Enhanced Slow-Wave Activity Within NREM Sleep in the Cortical and Subcortical EEG of the Cat After Sleep Deprivation

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1 Sleep, 15(2): American Sleep Disrders Assciatin and Sleep Research Sciety Enhanced Slw-Wave Activity Within NREM Sleep in the Crtical and Subcrtical EEG f the Cat After Sleep Deprivatin *Marike Lancel, t Henk van Riezen and t Alfred Glatt *Max-Planck nstitute f Psychiatry, Munich, Germany, and tresearch and Develpment Department, Pharmaceuticals Divisin, Ciba-Geigy Ltd., Basel, Switzerland Summary: Electrencephalgrams (EEGs) f the crtex and f seven subcrtical structures were recrded during tw baseline days and during a recvery day fllwing a l2-hur perid f sleep deprivatin (SD) in eight cats. The EEGs were analyzed by visual scring and by spectral analysis. The fllwing subcrtical structures were studied: hippcampus, amygdala, hypthalamus, nucleus centralis lateralis f the thalamus, septum, nucleus caudatus and substantia nigra. The EEGs f all brain structures exhibited sleep state-dependent changes. n general, slw-wave activity (SWA, ) during nnrapideye mvement (NREM) sleep exceeded that f REM sleep. The pwer spectra ( ) in NREM, as well as the relatinship between the pwer spectra fnrem and REM sleep, differed between the recrding sites. Mrever, the rate f increase fswa in the curse f an NREM episde and the rate f decrease f SW A at the transitin frm NREM t REM sleep differed between the brain structures. During the first 12 hurs fllwing SD, the duratin f NREM increased due t a prlngatin f the NREM episdes. REM increased by a rise in the number f REM episdes. During the same perid, the NREM EEG pwer density in the delta and theta frequencies was enhanced in all brain structures. Furthermre, in all structures the enhancement f SW A was mst prnunced at the beginning f the recvery perid and gradually declined thereafter. SD als induced a rise in the rate f increase f SWAin the NREM episdes in all recrding sites. This indicates that the enhancement f EEG pwer density was nt nly due t prlngatin f the NREM episdes. The EEG activity during REM was barely affected by the SD. t is cncluded that, in all brain structures studied, the EEG during NREM is characterized by high levels fsw A. Furthermre, in each brain structure, SWA within NREM sleep is enhanced after a prlnged vigil. These data may indicate that SW A reflects a recvery prcess in crtical and subcrtical structures. Key Wrds: Sleep-Sleep hmestasis-eeg spectral analysis Subcrtical structures-cat. One f the mst appealing theries cncerning the functin f nnrapid eye mvement (NREM) sleep is that during this phase physilgical restratin frm the wear and tear f prir wakefulness takes place and that this prcess is f special imprtance fr the brain (1,2). One predictin f this hypthesis is that NREM sleep depends n the preceding histry f sleep and wakefulness. Actually, it has been shwn fr several mammalian species that extended perids f wakefulness may be fllwed by a cmpensatry increase f NREM sleep (3-5) and, in humans, shrtened perids f waking, due t naps, result in a decrease fnrem (6). Hwever, the duratin fnrem is neither a linear nr a mntnic functin f preceding waking time: Accepted fr publicatin Nvember Address crrespndence and reprint requests t M. Lancel, Max Planck nstitute f Psychiatry, Kraepelinstrasse 2, 00 Munich 40, Germany. 102 Dwnladed frm n 28 June 2018 Prlnged vigil des nt necessarily increase the duratin f NREM, and, when a rebund ccurs, it is generally smaller than ne wuld expect n the basis f prir waking time (e.g. 4,5,70). Furthermre, in many mammals, NREM prpensity depends highly n the circadian phase at which sleep takes place (e.g. 4,7,8,11). n recent years research has been devted t the quantitative analysis f the electrencephalgram (EEG). Mst studies have cncentrated n the slwwave activity (SWA) recrded within NREM (ca ), which has been cnsidered an intensity measure f sleep. n cntrast t the duratin f NREM, SW A within NREM appeared t be a mntnic functin f preceding waking time. n several mammals, SW A was fund t be maximal at the beginning f the sleep perid and t decline prgressively during the curse f the sleep perid (e.g. 5,8, 125). By extending waking, SW A (and, when measured, als the activity

