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Interaction between the activity of an epileptic focus and discrete skilled movements in rats
Electroencephalography and Clinical Neurophysiology, 1975, 39:651-656 ,~ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
651
INTERACTION BETWEEN THE ACTIVITY OF AN EPILEPTIC FOCUS AND DISCRETE SKILLED MOVEMENTS IN RATS S. ISLAM 1 AND J. BURE~
Institute 0[ Physiology, Czechoslovak Academy ~?[Sciences, Prague (Czechoslovakia) (Accepted for publication: July 18, 1975)
Experimental evidence, recently reviewed by Woodruff (1974), indicates that cortical epileptic foci interfere with learning but not with retrieval. It is less clear how local epileptic discharges affect highly coordinated neural activity underlying discrete movements with a well known cortical localization. Lateralized reaching and grasping movements (Peterson 1934), which are typical manifestations of handedness in rats, are well suited for the investigation of this problem. Localization of the critical motor area has been established by extirpation experiments (Peterson and Devine 1963; Castro 1972) and localized electrophysiological correlates of the reaching movements have been recently described by Megirian et al. (1974). The purpose of the present paper is to examine the interaction between the activity of a picrotoxin focus, acutely established in the "hand area" of the rat motor cortex, and the performance of the overtrained reaching habit. METHODS
Subjects Sixteen male hooded rats (Druckrey strain) were reduced to 80 % of initial body weight and maintained on a 24 h food deprivation schedule with water freely available. Apparatus The experiments were performed in a plastic chamber (30 x 18 x 15 cm) with a circular opening in the center of the front wall, 5 cm above the floor. A perspex feeder, a tube 4.5 cm long with a 1.1 cm internal diameter, was attached to the 1Visiting scientist from the Government College Mardan, Pakistan.
wall opening from the outside. A hole in the upper part of the tube made it possible to introduce into the feeder small pellets (30-50 mg) prepared from Larsen's wet rat chow. The distance of the pellet from the feeder entrance was controlled by an adjustable piston. A plastic ring fitting the outside diameter of the feeder was equipped with a miniature light bulb facing a phototransistor. The photoelectric system could be fixed in a suitable position between the feeder entrance and the food so that the reaching of the forelimb interrupted the beam and reduced the current across the phototransistor.
Procedure Food-deprived rats were introduced into the apparatus and offered food placed close to the feeder entrance. The pellets were gradually moved into the feeding tube until the animal could only reach them with one forepaw. Usually rats preferred to perform this movement with the left or right forepaw, the preference becoming consistent after 2-3 days of training. Fifty pellets were given per day and training continued until the animal was able to get food placed 2-3 cm deep into the feeder. Surgery Well trained animals were anesthetized with Nembutal (40 mg/kg) and silver cannulae for picrotoxin application and ECoG recording were implanted. Two trephine openings 2 mm in diameter were made 1.5 mm rostral to the bregma and 3,0 mm lateral to the midline. Silver tubes (2.0 mm outside and 1.4 mm inside diameter, 10 mm long) were placed in the trephine openings and a silver screw reference electrode (2 mm diameterl was fixed in the frontal bone 7 mm
652
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rostral to bregma. Thin silver wires connected the electrodes with a subminiature 5-pin transistor socket. The whole implant was fixed to the skull with anchoring screws and acrylic resin. Between experiments the silver cannulae were closed with tightly fitting mandrels.
them a picrotoxin focus was established in the hemisphere contralateral to the preferred forepaw, in the other picrotoxin was applied to the ipsilateral cortex.
Recordin9 and data processin9
1. Development of the epilepticfocus
Two days after surgery the animal was connected by a light-weight suspended cable with the input of a conventional ECoG apparatus. To limit movement artifacts a miniature operational amplifier built in the connector was used as a signal follower, with output impedance of 2K. The mandrel was removed and the cannula was filled with 5 #1 o f 1 ~ picrotoxin solution. The animal was then placed in the training box and E C o G recording was started. When picrotoxininduced seizure activity developed, food was introduced into the feeder at irregular 20-40 sec intervals. EEG activity and the photoelectric signals of reaching were recorded on a 4-channel F M tape recorder. The analog record was processed with the LINC 8 computer, using a program for plotting pre- and post-reaching spike histograms during a period of 512 msec before and 512 msec after beam interruption (limb extension). The histograms were plotted on an incremental plotter. Usually two experiments were performed on 2 consecutive days in the same animal. In one of
Application o f 1 ~ picrotoxin to the exposed dura triggered, after several minutes, epileptic spikes which rapidly grew in amplitude and could be recorded also in the other hemisphere. The rate of discharge increased during approximately 20 min to a maximum of 1-2/sec and then slowly subsided. Ictal discharges usually developed at the height of the effect and were maintained even when the interictal activity already started to decline. The ictal discharge usually lasted for 10-20 sec and was followed by a 30 to 200 sec interictal interval. Typical records of the fully developed focal activity are shown in Fig. 1 and 2. The E C o G discharges were accompanied by jerking movements o f the contralateral forelimb which were essentially similar to those described with cobalt epileptic foci by Dawson and Holmes (1966). The jerking sometimes spread also to the contralateral hind limb, and was most pronounced when the animal was suspended. The ipsilateral forepaw was usually unaffected. In spite of the jerking the animal was able to perform the reaching movement and to get the pellet from
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Fig. 1. Examples of representative experiments showing relationship between the activity of the picrotoxin focus and the reaching movementsof the contralateral (C) or ipsilateral (I) forepaw. R-output of the photocell; extension of the forepaw into the feedingtube is indicated by upward deflection. S-surfaceEEG recordingfrom the picrotoxin-treatedcortex.
