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Focal anterior temporal spikes from external rectus muscle
CLINICAL AND L A B O R A T O R Y NOTES Editor for Western Hemisphere and P a r East, R. S. SCHWAB, M.D., Boston, U.S.A. Editor for Europe and Middle East, F. B U C H T H A L , M.D., Copenhagen, Denmark FOCAL ANTERIOR
T E M P O R A L SPIKES F R O M R E C T U S M U S C L E 1. a
EXTERNAL
K~qNmrH A. BLmN, M.D.
Neuropsychiatry Service, VeteTans Administration Hospital, Long Beach, Call[. (Received for publication: October 1, 1954) INTRODUCTION Focal anterior temporal spikes have become widely ]ecognized as an electrographie finding associated with the clinical features of psychomotor epilepsy. I t is not appropriate to this presentation to delve into the problem of whether such spikes arise exclusively in the anterior portions of the temporal lobe, in the orbital surfaces of the frontal lobe, in the amygdala, or elsewhere. They are often found independently in both hemispheres. A t any rate, placement of electrodes in the anterior temporal areas of the scalp has become routine in most E E G laboratories when epilepsy of any type is suspected. The purpose of this paper is to describe a focal, anterior temporal, spike-like a r t i f a c t which results from eyemovements. This a r t i f a c t may be familiar to most readers; but it has not, to the a u t h o r ' s k~owledge, been described in the literature of electroeneephalo graphy. GENERAL DESCRIPTION Eye-movement potentials have been described by Mowrer, Rueh, and Miller (1936), J u n g (1939), J u n g and Mittermaier (1939), Lyman (1941), Gibbs and Gibbs (1945), and by Gelbin, Zee Zang Zao, and R~mond (1952). The potentials are due to movements of an electrical dipole formed by the resting potential between the retinal and eorneo-scleral layers of the eye-ball. The familiar frontal, bilaterally synchronous slow artifacts are caused by vertical eyemovements or by palpebral blinking. I n the latter case, the potentials probably are due at least partially to spatial rearrangement of semi-conducting tissue around the dipole, which changes the configuration of its electro-static field. As illustrated in the G i b b s ' Atlas, slow potentials arise in the anterior temporal areas during
horizontal eye-movements. I t is easy to demonstrate t h a t purely vertical movements may produce highamplitude slow artifaets in the frontal electrodes without appreciable conduction to the anterior temporal areas, and that, conversely, purely horizontal movements may produce large potentials in the anterior temporal areas with little or no conduction to the frontal electrodes. As the illustration in the G~bbs' Atlas fails to show, anterior temporal slow potentials reduced by voluntary horizontal movements are often initiated by small, spike-like deflections which look like isolated muscle potentials. These are easily recogmzed as being a component of the eyemovement a r t i f a c t when the latter is of considerable magnitude. However, when horizontal eye-movements are involuntary, they usually become quick and of slight amplitude; in this case, the spike defleetions may become relatively great in amplitude and duration, while the dipole-induced slow potentials diminish to almost negligible size. Thus, an a r t i f a c t which closely approaches in appearance a small cortical spike with its small after-potential is produced focally m the anterior temporal area. Potential-mapping with closely spaced surface electrodes and correlation of individual spikes with the eye-movements which generate them have shown t h a t they originate in the external rectus muscle of the eye (figs. 1 and 2). DIFFERENTIAL
FEATURES
1. Extent of spread. Cortical spikes are subject bgth to volume conduction through inert i s s u e and neural conduction through white matter or eortex. The sharp wave which often occurs coincidentally in the eontralateral homologous area is presumably a conducted spike which has been blunted by transsynoptic and trans-neuronal spacio-temporal dispersion. The external rectus muscle spikes are spread solely 1 Published with the permission of the Chief Medical Director, Department of Medicine anli Surby volume conduction. There is a greater latitude of gery, Veterans Administration, who assumes' no re- . spread than is seen in ordinary temporalis or fron, sponsibility for the opinions expressed or eoncldsions tails muscle motor unit discharges because of the eomdrawn by the author. 2 Read before The Western Society of EEG, March paratively deep position in the skull of the rectu~ 2, 1952. muscle. For .1 given eleetrieal impedance of tide [ 299
]
300
KENNETH
tissue, the amount of spread depends upon the volume conduction p a t t e r n through the s t r a t a of skin, fascm, muscle, and bone. A deeper origin obviously implies a wider area of arrival at the surface. The external rectus spike closely approaches the cortical spike in th]s regard (fig. ~).
