Activation Pattern in Lower Level in the Neo-,Paleo-,And Archicortices

ACTIVATION PATTERN IN LOWER LEVEL IN THE NEO-,PALEO-,AND ARCHICORTICES

Goro IMAMURA* AND Hiroshi KAWAMURA**

Laboratory of Neurophysiology,Institute of Brain-Research, School of Medicine,University of Tokyo

In the classical works of brain physiology,solely the neocortical electrical activity was recorded in the most cases,and two different patterns;low voltage fast waves and slow waves with spindle bursts were classified as an indi- cator of the functional level of the brain.These two patterns,namely arousal pattern and sleep pattern of the neocortex respectively,were utilized to study the effects of various kinds of physiological procedures and the effects of drugs upon the brain. After the administration of some kinds of central depressants,especially narcotics(dial-urethane,pentobarbital etc.)often occurred a peculiar anesthetized pattern in the neocortex,and high voltage"arousal"pattern appeared by stimulation.For example,in the works of MURPHY & GELLHORN(1945)1), electrical stimulation of the posterior hypothalamus did not produce ordinary low voltage fast waves in the neocortex under dial-urethane anesthesia,and instead,4-8 cps high amplitude sinusoidal waves were elicited.SLOAN et al. (1950)2)also showed that electrical stimulation of the anterior limbic lobe elicited in some cases high voltage"arousal"pattern in the neocortical area. Similar pattern was also observed in the paleo-cortex(pyriform lobe)and its subcortical nuclei(amygdala),by MACLEAN et al.(1952)3)and described as olfactory-like responses.FEINDEL & GLOOR(1954)"also described 12-16 cps high amplitude waves as"arousal"pattern in the amygdala under pentobarbital anesthesia. In the present paper,the observation of this peculiar pattern in the neo-, paleo-,and archicortices was made and named as the activation pattern in lower level,and the conditions for appearance of this pattern were discussed.

Received for publication April 22,1962. 今村護郎,川村浩 *Present Address:Department of Psychology,Faculty of Letters,University of Tokyo **Present Address:2nd Department of Physiology,Yokohama University School of Medicine.

494 LOWER LEVEL ACTIVATION PATTERN OF EEG 495

METHODS

Experiments were carried out on cats.The animals were prepared under ether anesthesia,tracheal and venal canulae were inserted.After the animal was fixed on a stereotaxic apparatus(Todai-Noken type),ether was removed and d-tubocurarine chloride was injected,and respiration was maintained artificially.Then trepanation of the skull was performed.Concentric needle electrodes,distance of the tips,0.5mm apart,were inserted stereotaxically in the amygdala,hippocampus,midbrain reticular formation,preoptic region and posterior part of the hypothalamus and some other subcortical nuclei.EEG from the neocortex was led by the silver-ball electrodes,ball diameter 1mm and polar separation being 2mm.Square wave pulses for stimulation were delivered from an electronic stimulator(Nihon-Koden MSE 3 type)and for re- cording of EEG a 12-channel ink-writing electroencephalograph(San'ei model EG 126) was used. At the end of each experiment,the brain was fixed and the positions of electrode tips were subsequently determined by histological examination.To provoke the activation pattern in lower level in the electrical activity of the brain,various kinds of central depressants(narcotics:pentobarbital,hexobarbital etc.;tranquillizers:chlorpromazine,meprobamate)were used.In some cases,to elevate the activity level of the brain,central excitants(caffein,megimide,and pentylene-tetrazol)were also used.

