EXPERIMENTAL
NEUROLOGY
336-338 (1975)
49,
RESEARCH
NOTE
A Trigemino-Abducens M.
and
BRATZLAVSKY
Drpartwzent
of Neurology, Received
Reflex H.
VANDER
Ukz~ersity May
in Man EECKEN
of Ghent,
Ghent,
1
Belgium
28,197S
Although several studies have been devoted to the proprioceptive reflex control of human extrinsic eye muscles (4, 6, 9), no data have been published concerning exteroceptive reflex influences in these muscles in man. In decerebrated cats, a retraction reflex of the eyeball has been reported upon touching the conjunctiva (7). Direct electromyographic recordings in anesthetized cats, revealed that high-intensity stimulation of the infraorbital nerve elicits in addition to a reflex response in the retractor oculi muscle, a small reflex discharge in the lateral rectus muscle (2). Recently the m. levator palpebrae in man has been shown to be the site of a short and a long latency bilateral reflex inhibition upon periorbital cutaneous stimulation (3). The aim of the present study was to further investigate possible exteroceptive reflex influences in human extrinsic eye muscles. The study was carried out with four normal adults and two patients with unilateral retrogasserian neurotomy, who were all volunteers for the examination. The subjects were examined while seated comfortably in a chair with their eyes directed straight ahead, or slightly to the right or to the left. Graded single rectangular electrical shocks of 0.5 msec duration were delivered to the periorbital skin through two flat silver disc electrodes (placed 2 cm apart), by a constant-current stimulator at a frequency of 1 per 3 sec. Similar electrical stimuli were applied to other facial regions by means of a manual bipolar skin electrode (interpolar distance 2 cm). The lateral and medial recti muscles were analyzed electromyographically with coaxial needle electrodes (interelectrode distance 0.2 mm), inserted after suitable conjunctival anesthesia (Novesine collyrium 0.4%). Each of both muscles was tested separately. When the eye was in primary 1 This investigation voor Wetenschappelijk
was supported Onderzoek.”
by a grant
336 Copyright All rights
0 1975 by Academic of reproduction
Press, Inc. in any form reserved.
from
the Belgian
“Nationaal
Fonds
TRIGEMINO-ABDUCENS
REFLEX
337
i 1
FIG. 1. EMG recording ful electrical stimulation mV; 40 msec.
in lateral rectus of homolateral
muscle of normal supraorbital skin.
man. Response to painCalibration marks : 0.1
position, they usually exhibited a continual tonic background activity, which could however be removed by a slight voluntary movement of the eyeball is opposite direction of the tested muscle. After amplification, the muscular activities were displayed on the cathode ray oscilloscope of an electromyographical apparatus and were filmed on direct print paper. Low intensity electrical stimulation of the periorbital area was incapable of eliciting any response in the lateral or medial recti muscles. Not until a strong electrical stimulus (lo-15 ma) was delivered at periorbital level, causing a painful sensation in the examined subject, did an excitatory response appear in the lateral rectus muscle (Fig. 1) This response could never be evoked upon stimulation of the operated side in patients with unilateral retrogasserian neurotomy, which proves its reflex nature and trigeminal afferent pathway. The reflex was bilateral and had a low amplitude. It occurred after a latency of 2Lc30 msec and lasted lo-20 msec. The contralateral discharge was less pronounced than the ipsilateral one. The medial rectus muscle did not show any response upon periorbital stimulation, even of high intensity. The reflex in the lateral rectus muscle was most easily evoked when the stimulus was applied close to the eyeball. As soon as the stimulus was removed from the orbital margin and applied to other facial areas, the threshold of the reflex rose markedly and it was only rarely evokable upon stimulation of the inferior facial region. This low amplitude bilateral excitatory reflex in human lateral rectus muscle appears related to the cat’s trigemino-abducens reflex, which influences mainly the retractor bulbi muscle (2, 7). The latter muscle contains only motor units of the fast twitch type (1, 5) and has a protective function for the cat’s eye by retracting it into the orbit and pushing up the nictitating membrane (1, 8). Possibly the presently described reflex in human lateral
338
BRATZLAVSKY
AND
VANDER
EECKEN
rectus muscle represents a vestige of reflex connections which are of real functional significance in speciespossessinga nictitating membrane. REFERENCES 1.
