Somatosensory feedback mechanisms in tongue and speech muscle movements

The silent period of the tongue muscles was examined in two groups of 3 patients after operation upon the two main somatosensory pathways of the tongue in order to find out whether the servocontrol theory is also applicable to tongue and speech movements. The silent period was found to be in the normal range in the first group of patients (group I) who underwent surgery to the three upper cervical roots and was not detectable in the second group of patients (group II) who had undergone surgery to both trigeminal nerves. None of the patients in group I had any postoperative alteration of articulation or of the non-articulatory tongue movements, whereas the patients in group II showed a marked orolingual ataxia without disturbance in articulation. These results imply that the servocontrol theory is not completely applicable to the tongue movements and that the speech organ operates independently from a feedback control of the muscle spindles of the tongue. The speech process seems to be preprogrammed.