RESULTS

Activation pattern in lower level in the neocortex.High voltage 10-15cps(in some cases down to 4-8cps or up to 20cps)activation pattern in lower level in the neocortex was easily elicited after the administration of a small dose of barbiturates.FIG.1 shows the effect of intravenous injection of pentobarbital(8mg/kg)upon the electrical activity of the paleocortex and neocortex. Before the injection of the drug,high frequency electrical stimulation(100 cps, 1msec,1.6volt)of the midbrain reticular formation elicited low voltage fast activity both in the anterior sigmoid gyrus and in the pyriform lobe.Olfactory bulb remained almost unchanged.Ten minutes after intravenous injection of pentobarbital,reticular stimulation with the same parameter showed the different effrect in the EEG patterns.Thus,the pyriform lobe showed high amplitude 12cps waves during reticular stimulation,and the neocortex also occurred 13-14cps rhythmic waves of high amplitude. Similar effect on the electrical activity was seen after the administration of hexobarbital(5mg/kg,i.p.).By this dose,the activation pattern in lower level was obtained only in the neocortex,while other portions of the brain showed rather ordinary low voltage fast waves.Slow waves were reduced by pain stimulation in the amygdala,and this tendency was also observed in the caudate nucleus.The hippocampus showed regular slow arousal waves with superimposed enhanced fast waves(FIG.2). The activation pattern of high voltage 10-15cps waves was observed in the spontaneous recovery process from deep anesthesia or by addition of cen- 496 G.IMAMURA AND H.KAWAMURA

BEFORE

AFTER PENTOBARBITAL 8MG/KG I.V.

FIG.1.•@ Activation pattern in lower level in the neocortex and paleocortex evoked by high frequency electrical stimulation of the midbrain reticular formation(100 cps,1msec,1.6 volt).Upper traces:control records.Lower traces:after intravenous injection of 8mg/kg pentobarbital.High amplitude rhythmic waves were produced in the pyriform lobe(12 cps)and anterior sigmoid gyrus(13-14

cps)instead of low voltage fast activity . Abbreviations;PYR;pyriform lobe,OB;olfactory bulb,ANT .SIG;anterior sigmoid gyrus,AMY;amygdala,HIP;hipnocampus.NC:caudate nucleus .ANT. CIN;anterior cingulate gyrus,POST.CIN;posterior cingulate gvrus .ECT.SY; ectosylvian gyrus,LAT;lateral gyrus,SEP;septal nuclei .

FIG.2.•@ Activation pattern in lower level in the neocortex.Noxious stimulation of pinching paw of the hind leg produced high voltage activation pattern solely in the neocortex(anterior sigmoid gyrus),after the intravenous administration of hexobarbital(5mg/kg).Note the mixed pattern in the hippocampus with regular slow waves and intermingled fast activity.Caudate nucleus and amygdala showed low voltage fast pattern. LOWER LEVEL ACTIVATION PATTERN OF EEG 497

tral excitants(caffein or megimide)to the deeply anesthetized animal.FIG.3 shows the activation pattern in lower level produced in all areas of the brain by reticular stimulation(100 cps,1 msec.2 volts)after addition of caffein 10 mg/kg intravenously,to a cat previously administered a large dose of meprobamate(1g/kg,i.p.). Among tranquillizers,meprobamate easily produced this activation pattern especially in the neocortex.Frequency of this high amplitude waves decreased with lowering of the activity level of the animal(by hypothermia,administration of larger dose of central depressants). Activation pattern in lower level in the archicortex.Similar 10-15 cps activation pattern of high amplitude was also observed in the hippocampus.FIG.4 shows 14 cps high amplitude rhythmic waves in the hippocampus during electrical stimulation of the midbrain reticular formation.In this case,no central depressant drug was used.This pattern more easily appeared in the hippocampus than in the neocortex and paleocortex without any drug administration. FIG.5 shows the different effects of reticular and hypothalamic stimulation. upon EEG pattern of the hippocampus and neocortex.Stimulation of the midbrain reticular formation suppressed slow waves,and produced fast activity in the neocortex,while posterior hypothalamic stimulation elicited fast activity in the hippocampus and almost no effect on the electrical activity of the neocortex. As was reported in the previous papers5)6),stimulation of the preoptic region desynchronized the hippocampal regular slow waves and stimulation of the posterior hypothalamus produced marked hippocampal arousal waves.After the administration of a moderate dose of barbiturate,however,both preoptic and posterior hypothalamic stimulation produced the activation pattern in lower level in the hippocampus. In the state of light anesthesia,posterior hypothalamic stimulation produced regular slow waves intermingled with fast waves,which seemed to suggest the different origin of regular slow waves and fast waves in the hippocampus. Activation pattern in lower level in the paleocortex.As was seen in FIG.1,the administration of 10mg/kg barbiturate elicited the activation pattern of high amplitude in the paleocortex and amygdala as well as in the neocortex.These waves also appeared during spontaneous awakening from deep barbiturate anesthesia or by addition of the central excitant drugs(caffein or megimide) to the deeply anesthetized animal.FIG.6 shows the marked 12 cps high amplitude activation pattern in the paleocortex and amygdala elicited by noxious stimulation 2hours after the intraperitoneal injection of 35mg/kg pentobarbital. In this case,the neocortical area(lower three traces)showed almost no change in their pattern of electrical activity and the hippocampus showed less change than the amygdala and pyriform lobe. 498 G.IMAMURA AND H.KAW AMURA

