Mental operations in rhythm: motor-to-sensory transformation mediates imagined singing

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 networkthe 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-tosensory transformation neural network mediates the internal construction of perceptual representation and forms the neural computation foundation for inner speech during verbal thinking.

Metamodal Coupling of Vibrotactile and Auditory Speech Processing Systems Through Matched Stimulus Representations

“…Previous studies have suggested that metamodal engagement is a result of top-down processes such as mental imagery rather than bottom-up processes (Lacey et al, 2009). However, given that in our study, subjects in both algorithm groups were equally proficient at recognizing VT stimuli as words, mental-imagery accounts (Borst and Gelder, 2016; Li et al, 2020; Oh et al, 2013; Tian et al, 2018) in this case would predict that both groups should engage auditory perceptual representations in the mid-STG. Yet, we found no evidence that the token-based VT stimuli engaged this area after training in the same way as auditory speech (see also (Siuda-Krzywicka et al, 2016; Striem-Amit et al, 2012)).…”

Imagined speech can be decoded from low- and cross-frequency features in perceptual space

“…This finding aligns well with the notion that the beta band plays an important role in endogenous processes, notably in relation with top-down control, in particular in the context of language (Arnal and Giraud, 2012; Bowers et al, 2019; Fontolan et al, 2014; Pefkou et al, 2017). Although repeating a heard or written word engages automatic, almost reflex, neural routines, imagined speech is a more voluntary action requiring enhanced endogenous control from action planning frontal regions (Buschman et al, 2012; Li et al, 2020; Morillon et al, 2019). These results must however be taken with caution as spurious CFC can result from non-linearity, non-stationarity, and power changes across conditions in the signal (Aru et al, 2015; Hyafil, 2015).…”