Sensorimotor integration in cranial muscles tested by short- and long-latency afferent inhibition

Objective: To compressively investigate sensorimotor integration in the cranial-cervical muscles in healthy adults. Methods: Short- (SAI) and long-latency afferent (LAI) inhibition were probed in the anterior digastric (AD), the depressor anguli oris (DAO) and upper trapezius (UT) muscles. A transcranial magnetic stimulation pulse over primary motor cortex was preceded by peripheral stimulation delivered to the trigeminal, facial and accessory nerves using interstimulus intervals of 15-25 ms and 100-200 ms for SAI and LAI respectively. Results: In the AD, both SAI and LAI were detected following trigeminal nerve stimulation, but not following facial nerve stimulation. In the DAO, SAI was observed only following trigeminal nerve stimulation, while LAI depended only on facial nerve stimulation, only at an intensity suprathreshold for the compound motor action potential (cMAP). In the UT we could only detect LAI following accessory nerve stimulation at an intensity suprathreshold for a cMAP. Conclusions: The results suggest that integration of sensory inputs with motor output is profoundly influenced by the type of sensory afferent involved and by the functional role played by the target muscle. Significance: Data indicate the importance of taking into account the sensory receptors involved as well as the function of the target muscle when studying sensorimotor integration, both in physiological and neurological conditions.