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Fig. 2. Ictal discharge and reachingwith the ipsilateral (I) or contralateral (C) forepaw. Other description as in Fig. 1. the tube, although sometimes more attempts were required than under normal conditions. Typical examples are shown in Fig. 1. The upper record shows low rate interictal activity (about 2 spikes/10 sec) which was activated by contralateral reaching. A more frequent contralateral focus (about 10 spikes/10 sec) was inhibited by reaching (middle record). Activity of an ipsilateral focus (lower record) was increased by reaching, to the provocation of an ictal discharge. Reaching movements continued during ipsilateral ictal activity, but prolonged extensions indicated poor coordination. During the second ictal episode reaching stopped. Fig. 2 indicates that ictal discharge in the ipsilateral focus is compatible with reaching (above), whereas similar activity in the contralateral focus prevents reaching (below).
2. Quantitative relationships between epileptic activity and reaching In an attempt to prove the statistical significance o f the changes illustrated by Fig. 1 and 2, spikes and reaches were counted for each page of recording ( = 4 0 sec). Data were averaged in 200 sec blocks and the individual records were synchronized by the maximum discharge rate. The upper part of Fig. 3 shows that the maximal discharge rates were 41 _+ 5 and 50,+ 5 spikes/40 sec in the contralateral and ipsilateral foci respectively. The maximum was significantly different from the activity recorded 10 min earlier ( P < 0.01) or 7 min later (P < 0.05). The increase o f discharge rate was accompanied by increased frequency of ipsilateral reaching ( P < 0.05). The lower part of Fig. 3 shows that the contralateral reaching rate is inversely related to the frequency of the focal discharge.
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Fig. 3. Development of the seizure focus (above) and the related changes of reaching with the contralateral (C) or ipsilateral (I) forepaw (below). Ordinate: averagenumber of spikes (S) or reaches (R) per 40 sec interval. Blocks of 200 sec. Abscissae: time before ( - ) and after (+) culmination of the focal discharge. Records from differentanimals were synchronized in such a way that the 200 sec period with maximum spike frequencyfollowszero. Since the gross character of the above measurements may obscure the finer relationship between the electrical and motor events, the data were analyzed in a different way. The reaching time (interval between the first and last reach in each series o f reaches) was cumulatively measured during the whole recording, together with the total number o f spikes and the number of spikes occurring during the reaching time. The average frequencies were 0.73 and 0.68 spikes/sec for the ipsilateral and contralateral foci and increased
654
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Fig. 4. Changes in the activity of the picrotoxin focus induced by reaching with the contralateral (C) or ipsilateral 1I) forepaw. S-slow interictal activity (f< 0.5/sec); F-fast interictal activity (f > 0.5/sec). Above: ~o of animals showing increase (empty columns) or decrease (black columns) of discharge rate during the reaching time. Below: average magnitude of the change of discharge rate during reaching expressed in o/,, of the non-reaching activity. CS: n = 7 ; CF: n =9; IS: n = 7 ; IF: n = 8 .
during reaching to 0.96 and 0.76 spikes/sec, respectively. When the focal activity was arbitrarily divided into two groups of approximately equal size, with the discharge rate below and above 0.5 spikes/see, the first group was activated and the second inhibited by contralateral reaching. Ipsilateral foci were activated by reaching, independent of their discharge rate (Fig. 4).
3. Changes of spike incidence associated with reachin9 Fine peri-reach changes of spike incidence were revealed by computer analysis performed in 8 rats. Typical examples are shown in Fig. 5. In histogram A probability of spike occurrence in the contralateral focus is decreased between - 3 5 0 and - 8 0 msec (minimum at - 160 msec) before reaching. The spike incidence is briefly increased during extension and unaffected during the post-reach period. Gross analysis described in the previous section showed in this experiment
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Fig. 5. Examples of typical peri-reach distributions of focal epileptic discharges. Abscissae : time (msec) before (negative values) and after (positive values) the onset of the extension. Ordinates: number of spikes in 16 msec bins. The histogram A is based on 1536 reaches, histograms B, C and D on 512 reaches each. Histograms A, C and D are from contralateral, histogram B from ipsilateral epileptic foci.