A. B L I N N 2. Amphtude and duratwn. Cortieal spikes may be extremely small and focal and still be detectable at the surface of the scalp. They can have amplitudes of less than 50 tLV. clurations as small as 20 msec., and simple, monophaslc after-potentials of small magnitude. The primary discharge in such instances is
I-2 2-7
4-3 12
14 11-12
12 - 17
17-14
IO0,uV
, ISOC. •
14-13
Fig. Z Bipolar leads designed to emphasize phase-reversals over the anterzor temporal areus. A small cerebral spike arises in the right anterior temporal area and is evident to a lesser extent in the mid-temporal and frontal areas. A conducted sharp-wave appears in the homologous areas of the left hemisphere. I-2
2-7
7-4
4-3
-12
12
12-17 17-14
t4-13 lOOpV
. tsea.
•
Fig. 2 Wzth the same lead arrangement as figure 1, an external re(tus muscle spike and zts associated ocular d~pole potel~t]al are shown for comparison. The left ~Jde produces only a d~pole p o t e n h a h Note phase relationships described in text.
ANTERIOR TEMPORAL SPIKE ARTIFACTS
301
with its dipole-movement-induced " a f t e r - p o t e n t i a l " depends upon the type of eye-movement which causes it. The sp~ke is apparently generated by integral contraction of many motor umts in the muscle.1 This type of contraction occurs when horizontal eye-movements are very quick and of low amphtude, i.e., in spontaneous, lnvolantary, nystagmoid movements. Ewdently, no m a t t e r how wide the eye-ball movement, the muscle spike ~ncreases in height and duration only as the i m t l a t m g muscle contraetmn increases in abruptness (figs. 4 and 5).
AMPLITUDE DISTRIBUTION OF EXTERNAL RECTUS MUSOLE POTENTIALS Amphtude potentials.
dmtribution
Fig. 3 of external
rectus
muscle
3. Condzt~ons of occurrence. The anterior temporal spiking associated w]th psychomotor epilepsy, if not •present in the relaxed, waking state, may be evoked usually by h g h t sleep, Metrazol activation, photostimulation, hyperventflatmn, or combinations of these. External rectus muscle spikes are best elicited by shining a fine beam of hg.ht obhquely into the eye and then hawng the subject close his eyes. I f the light produces an after-image j u s t lateral or medial to the maeula, the eyes engage in quick.
2
2-3 i8-13
12
15-13 17-13 i2- i3 [IO0)JV
Isec.. Fig. 4
Representative potential-mapping leads. Rectus muscle spikes exceeding 100 ~V. are elicited by having subject shift gaze quickly between two horizontally spaced objects. Note alternating laterality of spikes and of dipole potential positivity. usually confined to a single, minor gyrus. The pathology is probably a minute ictogemc lesion with a relatively narrow surrounding h m b u s of hyper-lrritable cortex. W]th the rectus muscle discharge, spike amplitudes of 100 /~V. or more and durations up to 20 reset. are attained. TIRe wave-form of the muscle discharge
1 Bj6rk and Kugelberg (1953) failed to observe these large spikes in their needle-electrode studies of the extrmme muscles of the eye. Kugelberg (1954) has agreed t h a t this may have been because of the relative slowness of the movements studied. The " q u i c k change of f i x a t i o n " illustrated by these authors (op. cir., fig. 6) actually has a duration of about 1/11 sec.
302
KENNETH
nystag'moid, horizontal movements in a semi-involuntary effort to center the image on the macula. A method of encouraging a more random, less repetitive type of spiking contraction is to relax the subject, with eyes open, in a dimly lighted room. Here, the eyes soon exhibit an irregular searching motion, apparently in an unpremeditated attempt to center v~smn on a tangle point ~n the room.
[IOOJJV
A. B L I N N The clearest distmchon between cerebral and rectus muscle spikes, at ordinary recording paper speeds, hes in the polarity of the accompanying slow potentials. The dipole potentmls following muscle spikes are of opposite polamty in the two hemispheres; the after-potentmls of cerebral spikes, when present bilaterally, are of the same polarity (review fig. 1 and 2).
