Evoked electromyograms (EMGs) of the muscles of the lower limbs were induced by galvanic stimulation of the labyrinth in this study of vestibulo-spinal reflexes.
A subject was asked to stand with his eyes closed and his feet close together on a stabilometer and was stimulated with a galvanic current of 1 mA for 3 s by the bipolar-biaural method. In this study, all examinations were carried out with the cathode on the right ear and the anode on the left ear. Evoked EMGs in the soleus, gastrocnemius, tibialis anterior, biceps femoris, rectus femoris and gluteus maximus muscles were observed with the head facing forward and with the head turned to the right and the left.
With the head facing forward, the activities of the soleus, gastrocnemius, biceps femoris and gluteus maximus muscles increased on the right side and decreased on the left side. The activities of the rectus femoris muscles decreased on the right side and increased on the left side. The activities of the tibialis anterior muscles increased on the right side and could not be observed on the left side. With the head turned to the right, the activities of the soleus, gastrocnemius, biceps femoris and gluteus maximus muscles decreased on both sides and the activities of the tibialis anterior and rectus femoris muscles increased on both sides. With the head turned to the left, the activities of the soleus, gastrocnemius, biceps femoris and gluteus maximus muscles increased on both sides and the activities of the tibialis anterior and rectus femoris muscles decreased on both sides.
The muscles of the dorsal surfaces of the lower limbs, such as the gluteus maximus, biceps femoris, gastrocnemius and soleus muscles, showed synergic action, and the muscles of the front of the lower limbs, such as the rectus femoris and tibialis anterior muscles, acted synergically.
These muscle activities were modulated by the head position in spite of having the same galvanic stimulation. The result indicates that when the stimulation is replaced with stimulation by linear acceleration, body deviation occurs in a counter direction to the linear acceleration at any head position. The compensatory body deviation serves to maintain balance
The modulation of the labyrinthine-evoked EMGs of the lower limbs by the head position indicates that the vestibulo-spinal reflexes are regulated by input from the neck proprioceptors.
