Responses to auditory stimulation, sleep loss and the EEG stages of sleep

ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY

269

R E S P O N S E S TO A U D I T O R Y S T I M U L A T I O N , SLEEP LOSS A N D THE EEG STAGES OF SLEEP HAROLD L. WILLIAMS, PH.D., JOHN T. HAMMACK, P H . D . , ROBERT L. DALY, M.A.,

WILLIAM C. DEMENT, M.D. AND AROIE LUBIN, PH.D. 1 Department of Clinical and Social Psychology, Walter Reed Army Institute of Research, Washington, D.C.; The Washington School of Psychiatry, Washington, D.C.; Veterans Administration Center, San Juan, Puerto Rico; and Stanford University, Palo Alto, Calif. (U.S.A.) (Received for publication: November 5, 1962) (Resubmitted: March 11, 1963) 1NTRODUCT1ON

One of the most troublesome problems in understanding the functional significance of the EEG has been the clarification of the relationship of its various patterns to depth of sleep. In this experiment the effect of controlled auditory stimulation on three criteria of excitation during various EEG patterns of sleep was examined. These effects were studied both before and after 64 h of acute sleep deprivation. The specific purposes of the experiment were to examine: 1. The effects of stimulus intensity on three responses as indices of activation: the electroencephalographic response, EER; the vasoconstrictor response, VCR; and a behavioral response, BR. 2. The changes in these effects of stimulation as a function of the background EEG pattern (stage of sleep). 3. The effect of acute sleep deprivation on the EER, VCR, and BR to auditory stimuli, and on the distribution of stages of sleep. As a human subject sleeps, the potentials of the EEG show continuous fluctuation, but within this flux, a recurring cycle of more or less stable patterns has been identified. Dement and Kleitman (1957) classified these patterns into the following discrete stages of sleep: (1) a low voltage phase with irregular frequency; (2) a phase characterized by 14 c/sec sleep spindles and K-complexes in a low voltage background; (3) a phase during which random delta waves appear and (4) a period in which the EEG is composed almost entirely of large delta waves. After the onset of 1 Walter Reed Army Institute of Research, Washington, D.C.

sleep, most subjects move rapidly through this succession of patterns, remaining in stage 4 for about half an hour. Stage 4 then gives way to stage 3 or 2, after which a low voltage irregular phase emerges which is similar to the pattern seen at the beginning of sleep. During a normal night of sleep the cycle described above is repeated about every 90 to 120 min but with decreasing amounts of stage 4. Loomis et aL (1937) first reported an association between EEG patterns and depth of sleep. They proposed a classification of the patterns into stages A to E which they thought represented a gradient ranging from light to deep sleep. The Dement-Kleitman stages 2, 3 and 4 correspond rather well to stages C, D and E. Stages A and B are covered by the Dement-Kleitman stage 1. In this article, A is used to designate the awake stage. There has been controversy concerning the classification of the emergent low voltage phase. In this stage, thresholds for awakening are considerably higher than for stage 1 at the onset of sleep (Dement and Kleitman 1957). Bursts of rapid eye movements (REM), apparently correlated with dreaming, are observed, and these are accompanied by low voltage sharp waves in the EEG (Schwartz 1962). Berger (1961) has shown that certain muscle groups in the neck are generally active during stage 1 and always inactive during this emergent low voltage REM phase. To distinguish it from stage 1, this phase is termed s t a g e lrem2. o Stage I (without REM) occurs at other times besides the initial sleep onset; e.g., after body movements and awakenings. Special care is needed to score periods of stage 1 which follow awakening from stage I rein.

Electroenceph. clin. Neurophysiol., 1964, 16:269-279

270

H.L. WILLIAMSet al.

By the use of controlled auditory stimulation as well as the analysis of both behavioral and physiological indicators, it should be possible to systematize and clarify the relations of EEG patterns to depth of sleep. It is known that the type of E E G response evoked by auditory stimulation is partially dependent upon the EEG background (Davis et al. 1939; Roth et al. 1956; Geisler 1960; Williams et al. 1962b). The vasoconstrictor response to auditory stimulation during sleep has been analyzed by Ackner and Pampiglione (1955). There have been no studies, however, where the BR, the EER, and the VCR have been measured simultaneously while auditory stimuli were administered repeatedly throughout the night, nor have the effects of sleep deprivation on these responses been studied. MATERIAL AND METHODS

