Behavioral and EEG changes following chronic brain stem lesions in the cat

B E H A V I O R A L A N D EEG C H A N G E S F O L L O W I N G C H R O N I C B R A I N S T E M LESIONS I N T H E C A T 1 L. H. SCIIREINER,M.D., W. B. K~owL~s, M.S. a nd H . W . MAc.OUN, Ph.D. Departments of Anatomy and Psychology, Northwestern University, Chicago

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Each twenty-four hours of their exmtence, m permds that often correspond approxxmately with daylight and darkness, man and most ammals are alternately aware of environmental changes and respond more or less purposefully to them, in a state called wakefulness, or are out of touch with the world about and lie inert and, except for mternal processes, motmnless, m a state called sleep It ~s apparent that pronounced alterations m central neural activity underly these contrastm9 condltmns Electroencephalography, which has provided a means of samphn9 this activity directly, has revealed that alert wakefulness Is associated with low voltage, fast discharge of the cerebral cortex, while high voltage slow wave8 charactemze electrocortlcal activity in drowsiness and sleep Th e present approach to study of central neural alteratmns m sleep and wakefulness had its mceptmn m the dxscovery that exciting the reticular core of the brain stem and the basal dlencephalon abolished exmtmg electrocortlcal synchrony and substituted low voltage, fast activity m Its place, thus reproducing the E E G change seen in spontaneous awakening or in the arousal reactmn to natural stlmuh (Moruzzl and Magoun, 19'}9) In the waking "enc~phale mol~" acute brain stem lesions in a position to Interrupt this reticular activating system were next found to abohsh the E E G pattern of wakefulness and to result m recurring slow waves and spindle bursts, like those of sleep or barbiturate anesthesia (Lmdsley. Bowden and Magoun, 19'19) W i t h this background, it seemed desirable to determine to what extent correlated Aided by a grant from the Commonwealth Fund

behavioral and E E G observation of ammals with chromc lemons of the brain stem would support the seemingly xmportant role of ~ts reticular activating system xn the reduction and maintenance of the waking state. W i t h every attempt to make the operated animal's sltuatmn a natural one, E E G s were repeatedly recorded during the survival period and, when the animal was drowsy or asleep, the arousing effect of sensory stimulation was tested METHODS In a series of cats, electrolytic lesions were placed in the brain stem under aseptic precautions with the Horsley-Clarke techtuque T h e animals were followed for survival periods between three weeks and two months, receiving all the postoperative care necessary to maintain them E E G s were repeatedly recorded with a Grass model III amplifier and mkwnter. Pickup electrodes consisted of the balled tips of silver w~res implanted in the calvanum so as to rest upon the dura T h e y were either embedded in a threaded plastic cylinder screwed into a tapped trephine openm o (Ingram, Knott and Wheatley, 19't9). or were forced into a small burr hole, with the insulated length of the wire passm 9 under the skin to emerge from the back of the neck (Rhemberger and Jasper, 1937). The latter type was most often used, three electrodes being Inserted over each hemmphere and records bern 9 obtained between pairs of them RESULTS Before presenting the consequences o[ lesions of the brain stem, the E E G events associated with wakefulness and sleep m the

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mmtakably to sleep, ultimately to reawaken. During wakefulness, its E E G was marked by low voltage, fast actlvlty (fig. 1, A ) . W i t h drowsiness, large slow waves appeared at random m the record and more moderate amphtude synchrony was present between

normal cat may briefly be described. The records shown m figure 1 are selections from a run m which the normal ammal, mltrolly awake, arranged itself m a comfortable rechnm 0 positron, drowsed for a t~me, occasionally openm 0 ~ts eyes, then went unL ANT

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The E E G of a normal cat m wakefulness and sleep The ammal m z m t ~ l y awake ( A ) , d r ~ , s e s (B), goes to sleep (C and D ) and reawakens (E) ChanneLs record activity m the anterior and posterior parts of the left and rtght hemtsphere, as indicated Speed m D and E Is half that m A-C The strips are not continuous LA

