Firing pattern of motor units in the vocal muscle during phonation.

Electromyographic activity of the vocal muscle was analysed in 10 subjects during the phonation of different vowels and with different voice pitches. Analysis of the firing pattern of single or a few motor units was performed with the aid of an amplitude discriminator on the computer. The firing rate increases with increasing voice pitch (in the region co-ho the decrease of mean interspike interval with the slope 30-40 msec/octave was found). In the firing pattern of several motor units the periodicity was observed to be correlated with the voice pitch. The period of 8 msec corresponding H, 123 Hz, decreased to about 6 msec during phonation of do, 147 Hz. The periodicity was present both in units with pure prephonatory activity and in units which were active during phonation. It seems possible that the activity in the vocal muscle changes characteristically during the phonation of different vowels.