that the average discharge rate of 1.39/sec dropped during reaching to 1.15/sec. Histogram B represents a prolonged prereach increase of discharge rate in an ipsilateral focus (average discharge rate increased during reaching from 1.29 to 1.75/sec). A prolonged pre-reach increase is also shown in the histogram C, where it is combined with a poorly expressed pre-extension inhibition and with a brief increase (64 msec) immediately following the contralateral extension (reaching increased in this case the average discharge rate from 0.49 to 0.99/sec). Histogram D illustrates a contralateral focus with a better developed pre-extension and post-extension inhibition. The average discharge rate dropped during reaching from 0.76 to 0.53/sec. Although the shape of the histogram varied from animal to animal, increase of activity coinciding with the extension was a common finding, both in contralateral and ipsilateral foci (11 times in 13 experiments). The central peak was often preceded by inhibition, which was prominent in contralateral foci. The post-extension inhibition was less expressed and irregular. DISCUSSION
Behavioral arrest during focal seizures is a
655
EPILEPTIC FOCUS AND SKILLED MOVEMENTS
well known clinical phenomenon, which has been repeatedly confirmed in animal studies (for review see Woodruff 1974). An epileptic focus usually impairs acquisition more than retrieval (Schmaltz 1971; Aquino-Cias et al. 1972) and avoidance more than escape (Hamilton and Isaacson 1970; Olton 1970). The present results support the notion (Stamm and Pribram 1960, 1961; Stamm and Warren 1961) that retention of an overtrained habit is rather resistant to focal seizure activity in the corresponding cortical projection areas. Reaching remained preserved during ictal discharge, projected to the sensorimotor cortex contralateral to the preferred forelimb from the other hemisphere, but was arrested by the ictal discharge directly generated in this region. It is difficult to decide whether this effect is due to interference with the integrative mechanisms or to motor impairment caused by the peripheral spasms. Interictal activity did not interfere with reaching and could be, therefore, employed as an index of excitability changes associated with reaching. The comparison of average spike discharge and reaching rates reveals reciprocal effects of ipsilateral and contralateral foci. The facilitation of reaching induced by the ipsilateral focus is probably only an apparent one: it may reflect the increased effort required to get food in spite of the slightly disturbed coordination. The inhibition observed during development of a contralateral focus is real and results into decreased retrieval of food. The relatively weak impairment of reaching caused by a focus in the ipsilateral hemisphere supports Crowell's (1970) finding that responses of sensorimotor cortex to the stimulation of the ventro-lateral thalamus are little affected by paroxysmal activity in the opposite hemisphere. Also, the observation that focal penicillin discharges can be triggered by contralateral but not by ipsilateral sciatic nerve shocks (Mare~ and Wirthovfi 1975) shows that the interaction between the epileptic focus and the sensory influx is restricted to the direct projection. The gross effects of reaching on discharge incidence indicate that the excitability changes accompanying the elaboration of movement and the feedback signals generated by its perform-
ance, facilitate discharge generation in ipsilateral foci and in slow contralateral foci. Inhibition of fast contralateral foci may be due to reciprocal relations between the integrated activity triggered by reaching and the diffuse discharge elicited by the chemical stimulus. According to the concept of the dominant (Ukhtomsky 1926; Rusinov 1965) the active reflex center attracts the excitation generated by neutral stimuli. Increased excitability of motor cortex during conditioned eye blinks in the cat was reported by Woody et al. (1970). Low rate epileptic foci can be used as sensitive detectors of excitability changes. An alternative explanation assumes that inhibition of the fast epileptic discharge is apparent and that the decreased incidence of spikes during the reaching time expresses the tendency of the rat to reach during relatively discharge-free intervals. This explanation is supported by the computer-plotted histograms of pre- and post-reach distributions of focal discharge. Almost all histograms showed an increase of activity during the actual reaching movement. This brief increase overlapped with the average motor potential (Megirian et al. 1974) which was recorded in the same region during reaching with the contralateral forepaw. The pre-reach troughs (Fig. 5, histograms A and D) suggest that the probability of reaching increases with the duration of the discharge-free interval. The initial phases of movement elaboration seem to be reset by the repetitive discharge. On the other hand, the movement once started increases even the fast activity. The post-reach inhibition then reflects the periodicity of the discharge or reaching. Since the reaching rate varies between 2 and 5/ sec (Megirian et al. 1974) the more distant perireach intervals are likely to be affected by other reaches (see the spurious periodicity in histograms C and D in Fig. 5). SUMMARY