2 SPECTRAL ANALYSS OF SUBCORTCAL EEG 103 in sme higher frequency regins) is enhanced, especially in the first part f recvery sleep (e.g. 5,8-10,136). n humans a reductin f preceding waking time results in a decrease f SW A (17) and f the integrated amplitude f SWA (6). Als, the dynamics f SW A within an NREM episde are affected by the duratin f prir wakefulness: n humans and rats the rise f SWAin the curse f an NREM episde as well as its maximal level increased after sleep deprivatin (SD) (15,18). Sme evidence indicates that the circadian phase during which sleep ccurs may influence the time curse f SWA (19,20). Hwever, SW A is primarily regulated as a hmestatic prcess. t has been pstulated that SW A may be the electrphysilgical crrelate f a recvery prcess (21). Until nw, the effects f extending the duratin f prir wakefulness have been studied almst exclusively by epicrtical r scalp EEG recrdings, which are thught t reflect primarily the field ptentials f the crtex. The few studies in which intracranial EEG recrdings were btained revealed that in undisturbed cnditins, the electrical activity f subcrtical structures like the hippcampus, amygdala and the nucleus caudatus (e.g ) als varies in parallel with changes in sleep and wakefulness. t is nt knwn whether the changes ccurring in the EEG after prlnged vigil are limited t the crtex r are als present in subcrtical structures. Therefre, we analyzed the EEG recrded frm the crtex and frm several subcrtical structures during sleep under baseline cnditins and after a 12- hur SD. The EEG characteristics f the subcrtical structures were then cmpared with thse fthe crtex. METHODS Electrde placement prcedures Because histlgical verificatin f electrde psitin is pssible nly after investigatin, and the cats had t be used in several experiments, electrphysilgical electrde placement prcedures were established t ascertain that the electrdes were placed crrectly. These prcedures culd be perfrmed during the peratin and were validated in a separate experiment as described belw. Eleven adult female cats with a bdy weight ranging frm 3.0 t 4.1 kg were anesthetized with Alfaxalne [Saffan, initiatin with 18 mg/kg intramuscularly (i.m.) and maintenance with 0.1 t 0.2 mg/kg/min intravenusly (i.v.)]. At the beginning f the peratin three stainless-steel electrdes were implanted abve the crtex (C: A 28, L 0; C2: A 26, L 2; C3: A 24, R4) (25), and a reference electrde was placed in the frntal bne (A 35, L 0). Crtical EEG as well as heart rate were recrded cntinuusly n paper t mnitr the depth f anesthesia. Fr each selected subcrtical structure, a stainless-steel, biplar electrde (NEX-lOO, Rhdes Medical nstruments, nc., 0.5 mm diameter, with ples 0.5 mm apart and 0.5 mm bared tip) was steretaxically implanted a few millimeters abve the structure and was then lwered stepwise (0.5- r 1-mm steps). At each step, the electrde placement prcedure was perfrmed. Fr later histlgical verificatin, a lesin was made (0.5 ma, 20 secnds) at the lcatin where the expected reactin had ccurred. Thereafter, the electrde was remved. At the end f the peratin the cats were sacrificed by an verdse f Alfaxalne, and the brains were perfused with a ph 7 phsphate buffer. Brains were remved frm the skull and placed in 5% frmalin. After fixatin, -pm-thick brain sectins were cut using frzen tissue techniques. The sectins were stained with Sudan black. The reliability f the electrde placement prcedures was verified histlgically by cmparing the site f the lesin with the electrphysilgical findings. The electrde placement cntrl prcedures fr each f the subcrtical structures are described belw. 1) Hippcampus drsalis (HP) (crdinates where the expected reactin was usually btained: A 5, L 4, H 17.5) (26). The EEG signal recrded by the HP electrde is amplified (Grass 7DA) and recrded n paper. When the electrde enters the hippcampus, characteristic impalement ptentials appear that diminish with time (Fig. A). 2) Nucleus caudatus (NC) (A 15, R 6, H 7) (25). The NC electrde is electrically stimulated (Grass S88 stimulatr, single square wave pulses, 0.5, millisecnd, 3-5 V). The stimulatin induces spindling in all crtical EEG traces, when the electrde is lcated in the NC (e.g. 27) (Fig. lb). r... FG. 1. Examples f the electrde placement prcedures. n all examples psitivity is upwards. A. mpalement ptentials ccurring in HP when the electrde was lwered frm H 18 t H 17. Ninety secnds later the respnse has disappeared. B. Spindling in the crtex as a result f a 4-V stimulatin f the NC electrde at H 8. C. EP (averaged ver 16 trials) recrded in AM at H -5 in respnse t phtstimulatin. D. The ccurrence f an EDR in the frepaw evked by a 4-V stimulatin f the HYP electrde at H - 3, and a larger EDR at H -4. E. EP (averaged ver 16 trials) recrded in the SEP electrde when it was lcated near SEP (ca. A 15.5, L 2, H 2) and within SEP (ca. A 15.5, L 1.5, H 1.5) in respnse t electrical stimulatin f AM. F. Recruiting respnses in the crtex elicited by a 2-V stimulatin f the NCL electrde lcated at H 6 and H 5. G. EP (averaged ver 16 trials) recrded in GL at H -4 in respnse t phtstimulatin. H. EP (averaged ver 16 trials) recrded in the SN electrde lcated near SN (ca. A 3.5, L 6, H - 2.5) and within SN (ca. A 3.5, L 5.5, H - 3.5) evked by a 5-V stimulatin f the NC. Dwnladed frm n 28 June 2018 Sleep. Vl. 15. N

3 104 M. LANCEL ET AL. A 1 1!!! hlipcampus '""'llt H19-H18 E V 8 '-- >- R 0-40 near septum septum V J1 in septum i.- -, msec t90 sec. later F H7 G,-C, nucleus centralis lateralis B nucleus caudatus H9 C2 -Ca Ca-ref. 100 vlrrr1mm,",nlt.'-"hllw..j 2V H8 C,-C, C 3 -ret. 100vl 1 sec c V ' Jl amygdala msec. hypthajamus H-2 5vl----= V H-4 50vl 1 sec V 4V G H V V '-- - geniculatum lateralis ) V --J msec substantia nigra near substantia nigra ijv in substantia nigra,- T 0 la :,.., - J msec j ---" - { sec Sleep, Vl. 15, N.2, 1992 Dwnladed frm n 28 June 2018

4 SPECTRAL ANALYSS OF SUBCORTCAL EEG 105 3) Amygdala baslateralis (AM) (A 11, L 11, H -6) (25). Because the steretaxic placement appeared sufficiently accurate, the electrde is immediately placed at the steretaxic crdinates. T check this placement and the functining f the electrde, the EEG signal recrded at the AM electrde tip is amplified and recrded n a cathde ray scillscpe (CRO). Phtstimulatin (Grass PS22 pht stimulatr, single pulses, intensity 16) induces evked ptentials (EPs) in the AM (e.g. 28) (Fig. lc). 4) Hypthalamus psterir (HYP) (A 9, L 2, H -4) (25). The HYP electrde is electrically stimulated (20, 1.5 millisecnds, 2 secnds, 2-4 V). Fr the recrding f electrdermal respnses (EDRs) (e.g. 29) a stainless steel electrde is inserted in the glabrus skin f the right frepaw and a reference electrde is inserted in a furry regin f the same frepaw. The electrical activity is amplified (Grass 7PF lw-level DC preamplifier with a time cnstant f 0.8 secnd) and recrded n paper. Befre the HYP electrde is in the crrect psitin, n EDR can be bserved. Then (at H - 3) a small EDR can be seen. When the electrde is lwered anther 1 mm, a larger EDR can be induced (Fig. D). Mrever, repetitin f the stimulatin (at -min intervals) results in an increase f the EDR at H - 3, whereas it remains the same r even decreases at H -4. 5) Septum (SEP) (A 15, L 1, H 4) (25). The electrde is inserted under a lateral slpe f 60 thrugh the ipsilateral hemisphere. The signals f the SEP electrde are amplified and recrded n CRO. Electrical stimulatin f the AM (Grass S88 stimulatr, Grass cnstant current unit, single pulses, 0.5, 0.3 millisecnd, 0.3 ma) induces a biphasic EP (e.g. 30) that is small when the electrde appraches SEP and large when it enters SEP (Fig. 1 E). 6) Nucleus centra lis lateralis thalami (NCL) (A 9.5, R 4, H 4) (25). The NCL electrde is electrically stimulated (8, 1 millisecnd, 4 secnds, 1-5 V). When the NCL electrde is placed in the NCL, lw threshld recruiting respnses with clear waxing and waning characteristics can be bserved in all crtical EEG traces (e.g. 31) (Fig. F). 7) Geniculatum latera lis (GL) (A 6, RO, H 4) (25). The signals recrded by this electrde are amplified and recrded n CRO. When the electrde is in the GL, pht stimulatin induces EPs (e.g. 32) that are particularly prnunced and lng lasting and cnsist f many cmpnents at ca. H 4 (Fig. 1 G). 8) Substantia nigra (SN) (A 4, R 5, H 4) (25). The electrde is inserted at a lateral angle 0[70 thrugh the ipsilateral hemisphere. The EEG recrded by this electrde is amplified and recrded n a CRO Dwnladed frm n 28 June 2018 t recrd EPs elicited by electrical stimulatin f the NC (single square pulses, 0.5, 1 millisecnd, 5 V) (e.g. 27). Large biphasic EPs can be bserved when the electrde enters the SN (Fig. 1 H). Experimental animals and electrde implantatin Adult, female cats (ther than the nes used in the experiment described abve) were perated n under Alfaxalne anesthesia. n additin, a single dse fthe anti histaminic drug Vetibenzamin 2% (1 mg/kg, i.m.) was injected t antagnize the initial Alfaxalne-induced histamine release. The subcrtical electrdes were placed in the rder and accrding t the placement cntrl prcedures described abve. The electrdes were chrnically fixed t the skull with dental acrylic cement. At the end f the peratin, the crtical electrdes C 1 and C2 were remved. All leads were cnnected t a scket munted n the skull. After the peratin, the cats were kept islated fr 7 days and were injected daily with penicillin (lccillin, 0.1 mg/ kg subcutaneusly) during this perid. Frm the grup f perated animals, eight cats were selected fr this experiment. Their bdy weight ranged frm 3.5 t 4.8 kg. The cats lived in clnies, under a l2-hur light/12-hur dark schedule (lights n frm 0730 t 1930 hurs). During recrding, the cats were kept islated in cages (66 x 47 x cm) cntaining a sandbx, several tys, ample fd and water. The cages were placed in a ventilated, sund-attenuated Faraday rm, with an ambient temperature f 23 C and a l2-hur light/12-hur dark schedule (lights n frm 0730 t 1930 hurs, light intensity ca. 90 lux). Fd and water were replenished at 0730 and 1920 hurs. Design f the experiment Fr at least 2 mnths after the peratin, the cats were adapted extensively t the recrding cnditins. T prevent anticipatin effects, the timing f the adaptatin perids, caretaking and fd replenishment during the adaptatin perids were randmized. During the first 24-hur baseline day f the experiment, starting at the beginning f the light perid, the EEG was recrded cntinuusly. On the next day, the animals were sleep deprived by playing with them during the entire l2-hur light perid. Recvery measurements were made fr 24 hurs thereafter. Three t fur days later, a secnd 24-hur baseline recrding was made. This cmmenced at the beginning f the dark perid. Recrding The EEG signals f all leads were transmitted by cable. The cable was prvided with a slip ring and with Sleep. Vl. 15. N