AFTER PMEPROBAMATE a CAFFEIN

FIG.3.•@ High voltage activation pattern in the whole cortical and subcortical areas.Four hours after intraperitoneal injection of 1g/kg meprobamate,10mg/

kg caffein was added intravenously.Under this condition,reticular stimulation

(100 cps,1 msec,2 volts)produced high voltage activation pattern in lower level in the whole cortical and subcortical areas.

FIG.4.•@ Activation pattern in lower level in the hippocampus.High voltage

14 cps rhythmic waves appeared in the hippocampus by high frequency reticular stimulation(100 cps,1 msec,2 volts).In this case,no central depressant drug

was used.

A larger dose of chlorpromazine easily produced the activation pattern in

lower level of 10-15 cps high amplitude in the paleccortex.Seizure discharges

provoked by chlorpromazine in the amygdala and pyriform lobe which was

described by PRESTON(1956)7),OGIU et al.(1957)8)scarcely occurred.These 10-

15 cps high amplitude regular waves in the paleocortex and amygdala were, LOWER LEVEL ACTIVATION PATTERN OF EEG 499

RE STIMULATION

POST.HYP STIMULATION

EIG.5.•@ Effect of reticular and posterior hypothalamic stimulation on the electrical activity of the neocortex and hippocampus.Comparison of the effect in the same cat.Stimulation of the midbrain reticular formation(100 cps,1 msec, 1 volt)elicited low voltage fast activity in the anterior sigmoid gyrus anterior and posterior cingulate gyrus,while the hippocampus showed very slight fast activity.Posterior hypothalamic stimulation(2 volts)elicited the typical activation pattern in lower level with slight regular slow waves in the hippocampus, while the neocortical areas showed almost no change.

2 HOURS AFTER PENTOBARBONL 33M/KG I.P.

FIG.6.•@ Activation pattern in lower level in the paleocortex and amygdala. Two hours after intraperitoneal injection of 35mg/kg pentobarbital.Pyriform lobe and amygdala showed marked high amplitude 12 cps waves by pinching paw of the hind leg,while the hippocampus revealel relatively slight change,and the neo-cortical areas(lower 3 traces)remained almost unchanged. 500 G.IMAMURA AND H.KAWAMURA

according to the author's observation,closely resemble to the induced waves by air blowing into the nostril,though usually their frequency was somewhat higher in the latter. FIG.7 shows the similar activation pattern of high amplitude in the amygdala and pyriform lobe elicited by drugs.Thus,on a cat administered meprobamate and caffein,reticular stimulation(2 volts)produced this activation pattern in the whole areas of the brain(in the upper traces).High amplitude waves induced in the paleocortex by a large dose of chlorpromazine

AFTER MEPROBAMATE a CAFFEIN

AFTER CHLORPROMAZINE

FIG.7.•@ Activation pattern in lower level provoked by drugs.Reticular stimulation(100 cps,1 msec,2 volts)produced the high voltage activation

pattern in the whole cortical and subcortical areas after the administration of meprobamate and caffein (upper records).A larger dose of chlorproma-

zine(30mg/kg i.v.)provoked high voltage activation pattern in the pyriform lobe and amygdala,which was suppressed by stronger reticular

stimulation(4 volts).Note the high voltage pattern in the hippocampus

during stimulation(lower records).