Sixteen male hooded rats were trained to reach into a narrow feeding tube for small food pellets. The paw movements were photoelectrically detected. An epileptic focus established by local application of 1 7opicrotoxin on the exposed motor cortex increased the frequency of reaching
656
with the ipsilateral paw and impaired reaching with the contralateral paw. Interictal discharge rate of all ipsilateral foci was increased by reaching in the same way as the slow activity (< 0.5/sec) of contralateral foci. On the other hand, fast activity (> 0.5/sec) of contralateral foci was decreased by reaching. Computer analysis of interictal discharge incidence during 512 msec before and after reaching onset showed that the brief facilitation of discharge (50 msec) during the actual movement was often preceded and followed by more prolonged inhibition (200 msec). The inhibition was better expressed in the contralateral hemisphere. The results are interpreted as due to changes of cortical excitability associated with reaching and to interference of the epileptic focus with the cortical elaboration of the skilled movement. RESUME INTERACTION ENTRE L'ACTIVITE D'UN FOYER EPILEPTIQUE ET LES MOUVEMENTS ELABORES DISCRETS CHEZ LE RAT
Seize rats mfiles ont 6t6 dress6s/l atteindre un pellet alimentaire dans un tube 6troit. Les mouvements du membre ant6rieur 6taient d6tect6s photo61ectriquement. Un foyer 6pileptique 6tant obtenu par application locale de picrotoxine/~ 1 ~o sur un cortex moteur expos& il en r6sultait une augmentation de la fr6quence des mouvements d'atteinte par le membre ipsilat6ral et une diminution, par le membre contralat6ral. Le taux de d6charges interictales de tous les foyers ipsilat6raux 6tait accru par le mouvement de pr6hension, tout autant que les activit6s du foyer contralat6ral fi basse cadence (<0.5/sec). En revanche, l'activit6 rapide (>0,5/sec) du foyer contralat6ral 6tait d6crue par ce mouvement. Une analyse quantitative de l'incidence des d6charges interictales au cours des 512 msec pr6c6dant et suivant le d6but de pr6hension, a mis en 6vidence une facilitation br6ve (50 msec) des d6charges pendant le mouvement, souvent pr6c6d6e et suivie par une inhibition durable (200 msec). L'inhibition 6tait plus claire dans l'h6misph~re contralat~ral. Ces r6sultats sont attribu6s /~ des modifications de l'excitabilit6 corticale, en rapport avec
S. ISLAM AND J. BURES
le mouvement de prdhension, et g l'interfdrence entre l'activit6 6pileptique focale et l'61aboration corticale du mouvement fin. REFERENCES AQU1NO-CiAS, J., ANEIROS-RIBA, R., FERN~.NDEZ-YERo, F. and HERNANDEZ-MESA,N. Effects of epileptic foci in the visual cortex of the rat on passive avoidance learning. Physiol. Behav., 1972, 8: 957-961. CASTRO, A. J. The effects of cortical ablations on digital usage in the rat. Brain Res., 1972, 37:173 185. CROWELL, P. M. Distant effects of a focal epileptogenic process. Brain Res., 1970, 18:137 154. DAWSON, G. D. and HOLMS, O. Cobalt applied to the sensorimotor area of the cortex cerebri of the rat. J. Physiol. (Lond.), 1966, 185: 455~,70. HAMILTON, G. and ISAACSON, R. L. Changes in avoidance behavior following epileptogenic lesions of the mesencephalon. Physiol. Behav., 1970, 5:1165 1167. MAREL P. and WIRTHOV~,, Z. Triggering discharges of a cortical epileptogenic focus by sciatic nerve stimulation in rats. Physiol. Bohemoslov., 1975, in press. MEG1RIAN, D., BURE~OV,~, O., BUREt, J. and DIMOND, S. Electrophysiological correlates of discrete forelimb movements in rats. Electroenceph. olin. Neurophysiol., 1974, 36: 131-139. OLTON, D. S. Specific deficits in active avoidance behavior following penicillin injection into hippocampus. Physiol. Behav., 1970, 5: 957-963. PETERSON, G. M. Mechanisms of handedness in the rat resulting from cortical lesions after limited forced practice. Comp. Psychol. Mono,qr., 1934, 9: 1. PETERSON,G. M. and DEVINE, 1. M. Transfer in handedness in the rat resulting from cortical lesions after limited forced practice. J. camp. physiol. Psychol., 1963, 56: 752 756. RUSlNOV, V. S. Dominant area and its role in the formation of temporal connections. Proe. 23rd Int. Congr. Physiol. Sci., Tokyo, 1965, 4: 613-617. SCHMALTZ, L. W. Deficit in active avoidance learning in rats following penicillin injection into hippocampus. Physiol. Behat,., 1971, 6:667 674. SVAMM, J. S. and PRmRAM, K. H. Effects of epileptogenic lesions in frontal cortex on learning and retention in monkeys. J. Neurophysiol., 1960, 23:552 563. STAMM, J. S. and PRIBRAM, K. H. Effects of epileptogenic lesions of inferotemporal cortex on learning and retention in monkeys. J. comp. physiol. Psychol., 1961, 54: 614-618. ISTAMra, J. S. and WARREN, A. Learning and retention by monkeys with epileptogenic implants in posterior parietal cortex. Epilepsia (Amst.), 1961, 2: 229-242. U KHVOMSKY,A. A. [Concerning the conditions of excitation in the dominant.] (in Russian). Nov. Refl. Fiziol. Nerv. Sist., 1926, 2: 3-15. WOODRUFV, M. L. Subconvulsive epileptiform discharge and behavioral impairment. Behav. Biol., 1974, 11 : 431M58. WOODV, C. D., VASILEVSKV,N. N. and ENGEI_ JR., J. Conditioned eye blink: Unit activity at coronal precruciate cortex of the cat. J. Neurophysiol., 1970, 33 : 851-864.
