Continuous theta burst stimulation over the dorsolateral prefrontal cortex improves force steadiness during submaximal contractions without visual feedback.
BACKGROUND Without visual feedback, the central nervous system must rely on the integration of internal models and proprioceptive information. While the dorsolateral prefrontal cortex (DLPFC) is involved in motor control and sensorimotor monitoring, whether it causally influences force steadiness and whether any such influence is dependent on corticospinal excitability remains unclear. OBJECTIVE This study aimed to investigate whether modulating DLPFC activity using theta burst transcranial stimulation (TBS) influences force steadiness during submaximal contractions performed without visual feedback, and whether this depends on corticospinal excitability. METHODS Twenty-eight healthy volunteers were randomly assigned to receive either inhibitory continuous TBS (cTBS) or facilitatory intermittent TBS over the left DLPFC. Participants performed a 35% submaximal isometric wrist flexion task without visual feedback. We assessed the submaximal force and its coefficient of variation. Motor evoked potentials (MEPs) and maximal voluntary contraction force were also measured at pre, 15 min, and 30 min poststimulation. RESULTS Following cTBS, the coefficient of variation of submaximal force significantly decreased at 15 min poststimulation (P = 0.013), indicating improved force steadiness. This improvement occurred without any significant changes in MEP amplitudes, maximal voluntary contraction force, or the mean level of submaximal force production. CONCLUSION Transient inhibition of the left DLPFC may enhance force steadiness without visual feedback. This enhancement was not accompanied by detectable changes in resting corticospinal excitability. These results suggest that the DLPFC contributes to the qualitative stability of motor output, possibly by optimizing sensorimotor integration and mitigating maladaptive monitoring of internal feedback under limited-feedback situations.