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Fig 3 Large lemon of the ponto-mtdbram tegmentum whose dtstrtbutlon ts prolected upon a reconstruction of the mtdsagttal plane ( A ) and ts shown m transverse secttons (B-D). the levels of whtch are indicated at the base m A Abbrevlattons for all hgures are as follows A ~ aqueduct. A C - - anterior commsssure. A D anterodorsal nucleus, A M - - anteromedtal nucleus, BIC - - brachmm inferior colhculus, BP - - basts peduncuh, BRC - - brachmm conluncttvum, BSC - - brachmm superior colhculus, C - - nucleus centrahs, C A - - caudate nucleus. C E R - - cerebellum. CL - - nucleus centrahs laterahs. C M centre medmn, C T - - central tegmental tract, D - - dentate nucleus, E N ~ entopeduncular nucleus, G P - - globus palhdus, H - - habenulopeduncular tract. IC - - internal capsule, IP ~ mterpeduncular nucleus, L - - lateral thalamtc nucleus, LL .-- lateral lemniscus. L G ~ lateral gemculate body, M - - medtal nucleus, MB - - mammtllary body, M F - - medml iongttudmal fasctculus, M G - - medial gemculate body, MI - - massa mtermedta, M L - - medial lemmscus, M P - - mammfllary peduncle, O C - - opttc chmsma. O T - - o p t t c tract, P - - pons. P C - - posterior commmsure. PL - - pulvinar, P Y - - pyramid, R - - resttform body, R N - - red nucleus, SC - - supertor colhculus, S N - - substantm mgra, S P T - - lateral spmo-thalamtc tract, S V N - - spinal fifth tract, T H A L - - thalamus, V A - - ventrahs antertor. V L - - ventrahs laterahs, V M - - ventrahs medmhs, V P L - - ventrahs postero. laterahs, V P M - - ventralts posteromedtahs, III - - thtrd venmcle, I V - - fourth ventricle Llpon awakening, these varmtms synchrony gave way once more v o l t a g e , f a s t r e c o r d ( f i g . 1, E ) .

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ralsmq of the head, with concomitant cessation of slow waves and spindle bursts m the E E G and the appearance and prolonqed maintenance of low voltaqe fast actiwtv tn cons~dermq next the extent to x~hlch sleep and x~akefulne% and the E E G alteratmns associated with them were influenced by mlurv to the rostral brain stem, the results follov,,nq interruption of the ascendmq reticular actlxatmq system (A) may be corn-

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Durra 9 the first u eek, the cat exhzbited recurrmq bouts ot runnmq movements and extensor hypertonus, increased by handhnc3 Runmnq movements were absent durln 9 the ~econd and third weeks of lt~ 22 days surx lxal and when undl,4urbed durm q this perzod, the ammal lay on its s~de, with eyes almost closed and was motionless except for o(caslonal arching of the back and extension ot ~he leqs augmented by nocicepn~e stim-

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pared with those obser,,ed when this system was spared while other relevant functional components were destroyed (B) A LESION OF THE RETICULAR ACTIVATING SYSTEM

lnlurzt to the ponto-mzdbram tegmentum T h e most caudal of the lesions in the reticular formation interrupted most of the tegmentum of the brain stem, in a plane passln 9 ventrally through the front of the pons, whde sparta 9 more lateral structures (fi9 3)

ulanon Its head was elexated and it appeared awake at the start of six E E G tests between the third and m9hteenth days and, on the third and eighth days, it was ~mposs~bte to 9et the animal to sleep At these nines its E E G was characterized by small fast waves shghtly more synchronous than those of a normal wakmq record W i t h the passage of nine m the remainder of these tests and m others, the animal's head sank to the table and lrreqular slow waves ap-

BRAIN STEM LESIONS IN THE CAT peared m the E E G , wh,ch was usually lackm 9 m spmdte bursts, and contained more sharp, fast waves than are normally present durra 9 sleep (ficj 4). W h e n such E E G sync h r o n y was estabhshed, both somahc and a u & t o r y stimul, abohshed ,t and introduced varmble permds of low voltage fast a c h w t y (fig 4, A and B)

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Thereafter, either auditory or somatic st~mulatmn blocked E E G synchrony and promptly introduced low ~oltaqe, fast achv~ty m its place (fig. 7, A - C ) . Such typical activation was characteristically maintained only for the duration of the stimulus or for a few seconds thereafter, and the instances shown m figure 7 Hlustrate some of the lonqer last-