651
INTERACTION BETWEEN THE ACTIVITY OF AN EPILEPTIC FOCUS AND DISCRETE SKILLED MOVEMENTS IN RATS S. ISLAM 1 AND J. BURE~
Institute 0[ Physiology, Czechoslovak Academy ~?[Sciences, Prague (Czechoslovakia) (Accepted for publication: July 18, 1975)
Experimental evidence, recently reviewed by Woodruff (1974), indicates that cortical epileptic foci interfere with learning but not with retrieval. It is less clear how local epileptic discharges affect highly coordinated neural activity underlying discrete movements with a well known cortical localization. Lateralized reaching and grasping movements (Peterson 1934), which are typical manifestations of handedness in rats, are well suited for the investigation of this problem. Localization of the critical motor area has been established by extirpation experiments (Peterson and Devine 1963; Castro 1972) and localized electrophysiological correlates of the reaching movements have been recently described by Megirian et al. (1974). The purpose of the present paper is to examine the interaction between the activity of a picrotoxin focus, acutely established in the "hand area" of the rat motor cortex, and the performance of the overtrained reaching habit. METHODS
Subjects Sixteen male hooded rats (Druckrey strain) were reduced to 80 % of initial body weight and maintained on a 24 h food deprivation schedule with water freely available. Apparatus The experiments were performed in a plastic chamber (30 x 18 x 15 cm) with a circular opening in the center of the front wall, 5 cm above the floor. A perspex feeder, a tube 4.5 cm long with a 1.1 cm internal diameter, was attached to the 1Visiting scientist from the Government College Mardan, Pakistan.
wall opening from the outside. A hole in the upper part of the tube made it possible to introduce into the feeder small pellets (30-50 mg) prepared from Larsen's wet rat chow. The distance of the pellet from the feeder entrance was controlled by an adjustable piston. A plastic ring fitting the outside diameter of the feeder was equipped with a miniature light bulb facing a phototransistor. The photoelectric system could be fixed in a suitable position between the feeder entrance and the food so that the reaching of the forelimb interrupted the beam and reduced the current across the phototransistor.
Procedure Food-deprived rats were introduced into the apparatus and offered food placed close to the feeder entrance. The pellets were gradually moved into the feeding tube until the animal could only reach them with one forepaw. Usually rats preferred to perform this movement with the left or right forepaw, the preference becoming consistent after 2-3 days of training. Fifty pellets were given per day and training continued until the animal was able to get food placed 2-3 cm deep into the feeder. Surgery Well trained animals were anesthetized with Nembutal (40 mg/kg) and silver cannulae for picrotoxin application and ECoG recording were implanted. Two trephine openings 2 mm in diameter were made 1.5 mm rostral to the bregma and 3,0 mm lateral to the midline. Silver tubes (2.0 mm outside and 1.4 mm inside diameter, 10 mm long) were placed in the trephine openings and a silver screw reference electrode (2 mm diameterl was fixed in the frontal bone 7 mm
652
s . I S L A M A N D J. B U R E S
rostral to bregma. Thin silver wires connected the electrodes with a subminiature 5-pin transistor socket. The whole implant was fixed to the skull with anchoring screws and acrylic resin. Between experiments the silver cannulae were closed with tightly fitting mandrels.
them a picrotoxin focus was established in the hemisphere contralateral to the preferred forepaw, in the other picrotoxin was applied to the ipsilateral cortex.
Recordin9 and data processin9
1. Development of the epilepticfocus
Two days after surgery the animal was connected by a light-weight suspended cable with the input of a conventional ECoG apparatus. To limit movement artifacts a miniature operational amplifier built in the connector was used as a signal follower, with output impedance of 2K. The mandrel was removed and the cannula was filled with 5 #1 o f 1 ~ picrotoxin solution. The animal was then placed in the training box and E C o G recording was started. When picrotoxininduced seizure activity developed, food was introduced into the feeder at irregular 20-40 sec intervals. EEG activity and the photoelectric signals of reaching were recorded on a 4-channel F M tape recorder. The analog record was processed with the LINC 8 computer, using a program for plotting pre- and post-reaching spike histograms during a period of 512 msec before and 512 msec after beam interruption (limb extension). The histograms were plotted on an incremental plotter. Usually two experiments were performed on 2 consecutive days in the same animal. In one of
Application o f 1 ~ picrotoxin to the exposed dura triggered, after several minutes, epileptic spikes which rapidly grew in amplitude and could be recorded also in the other hemisphere. The rate of discharge increased during approximately 20 min to a maximum of 1-2/sec and then slowly subsided. Ictal discharges usually developed at the height of the effect and were maintained even when the interictal activity already started to decline. The ictal discharge usually lasted for 10-20 sec and was followed by a 30 to 200 sec interictal interval. Typical records of the fully developed focal activity are shown in Fig. 1 and 2. The E C o G discharges were accompanied by jerking movements o f the contralateral forelimb which were essentially similar to those described with cobalt epileptic foci by Dawson and Holmes (1966). The jerking sometimes spread also to the contralateral hind limb, and was most pronounced when the animal was suspended. The ipsilateral forepaw was usually unaffected. In spite of the jerking the animal was able to perform the reaching movement and to get the pellet from
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Fig. 1. Examples of representative experiments showing relationship between the activity of the picrotoxin focus and the reaching movementsof the contralateral (C) or ipsilateral (I) forepaw. R-output of the photocell; extension of the forepaw into the feedingtube is indicated by upward deflection. S-surfaceEEG recordingfrom the picrotoxin-treatedcortex.