5 106 M. LANCEL ET AL. an autmatic tensin cntrl, which adjusted the length fthe cable as required by the psitin and mvement f the cat. This system insures that the cat is unable t play with the cable and feels n tensin frm it either. The signals were recrded biplarly, except fi)r C (= C3, smatsensry crtex) and AM, which were recrded against the reference electrde. The signals were high-pass filtered (1/2 amplitude lw frequency: 1, time cnstant: 0.1 secnd), amplified (Grass 7P5B) and recrded by a Glnner videmetry prcessr and JYC HR-D330E vide cassette recrder. Later, the signals were lw-pass filtered (30, 20 db/ct), digitized (sampling rate 64 ) and subjected t a fast Furier transfrm rutine (csine taper) run n a PDP 11/44. Fr each 4-secnd epch, a pwer spectrum was cmputed fr the frequencies between 0.5 and The data were cllapsed in 0.5- ( ) and in - bins ( ). The pwer spectra were averaged ver 12-secnd epchs. The EEG signals were simultaneusly recrded n paper (paper speed 5 mm/ secnd) with a time mark that was generated by the cmputer every 12 secnds. This allwed matching f the paper recrdings t the pwer spectra. Accrding t the criteria f Ursin and Sterman (33) the paper recrdings were classified manually n the basis f the EEG traces f C, HP and G L fr each 12-secnd epch in the states wake, NREM sleep (= SWS and SWS- 2) and REM sleep. Epchs cntaining artifacts (identified n paper fr each lead separately) ccurred mainly during waking and were mitted frm the spectral analysis. Based n the results f the electrde placement prcedures perfrmed during peratin and n the quality f the recrded EEG signals, the number f bservatins per structure that culd be analyzed was: C, n = 8; HP, n = 6; NC, n = 8; AM, n = 7; SEP, n = 7; HYP, n = 5; NCL, n = 7; and SN, n = 7. The signals f GL were nt analyzed because the pnt-geniculccipital spikes (PGOs) influenced the pwer spectra. Data analysis and statistics N majr differences were bserved between the data f the 2 baseline days, and therefre, unless stated therwise, the data were averaged ver the 2 baseline days. Average values fr baseline and recvery were always cmputed separately fr each cat and fr each lead. Differences in the ttal duratin f the states and in the duratin and frequency f the NREM and REM episdes between crrespnding perids f baseline and recvery were analyzed with a tw-sided, paired t test. Fr baseline, an average EEG pwer spectrum was cmputed separately ver all NREM epchs and ver Sleep, Vl. 15, N.2, 1992 Dwnladed frm n 28 June 2018 all REM epchs. The average pwer densities btained fr NREM sleep were summed ver all frequency bands. This value was set at 100%, and, t standardize the data, all ther values were expressed relative t this reference. Differences in pwer density between NREM and REM were analyzed fr each lead with a tw-sided paired Wilcxn test. Fr NREM, differences between the leads in the distributin f relative pwer density ver the frequency bands were analyzed with a twfactr repeated measures ANOV A (analysis f variance, General Linear Mdel prcedures, Huynh-Feldt adjusted) (34), with the repeated factr "frequency" and the factr "lead". Pst-hc testing was dne by means f the Dunnett's multiple cmparisn test, with the data f the crtex treated as cntrl values. T analyze changes in NREM EEG during recvery cmpared t baseline, average pwer densities were cmputed ver all NREM epchs fr the light perid and dark perid f baseline and recvery. T nrmalize the data, these values were first expressed in percent f the average pwer density in NREM recrded during the 2 baseline days and then lg-transfrmed. The data were analyzed with a tw-sided paired Wilcxn test. The EEG activity during REM was analyzed similarly. T analyze the time curse fnrem SW A (average pwer density between 0.5 and 4.0 ) ver 24-hur perids, SW A was cmputed fr each 4-hur interval f baseline and recvery. Fr nrmalizatin the data were expressed in percent f SW A recrded in NREM during the 2 baseline days. Thereafter, the data were lg-transfrmed. The baseline data were analyzed with a tw-factr repeated measures ANOY A (Huynh-Feldt adjusted, repeated factr: "interval" and factr: "lead"). Differences between baseline and recvery were analyzed with a three-factr repeated measures ANOYA, with the repeated factr "baseline versus recvery" added. Fr the analysis f the intra-episdic rate f increase and rate f decrease f SW A during baseline and recvery, the first 90 NREM-REM cycles that met criteria mentined belw were selected frm the EEG f the dark perid f baseline day 1 and recvery. The selectin criteria were: 1) The cycle was preceded by at least tw epchs (24 secnds) f waking. 2) The NREM episde lasted at least 15 epchs (1 secnds). 3) The REM episde lasted at least three epchs (36 secnds). SW A was cmputed fr the 24-secnd interval f waking, fr the first fur 36-secnd intervals fnrem, fr the last tw 36-secnd intervals fnrem and fr the 36-secnd interval f REM. The values were averaged ver the selected cycles. The data were nrmalized by expressing them as percent f the average SW A within NREM during the 2 baseline days. The rate f increase was cmputed by subtracting SW A during waking frm SW A during the furth 36-secnd