, lOOM sec
•
Fig. 5 Double beam oscilloseope traces of right and left anterior temporal areas (referred to ipsilateral earlobes), illustrating an ordinary motor unit discharge near the beginning of the trace and a right external rectus spike near the end. The small synchronous spike in the lower trace probably comes from the contralateral internal rectus muscle; in most subjects, it is of negligible amplitude. Hypervenhlation, photo-stlmulatmn, and analephc drugs such as Metrazol and caffeine all tend to increase the incidence of external rectus spikes (possibly by increasing nervous excitement and general muscle tone). I n these respects, they are mmflar to cortical spikes. I n contrast to seizure discharges, they tend to be abolished by hypnogogy and sleep. 4. General constderatwns. W~th only bmef acquaintance, external rectus muscle artifacts are easy to identify when they are a b u n d a n t and anticipated. The alternating laterahty, the characteristic dist r i b u t m n of the spikes, and the disproportionately large after-potentials make them uniform and unique in appearance. However, i f they occur rarely and randomly, as is the case in states of good relaxatmn and drowsiness, the danger of nnsinterpretation becomes great because of uncharactemstic waveform and the possibility of intervening cerebral slow wave act~vlty. Even the alternating l a t e r a h t y (fig. 4) does not always obtain; if a lateral eye-movement is truly nystagmoid, the restoring morton is too slow to reduce an integrated, spike-hke muscle discharge. Thus, the spikes may be confined to one side of the head.
REFERENCES ]~JOaK, A. and KUGELBER(~, E. The electrical activity of the muscles of the eye and eyelids in various positions and during movement. EEG Clin. Neurophys~ol., 1953, 5: 595-602. G~LmN, R. M., ZE~ ZANO ZAO, et R~OND, A. Le champ 61ectmque de l'ceil. EEG Chn. Neurophysml., 1952, 4: 237. GIBBS, F. A. and GIBBS, E. L. Atlas of Electroencephalography. Cambridge, Addison-Wesley Press, Second Edition, 1945. JUNG, R. Eine elektrische Methode zur mehrfachen Reglstrlerung yon Augeubewegungen und Nystagmus. K h n . Wchnsehr., 1939, 18: 21-24. Jv~¢o, R., und MITTER~AIEa, R. Zur objektiven Regmtrlerung und Analyse verschiedener Nystagmusformen: vestlbularer, optokinetlscher und spontaner Nystagmus m ihren Wechselbeziehungen. Arch. Ohren-, Nasen-, Ohrenh., 1939, 46: 320-323. KUGELBERG, E. Personal communication. 1954. I,Y~A~, R. S. Eye movements m the electroencephalogram. Bull. Johns ttopb~ns Hosp., 1941, 68: 1. M0WRER, O. H., Rucg, T. C., and MILLER, N. E. The corneo-retinal potential difference as the basis of the galvanometric" method of recording eye movements. Amer. J. Physml., 1936, 114: 423428.
Reference: BLINN, K. A. Focal anterior temporal spikes from external rectus muscle. EEG Chn Neurophyslol., 1955, 7: 299-302.
T E M P O R A L SPIKES F R O M R E C T U S M U S C L E 1. a
EXTERNAL
K~qNmrH A. BLmN, M.D.
Neuropsychiatry Service, VeteTans Administration Hospital, Long Beach, Call[. (Received for publication: October 1, 1954) INTRODUCTION Focal anterior temporal spikes have become widely ]ecognized as an electrographie finding associated with the clinical features of psychomotor epilepsy. I t is not appropriate to this presentation to delve into the problem of whether such spikes arise exclusively in the anterior portions of the temporal lobe, in the orbital surfaces of the frontal lobe, in the amygdala, or elsewhere. They are often found independently in both hemispheres. A t any rate, placement of electrodes in the anterior temporal areas of the scalp has become routine in most E E G laboratories when epilepsy of any type is suspected. The purpose of this paper is to describe a focal, anterior temporal, spike-like a r t i f a c t which results from eyemovements. This a r t i f a c t may be familiar to most readers; but it has not, to the a u t h o r ' s k~owledge, been described in the literature of electroeneephalo graphy. GENERAL DESCRIPTION Eye-movement potentials have been described by Mowrer, Rueh, and Miller (1936), J u n g (1939), J u n g and Mittermaier (1939), Lyman (1941), Gibbs and Gibbs (1945), and by Gelbin, Zee Zang Zao, and R~mond (1952). The potentials are due to movements of an electrical dipole formed by the resting potential between the retinal and eorneo-scleral layers of the eye-ball. The familiar frontal, bilaterally synchronous slow artifacts are caused by vertical eyemovements or by palpebral blinking. I n the latter case, the potentials probably are due at least partially to spatial rearrangement of semi-conducting tissue around the dipole, which changes the configuration of its electro-static field. As illustrated in the G i b b s ' Atlas, slow potentials arise in the anterior temporal areas during
