Resting-state functional connectivity changes following audio-tactile speech training

Understanding speech in background noise is a challenging task, especially if the signal is also distorted. In a series of previous studies we have shown that comprehension can improve if simultaneously to the auditory speech, the person receives speech-extracted low-frequency signals on fingertips. The effect increases after short audio-tactile speech training. Here we use resting-state functional magnetic resonance, measuring spontaneous low-frequency oscillations in the brain while at rest, to assess training-induced changes in functional connectivity. We show enhanced connectivity within a right-hemisphere cluster encompassing the middle temporal motion area (MT), and the extrastriate body area (EBA), and lateral occipital cortex (LOC), which before training is found to be more connected to bilateral dorsal anterior insula. Furthermore, early visual areas are found to switch from increased connectivity with the auditory cortex before, to increased connectivity with an association sensory/multisensory parietal hub, contralateral to the palm receiving vibrotactile inputs, after. Also the right sensorimotor cortex, including finger representations, is more connected internally after training. The results alltogether can be interpreted within two main complementary frameworks. One, speech-specific, relates to the pre-existing brain connectivity for audio-visual speech processing, including early visual, motion and body regions for lip-reading and gesture analysis in difficult acoustic conditions, which the new audio-tactile speech network might be built upon. The other refers to spatial/body awareness and audio-tactile integration, including in the revealed parietal and insular regions. It is possible that an extended training period may be necessary to more effectively strengthen direct connections between the auditory and sensorimotor brain regions, for the utterly novel speech comprehension task. The outcomes of the study can be relevant for both basic neuroscience, as well as development of rehabilitation tools for the hearing impaired population.