6 SPECTRAL ANALYSS OF SUBCORTCAL EEG 107 TABLE 1. Duratin f the sleep-wake states (% f the recrding perid)a States Wake NREM sleep REM sleep BAS 24-hur perid 52.9 (10.9) 34.9 (7.2) 12.2 (3.9) BAS dark perid 55.8 (16.4) 31.8 (10.1) 12.4 (6.5) BAS light perid 50.6 (5.5) 37.4 (4.4) 12.0 (1.9) REC 24-hur perid 45.2** (8.0) 38.8** (6.5) 16.0** (2.4) REC dark perid 36.1 ** (10.5) 44.4** (8.9) 19.5** (2.8) REC light perid 54.0 (6.6) 33.7* (5.0) 12.3 (2.6) a The data represent mean values fr baseline (BAS) and recvery (REC); SD in parentheses. The baseline values are averaged ver the 2 baseline days fr each animal. n = 8 fr all perids, except fr the recvery 24-hur perid and fr the recvery light perid (n = 7). *p < 0.05, **p < 0.0 ; tw-sided paired t test. were significantly increased cmpared t baseline. These rebund effects mainly ccurred during the dark perid. During the succeeding light perid the amunt f NREM was, in fact, significantly decreased. During the 24-hur recvery perid the NREM episdes were prlnged cmpared t baseline (Table 2). As was bserved fr the ttal duratin fnrem, this effect was restricted t the first 12 hurs f recvery. The number f ccurrences remained at the same level during baseline and recvery. n cntrast t the NREM episdes, the duratin f the REM episdes was nt changed after SD. Rather, the number f ccurrences was increased during the 24-hur recvery perid. This effect was significant nly fr the dark perid. interval fnrem and dividing this value by 4 (gives % increase per 36 secnds). The rate f decrease was cmputed by subtracting SW A during REM frm SW A during the next t the last 36-secnd interval fnrem, divided by 2 (gives % decrease per 36-secnd perid). The baseline data were analyzed with a ne-factr ANOV A (factr: lead). Pst-hc testing was dne by means f the Dunnett's multiple cmparisn test, with the data fr the crtex taken as cntrl values. Differences between baseline and recvery were analyzed with a tw-factr repeated measures ANOV A (Huyhn Feldt adjusted), with the repeated factr "baseline versus recvery" and the factr "lead". RESULTS Ttal duratin f the sleep-wake states and the duratin and frequency f the NREM and REM episdes The duratin f the sleep-wake states recrded during baseline and recvery and the results f the statistical analysis are given in Table 1. During the 24-hur recvery perid the amunts f bth NREM and REM Relative pwer density in NREM and REM during baseline Figure 2 shws an example f the riginal EEG f ne cat recrded frm all leads during the transitin frm wake t NREM (A), during NREM (B) and during the transitin frm NREM t REM (C). Althugh the EEG traces f the varius leads are quite dissimilar, the recrded signals are clearly state dependent in all leads. n Fig. 3, the relative EEG pwer densities are pltted fr NREM and REM n a lgarithmic scale. Differences in pwer density between the sleep states are indicated at the bttm f the plts. n the crtex (C), pwer density is maximal in the delta frequency regin during bth NREM and REM. Pwer density during NREM exceeds that f REM in all frequency bands. The differences are mst prminent in the lwer half f the frequency range. A highly similar pattern emerged fr five subcrtical leads. The nly prnunced deviatins frm this pattern can be bserved fr HP and SN. n HP, the marked theta activity during REM resulted in cmparable pwer densities in the theta frequency bands during NREM and REM. n SN, pwer densities in a part f the delta frequency regin are higher during NREM cmpared t REM, TABLE 2. NREM and REM sleep episdes" '. BAS 24-hur perid BAS dark perid BAS light perid REC 24-hur perid REC dark perid REC light perid Episde duratin (minutes) NREM 3.9 (0.8) 3.5 (1.1) 4.4 (0.8) 4.5* (0.6) 4.8** (0.8) 3.5 (1.5) REM 4.0 (0.9) 4.1 (1.6) 3.9 (0.6) 4.2 (0.7) 4.6 (0.8) 3.2 (1.5) NREM Number f ccurrences REM (24.3) 42.6 (12.5) 64.4 (12.8) 20.4 (7.7) 62.4 (13.6) 22.2 (5.3) (27.7) 52.4* (17.1) 66.9 (8.8) 31.1 ** (8.8) 52.6 (23.2) 21.3 (10.6) a Values are means [baseline (BAS) values are averaged ver the 2 baseline days fr each animal]; SD in parentheses. n = 8 fr all perids, except fr the recvery (REC) 24-hur perid and fr the recvery light perid (n = 7). Fr the cmputatin f the NREM episdes all NREM episdes were used, nt just the nes fllwed by REM, and an interruptin by waking f < 12 secnds was allwed. *p < 0.05, **p < 0.0 ; tw-sided paired t test. Dwnladed frm n 28 June 2018 Sleep, Vl. 15, N.2, 1992