2.
3.
4. 5.
6. 7. 8. 9.
P. 1971. Neurophysiology of eye movements, pp. 7-45. In. “The Control of Eye Movements.” P. Bach-Y-Rita, C. C. Collins, and J. E. Hyde [Eds.]. Academic Press, New York. BALDISSERA, F., and G. BROGCI. 1968. Analysis of a trigeminoabducens reflex in the cat. Brain Res. ‘7 : 313-316. BRATZLAVSKY, M. 1975. Behaviour of human brainstem reflexes in muscles with antagonistic function. In “Motor System-Neurophysiology and Muscle Mechanism.” M. Shahani [Ed.]. Elsevier, Amsterdam. (In press.) BREININ, G. M. 1957. Electromyographic evidence for ocular muscle proprioception in man. A.M.A. Arch Ophtalmol. 57: 176-180. LENNERSTRAND, G. 1974. Mechanical studies on the retractor bulbi muscle and its motor units in the cat. I. Pkysiol. (Londolz) 236 : 43-55. MARUO, T. 1964. Electromyographical studies on stretch reflex in human extraocular muscle. Zap. J. Ophtalmol, 8: 97-111. MCCOUCH, G. P., and F. H. ADLER. 1932. Extraocular reflexes. Amer. J. Physiol. 100 : 78-88. MOTAIS, E. 1885. Recherches sur l’anatomine humaine et 1:anatomie comparee de l’appareil moteur de l’oeil (Part 3). Arch. Ophtalmol. (Paris) 5 : 143-158. SEARS, M. L., R. D. TEASDALL, and H. H. STONE. 1959. Stretch effects in human extraocular muscle ; An electromyographic study. Bull. Johns Hopkins Hosp. 104 : 174-178. BACH-Y-RITA,
NEUROLOGY
336-338 (1975)
49,
RESEARCH
NOTE
A Trigemino-Abducens M.
and
BRATZLAVSKY
Drpartwzent
of Neurology, Received
Reflex H.
VANDER
Ukz~ersity May
in Man EECKEN
of Ghent,
Ghent,
1
Belgium
28,197S
Although several studies have been devoted to the proprioceptive reflex control of human extrinsic eye muscles (4, 6, 9), no data have been published concerning exteroceptive reflex influences in these muscles in man. In decerebrated cats, a retraction reflex of the eyeball has been reported upon touching the conjunctiva (7). Direct electromyographic recordings in anesthetized cats, revealed that high-intensity stimulation of the infraorbital nerve elicits in addition to a reflex response in the retractor oculi muscle, a small reflex discharge in the lateral rectus muscle (2). Recently the m. levator palpebrae in man has been shown to be the site of a short and a long latency bilateral reflex inhibition upon periorbital cutaneous stimulation (3). The aim of the present study was to further investigate possible exteroceptive reflex influences in human extrinsic eye muscles. The study was carried out with four normal adults and two patients with unilateral retrogasserian neurotomy, who were all volunteers for the examination. The subjects were examined while seated comfortably in a chair with their eyes directed straight ahead, or slightly to the right or to the left. Graded single rectangular electrical shocks of 0.5 msec duration were delivered to the periorbital skin through two flat silver disc electrodes (placed 2 cm apart), by a constant-current stimulator at a frequency of 1 per 3 sec. Similar electrical stimuli were applied to other facial regions by means of a manual bipolar skin electrode (interpolar distance 2 cm). The lateral and medial recti muscles were analyzed electromyographically with coaxial needle electrodes (interelectrode distance 0.2 mm), inserted after suitable conjunctival anesthesia (Novesine collyrium 0.4%). Each of both muscles was tested separately. When the eye was in primary 1 This investigation voor Wetenschappelijk
was supported Onderzoek.”