EPILEPTIC FOCUS AND SKILLEDMOVEMENTS p.
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Fig. 2. Ictal discharge and reachingwith the ipsilateral (I) or contralateral (C) forepaw. Other description as in Fig. 1. the tube, although sometimes more attempts were required than under normal conditions. Typical examples are shown in Fig. 1. The upper record shows low rate interictal activity (about 2 spikes/10 sec) which was activated by contralateral reaching. A more frequent contralateral focus (about 10 spikes/10 sec) was inhibited by reaching (middle record). Activity of an ipsilateral focus (lower record) was increased by reaching, to the provocation of an ictal discharge. Reaching movements continued during ipsilateral ictal activity, but prolonged extensions indicated poor coordination. During the second ictal episode reaching stopped. Fig. 2 indicates that ictal discharge in the ipsilateral focus is compatible with reaching (above), whereas similar activity in the contralateral focus prevents reaching (below).
2. Quantitative relationships between epileptic activity and reaching In an attempt to prove the statistical significance o f the changes illustrated by Fig. 1 and 2, spikes and reaches were counted for each page of recording ( = 4 0 sec). Data were averaged in 200 sec blocks and the individual records were synchronized by the maximum discharge rate. The upper part of Fig. 3 shows that the maximal discharge rates were 41 _+ 5 and 50,+ 5 spikes/40 sec in the contralateral and ipsilateral foci respectively. The maximum was significantly different from the activity recorded 10 min earlier ( P < 0.01) or 7 min later (P < 0.05). The increase o f discharge rate was accompanied by increased frequency of ipsilateral reaching ( P < 0.05). The lower part of Fig. 3 shows that the contralateral reaching rate is inversely related to the frequency of the focal discharge.
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Fig. 3. Development of the seizure focus (above) and the related changes of reaching with the contralateral (C) or ipsilateral (I) forepaw (below). Ordinate: averagenumber of spikes (S) or reaches (R) per 40 sec interval. Blocks of 200 sec. Abscissae: time before ( - ) and after (+) culmination of the focal discharge. Records from differentanimals were synchronized in such a way that the 200 sec period with maximum spike frequencyfollowszero. Since the gross character of the above measurements may obscure the finer relationship between the electrical and motor events, the data were analyzed in a different way. The reaching time (interval between the first and last reach in each series o f reaches) was cumulatively measured during the whole recording, together with the total number o f spikes and the number of spikes occurring during the reaching time. The average frequencies were 0.73 and 0.68 spikes/sec for the ipsilateral and contralateral foci and increased
654
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F
Fig. 4. Changes in the activity of the picrotoxin focus induced by reaching with the contralateral (C) or ipsilateral 1I) forepaw. S-slow interictal activity (f< 0.5/sec); F-fast interictal activity (f > 0.5/sec). Above: ~o of animals showing increase (empty columns) or decrease (black columns) of discharge rate during the reaching time. Below: average magnitude of the change of discharge rate during reaching expressed in o/,, of the non-reaching activity. CS: n = 7 ; CF: n =9; IS: n = 7 ; IF: n = 8 .
during reaching to 0.96 and 0.76 spikes/sec, respectively. When the focal activity was arbitrarily divided into two groups of approximately equal size, with the discharge rate below and above 0.5 spikes/see, the first group was activated and the second inhibited by contralateral reaching. Ipsilateral foci were activated by reaching, independent of their discharge rate (Fig. 4).
3. Changes of spike incidence associated with reachin9 Fine peri-reach changes of spike incidence were revealed by computer analysis performed in 8 rats. Typical examples are shown in Fig. 5. In histogram A probability of spike occurrence in the contralateral focus is decreased between - 3 5 0 and - 8 0 msec (minimum at - 160 msec) before reaching. The spike incidence is briefly increased during extension and unaffected during the post-reach period. Gross analysis described in the previous section showed in this experiment
. -480
. -320
.
-160
.
. 0
. .160
.