7 108 M. LANCEL ET AL. A B C lv crtex 2001 '..._...,.'"..."". hippcampus 4001_ geniculatum lateralis ",...,-,...,.""'""""""... _..., septum 1001 nucleus caudatus 200J, -W '''''lt </ill hypthalamus 20Jy Nj#!N4 ljffltjj nucleus centra lis lateral is 40, _ substantia nigra 401 amygdala 4001 tjj 1sec FG. 2. Example f the EEG activity f all leads (A) during the transitin frm wake t NREM sleep, (B) during NREM and (C) during the transitin frm NREM t REM sleep (psitivity up). n this cat the electrde placements were als histlgically verified. but d nt differ significantly. This is due t a rather peculiar phenmenn: the amplitude f the EEG activity in SN is lw at the beginning f a REM episde but rises during the curse f the REM episde (Fig. 4). Furthermre, the REM pwer densities in the frequency range significantly exceeded thse fnrem. n the tp left plt f Fig. 5, the NREM pwer densities fr the eight leads are pltted n a lgarithmic scale. n general, pwer density is maximal in the delta regin and declines mntnically ver the remaining part f the frequency range. The ANOV A revealed a significant effect fr the factr "frequency" (F29,130S = 818.8, p < ). As the data are standardized, a main effect fr the factr "lead" cannt be cmputed. The interactin between the factrs was highly significant (F203,130S = 11.83, P < ). Thus, pwer densities are nt distributed equally ver the frequency bands, and the distributin differs between the leads. T explre this last effect in mre detail, differences in relative pwer density between the crtex and the subcrtical leads were analyzed. n the ther graphs f Fig. S the relative pwer spectrum f each subcrtical lead is pltted tgether with that f C, n bth a linear scale and a lgarithmic scale, t visualize differences in the lwer and higher frequency regins. The results f the pst-hc tests are indicated at the tp f the graphs. When cmparing relative pwer densities it is imprtant t bear in mind that nly differences in distributin f pwer ver the frequencies can be studied and that a difference in ne frequency band can au- tmatically result in differences in ther bands. n C, pwer density peaks at 1.5 and declines prgressively thereafter, with the exceptin f a small rise in the spindle frequency range. The leads AM, SEP, and NC shw the same peak frequency. Hwever, the pwer density values in AM are significantly lwer in the delta frequency range and higher in the theta frequency range than C. n SEP, the values are lwer in sme parts f the delta frequency regin cmpared t the values fr C. Higher values were bserved frm 19.5 t The pwer density values f NC rarely differ significantly frm that fc. The leads HYP, NCL and SN shw high pwer densities at 0.5 and a peak value at 1. Thereafter, pwer density declines sharply, resulting in lwer values at 1.S and at sme fllwing frequency bands cmpared t C. n the highest frequency regins, the values exceeded that f C in all three leads. Fr NCL, pwer density was als higher in ne bin f the spindle frequency regin. The relative pwer spectrum fr HP deviates strngly frm that f C: nstead f a sharp peak frequency, pwer densities are high in a rather brad frequency regin, resulting in lwer values in the delta frequency range and higher values in nearly all ther frequency bands. Pwer density in NREM and REM during recvery frm sleep deprivatin The changes ccurring in EEG pwer density during NREM sleep after the 12-hur SD are depicted in Fig. 6 fr the dark perid and fr the light perid. The EEG Sleep. Vl. 15. N Dwnladed frm n 28 June 2018

8 SPECTRAL ANALYSS OF SUBCORTCAL EEG 109 '; " Lg EEG Pwer Density (%) pwer densities recrded during recvery are expressed 2 crtex (8) 2 amygdala (7) as percent f the EEG pwer densities recrded during _NREMS the crrespnding baseline perid. The results f the. REMS Wilcxn tests are pltted at the bttm f the graphs. The number f bservatins during recvery was reduced, especially during the recvery light perid. This was due t the appearance f artifacts in sme EEG signals and discnnectin f the cable in ne cat. Therefre, in sme cases, the small n precluded use f -2.j.=::j:::=/==F===j -2.+==t==:t====t===l the Wilcxn test. Therefre, in thse cases when n < , tendencies (p < 0.1) are als indicated. 2 hippcampus (6) 2 hypthalamus (4) -2.J.=:...J-==t==l==:t=:=j nucleus centralis lateralls (7) septum (7) -2 -=::'+...=J==:::t:::=t:==l nucleus caudatus {8} 2 substantia nigra (6) -2.\==t==+= ===+=::j FG. 3. Distributin f EEG pwer density ver the frequency range fr NREM and REM sleep during baseline. Average pwer spectra were cmputed fr NREM and REM. The average pwer densities within NREM sleep were summed ver all frequencies. All values were first expressed as a percentage f this reference (thus the data represent relative pwer densities) and were then lg-transfrmed. Lines at the bttm f the graphs indicate significant differences in pwer density between NREM and REM (p < 0.05; twsided paired Wilcxn test). Fr HYP n = 4 and fr SN n = 6, because in ne cat lw frequency artifacts were present, and therefre the high-pass filter was set at 3. Cnsequently, the data had t be mitted frm this analysis. Fr HYP, n is t small fr the statistical analysis used. During the recvery dark perid in C, pwer density in the delta and theta frequency range was significantly enhanced cmpared t baseline. During the recvery light perid pwer densities did nt differ significantly frm baseline. n all subcrtical leads, the pwer densities in the delta and theta frequency range are enhanced during the recvery dark perid. AM and SEP elevatins are als present in sme higher frequency ' J bands. As bserved fr C, in mst subcrtical leads pwer densities were clse t baseline during the recvery light perid. Hwever, in NC, and t a lesser extent als in SN, a nticeable increase f pwer density in the frequency range f ccurred during the recvery light perid. 0 T cmpare the recvery effects between leads, the average pwer densities f the recvery dark perid were expressed as percent f the values f the baseline dark perid. These data were lg-transfrmed and subjected t a repeated measures tw-factr ANOYA (Huynh-Feldt adjusted), with the repeated factr "frequency" and the factr "lead". The effect ffrequency was highly significant (F29,1276 = 59.4, p < 0.000l). This effect reflects the declining tendency f the enhancements ver the affected frequency range. The effect f the factr "lead" was nt significant. Thus, the magnitude f recvery effects did nt differ significantly between leads. The interactin between bth factrs was significant (F203,1276 = 1.66, p = 0.05). Obviusly, the distributin f recvery effects ver the frequency range was nt similar in all leads. Pst-hc cmparisn f recvery effects fr each frequency band between C and the subcrtical leads (Dunnett's multiple cmparisn test) shwed that nly in AM did the enhancement f pwer density in the 7.5-, 8.5- and 9.5- bands exceed that f C (p < 0.01, p < 0.01 and p < 0.05, respectively). Missing data precluded further analysis f the data fr the recvery light perid. The EEG pwer densities recrded within REM during baseline and recvery were als analyzed with a tw-sided paired Wilcxn test. The data are nt shwn, because n cnsistent recvery effects culd be detected. Only in NC, similar t the findings fr NREM, the REM pwer densities in the frequency range f Dwnladed frm n 28 June 2018 Sleep, Vl. 15, N.2, 1992