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Leszon o[ rmdbram tegmentum In this case also, most of the extevt of the tegmentum was interrupted but at a somewhat more rostral level immediately behind the &encephalon (figs 5, 6). Again lateral afferent paths and the &encephalon itself were largely spared This ammal, when unmolested, lay motionless on lt~ side. w~th eyes closed, as though deeply asleep, throughout its 21 days of survival Its restm.q E E G consisted of large, recurrm 9, slow waves, with spindle bursts often interposed between them (figs 7, 20 B, B1). Durmfl the first four post-operahve days, ordinary stimulation had no effect upon the animal's somnolence or its E E G

m 9 examples observed Increasm 9 the mtensity of stimulation d~d not greatly proIon 9 the duration of E E G arousal, which

F~g 6 Photormcrograph of tegmenta] les~on at the level ol figure 5 C Wed stare

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m~ght occur without any behaworal counterpart or, when a noc~ceptwe stimulus was employed, be accompamed by rinsing or shaking of the head and growhnq Hgpothalam~c destruction T h e lesion seen m figures 8 and 9 almost completely destroyed the hypothalamus and invaded the medml subthalamus and ventromedml part of the thalamus, which was otherwise spared W h e n unmolested durmq its 25 d a y survival, the cat lay on its rode, sonmolent or asleep, and inert except for occasmnal shght LESION

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Fig 7 EEG of cat with tegmental lesion seen m figures 5 and 6 Arousm9 ef|ects of buzzer (A), whistle (B) and pinch (C) on 7th postoperative day Channels record acttvltv m left anterior-posterior, mght antertor-postermr, left-right, antertor (transcortlcal) and left-right posterior regions movements of the extremities Placed on Its feet, it slowly collapsed to a prone posmon Gradual tensmn m cranial muscles developed on auditory stimulation, and the animal responded to n o o c e p t w e stimulation by growling and baring Its teeth or spitting. By the third week, its E E G was usually charactenzed b y moderate amphtude 3-5/sec waves, which tended to wax and wane m runs (fig 10). Earher, and at times then, spindle bursts of larger amphtude and double this frequency occurred, together w~th larger slow waves, and the record looked more like that of normal sleep. Against whatever back-

rupt any connections entering the thalamus from below m the walls of the third ventricle A week after operation, the cat lay wherever it was placed, with eyes closed, and except for occasional stepping movements of the extremities m m a t e d no actwlty. Afferent stimulation was still capable of argusmg the ammal and actwatm o its E E G , but the duration of these effects was much reduced from those seen m preoperatwe tests obtained m this case. tn E E G desynchronlzatmn evoked by a buzzer, spindle bursts were abohshed for 40 ,~ec. before (fig. 12, A ) and for 10 sec. after operatmn (fig.

BRAIN STEM LESIONS IN THE CAT 12, B). Before operatmn, hearmcj another cat meow faintly abohshed regular slow waves for 30 sec (fig. 12, C) whale postoperatavely, blowing mr m the cat's ear, a stamulus which provoked spitting, several

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associated wath thin state eather exhabated the large slow waves and spindle bursts of natural sleep or other promanent synchrony, and low voltage fast actavlty was conspicuously absent.

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Fig 8 Large leston of hypothalamus projected upon a mtdsaglttal reconstruction (A) and shown m transverse sections (B-D) stereotyped yowls and pdoerectlon, prex,ented slow waves for only 10 succeeding seconds (fig. 12, D ) . Th o u g h varying m degree, the common behavioral result of each of these lesions m a position to block much or all of the cephahc end of the reucular actavatmg system was a postoperatwe somnolence or lethargy and hypokmesla, m whach the animal &splayed httle or no spontaneous actavlty of a purposeful sort and seemed unaware of ordreary environmental stlmuh The EEG

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Fig 10 EEG of eat w~th the hypothalamlc lesmn seen m hgures 8 and 9 Arousal reduced by buzzer (A), pinch {B) and mr on ear (C), on 25th postoperative day Channels pick-up between left anterior-posterior and left-r, ght anterior regmn Stops C 1-3 are continuous