horizontal eye-movements. I t is easy to demonstrate t h a t purely vertical movements may produce highamplitude slow artifaets in the frontal electrodes without appreciable conduction to the anterior temporal areas, and that, conversely, purely horizontal movements may produce large potentials in the anterior temporal areas with little or no conduction to the frontal electrodes. As the illustration in the G~bbs' Atlas fails to show, anterior temporal slow potentials reduced by voluntary horizontal movements are often initiated by small, spike-like deflections which look like isolated muscle potentials. These are easily recogmzed as being a component of the eyemovement a r t i f a c t when the latter is of considerable magnitude. However, when horizontal eye-movements are involuntary, they usually become quick and of slight amplitude; in this case, the spike defleetions may become relatively great in amplitude and duration, while the dipole-induced slow potentials diminish to almost negligible size. Thus, an a r t i f a c t which closely approaches in appearance a small cortical spike with its small after-potential is produced focally m the anterior temporal area. Potential-mapping with closely spaced surface electrodes and correlation of individual spikes with the eye-movements which generate them have shown t h a t they originate in the external rectus muscle of the eye (figs. 1 and 2). DIFFERENTIAL
FEATURES
1. Extent of spread. Cortical spikes are subject bgth to volume conduction through inert i s s u e and neural conduction through white matter or eortex. The sharp wave which often occurs coincidentally in the eontralateral homologous area is presumably a conducted spike which has been blunted by transsynoptic and trans-neuronal spacio-temporal dispersion. The external rectus muscle spikes are spread solely 1 Published with the permission of the Chief Medical Director, Department of Medicine anli Surby volume conduction. There is a greater latitude of gery, Veterans Administration, who assumes' no re- . spread than is seen in ordinary temporalis or fron, sponsibility for the opinions expressed or eoncldsions tails muscle motor unit discharges because of the eomdrawn by the author. 2 Read before The Western Society of EEG, March paratively deep position in the skull of the rectu~ 2, 1952. muscle. For .1 given eleetrieal impedance of tide [ 299
]
300
KENNETH
tissue, the amount of spread depends upon the volume conduction p a t t e r n through the s t r a t a of skin, fascm, muscle, and bone. A deeper origin obviously implies a wider area of arrival at the surface. The external rectus spike closely approaches the cortical spike in th]s regard (fig. ~).
A. B L I N N 2. Amphtude and duratwn. Cortieal spikes may be extremely small and focal and still be detectable at the surface of the scalp. They can have amplitudes of less than 50 tLV. clurations as small as 20 msec., and simple, monophaslc after-potentials of small magnitude. The primary discharge in such instances is
I-2 2-7
4-3 12
14 11-12
12 - 17
17-14
IO0,uV
, ISOC. •
14-13
Fig. Z Bipolar leads designed to emphasize phase-reversals over the anterzor temporal areus. A small cerebral spike arises in the right anterior temporal area and is evident to a lesser extent in the mid-temporal and frontal areas. A conducted sharp-wave appears in the homologous areas of the left hemisphere. I-2
2-7
7-4
4-3
-12
12
12-17 17-14
t4-13 lOOpV
. tsea.
•
Fig. 2 Wzth the same lead arrangement as figure 1, an external re(tus muscle spike and zts associated ocular d~pole potel~t]al are shown for comparison. The left ~Jde produces only a d~pole p o t e n h a h Note phase relationships described in text.
ANTERIOR TEMPORAL SPIKE ARTIFACTS
301
with its dipole-movement-induced " a f t e r - p o t e n t i a l " depends upon the type of eye-movement which causes it. The sp~ke is apparently generated by integral contraction of many motor umts in the muscle.1 This type of contraction occurs when horizontal eye-movements are very quick and of low amphtude, i.e., in spontaneous, lnvolantary, nystagmoid movements. Ewdently, no m a t t e r how wide the eye-ball movement, the muscle spike ~ncreases in height and duration only as the i m t l a t m g muscle contraetmn increases in abruptness (figs. 4 and 5).
AMPLITUDE DISTRIBUTION OF EXTERNAL RECTUS MUSOLE POTENTIALS Amphtude potentials.
dmtribution
Fig. 3 of external
rectus
muscle
3. Condzt~ons of occurrence. The anterior temporal spiking associated w]th psychomotor epilepsy, if not •present in the relaxed, waking state, may be evoked usually by h g h t sleep, Metrazol activation, photostimulation, hyperventflatmn, or combinations of these. External rectus muscle spikes are best elicited by shining a fine beam of hg.ht obhquely into the eye and then hawng the subject close his eyes. I f the light produces an after-image j u s t lateral or medial to the maeula, the eyes engage in quick.