were suppressed by relatively high voltage electrical stimulation of reticular

formation(4 volts,in the lower traces),posterior hypothalamus and peripheral

nerve as well as by noxious stimulation of pinching paw of the hind leg.The

effectiveness of various kinds of stimuli for eliciting these waves seemed to

suggest that this pattern is not the paroxismal seizure activity,but the de- LOWER LEVEL ACTIVATION PATTERN OF EEG 501 finit eelectrical activity corresponding to some functional level of the brain. Maximum frequency of the evoked electrical activity of the amygdala and pyriform lobe by repetitive olfactory bulb stimulation markedly reduced after the administration of central depressants.As shown in FIG.8,evoked waves in the amygdala by olfactory bulb stimulation(1 msec,2 volts)did not follow over 30 cps,and reduced in half 15 cps)by repetitive stimulation of 30 cps.

BEFORE

AFTER PENTOBARBITAL LOMG/KG I.V.

FIG.8.•@ Response of the amygdala to the repetitive stimulation of the olfactory bulb.Top frequency of the amygdaloid activity which could

follow to the olfactory bulb stimulation(1 msec,2 volts)was reduced to 12 cps after 10mg/kg pentobarbital injection.

After intravenous administration 10mg/kg pentobarbital,the maximum frequency of the paleocortical activity which could follow to repetitive stimulation. of olfactory bulb decreased to 12 cps.The change of frequency of evoked waves in the amygdala seemed to correspond to the frequencyof spontaneous electrical activity of the amygdala in the arousal pattern and in the activation pattern in lower level respectively. 502 G. IMAMURA AND H. KAWAMURA LOWER LEVEL ACTIVATION PATTERN OF EEG 503

All these data taking into consideration,the authors classified the pattern of electrical activity in the neo-,paleo-,and archicortical systems into 5 grades in the acute experiments.They are arousal,activation in lower level,drowsy, sleep and deep anesthesia pattern as is shown in FIG.9.In the most cases, each cortex revealed the same electrical activity level and they shifted simul- taneously and in parallel.In some conditions,however,the discrepancy or dissociation of the electrical activity level between the neo-,paleo-,and archicortices was observed,as is shown in FIG.2,4,5,6.

DISCUSSION

Activation pattern of high voltage in the neocortex was often observed from the earlier experiments of many authors,who used narcotized animals for their experiments(dial-urethane:MURPHY & GELLHORN,1945;chloralose: MAGOUN et al.,19499)). This pattern was often described as one of the"arousal"patterns,but the behaviour of the animals in the state showing this activation pattern was different from that in the real arousal state.Thus,animals lied on the floor and moved their legs in locomotive manner,and responsivity to the various kinds of stimuli was much diminished and insufficient10). These high voltage 10-15 cps waves of activation pattern in lower level were suppressed in amplitude by repeated strong stimulation of the brain stem activating structure or peripheral nerve,and more and more marked low voltage fast activity appeared.From these findings,it was suggested that this pattern was an electrical indication of a definite level of the brain activity which succeeded the usual low voltage fast arousal pattern in the neocortex. Diminished excitability cycle of the activity should be supposed as the back- ground of"synchronization mechanism"of the electrical activity,which elicited the activation pattern in lower level of high amplitude 10-15 cps. As for the hippocampus,2-6 cps regular slow waves were well-known in the arousal state of the animals,though 20-30 cps fast waves,which became more marked in the drowsy state,were often superimposed on them.Electrical stimulation of the preoptic region,septal area and amygdala blocked regular slow arousal waves and enhanced this fast activity as was reported previously6). High voltage fast(10-15 cps)activation pattern in lower level in the hippocampus might have the same origin with 20-30 cps fast waves,not with the regular slow arousal waves.Though this activation pattern in lower level resembles to MACLEAN's seizure activity,it seems to be not a real seizure pattern,because the conditions for its appearance and the responsivity to the activating stimuli were quite different from those of the seizure activity. The discrepancy of the electrical activity level between the neo-,paleo-, and archicortices which was shown in FIG.2,4,5,6,supported the presence 504 G.IMAMURA AND H.KAWAMURA. of the specific activating mechanism for each cortex11).Precise study of this phenomenon with relation to the animal behaviour or with relation to the effects of various kinds of central depressant and excitant drugs will make much contribution to the brain physiology and neuropharmacology.