Apparatus

The EEG, eye movements and finger pulse volume were amplified and recorded by a fourchannel Grass Model 1II EEG. Monopolar EEG recording was used with the active electrodes placed on the left frontal prominence, Fpl, and on the left parietal area, Pa (Jasper 1958). The reference electrodes were on the two ear lobes. The electrical activity from the parietal lead was recorded continuously throughout the night. The pen recording from the frontal lead was switched to the eye movement leads at appropriate intervals in the cycle of sleep. Bipolar horizontal eye movement leads were placed on each outer canthus. A photoelectric plethysmograph (Robinson and Eastwood 1959) measured finger vasodilation and vasoconstriction from the subject's left index finger. One EEG channel was used to mark both the auditory stimuli and the behavioral response - - the subject's closing of a microswitch taped in the palm of his right hand. For the auditory stimulus, random noise was presented in burst trains lasting 5 sec. Each burst had a duration of 90 msec, a rise-decay time of 5 msec and was separated from the next burst by a 90 msec silent interval. The stimuli were recorded on magnetic tape with a professional quality recorder, a step attenuator being used to provide 10 db steps between the four levels of stimulus intensity employed in the tape program.

Both periodic and aperiodic programs of auditory stimili were recorded. The periodic schedule was composed of 55 rain of 5 sec burst trains with a 2 min interval between each of the 28 stimuli. In the aperiodic program 24 stimuli were presented at randomly arranged inter-stimulus intervals from 45 sec to 3.5 min with a mean interval of 2.5 min. The order of stimulus intensities in each program was random within the restriction that each stimulus intensity appeared an equal number of times. A high quality tape playback transmitted the stimulus program into the EEG cage where it was transduced by a hearing aid type insert earphone worn by the subject. Before presenting the tape, a waking noise threshold was obtained for the subject. Thresholds were measured in the EEG cage where the ambient noise level within the band pass of the playback system remained constant at approximately 60 db, re: 0.0002 dynes/cmL After establishing threshold, the playback attenuator was set so that the lowest stimulus intensity on the tape corresponded to a 5 db sensation level, and the highest stimulus intensity was 35 db above the subject's waking threshold. The stimulus tape was presented continuously throughout the nighl. Six subjects received the periodic and four the aperiodic program. The analysis of results revealed no consistent differential effect of the periodic and aperiodic programs on any of the three response variables. Therefore, the ten subjects were treated as a single group. Subjects

Ten Army enlisted men of average intelligence, ranging in age from21 to 35, served as volunteers for this study. Audiometric thresholds were obtained on each subject prior to the experiment. All subjects demonstrated normal hearing acuity when tested both by conventional pure tone and by Bekesy audiometric techniques. Procedure

The subject slept in an electrically shielded cage for two baseline nights (B1 and Bz) and two recovery nights (R1 and Rz). Recovery sleep followed 64 h of sleep deprivation. The general laboratory setting and details of procedure have been described by Williams et al. (1959, 1962a). Electroenceph. clin. Neurophysiol., 1964, 16:269-279

271

RESPONSES TO AUDITORY STIMULI DURING SLEEP

TOTAL BI

MINS. %

A"

III

27

51

12

I

I rein 2-

186 44

3-

30

7

4-

33

8

65

15

B2

AI

33

8

225

54

42

I0

42

I0

0 3

0 I

I rem 2-

13_ hi l.tJ ..-I U3

4-

LL 0

A-

(/3 LIJ (.9

I

I-U3

3-

~

_

~

U RI

138 33

I rem 2L_

5-

69

16

I02 24

4A-

R2

0 3

I

0 I

14.4 34

I rein 2.

162

38

3-

45

II

4.

66

16

2'3o ot'3o o2'30 o3'3o oX3o o5'3o o '3o TIME OF NIGHT Fig. l Effect of sleep loss on the distribution of EEG stages of sleep for one subject (Be). Sleep loss produced a decrease in the time taken to go to sleep as well as in the amounts of stage ! add stage 2. The amounts of stages 3, 4, and lrem increased following sleep loss. Subjects were p u t to b e d at a b o u t 11.20 p.m. a n d a w a k e n e d at a b o u t 6.30 a.m. for a t o t a l o f a b o u t 7 h sleep per night.

Scoring T h e E E G records o f all subjects were scored for stages o f sleep a c c o r d i n g to the system o f D e m e n t a n d K l e i t m a n (1957). Special care was t a k e n to distinguish p e r i o d s o f stage 1 following a w a k e n i n g From p e r i o d s o f stage lrem.

