Abstract
What enables us to think verbally? We hypothesized that the interaction between motor and sensory systems induced speech representation without external stimulation or overt articulation. This motor-to-sensory transformation formed the neural basis that enabled us to think verbally. Analogous to the frequency tracking of neural responses to auditory stimuli, we asked participants to imagine singing lyrics of famous songs rhythmically while their neural electro-magnetic signals were recorded using magnetoencephalography (MEG). We found that when participants imagined with less temporal variation, the neural oscillation at the delta band (same frequency band as the rhythm in the songs) showed more consistent phase coherence across trials. This neural phase tracking of imagined singing was observed in a frontal-parietal-temporal network – the proposed motor-to-sensory transformation pathway, including inferior frontal gyrus (IFG), insula, premotor, intra-parietal sulcus (IPS), temporal-parietal junction (TPJ), primary auditory cortex, and superior temporal gyrus and sulcus (STG & STS). These results suggest that neural oscillations can entrain the rhythm of our mental activity. The coherent activation in the motor-to-sensory transformation neural network mediates the internal construction of perceptual representation and forms the neural computation foundation for inner speech during verbal thinking.