9 110 M. LANCEL ET AL. crtex hippcampus geniculatum latera lis substantia nigra 1 sec FG. 4. Example f the EEG recrded in C, HP, GL and SN at the transitin frm NREM t REM and during REM sleep (psitivity up) were significantly elevated during the recvery light perid cmpared t baseline. The pwer densities in SN were affected crrespndingly, althugh even a statistical tendency (p < 0.1) was nt attained. The time curse f SW A during NREM sleep Figure 7 depicts SW A within NREM sleep fr each 4-hur interval f baseline and recvery as percent f SW A within NREM during the 2 baseline days. Baseline The ANOVA revealed a significant effect fr the factr "interval" (F5,235 = 37.8, p < ). Due t the nrmalizatin prcedure, n main effect culd be cmputed fr the factr "lead". The interactin between bth factrs was nnsignificant. Thus, the variatin in SW A ver the 24-hur perid is similar in all leads. T analyze the time curse in mre detail, a mean transfrmatin analysis (34) was applied t the data f each lead separately. This prcedure analyzes whether the values f a particular interval differ frm the mean f the values f all the ther intervals. The general trend was that SW A was significantly belw the mean level during the last interval f the dark perid. t was abve the mean during the first interval f the light perid. interactin between these factrs (F5,185 = 44.3, p < ). The main effect f the factr "lead", as well as the interactin effect with the ther factrs, was nt significant. These results indicate that the magnitude and time curse f SW A are changed after the SD in all leads and that these changes d nt differ substantially between the leads. SW A was cnsistently enhanced during the first three intervals f recvery (Fig. 7). Due t the gradual dissipatin f the enhancements, SW A exhibited a declining trend in the curse f the recvery dark perid. Rate f increase and rate f decrease f SW A within an NREM sleep episde Baseline Figure 8 shws that in all leads, SW A rises during the transitin frm wake t NREM and that it cntinues t rise ver cnsecutive 36-secnd intervals f NREM. The transitin frm NREM t REM is characterized by a sharp decline f SW A in all leads. The rates f increase and decrease are given in Table 3. The ANOVA revealed a significant effect f the factr "lead" fr bth rate f increase (F7,47 = 7.8, p < ) and decrease (F7,47 = 3.8, p < 0.003). Psthc analysis shwed that the rate f increase in HP (p < 0.01) and SN (p < 0.05) and the rate f decrease in HP (p < 0.05), SEP (p < 0.05) and SN (p < 0.01) were significantly lwer than that f C. Recvery The ANOV A f the baseline and recvery data shwed a significant effect fr the factrs "interval" (F5,185 = 38.7, p < ) and "baseline versus recvery" (F,37 = 76.8, P < ) and fr the Recvery After the SD, in all leads SW A remained at baseline levels during the transitin frm wake t NREM. n cntrast, SW A was prgressively enhanced during the curse f the NREM episde cmpared t baseline Sleep. Vl. 15, N.2, 1992 Dwnladed frm n 28 June 2018

10 Lg r , _ hippcampus - hypthalamus Relative EEG Pwer Density in NREMS (%) _._ THA septum --- nucleus caudatus substantia nigra Lg 2 ::::: amygdala -crtex Lin _ Lg Lin Lg Lin hippcampus T " -crtex hypthalamus -crtex =:::::t=:=-*---i Lg r r30... ****.. **** 10 5 Lin Lg Lin 2,------,-----,-----,------r------r ******... = 25 septum crtex Lg lin , _r * nucleus caudatus, Lg Lin ,-----,-----, ** 1... substantia nigra - crtex ' 'T' ********* **... *... * FG. 5, Relative EEG pwer density within NREM sleep during baseline. The curves cnnect mean values (see Fig. 3 and crrespnding legend fr the number f bservatins). The data are pltted n a lgarithmic scale (upper pair) and n a linear scale (lwer pair). Significant differences between C and the subcrtical structures are indicated at the tp f the plts (tw-sided Dunnett's multiple cmparisn test; *p < 0.05 and :p < 0.01). Dwnladed frm n 28 June 2018 Sleep. Vl. 15. N

11 112 M. LANCEL ET AL. EEG Pwer Density in NREMS during recvery (% f baseline) crtex dark 140 ight 140 amygdala (7) 60'6) !i hippcampus (6) **** (5)... 6d 5 ) 60'5) ! nucleus centralis lateralis ,J;... 'l... r.. T l". if. (7) ********* (6) **** ** **.a. *.. 60(7} ** a a ) nucleus caudatus substantia nigra ill r..1.1 J.Ll.l JUJ ,.., J.. ' (7) *********'... 6d 6.. ' 1 UJJ FG. 6. Effects f 12 hurs fsd n the average EEG pwer density within NREM sleep during the recvery dark perid and light perid. The data are expressed as percentage fthe average pwer density within NREM sleep in the same frequency band during the crrespnding baseline perids. Vertical bars, ± SEM. Number f bservatins are indicated at the bttm, n the left side f the graphs. Significant differences between baseline and recvery are indicated at the bttm f the plts fr the dark perid and light perid separately. When n < 7, tendencies are als indicated (tw-sided paired Wilcxn test; *p < 0.05 and "p < 0.1). Sleep, Vl. 15. N Dwnladed frm n 28 June 2018

12 SPECTRAL ANALYSS OF SUBCORTCAL EEG 113 SWA in NREMS during baseline and recvery (% f baseline) crtex 160"""""""" recvery..... baseline 140 amygdala , h interval r----,-----r _, h interval 5 6 hippcampus , 160 hypthalamus L L.. ' r----' ' h interval J-----,-----,,----,,----,,----,,----,, h interval nucleus centalis lateralis septum 160, _--... :r : ' r ' h interval , r----,-----r h interval nucleus caudatus 160, , 160 substantia nigra * 60J-----,-----,,----,-----,-----,-----, h interval 60J-----,,----,,----,,----, h interval FG. 7. Average SWA in NREM sleep per 4-hur interval fr the dark and light perid f baseline and recvery. The curves represent mean values (see Fig. 6 fr number f bservatins). The data are expressed as percentage f the average SWA within NREM sleep during the 2 baseline days (100%). Vertical bars, ± SEM. The dark bars at the tp refer t the dark perids. Significant differences between baseline and recvery are indicated by *p < 0.05 (tw-sided paired t test n the lg-transfrmed values). Dwnladed frm n 28 June 2018 Sleep, Vl. 15, N.2, 1992