In the c h r o n i c p e r i o d , s t a r t l i n g a u & t o r y o r noclceptlve stimulation were clearly able b o t h to a r o u s e the a n i m a l b e h a v i o r a l l y a n d to a c t i v a t e its E E G Motor effects were u s u a l l y limited to o p e n i n g of the e y e l i d s a n d r a i s i n g the h e a d , t h o u g h , ff the m i d b r a I n w e r e intact x o c a l l z a t l o n mhqht b e a d d e d The d e s , ~ v c h r o n l z a t l o n of e l e c t r o c o r t i c a l acw~ltv w a s quite d~ p r o n o u n c e d a s t h a t e x h i b i t e d b y a n o r m a l a n i m a l , b u t d i f f e r e d from the n o r m a l In the r e s p e c t s t h a t t h e i n t e n s i t y ot the a r o u s i n g s t i m u l u s n e e d e d to be h i g h and that achvatlon was short-lived, dlsapp e a r m q lmmedlatel,¢ o r soon a f t e r c e s s a t i o n of the stimulus thal h a d p r o v o k e d it M a n y m ~ t a n c e s c o u l d be a d d e d to t h o s e s h o w n , In which, u p o n the c e s s a t i o n of m o d e r a t e s t i m uh low ~ o l t a q e fast a c t i v i t y g a v e n a y ,aqthm a s e c o n d oI t,~o to the h i g h e r ~ o l t a g e

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F~q 13 Lesion destroying pertaqueductal grey and medial cerebellum projected upon mldsagittal plane (A) and" shown m transverse secttons (B and C) EEGs show arousal by buzzer (D) and spontaneous awakening (E) on 5th and 10th postoperahve days Channels pickup from left anterior, right ante lot, left-right anterior and left-right posterior of the hemisphere

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slow waves that marked the mmal record Even when the arousing stimulus was ml~ense, only a few seconds usually elapsed before E E G synchrony returned It should be emphasized, however, that during afferent stimulation and for a bmef period thereafter, low voltage fast activity was lust as low and lust as fast as though mesencephalic or hypothalamlc components of the reticular activating system had not been interrupted

medial part of the cerebellum extenswely (fig. 13, A-C), left the animal awake and alert from the first postoperative day, with no greater disposition to sleep than that exhibited by a normal cat W h e n the animal was asleep, wakefulness could readily be induced by afferent stimulation (fig 13, D) and often occurred spontaneously (fig 13, E ) . Once present, an activated E E G and the behavioral alertness assooated with ~t were charactemstlcalty maintained for long per,ods.

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B. LESION SPARING THE RETICULAR ACrlV,. ATING SYSTEM.

Lesions o[ the perlaqueductal greq were produced m two cases, one destroying its caudal and the other ,ts rostral part. The caudal of these lesmns, which also mlured the

The rostra1 lesion destroyed the cephahc portion of the central grey and invaded the caudal part of the thalamus (fig 1't, A - C ) . During the first postoperative week, the animal appeared asleep or drowsy, exhibited little or no spontaneous activity and could not

BRAIN STEM LESIONS IN THE CAT be aroused by afferent stlmulatmn. At this t~me, Its E E G resembled that of sleep, w~th large slow waves and spindle bursts, and could not be activated. Thereafter, the cat became progressively more wakeful and active and, two and three weeks after operatmn, ~ts E E G conmsted for the most part of

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vatlon by afferent stimulation showed no ~mpmrment. Leszon of sensory paths. In two ammals, lateral mesencephahc mlury severed long afferent paths and adjacent structures, ~mmedmtely behind the d~encephalon, whde sparmg the medml tegmental region m which the

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Fig 15 Les,on of sensory paths m lateral mldbram prolected upon reconstruction of mldsa91ttal plane (A) and shown m transverse section {B-D). low voltage fast act,vlty. W h e n drows,ness or sleep occurred, arousal by afferent st,mulatlon was readdy provoked and was prolonged (fig 14, D - F ) . In the chronic permd after destructmn either of the caudal or rostral part of the pemaqueductal grey. therefore, normal sleepwak,ng behav,or was present and E E G actP

reticular actlvatmg system is dtstrlbuted (figs. 15, 16, 18). These ammals were followed for two months and m the chromc period were able to stand and walk, though often standing on the dorsum of the foot and dmplaymg other abnormaht~es One exhibited compulsive walking and both were usually awake during the day (ftg 20 A) These