by a grant
336 Copyright All rights
0 1975 by Academic of reproduction
Press, Inc. in any form reserved.
from
the Belgian
“Nationaal
Fonds
TRIGEMINO-ABDUCENS
REFLEX
337
i 1
FIG. 1. EMG recording ful electrical stimulation mV; 40 msec.
in lateral rectus of homolateral
muscle of normal supraorbital skin.
man. Response to painCalibration marks : 0.1
position, they usually exhibited a continual tonic background activity, which could however be removed by a slight voluntary movement of the eyeball is opposite direction of the tested muscle. After amplification, the muscular activities were displayed on the cathode ray oscilloscope of an electromyographical apparatus and were filmed on direct print paper. Low intensity electrical stimulation of the periorbital area was incapable of eliciting any response in the lateral or medial recti muscles. Not until a strong electrical stimulus (lo-15 ma) was delivered at periorbital level, causing a painful sensation in the examined subject, did an excitatory response appear in the lateral rectus muscle (Fig. 1) This response could never be evoked upon stimulation of the operated side in patients with unilateral retrogasserian neurotomy, which proves its reflex nature and trigeminal afferent pathway. The reflex was bilateral and had a low amplitude. It occurred after a latency of 2Lc30 msec and lasted lo-20 msec. The contralateral discharge was less pronounced than the ipsilateral one. The medial rectus muscle did not show any response upon periorbital stimulation, even of high intensity. The reflex in the lateral rectus muscle was most easily evoked when the stimulus was applied close to the eyeball. As soon as the stimulus was removed from the orbital margin and applied to other facial areas, the threshold of the reflex rose markedly and it was only rarely evokable upon stimulation of the inferior facial region. This low amplitude bilateral excitatory reflex in human lateral rectus muscle appears related to the cat’s trigemino-abducens reflex, which influences mainly the retractor bulbi muscle (2, 7). The latter muscle contains only motor units of the fast twitch type (1, 5) and has a protective function for the cat’s eye by retracting it into the orbit and pushing up the nictitating membrane (1, 8). Possibly the presently described reflex in human lateral
338
BRATZLAVSKY
AND
VANDER
EECKEN
rectus muscle represents a vestige of reflex connections which are of real functional significance in speciespossessinga nictitating membrane. REFERENCES 1.
2.
3.
4. 5.
6. 7. 8. 9.
P. 1971. Neurophysiology of eye movements, pp. 7-45. In. “The Control of Eye Movements.” P. Bach-Y-Rita, C. C. Collins, and J. E. Hyde [Eds.]. Academic Press, New York. BALDISSERA, F., and G. BROGCI. 1968. Analysis of a trigeminoabducens reflex in the cat. Brain Res. ‘7 : 313-316. BRATZLAVSKY, M. 1975. Behaviour of human brainstem reflexes in muscles with antagonistic function. In “Motor System-Neurophysiology and Muscle Mechanism.” M. Shahani [Ed.]. Elsevier, Amsterdam. (In press.) BREININ, G. M. 1957. Electromyographic evidence for ocular muscle proprioception in man. A.M.A. Arch Ophtalmol. 57: 176-180. LENNERSTRAND, G. 1974. Mechanical studies on the retractor bulbi muscle and its motor units in the cat. I. Pkysiol. (Londolz) 236 : 43-55. MARUO, T. 1964. Electromyographical studies on stretch reflex in human extraocular muscle. Zap. J. Ophtalmol, 8: 97-111. MCCOUCH, G. P., and F. H. ADLER. 1932. Extraocular reflexes. Amer. J. Physiol. 100 : 78-88. MOTAIS, E. 1885. Recherches sur l’anatomine humaine et 1:anatomie comparee de l’appareil moteur de l’oeil (Part 3). Arch. Ophtalmol. (Paris) 5 : 143-158. SEARS, M. L., R. D. TEASDALL, and H. H. STONE. 1959. Stretch effects in human extraocular muscle ; An electromyographic study. Bull. Johns Hopkins Hosp. 104 : 174-178. BACH-Y-RITA,