13 :-...!'-'... '0 160 crtex recvery baseline 160 mygdala ---- Time curse f SWA within NREMS episdes (% f baseline) 160 hippcampus 160 hypthalamus - """.:/1../.1 r?.;r ;t:"" 1'", i ) W R NREMS time (36 sec interval) 160 nucleus central is lateralis O ".. 'f // j i 7/ W 1234 NREMS time (36 sec interval) 56 1 R septum 160, , 1 f.1 U \ " 11.1'.. 1"" 40" 1"" 1 40 : : : 7// W 1234 NREMS time (36 sec interval) 56 1 R nucleus caudatus 160 ' , 40 """" \ 40 // 7/ W 1234 substantia nigra NREMS time (36 sec interval) fz 1 ;r... t"" 56 1 R t tl1 '"-l f""' L **** //' W l 1234 NREMS time (36 sec interval) 56 1 R 0 * / W R 1 NREMS time (36 sec interval) " 0 * * " W R NREMS time (36 sec interval) y " 1 7. W, NREMS time (36 sec interval) 6,R FG. 8. Average SW A during 24 secnds f wake (W) preceding NREM sleep during the first fur 36-secnd intervals f NREM sleep, during the last tw 36-secnd intervals fnrem sleep preceding REM sleep and during the first 36 secnds f REM sleep (R) fr baseline dark and recvery dark. Fr each cat and fr each lead, averages were cmputed ver 90 selected NREM-REM cycles. These data are expressed as percentage f the average SWA within NREM sleep during the 2 baseline days. The curves represent mean values. Vertical bars, ± SEM. Significant differences between baseline and recvery are indicated at the bttm f the plts (*p < 0.05 and :p < 0.0, tw-sided, paired t test). Dwnladed frm n 28 June 2018

14 TABLE 3. Rates f increase and rates f decrease f SWA within NREM episdes (%/36 secnds)a Rate f increase SPECTRAL ANALYSS OF SUBCORTCAL EEG 115 Rate f decrease Lead Baseline Recvery Baseline Recvery C 18.4 (L8) 28.1 ** (5.0) 58.5 (9.5) 66.7 (5.4) AM 19.6 (2.9) 26.4** (3.2) 50.1 (12.1) 50.6 (10.5) HP 9.1 (6.2) 13.5 (10.1) 33.4 (15.4) 35.4 (8.7) HYP 14.3 (3.5) 18.7* (2.9) 43.2 (14.7) 42.1 (10.6) NCL 18.3 (2.5) 24.7** (4.2) 45.1 (11.2) 48.0 (9.5) SEP 17.3 (3.1) 20.5 (4.9) 36.6 (21.5) 45.8 (16.5) NC 18.6 (1.8) 26.7** (4.0) 46.4 (11.5) 51.3 (8.0) SN 13.2 (3.4) 17.6** (4.8) 24.6 (7.6) 30.8 (7.7) a Values are means; SD in parentheses. Baseline: C, n = 8; AM, n = 7' HP n = 6' HYP n = 5' NCL n = 7' SEP n = 7' NC n = 8' SN: n = 7. Recvery: C, n = '8; AM, n = 7; HP, n = 6; HYP, n,,: 5; NCL, n = 7; SEP, n = 7; NC, n = 7; SN, n = 6. Differences between baseline and recvery were tested with a tw-sided paired t test, *p < 0.05, **p < Abbreviatins are defined in the methds. (Fig. 8). The ANOV A shwed a significant effect f the factr "baseline versus recvery" bth fr rate f increase (F1,45 = 103.4, p < 0.001) and fr rate f decrease (F,45 = 8.1, p < 0.007). These effects reflect a general nhancement f the rate f increase and rate f decrease after SD. The statistical analysis f changes in rate f increase and decrease fr each lead separately (Table 3) revealed that the enhancement f the rate f decrease was nt statistically significant fr any f the leads. The ANOV A als revealed a significant effect f the factr "lead" (rate f increase: F7,45 = 8.5, p < and rate f decrease: F7,45 = 6.3, p < ). This effect relates t the differences already bserved during baseline. Mre imprtantly, fr bth rate f increase and decrease, the interactin between bth factrs did nt reach statistical significance. Thus, the changes in the dynamics f the intraepisdic SWA due t the SD did nt differ between the leads. Baseline DSCUSSON The ttal duratins f the sleep states and wakefulness (Table 1) are in gd agreement with earlier findings (e.g. 3,10,35-37). The bservatin that the ttal duratins f the states are highly similar fr the dark and the light perid cnfirms the general pinin that there is n predminant sleep perid in the cat (e.g. 10,35,36). The electrical activity f the crtex clearly differs between sleep states (Figs. 2 and 3): During bth NREM and REM, pwer density is maximal in the delta fre Quencies, but pwer densities within NREM exceed thse f REM, especially in the lwer frequency regins. n this aspect, the findings in the cat are very similar t thse bserved in the crtical EEG f, fr example, humans (5), rats (13) and hamsters (14). The present data shw that the EEG f each subcrtical structure exhibits cmparable sleep state-dependent characteristics: There is als a general tendency tward maximal pwer in the lwer (delta) frequency regin during bth NREM and REM. This activity is highest during NREM, a finding that is cnsistent with previus reprts n intracranial EEG recrdings in humans (e.g. 24) and chimpanzees (e.g. 23). This result supprts the idea that the prcesses underlying the ccurrence f SW A during NREM affect nt nly the electrical activity f the crtex but als that f subcrtical structures. One might cnsider the pssibility that the predminance f SW A in all recrdings may be due t field spread. Hwever, it is knwn that vlume cnductin inside the brain is very small (e.g. 38,39). Mrever, the biplar recrding technique with merely 0.5 mm f distance between the ples f the subcrtical electrdes virtually all but excludes this pssibility. n additin t the shared characteristics, the EEG pwer spectra differed markedly between the leads. This is t be expected, as the EEG recrded frm intracranial electrdes can change substantially ver very small distances (e.g. 39,40). n agreement with previus recrdings in humans (22) and chimpanzees (23), the NREM spectral pwer densities f the hippcampus deviated markedly frm the crtex and ther subcrtical structures (Fig. 5): nstead f a sharp peak frequency in the lwer part f the delta frequency range, pwer density is high in a brad frequency regin, including the upper part f the delta regin and the entire theta regin. Other differences in the relative pwer spectra f NREM between subcrtical structures and the crtex, e.g. a less prnunced SW A and lwer peak frequency, have been described fr several subcrtical structures in the chimpanzee (23). During REM, the mst utstanding deviatins between the crtex and the subcrtical structures were the typical ccurrence f theta activity in the HP and PGOs in the GL (Fig. 2). A new finding was the remarkable time curse f the EEG in the SN during REM: At the beginning f a REM episde, the EEG clearly differed frm that f NREM. Over the curse f the episde, the EEG changed tward a higher amplitude and a lwer frequency pattern (Fig. 4). Because we have nt studied this phenmenn in mre detail, we are unable t explain it. The change in EEG activity recrded frm the SN during REM is reminiscent f the build-up f SW A during NREM previusly described in all structures. This suggests a special rle fr the SN during REM, as it was nt seen in the ther recrding sites. t may reflect a physilgical prcess Dwnladed frm n 28 June 2018 Sleep. Vl. 15. N