*320
.480
Fig. 5. Examples of typical peri-reach distributions of focal epileptic discharges. Abscissae : time (msec) before (negative values) and after (positive values) the onset of the extension. Ordinates: number of spikes in 16 msec bins. The histogram A is based on 1536 reaches, histograms B, C and D on 512 reaches each. Histograms A, C and D are from contralateral, histogram B from ipsilateral epileptic foci.
that the average discharge rate of 1.39/sec dropped during reaching to 1.15/sec. Histogram B represents a prolonged prereach increase of discharge rate in an ipsilateral focus (average discharge rate increased during reaching from 1.29 to 1.75/sec). A prolonged pre-reach increase is also shown in the histogram C, where it is combined with a poorly expressed pre-extension inhibition and with a brief increase (64 msec) immediately following the contralateral extension (reaching increased in this case the average discharge rate from 0.49 to 0.99/sec). Histogram D illustrates a contralateral focus with a better developed pre-extension and post-extension inhibition. The average discharge rate dropped during reaching from 0.76 to 0.53/sec. Although the shape of the histogram varied from animal to animal, increase of activity coinciding with the extension was a common finding, both in contralateral and ipsilateral foci (11 times in 13 experiments). The central peak was often preceded by inhibition, which was prominent in contralateral foci. The post-extension inhibition was less expressed and irregular. DISCUSSION
Behavioral arrest during focal seizures is a
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EPILEPTIC FOCUS AND SKILLED MOVEMENTS
well known clinical phenomenon, which has been repeatedly confirmed in animal studies (for review see Woodruff 1974). An epileptic focus usually impairs acquisition more than retrieval (Schmaltz 1971; Aquino-Cias et al. 1972) and avoidance more than escape (Hamilton and Isaacson 1970; Olton 1970). The present results support the notion (Stamm and Pribram 1960, 1961; Stamm and Warren 1961) that retention of an overtrained habit is rather resistant to focal seizure activity in the corresponding cortical projection areas. Reaching remained preserved during ictal discharge, projected to the sensorimotor cortex contralateral to the preferred forelimb from the other hemisphere, but was arrested by the ictal discharge directly generated in this region. It is difficult to decide whether this effect is due to interference with the integrative mechanisms or to motor impairment caused by the peripheral spasms. Interictal activity did not interfere with reaching and could be, therefore, employed as an index of excitability changes associated with reaching. The comparison of average spike discharge and reaching rates reveals reciprocal effects of ipsilateral and contralateral foci. The facilitation of reaching induced by the ipsilateral focus is probably only an apparent one: it may reflect the increased effort required to get food in spite of the slightly disturbed coordination. The inhibition observed during development of a contralateral focus is real and results into decreased retrieval of food. The relatively weak impairment of reaching caused by a focus in the ipsilateral hemisphere supports Crowell's (1970) finding that responses of sensorimotor cortex to the stimulation of the ventro-lateral thalamus are little affected by paroxysmal activity in the opposite hemisphere. Also, the observation that focal penicillin discharges can be triggered by contralateral but not by ipsilateral sciatic nerve shocks (Mare~ and Wirthovfi 1975) shows that the interaction between the epileptic focus and the sensory influx is restricted to the direct projection. The gross effects of reaching on discharge incidence indicate that the excitability changes accompanying the elaboration of movement and the feedback signals generated by its perform-
ance, facilitate discharge generation in ipsilateral foci and in slow contralateral foci. Inhibition of fast contralateral foci may be due to reciprocal relations between the integrated activity triggered by reaching and the diffuse discharge elicited by the chemical stimulus. According to the concept of the dominant (Ukhtomsky 1926; Rusinov 1965) the active reflex center attracts the excitation generated by neutral stimuli. Increased excitability of motor cortex during conditioned eye blinks in the cat was reported by Woody et al. (1970). Low rate epileptic foci can be used as sensitive detectors of excitability changes. An alternative explanation assumes that inhibition of the fast epileptic discharge is apparent and that the decreased incidence of spikes during the reaching time expresses the tendency of the rat to reach during relatively discharge-free intervals. This explanation is supported by the computer-plotted histograms of pre- and post-reach distributions of focal discharge. Almost all histograms showed an increase of activity during the actual reaching movement. This brief increase overlapped with the average motor potential (Megirian et al. 1974) which was recorded in the same region during reaching with the contralateral forepaw. The pre-reach troughs (Fig. 5, histograms A and D) suggest that the probability of reaching increases with the duration of the discharge-free interval. The initial phases of movement elaboration seem to be reset by the repetitive discharge. On the other hand, the movement once started increases even the fast activity. The post-reach inhibition then reflects the periodicity of the discharge or reaching. Since the reaching rate varies between 2 and 5/ sec (Megirian et al. 1974) the more distant perireach intervals are likely to be affected by other reaches (see the spurious periodicity in histograms C and D in Fig. 5). SUMMARY
