Speech listening specifically modulates the excitability of tongue muscles: a TMS study

The precise neural mechanisms underlying speech perception are still to a large extent unknown. The most accepted view is that speech perception depends on auditory-cognitive mechanisms specifically devoted to the analysis of speech sounds. An alternative view is that, crucial for speech perception, it is the activation of the articulatory (motor) gestures that generate these sounds. The listener understands the speaker when his/her articulatory gestures are activated (motor theory of speech perception). Here, by using transcranial magnetic stimulation (TMS), we demonstrate that, during speech listening, there is an increase of motor-evoked potentials recorded from the listeners' tongue muscles when the presented words strongly involve, when pronounced, tongue movements. Although these data do not prove the motor theory of speech perception, they demonstrate for the first time that word listening produces a phoneme specific activation of speech motor centres.