15 116 M. LANCEL ET AL. related t the functin f REM. Alternatively, and rather speculatively, it may represent a crrelate f that prcess which serves t end REM. The variatin in crtical SW A within NREM ver the day was limited t relatively lw values at the end f the dark perid and t high values in the first part f the light perid (Fig. 7). t was bserved earlier that the circadian fluctuatin f SWAin NREM in the cat is nt very prminent (9, 10) cmpared t that f ther mammals like the rat (e.g. 8,12,13) and the hamster (14). This may be due t the absence fa predminant sleep perid in the cat. Mre imprtantly in this cntext, we fund that the time curse f SW A within NREM ver the day is similar in all recrded structures. The time curse f crtical SW A ver an NREM REM cycle cnsisted f a prgressive increase ver the 36-secnd intervals f NREM and a steep decrease during the transitin frm NREM t REM (Fig. 8). n humans and rats, SW A rises during an NREM episde until a plateau level is reached (15,18). This apparent discrepancy is due t the fact that nly the first fur 36-secnd intervals fnrem were analyzed, because many selected baseline NREM episdes were nt f much lnger duratin. The tempral evlutin fsw A ver the NREM-REM cycle was similar in crtex and subcrtical structures. This is in accrdance with results frm simultaneus recrdings f the EEG frm the scalp and the psterir parahippcampal gyrus in humans (24). Hwever, the exact rate f increase and rate f decrease differed between the leads and thus were structure dependent. n cnclusin, the baseline data shw that EEG characteristics are state as well as lcatin specific. Hwever, the changes in electrical activity in relatin t changes in vigilance and sleep fllw a similar pattern in the crtex and subcrtical structures. The data clearly indicate that the prcesses underlying SW A influence the activity f large parts f the brain. Recvery The 12-hur SD induced a cmpensatry increase in the ttal duratin f bth sleep states (Table 1). t was reprted earlier that SD can induce rebund effects in NREM and REM sleep in the cat (3,9,10). n agreement with an earlier study n the effects f 12 hurs f SD n sleep in the cat (3), the rebund f REM resulted frm an increase in the number f REM episdes (Table 2). The duratin f the REM episdes was unchanged. t may be that the high pressure fr NREM sleep cunteracted a prlngatin f the REM episdes. The rebund f NREM resulted frm a lengthening f the episdes. The number f ccurrences remained similar t baseline. n the study men- Sleep. Vl. 15. N Dwnladed frm n 28 June 2018 tined abve, NREM sleep was subdivided int light sleep and deep sleep. After SD, the duratin as well as the frequency f bth NREM states were increased. This cntradictin may be explained by the divisin fnrem, as mre frequent alternatins between light sleep and deep sleep during recvery wuld autmatically result in an increased frequency f bth states. SO affected nt nly sleep duratin but als the EEG activity recrded within NREM. During the dark perid immediately fllwing SO, the crtical EEG pwer densities during NREM were enhanced in the delta and theta frequency bands (Fig. 6). As it is knwn that the waking threshld rises with SW A (41), ur data may indicate an intensificatin f the sleep prcess after SD. The analysis fthe time curse fswa (Fig. 7) revealed that the enhancements were maximal during the first 4-hur interval f recvery and diminished gradually ver the tw succeeding 4-hur intervals. Previus reprts n the influence f SO n NREM have already shwn that the magnitude and time curse f SWAin the cat is a functin f sleep debt (9,10). Frm cmparable bservatins in the sleep f, fr instance, humans (e.g. 5,15,17) and rats (e.g. 8,13,16), it was hypthesized that EEG SW A is regulated as a hmestatic prcess. The present data supprt this hypthesis fr crtical SW A. Mre striking is the present bservatin that SD induced similar elevatins in the delta and theta pwer densities in each recrded subcrtical structure. This bservatin further supprts the idea that the prcesses respnsible fr SW A affect the electrical activity in large parts f the brain. Mrever, the magnitude and time curse f the recvery effects n SW A during NREM in the crtex and the subcrtical structures were highly cmparable (Fig. 7). Thus, the prpensity fsw A varies similarly in all recrded brain structures as a functin fthe sleep-wake histry. Earlier research in cats already revealed that the effects f SD n the EEG activity within NREM are independent f electrde lcatin n the crtex (10). SD als affected the dynamics f crtical SW A within the NREM-REM cycles. After SD, the rate f increase and the maximal level fsw A during the NREM episdes were particularly elevated (Fig. 8). These bservatins are in accrdance with crtical EEG recrdings in humans and rats befre and after SD (15,18). The present data indicate that the general enhancement f delta pwer density in NREM during the recvery dark perid (Fig. 6) results frm the cmbined effects f 1) a steeper increase f SW A in the curse f the NREM episde, 2) an increased maximal level fsw A in the NREM episdes, and 3) the prlngatin f NREM episdes. Similar phenmena are prbably respnsible fr the enhanced theta activity during NREM. As was bserved fr all SD-induced changes discussed

16 SPECTRAL ANALYSS OF SUBCORTCAL EEG 117 abve, the rise in rate f increase and maximal level f SW A was the same in the crtex and subcrtical structures. These data suggest that even changes in SW A measured ver intervals as shrt as 36 secnds are practically identical in all recrded structures. t was previusly bserved that after SD the pwer densities during REM were enhanced in the theta frequency range in rats (13,16) and in the delta and theta frequency range in humans (5). Frm these results it was hypthesized that, similar t the regulatin f NREM, REM recvery results frm an increase in bth duratin and intensity. n the present study, SD hardly influenced the EEG activity during REM. n the NC and SN nly, the pwer densities in the upper half f the frequency range were elevated during the recvery light perid. Hwever, the fact that these effects did nt ccur befre the secnd 12-hur recvery perid makes it highly unlikely that they represent recvery. Furthermre, similar effects were bserved during NREM, which indicates a general change in electrical activity f the NC and SN, independent f state. Fr the cat it has already been reprted that an 8-hur SD did nt affect the EEG activity recrded frm the crtex during REM (10). Our data suggest that, in cntrast t NREM, in the cat the EEG activity within REM des nt change after SD and it is therefre unlikely t have an intensity dimensin. n cnclusin, the data supprt the hypthesis that crtical SW A is regulated as a hmestatic prcess. Furthermre ur results clearly shw that EEG SW A in the subcrtical structures als respnds t sleep lss' t a similar extent and with a similar time curse as in the crtex. Thus, the prcesses underlying SW A prpensity influence the activity f many, if nt all, parts f the brain simultaneusly. The general enhancement f SW A after perids f extended wakefulness may suggest that the functinal state underlying SW A is f essential imprtance fr neurnal structures. 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