CONCLUSION

High amplitude 10-15 cps(sometimes down to 4-8 cps or up to 20 cps)

rhythmic waves named as the "activation pattern in lower level" in the neo-,

paleo-,and archicortices were studied on the curarized cats.

1.•@ The activation pattern in lower level occurred after the administration of

the narcotics and tranquillizers.Meprobamate and a small dose of barbiturate

easily produced this pattern only in the neocortex.In the recovery process

from deep anesthesia,this pattern was observed often at first in the amygdala

and pyriform lobe,then in the hippocampus and at last in the neocortex.The

same pattern in all cortical and subcortical areas was easily obtained by in-

jection of the central excitant(caffein or megimide)to the deeply anesthetized

animal.

2.•@ The activation pattern in lower level in the hippocampus more easily

occurred than in the neocortex and paleocortex under the condition of lowered

activity level of the animal without using any drugs.

3.•@ The activation pattern in lower level in the paleocortex and amygdala was

also observed after the administration of a large dose of chlorpromazine.

4.•@ EEG patterns in the neo-,paleo-,and archicortices were classified into 5

different levels corresponding to the activity levels of the animal behaviour.

The authors wish to express their sincere thanks to Prof.T.TOKIZANE for his

helpful suggestions,to Dr.Takehiko FUKUHARA(Dept.of Pharmacology,University

of Tokyo)for his kind advice and help to the experiment and to Miss M.TAKAHASHI for preparing histological section.These results were partly reported at the Annual

Meeting of Japan EEG Society in 1958 and 1959.

REFERENCES

1) MURPHY, J. P. and GELLHORN, E., The influence of hypothalamic stimulation on cortically induced movements and on action potentials of the cortex. J. Neuro- physiol., 8: 351-364, 1945. 2) SLOAN, N. and JASPER, H., Studies of the regulatory functions of the anterior limbic cortex. EEG Clin. Neurophysiol., 2: 317-327, 1950. 3) MACLEAN, P. D., HORWITZ, N. H.and ROBINSON, F., Olfactory like responses in the pyriform area to non-olfactory stimulation.Yale I. Biol. Med., 25: 159-172, 1952. 4) FEINDEL, W. and GLOOR, P., Comparison of electrographic effects of stimulation of the amygdala and brain stem reticular formation. EEG Clin. Neurophysiol., 6: 389-402, 1954. 5) KAWAMURA, H., The electrical activity of the limbic system. Seitai-no-Kagaku, LOWER LEVEL ACTIVATION PATTERN OF EEG 505

10: 73-80, 1959. 6) TOKIZANE, T., KAWAMURA, H. and IMAMURA, G., Hypothalamic activation upon electrical activities of paleo-, and archicortices. Neurologia medico-chirurgica, 2: 73-86, 1960. 7) PRESTON, J. B., Effects of chlorpromazine on the central nervous system of the cat; a possible neural basis for activation, J. Pharmacol. Exp. Therap., 118: 100- 115, 1956. 8) OGIU, K., TAKAGI, H., YAMAMOTO, S. and TAKAGI, S., Sites of action of reserpine, chlorpromazine and lysergic acid diethylamide in the central nervous system. Jap. J. Pharmacol., 53: 131, 1957. 9) MORUZZI, G. and MAGOUN, H. W., Brain stem reticular formation and activation of the electroencephalogram. EEG Clin. Neurophysiol., 1: 455-473, 1949. 10) IMAMURA, G., KAWAMURA, H. and MIYASAKA, M., Relation between animal behaviour and electrical activity of neo-, paleo-, and archicortices. Proc. VIIIth Annual Meeting of Japan EEG Society, 26, 1959. 11) KAWAMURA, H., NAKAMURA, Y. and TOKIZANE, T., Effect of acute brain stem lesions on the electrical activities of the limbic system and neocortex. Jap. J Physiol., 11: 564-575, 1961.