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animals could sleep, however, and both the behavmral and E E G features of their repose a p p e a r e d completely normal (figs 17. 19) W h e n asleep both a u & t o r y and somatic shmuh were still capable of awakening each of these ammals In the representahxe m stance sho,an in figure 17 a series of blasts on a pohce whistle aroused the a m m a l from sleep, tbe larqe slow wa'~eq and spindle bursts m ~ts E E G ~winq w a y to characteristic low voltac/e, fast activity (fLq 17. A and B) Seven minutes later the animal was stdl ax~ake (fig 17. C) and. 15 minutes after arousal the first " d r o w s y w a v e s " a p p e a r e d (fig 17 D ) Seventeen minutes after a w a -

~denttcal with the examples seen m figures 17 and 19, could also be ,nduced by somatic stimulation an each of these animals In terminal expe~ment~, click stimuli failed to evoke potentials m the auditory or other parts of the cortex m either of these cases In one. single shock shmuh to the sciatic nerve induced contralateral cortical potentials, presumed to be secondary responses, shown b y Morlson and D e m p s e y (1942) to be conducted through the central porhon of the MIDBRAIN

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F~g 16 Photomicrograph of lateral mesencephahc lesions at level of figure 15 D The three dark verhcat streaks on the right s~de are not neural tissue but coagulum. Wed stare kenmg, the cat had returned to sleep (fag. 17, E) T h e only unusual feature of the E E G arousal was the rather long latency of ~ts lnltmtlon, for a permd of from 2 to 3 sec from the beginning of a u & t o r y st~mulatmn ensued before an acttvatmn pattern became fully estabhshed T h o u g h not always as prolonged, such latency was seen on most occasions H N h intensity of stlmulatmn was not essentml for arousal, however It m~ght be provoked by a buzzer and figure 19 shows an instance of awakening, m the second of these cats, induced s~mply b y the sound of one of the mvestLqators (L H S ) walking in the room A w a k e n i n g and E E G arousal,

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I:sE(j of cat v~th ]ateraI mldbraln lesions s h o w n in figures 15 and 16 Arousal b3 whistle blasts on 12th postoperat:ve day Str,ps A and B are continuous, C ~s 7 m,n after A, D. t5 mm after A and E, 17 mm after A Channels p~ckup between left anterior-temporal, right anter~or-ternporal, left temporal-postemor and right temporal-postemor reg~on~ m~dbram Terminal stimulation of the bulbar rehcular formation r e a d d y d e s y n c h r o m z e d the E E G , as m the acute experiments of Moruzzl and M a ~ o u n (1949). m which only the central mesencephalon connected the lower brain stem w~th the cerebrum In the chromc period, therefore, followm9 interruption of known a u & t o r y and somatic afferent p a t h w a y s ~mmedmtebt behind the &encephalon, w h d e sparing the central m~dbrain tegmentum, the a m m a l s showed no

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disposltmn to pathological somnolence W h e n tested durra 9 sleep, both auditory and somahc stxmulahon readily evoked behavioral arousal and act~vation of the E E G T h e latter often reqmred a second or two to develop but exhibited no other a b n o r m a h t y and, once reduced, was characterlshcally prolon9ed DISCUSSION Present conceptmns of sleep date from 1935, when Bremer discovered that the forebrain isolated from lower portmns of the nervous system, by mesencephahc transechon exhibits electrical activity ~denhcal w~th that m natural sleep or anesthesm From this, Bremer concluded that sleep is the consequence of functional dea[ferentatmn of the cerebrum for, at that t~me, the only known cort~c~petal influences to whose mterruptmn the results could be attnbu*ed were those conducted in classical sensory paths More recently, Moruzz~ and M a g o u n (19d9) tden-

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t~f~ed an act,vatmg system ascendm~ through the bra,n stem reticular formatmn, whose direct st,mulatmn reduced E E G changes s~mulatm~ those of wakefulness At the same time, L, ndsley, Bowden and Ma0oun (1949) determ,ned that acute mlury to the upper end of thin reticular activating system was the factor responsible for the sleep changes in the cerebrum which Bremer had earher descr,bed