2
2-3 i8-13
12
15-13 17-13 i2- i3 [IO0)JV
Isec.. Fig. 4
Representative potential-mapping leads. Rectus muscle spikes exceeding 100 ~V. are elicited by having subject shift gaze quickly between two horizontally spaced objects. Note alternating laterality of spikes and of dipole potential positivity. usually confined to a single, minor gyrus. The pathology is probably a minute ictogemc lesion with a relatively narrow surrounding h m b u s of hyper-lrritable cortex. W]th the rectus muscle discharge, spike amplitudes of 100 /~V. or more and durations up to 20 reset. are attained. TIRe wave-form of the muscle discharge
1 Bj6rk and Kugelberg (1953) failed to observe these large spikes in their needle-electrode studies of the extrmme muscles of the eye. Kugelberg (1954) has agreed t h a t this may have been because of the relative slowness of the movements studied. The " q u i c k change of f i x a t i o n " illustrated by these authors (op. cir., fig. 6) actually has a duration of about 1/11 sec.
302
KENNETH
nystag'moid, horizontal movements in a semi-involuntary effort to center the image on the macula. A method of encouraging a more random, less repetitive type of spiking contraction is to relax the subject, with eyes open, in a dimly lighted room. Here, the eyes soon exhibit an irregular searching motion, apparently in an unpremeditated attempt to center v~smn on a tangle point ~n the room.
[IOOJJV
A. B L I N N The clearest distmchon between cerebral and rectus muscle spikes, at ordinary recording paper speeds, hes in the polarity of the accompanying slow potentials. The dipole potentmls following muscle spikes are of opposite polamty in the two hemispheres; the after-potentmls of cerebral spikes, when present bilaterally, are of the same polarity (review fig. 1 and 2).
, lOOM sec
•
Fig. 5 Double beam oscilloseope traces of right and left anterior temporal areas (referred to ipsilateral earlobes), illustrating an ordinary motor unit discharge near the beginning of the trace and a right external rectus spike near the end. The small synchronous spike in the lower trace probably comes from the contralateral internal rectus muscle; in most subjects, it is of negligible amplitude. Hypervenhlation, photo-stlmulatmn, and analephc drugs such as Metrazol and caffeine all tend to increase the incidence of external rectus spikes (possibly by increasing nervous excitement and general muscle tone). I n these respects, they are mmflar to cortical spikes. I n contrast to seizure discharges, they tend to be abolished by hypnogogy and sleep. 4. General constderatwns. W~th only bmef acquaintance, external rectus muscle artifacts are easy to identify when they are a b u n d a n t and anticipated. The alternating laterahty, the characteristic dist r i b u t m n of the spikes, and the disproportionately large after-potentials make them uniform and unique in appearance. However, i f they occur rarely and randomly, as is the case in states of good relaxatmn and drowsiness, the danger of nnsinterpretation becomes great because of uncharactemstic waveform and the possibility of intervening cerebral slow wave act~vlty. Even the alternating l a t e r a h t y (fig. 4) does not always obtain; if a lateral eye-movement is truly nystagmoid, the restoring morton is too slow to reduce an integrated, spike-hke muscle discharge. Thus, the spikes may be confined to one side of the head.
REFERENCES ]~JOaK, A. and KUGELBER(~, E. The electrical activity of the muscles of the eye and eyelids in various positions and during movement. EEG Clin. Neurophys~ol., 1953, 5: 595-602. G~LmN, R. M., ZE~ ZANO ZAO, et R~OND, A. Le champ 61ectmque de l'ceil. EEG Chn. Neurophysml., 1952, 4: 237. GIBBS, F. A. and GIBBS, E. L. Atlas of Electroencephalography. Cambridge, Addison-Wesley Press, Second Edition, 1945. JUNG, R. Eine elektrische Methode zur mehrfachen Reglstrlerung yon Augeubewegungen und Nystagmus. K h n . Wchnsehr., 1939, 18: 21-24. Jv~¢o, R., und MITTER~AIEa, R. Zur objektiven Regmtrlerung und Analyse verschiedener Nystagmusformen: vestlbularer, optokinetlscher und spontaner Nystagmus m ihren Wechselbeziehungen. Arch. Ohren-, Nasen-, Ohrenh., 1939, 46: 320-323. KUGELBERG, E. Personal communication. 1954. I,Y~A~, R. S. Eye movements m the electroencephalogram. Bull. Johns ttopb~ns Hosp., 1941, 68: 1. M0WRER, O. H., Rucg, T. C., and MILLER, N. E. The corneo-retinal potential difference as the basis of the galvanometric" method of recording eye movements. Amer. J. Physml., 1936, 114: 423428.
Reference: BLINN, K. A. Focal anterior temporal spikes from external rectus muscle. EEG Chn Neurophyslol., 1955, 7: 299-302.