Pilot studies i n d i c a t e d t h a t d u r i n g stimulation, the p r o b a b i l i t y o f occurrence o f each o f several E E G responses had increased with stimulus intensity. A c c o r d i n g l y , the following qualitative events were a c c e p t e d as responses to stimuli: a decrease or increase in frequency, a n increase in voltage, a change in E E G p a t t e r n (stage o f sleep), a K - c o m p l e x , either as " o n " or " o f f " response. These E E G changes were s c o r e d as responses to a stimulus if they occurred within a 6 sec interval

Electroenceph. clin. Neurophysiol., 1964, 16:269-279

272

H.L. WILLIAMSet al.

beginning with the onset of the stimulus, and ending 1 sec after its termination. The E E G changes were identified by comparing this interval with the 6 sec period just preceding stimulus onset. Voltage and frequency changes were scored as responses only if they had a duration o f at least half o f the 6 sec scoring interval. I f any response, say increase in frequency, occurred within the scoring interval it was assigned a score o f unity. If a stimulus induced both an increase in frequency and an increase in amplitude, the response was assigned a score o f two. A stimulus sometimes induced several events such as the following: a K-complex, followed by a train o f high voltage slow waves which were accompanied by a fast r h y t h m in the 8 to 12 c/sec range. Such a response received a score of four, one point for the K-complex, one for the persistent increase in voltage, one for the slow and one for the fast frequency. Thus scored responses were added to obtain a single summed E E R score for each stimulus. This score which can range f r o m 0 to 6 is similar to ratings used by Derbyshire and McD e r m o t t (1958) and by Derbyshire and Farley (1959) in their studies o f audiometric thresholds during sleep. The vasoconstriction response (VCR) usually begins 2 to 4 sec after the onset o f a stimulus, and lasts for several seconds. Pilot studies showed that of the several possible measures o f V C R , the measure that had the strongest relation to stimulus intensity, and was easiest to obtain, was the n u m b e r of pulse beats during the period of vasoconstriction. The V C R for each stimulus was defined, therefore, as the n u m b e r of pulse beats in the interval extending f r o m the last pulse beat prior to vasoconstriction (Bo) t h r o u g h the point o f maximal vasoconstriction (Bm) to the first pulse beat exceeding Bm in amplitude by 2 m m or more. If no vasoconstrictor response began within 4 sec o f the termination of the stimulus, the score was recorded as zero. The subject was instructed to press the microswitch as quickly as possible whenever he heard a stimulus. A response on the switch, if it occurred within 15 sec o f the onset o f the stimulus, was recorded as a BR. To obtain control data for each night, " n u l l " intervals were selected during which no stimulus had been presented. After the records were scored

for stages o f sleep, the periods between stimuli were divided into 6 sec blocks and the blocks were numbered. R a n d o m numbers were used to identify 25 null intervals (five for each stage o f sleep) with the restriction that they must be periods during which no stimulus had been presented for at least 30 sec. The EER, V C R and B R were scored for the null intervals just as in the stimulus intervals. RESULTS 1

The effect of sleep loss on the EEG stages of sleep The cyclic patterns o f sleep observed during the baseline period were very similar to those described by D e m e n t and Kleitman (1957). After sleep deprivation, the subjects went to sleep almost immediately, and reached stage 4 within a few minutes. Sleep loss caused increases in stages 3 and 4, decreases in stage 1 and in the time taken to go to sleep. The upper half of Fig. 1 shows the cyclic patterns of E E G stages o f sleep for a typical subject (Be) during the two baseline nights. N o t e that the subject awakens periodically during the baseline nights, the average a m o u n t of stage A being 87 min. The average a m o u n t o f stage 4 is a b o u t 38 min per night. The lower half o f Fig. 1 shows the effect of 64 h o f sleep loss on the cyclic E E G pattern for R1 and R2, the first and second recovery nights. During R1, the subject goes to sleep almost immediately, and after about 12 min 1 Statistical analyses for each of the three response measures were carried out as follows: 1. Within each stage of sleep, the data from the two baseline days, B1 and B2 were compared by analysis of variance (subjects x days × stimulus intensity). Since there were no significant day x stimulus intensity interactions, the 2 days were combined for further analysis. The 2 recovery days, RI and Rz, were compared in the same way, with the same result. Therefore R1 and Rz were also combined. 2. Wherever possible, the data from each stage of sleep were analyzed by analysis of variance for each individual subject to determine the linearity of the relation between response and db level. 3. The data from the several EEG stages of sleep were compared for each subject to determine whether there were significant differences between stages with respect to the regression of the response measure on stimulus intensi/y.

4. Rank order tests were carried out to determine whether the differences in average responses were significant for the various EEG stages of sleep.