Sixteen male hooded rats were trained to reach into a narrow feeding tube for small food pellets. The paw movements were photoelectrically detected. An epileptic focus established by local application of 1 7opicrotoxin on the exposed motor cortex increased the frequency of reaching
656
with the ipsilateral paw and impaired reaching with the contralateral paw. Interictal discharge rate of all ipsilateral foci was increased by reaching in the same way as the slow activity (< 0.5/sec) of contralateral foci. On the other hand, fast activity (> 0.5/sec) of contralateral foci was decreased by reaching. Computer analysis of interictal discharge incidence during 512 msec before and after reaching onset showed that the brief facilitation of discharge (50 msec) during the actual movement was often preceded and followed by more prolonged inhibition (200 msec). The inhibition was better expressed in the contralateral hemisphere. The results are interpreted as due to changes of cortical excitability associated with reaching and to interference of the epileptic focus with the cortical elaboration of the skilled movement. RESUME INTERACTION ENTRE L'ACTIVITE D'UN FOYER EPILEPTIQUE ET LES MOUVEMENTS ELABORES DISCRETS CHEZ LE RAT
Seize rats mfiles ont 6t6 dress6s/l atteindre un pellet alimentaire dans un tube 6troit. Les mouvements du membre ant6rieur 6taient d6tect6s photo61ectriquement. Un foyer 6pileptique 6tant obtenu par application locale de picrotoxine/~ 1 ~o sur un cortex moteur expos& il en r6sultait une augmentation de la fr6quence des mouvements d'atteinte par le membre ipsilat6ral et une diminution, par le membre contralat6ral. Le taux de d6charges interictales de tous les foyers ipsilat6raux 6tait accru par le mouvement de pr6hension, tout autant que les activit6s du foyer contralat6ral fi basse cadence (<0.5/sec). En revanche, l'activit6 rapide (>0,5/sec) du foyer contralat6ral 6tait d6crue par ce mouvement. Une analyse quantitative de l'incidence des d6charges interictales au cours des 512 msec pr6c6dant et suivant le d6but de pr6hension, a mis en 6vidence une facilitation br6ve (50 msec) des d6charges pendant le mouvement, souvent pr6c6d6e et suivie par une inhibition durable (200 msec). L'inhibition 6tait plus claire dans l'h6misph~re contralat~ral. Ces r6sultats sont attribu6s /~ des modifications de l'excitabilit6 corticale, en rapport avec
S. ISLAM AND J. BURES
le mouvement de prdhension, et g l'interfdrence entre l'activit6 6pileptique focale et l'61aboration corticale du mouvement fin. REFERENCES AQU1NO-CiAS, J., ANEIROS-RIBA, R., FERN~.NDEZ-YERo, F. and HERNANDEZ-MESA,N. Effects of epileptic foci in the visual cortex of the rat on passive avoidance learning. Physiol. Behav., 1972, 8: 957-961. CASTRO, A. J. The effects of cortical ablations on digital usage in the rat. Brain Res., 1972, 37:173 185. CROWELL, P. M. Distant effects of a focal epileptogenic process. Brain Res., 1970, 18:137 154. DAWSON, G. D. and HOLMS, O. Cobalt applied to the sensorimotor area of the cortex cerebri of the rat. J. Physiol. (Lond.), 1966, 185: 455~,70. HAMILTON, G. and ISAACSON, R. L. Changes in avoidance behavior following epileptogenic lesions of the mesencephalon. Physiol. Behav., 1970, 5:1165 1167. MAREL P. and WIRTHOV~,, Z. Triggering discharges of a cortical epileptogenic focus by sciatic nerve stimulation in rats. Physiol. Bohemoslov., 1975, in press. MEG1RIAN, D., BURE~OV,~, O., BUREt, J. and DIMOND, S. Electrophysiological correlates of discrete forelimb movements in rats. Electroenceph. olin. Neurophysiol., 1974, 36: 131-139. OLTON, D. S. Specific deficits in active avoidance behavior following penicillin injection into hippocampus. Physiol. Behav., 1970, 5: 957-963. PETERSON, G. M. Mechanisms of handedness in the rat resulting from cortical lesions after limited forced practice. Comp. Psychol. Mono,qr., 1934, 9: 1. PETERSON,G. M. and DEVINE, 1. M. Transfer in handedness in the rat resulting from cortical lesions after limited forced practice. J. camp. physiol. Psychol., 1963, 56: 752 756. RUSlNOV, V. S. Dominant area and its role in the formation of temporal connections. Proe. 23rd Int. Congr. Physiol. Sci., Tokyo, 1965, 4: 613-617. SCHMALTZ, L. W. Deficit in active avoidance learning in rats following penicillin injection into hippocampus. Physiol. Behat,., 1971, 6:667 674. SVAMM, J. S. and PRmRAM, K. H. Effects of epileptogenic lesions in frontal cortex on learning and retention in monkeys. J. Neurophysiol., 1960, 23:552 563. STAMM, J. S. and PRIBRAM, K. H. Effects of epileptogenic lesions of inferotemporal cortex on learning and retention in monkeys. J. comp. physiol. Psychol., 1961, 54: 614-618. ISTAMra, J. S. and WARREN, A. Learning and retention by monkeys with epileptogenic implants in posterior parietal cortex. Epilepsia (Amst.), 1961, 2: 229-242. U KHVOMSKY,A. A. [Concerning the conditions of excitation in the dominant.] (in Russian). Nov. Refl. Fiziol. Nerv. Sist., 1926, 2: 3-15. WOODRUFV, M. L. Subconvulsive epileptiform discharge and behavioral impairment. Behav. Biol., 1974, 11 : 431M58. WOODV, C. D., VASILEVSKV,N. N. and ENGEI_ JR., J. Conditioned eye blink: Unit activity at coronal precruciate cortex of the cat. J. Neurophysiol., 1970, 33 : 851-864.