of each finger stimulation showed a contralateral response at central sensors starting at 50 ms and peaking at about 140 ms of lag, followed by a bilateral response at about 240 ms. A series of analyses highlighted that reliable tactile TRF emerged after just 3 minutes of stimulation. Our results demonstrated for the first time the possibility of using EEG to measure the neural tracking of a naturalistic, continuous, and unpredictable stimulation in the somatosensory domain. Crucially, this approach allows the study of brain activity following individualized, idiosyncratic tactile events. This approach can potentially foster novel ways for investigating tactile processing by replacing artificial laboratory-constrained tasks with ecological real-world interactions.Significant StatementThis study expanded the horizons of research conducted on neural tracking, opening the exploration of idiosyncratic tactile events occurring in the real world and overcoming constraints of laboratory tasks that typically rely on discrete events. We validated a protocol for the ecological investigations of continuous tactile processing of the hands. This paradigm-shifting study redefines the possible employment of the EEG for the cracking of somatosensory neural representations, which have been inaccessible so far. Our findings unravel coherent neural responses to continuous and naturalistic touch and represent a novel frontier in EEG applications to bodily senses.