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Fig 20 mmmal w;th interrupt;on of sensory paths m the mtdbram, sparmcj central te0mentum, standm0 awake (A), w~th str~p of characteristic wakm0 EEG (A') Ammal with interruption of mesencephahc te~menturn, sparm~d sensory paths, lyre0 asleep, w~th characteristic str*p of sleepm0 EEG (B) Th e present study has verified this fmdm0 m a m m a l s with chronic lesions of the brain stem for, when the anterior end of the reticular activating system is interrupted m the mesencephahc tegmentum or basal diencephalon, the E E G is characterized by the large slow waves and spindle bursts of normal sleep, or by other synchrony, whde low voltage fast act,vxty associated with wakefulness is lacking (fig 20. B'). Behaviorally, such animals aDoear asleep and, when unmolested, persist in this state throughout their postoperative surv,vals (fl 9 20 B)

,n O ascendmq ,nfluences from the brain stem, but they indicate that ,t is the absence of ascendm.q influences of the reticular actlvatin 0 system, and not those conducted by class,cal sensory paths, that is of ]mportance The commonplace experience that afferent st, mulatlon will ,nduce and contribute to wakefulness, whde its absence favors sleep, seems opposed to this conclusion until the possib,hty is considered that collaterals from afferent paths may terminate in the reticular act~vatmq system and exert their influence indirectly by modlfym 0 its activity T h e

BRAIN STEM LESIONS IN THE CAT chronic animals of the present study served also to test this possibility for, in each of them, the arousing effect of somatic and auditory stimulation was repeatedly tested against a background of drowsiness or sleep. It may be said first that positive indication was obtained for such collateral excitation of the reticular actxvatm 9 system for, when both somatic and auditory paths were chronically interrupted at the front of the midbram, somatic and auditory stimuli were still regularly capable of arousing the sleeping ammal and activating its EEG. The alteration had a httle longer latency than usual but was otherwise typical and, once aroused, the animals usually remained awake for long perlods. In our opinion, such arousal was medinted by collaterals from afferent paths terminating in the brain stem reticular formation below the lesion and exerting their cephalic influence indirectly through its ascending relays. Anatomical evidence favoring thin posslbihty has recently been presented by Morro and O'Leary (1950). It should next be pointed out that when the front end of the reticular activating system is interrupted by large mesencephahc or hypothalam~c lesions, it is also possible to induce a degree of behaworal arousal and to activate the EEG by auditory and somatic st~mulation E E G activat~on was excellent but differed from normal in that it charactemstlcally terminated almost ~mmediately upon the cessation of the arousing stimulus and, even when this was intense, never per~sted for more than a few succeeding seconds. From these observations, it appears that afferent st~mulation can activate the E E G both by collateral excitation of the reticular formation below the mesencephalon and, addit~onally, by the direct armval of afferent impulses at some site above the mldbram or hypothalamus It is possible that act~vation occurs upon the armval of afferent impulses finally at the cortex, as is generally believed It seems more likely that such activation develops upon armval of afferent impulses at the thalamus, at which site presumably the ascending influences of the reticular activating system are elaborated for cortlcipetal

497

transmission. If this latter were the case, the identity of E E G activation by whichever route the afferent impulses reducing it are conducted, could more readily be understood. Wherever it is located, the site at which E E G activation is induced by afferent impulses coursing past the brain stem reticular tormat~on, in long sensory paths, is evidently cephalad to the n,eural focus at which selfpropagating activity continues to preserve the waking state for long periods after the arousing stimulus initiating it has ceased For, as remarked, arousal m the ammals under discussion was only brief and, being so d~rectly dependent for mamtenance upon the continued apphcatlon of the arousing stimulus, faded to serve the animal usefully. Stated m anatomical terms, lnterconnections between the thalamus and cortex, and the hypothalamus as well, are not by themselves capable of preserwng the waking state beyond the immediate period of their bombardment by afferent impulses from the periphery. It thus appears that maintained wakefulness following the cessation of art arousing stimulus depends upon excitation within the reticular activating system below the diencephalon. In these ammals with large hypothalamic or midbram tegmental lesions the excellence of the E E G activation induced by afferent st~mulation contrasted sharply with the poverty of associated behaworal arousal and the lesions appeared, m fact, to have dmsociated these two features of the waking state Th~s suggests that m addition to the cephalic influence of the reticular activating system upon the electrocortical act~wty, which has so far been emphasized here, attention should be focussed also upon caudally directed influences of this reticular formation which are known to be capable of prowdmg a facditatory background favoring motor performance (Rhmes and Magoun, 1946, Austin and Jasper, 1950) There now seem to be sufficient data to suggest that influences of the reticular activating system are directed both cephahcally upon the cerebrum and caudally upon levels of motor outflow, and to propose that the presence or absence

