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

Katarzyna Ciesla ^1* Tomasz Wolak ² Amir Amedi ¹

• ¹ Reichman University, Herzliya, Israel
• ² Institute of Physiology and Pathology of Hearing (IFPS), Warsaw, Masovian, Poland

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 imaging, measuring spontaneous low-frequency oscillations in the brain while at rest, to assess training-induced changes in functional connectivity. We show enhanced functional connectivity within a right-hemisphere cluster corresponding to 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 a sensory/multisensory association 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 altogether 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 framework refers to spatial/body awareness and audio-tactile integration, both necessary for performing the task, including in the revealed parietal and insular regions. It is possible that an extended training period is necessary to directly strengthen functional connections between the auditory and the sensorimotor brain regions for the utterly novel multisensory task. The results contribute to a better understanding of the largely unknown neuronal mechanisms underlying tactile speech benefits for speech comprehension and may be relevant for rehabilitation in the hearingimpaired population.