Abstract
Motor cortex transcranial direct current stimulation (tDCS) has been shown to enhance motor learning in healthy adults as well as various neurological conditions. However, there has been limited data on whether tDCS enhances jaw motor performance during different oral behaviors such as speech, maximum syllable repetition, and chewing. Because the effects of anodal and cathodal stimulation are known to be dependent on task demands, we hypothesized that tDCS would have a distinct effect on the jaw motor performance during these disparate oral behaviors. Ten healthy adults completed speech, maximum syllable repetition, and chewing tasks as their jaw movements were recorded using 3D optical motion capture during sham, anodal, and cathodal tDCS. Our findings showed that compared to the sham condition, jaw displacements during speech and syllable repetition were smaller during anodal stimulation, but larger during cathodal stimulation for syllable repetition and chewing indicating improved performance during anodal tDCS. On the other hand, there were no effects of anodal tDCS during chewing. These results confirm our hypotheses that: (1) tDCS induces a significant effect on jaw motor function; (2) its effects are polarity dependent; and (3) its effects are dependent on the task demands on jaw motor function. These findings support future studies exploring the effects of tDCS on persons with oral sensorimotor impairments and the development of therapeutic protocols.
Highlights
Transcranial direct current stimulation is a form of non-invasive brain stimulation that is widely being tested to enhance motor learning (Bolognini et al, 2009; Grimaldi et al, 2016)
We investigate if transcranial direct current stimulation (tDCS) has short-term effects on jaw motor function during three oral motor behaviors—speech, maximum syllable repetition, and chewing gum
Post hoc analysis revealed that duration became shorter, as compared to sham, with anodal tDCS, p < 0.001, and cathodal tDCS, p = 0.003
Summary
Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that is widely being tested to enhance motor learning (Bolognini et al, 2009; Grimaldi et al, 2016). Given that a motor behavior is a dynamic process and engages different neural areas according to the complexity of the task, the effects of tDCS depends on the task and relative neural engagement For complex behaviors, such as spoken word production, this entails that stimulation of the motor cortex is likely to affect the many concurrent processes (i.e., linguistic, cognitive, attention) engaged during speech production (Bohland et al, 2010) and level of skill required for the specific task. Given these complex interactions between polarity and task demands, it is critical to investigate the specific effects of tDCS on speech motor performance, as to optimize the outcomes of tDCS therapeutic trials (Bikson and Rahman, 2013)
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