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D B LINDSLEY, L H SCHREINER, W B KNOWLES and H W MAGOLIN

of the c a u d a l i n f l u e n c e of this a c t l v a t m 9 system is as i m p o r t a n t m c o n t r i b u t i n g to the behavioral differences exhibited m wakefulness a n d sleep as are varmt~ons m ~ts c e p h a h c i n f l u e n c e s m m o d i f y i n g electrocort~cal activity m these c o n t r a s t i n g states SUMMARY T h e effect u p o n b e h a w o r a n d the E E G of c h r o m c lesions m the r o s t r a l b r a i n stem has b e e n stud~ed in a seines of cats. O f les~ons m s e n s o r y paths, m the pemaq u e d u c t a l 0rey, or in the m l d b r a m t e g m e n t u m a n d b a s a l d~encephalon, o n l y the latter, m a positron to i n t e r r u p t the a s c e n d i n g r e t i c u l a r act~vatm 9 system, w e r e followed b y c h r o m c somnolence and EEG synchrony A c t w a t m n of the s y n c h r o m z e d E E G b y somatic a n d a u d i t o r y st~mulatmn w a s stdl r~oss~ble e~ther a f t e r the r e t i c u l a r a c t i v a t i n g s y s t e m or a f t e r long s e n s o r y p a t h s h a d b e e n i n t e r r u p t e d ~mmedmtely b e h i n d the t h a l a m u s C o l l a t e r a l s e n s o r y exc~tatmn of the rettculat act~vatm,q s y s t e m m the lower b r a i n stem. a n d the d~rect a r r i v a l of a f f e r e n t ~mpulses at some s~te a b o v e the m~dbram, thus serve e q u a l l y well to reduce E E G arousal. b u t o n l y m the former i n s t a n c e does prol o n g e d w a k e f u l n e s s follow P o v e r t y of b e h a v i o r a f t e r lesions of the reticular a c t i v a t i n g s y s t e m s u g g e s t s that ~ts

i n f l u e n c e s m a y be d i r e c t e d both c e p h a l i c a l l y to a c t i v a t e the E E G a n d c a u d a l l y to facdltate m o t o r activity, m m a i n t a i n i n g the w a k i n g qtate Addendum In a recent abstract INGRAM,W R, KNOTT, J R and XWHEATLEY,M D Electroencephaloqrams of cats with hypothalamlc lesions (EEG Chn Neurophgstol, 1949, 1 523), Ingram and his as~oclates state that "depression of slow high voltage waves associated wltt~ total and subtotal hypothalamlc destruction, m response to arousal st~muh, indicates that relatwely normal records may be briefly seen m these preparations" The present results confirm these observations REFERENCES AustIN G and JASPER H Dlencephahc mechamsms for facilitation and inhlbltmn Fed Proc, 1950, O 6 BREMER F Cerveau ~sole et physmlogle du sommefl C R Sac Btol, Paris. 1938, 118 1235-1242 INGRAM W R. KNOTT, ~ R and WrtEhTLEV, M D Electroencephalograms of cats under various experimental conditions Anat Rec, 1949, 103 157 LmDSLEY D B. BOWDEN, ] and MAc,ouN, H W Effect upon the EEG of acute mlury to the brain stem activating system EEG Chn Neurophyszo[, 1949 1 475-486 MORIN F and O LE,XRV, J L Ascending tracts of the anterolateral white column m Macaca mulatta Anat Rec 1950, 106 60 Monlso~ R S and DEMPSEY E W A study of thalamo-cortlcal relatmns Amer J Physml , 1942 135 281-292 Monuzzx G and MAGOUN, H W Brain stem reticular formatmn and actlvatmn of the EEG EEG Ch'n Neurophyslol. 194~, 1 455-473 RHEmBEnCER M B and JASPER, H H Electrical activity of the cerebral cortex m the unanesthetlzed cat Amer J Phvs~o! 193"/, 119 186-196

Reference L1NDSLEY,D B, SCHREINER, L H. KNOWLES W B and MAGOU'~ H VV Behavioral and EEG changes following chromc brain stem lesmns m the cat

EEG Chn Ncurophqslol

1950, 2 483-498