Anodal transcranial direct current stimulation over the right primary somatosensory cortex increases cough reflex sensitivity: a pilot randomised controlled crossover trial.

Background: The cough reflex is a protective reflex of the human body. Increases or decreases in cough reflex sensitivity may be related to chronic cough, aspiration pneumonia and other diseases. The right primary somatosensory cortex (RS1) is the main activation centre for the urge to cough. Here, we discuss the effects of transcranial direct current stimulation (tDCS) of RS1 on the cough reflex and urge to cough. In addition, we explored the role of the left dorsolateral prefrontal cortex (lDLPFC) in cough using tDCS. Methods: 24 healthy young adults completed this pilot randomised controlled crossover experiment. Each person was tested three times, receiving, in random order, anodal tDCS of RS1 or lDLPFC or sham stimulation. The current intensity was set to 2 mA, the stimulation time was 30 min and the interval between any two stimuli was ≥1 week. After each intervention, the citric acid cough challenge test was used immediately to assess the urge to cough and cough reflex sensitivity. Results: The cough reflex thresholds, expressed as LogC2 and LogC5, were significantly reduced after RS1 anodal stimulation compared to sham stimulation, accompanied by increased urge-to-cough sensitivity (urge-to-cough log-log slope 1.19±0.40 point·L·g-1 versus 0.92±0.33 point·L·g-1, p=0.001), but the threshold for the urge to cough did not change significantly. There were no significant changes in the urge to cough and cough reflex sensitivity after tDCS anodal lDLPFC stimulation. Conclusion: Anodal tDCS stimulation of the RS1 can increase urge-to-cough sensitivity and reduce cough reflex threshold. The effects of tDCS on cough reflex, as well as the underlying mechanisms driving those effects, should be explored further.