Electroenceph. clin. Neurophysiol., 1964, 16:269-279

273

RESPONSES TO AUDITORY STIMULI DURING SLEEP

of stages 2 and 3 proceeds to stage 4 where he remains for 40 min. The periodic awakening is completely gone. Altogether stage 4 occupies 102 rain of R1, more than double the amount of stage 4 shown on B1 and B2. On Re the total time of stage 4 drops to 66 rain, which is still substantially above B1 and Be. There is a great deal of rapid alternation between stage l rem and stage 2 (14 c/sec spindling). This latter finding is common after sleep deprivation. In most subjects, during a normal night of sleep, a period of stage lrem is unbroken for several minutes once it begins. TABLE I The effect of sleep loss on EEG patterns of sleep (minutes per stage) means Baseline days

Recovery days

Stages

B1

B2

R1

Ra

A 1 lrem 2 3 4

34 18 76 202 48 42

18 18 91 200 42 61

3 5 81 161 67 103

6 6 111 163 55 79

420

420

420

420

Standard Deviations Stages A 1 lrem 2 3 4

B1 26 11 22 50 19 24

B2 19 10 10 39 14 35

R1 2 9 48 63 18 33

R2 7 7 21 47 18 34

Table 1 shows the means and standard deviations in minutes for stage A and the five sleep stages during tbe four nights. Although Be showed an increase in stage 4 and decreases in stages A and 1, with only ten subjects these differences were not statistically significant 1. Where records showed alternation between stage l rem and periods of 14 c/see spindling, the spindling periods were assigned to stage 2. Compared to B2, R1 showed a significant (t test) increase in the amounts of stage 3 and 4, and a significant decrease in the 1 For this paper, unless otherwise specified, significant means the 0.05 level or better.

amount of stage 1 and in the time taken to go to sleep. From R1 to R2 there were significant increases in time taken to go to sleep, and in the amount of stage 1rem, with a significant decrease in the amount of stage 4. However there was still more stage 4 during Rz than in B2. These results confirm those reported by Berger and Oswald (1962).

The effect of the decibel level of the stimulus on the EER during the EEG sleep stages Fig. 2 shows, for B1 and Be, the overall relation between the EER and stimulus intensity during four stages of sleep. The null intervals are labeled zero on the abscissa. The periods of stage A and stage 1 were so short and infrequent that the 4 different levels of stimulus intensity and the null intervals were not adequately represented, so stages A and 1 are not included in the analysis• For most subjects the EER increases linearly as the decibel level goes up. However, the EER 4.2.

/ O Sloge 3

4.0.

/J

3.8"

I0

3.6.

A

(D I-Z bJ > bJ Q bJ .,r 0 > I,I

3.4'

/

3.2. /

3.0'

I

2.8, 2.6. 2.4.

/:"

2.0,

IJJ (.9 <~ tY LO

.."

/

I

.." .." ..•

.."

/0 :: /" / .,.' / / i t .6 / / .," ~)/ / ..' ./"

2.2.

h 0

0 Stoge 2

I

1.8.

I :" /::

1.6.

/:.o"

1.4

0 Stage 4

/ /"

~ S t Q g e

Irem

..,'

1.2. 1,0 ILl

0.80.6, 0.4 0.20

o

,'s

2'5

3's

STIMULUS INTENSITY (db)

Fig. 2 Effect of stimulus intensity on the EER during four stages of sleep (baseline). EER is the sum of EEG events evoked by each stimulus. E l e c t r o e n c e p h . clin. N e u r o p h y s i o l . ,

1964,

16:269-279

H.L. WILLIAMSet al.

274

increases faster with decibel level during stages 3 and 2 than during stages 4 and lrern. These differences in slope are highly significant and consistent for the ten subjects. Thus the E E R is not only copsistently greater in stages 2 and 3 then in stages 4 and lrem, but in stages 2 and 3 the E E R is more sensitive to increases in stimulus intensity, . The sensitivity of the E E R to near-threshold stimuli was evaluated by comparing the mean EERs for the null intervals with those at the 5 db point for each of the E E G stages in the ten subjects. A sign test revealed a significant tendency to respond at 5 db in stages 2 and 3, but not in stages 4 and lrem. It appears that during stages 2 and 3, EERs can be reliably evoked by near-threshold stimuli. During stages 4 and lrem, however, the threshold for the E E R appears to be increased. Since K-complexes are usually not found in stage lrem and are difficult to identify in stage 4, it might be supposed that the rank order of effect of E E G stages was at least partly a scoring arti-

2.2

f

18-

I ]

1.6/

1.403

/

_z 1.2-

]

/

iI I

[3:: LLI 1.0hi

~.,~ Stage 3

£

2"0 t

v

/J

/ .:'

Y

O .:'" G ~

.. 0""

I

/ f

D" .,"

~."

I

II

.o Stoge 2 ./

:

.~,"

.. :"

.o

/.f

j-/

.o Stage 4

/" ,lff" ~ , ~ Stage I rein ./'f/

j,O" '"J° :

0.80.60.40.2

i i & ; 15 25 :55 STIMULUS INTENSITY (db) Fig. 3 Effect of stimulus intensity on the EER with K-complexes subtracted (baseline).

323.0-

.0 Stage 3 , , . / , , D o Stage 4 Stage 2 ~r-J /

28~ ,z "' o, , , o~" > ,,, "O ,,, ~ rr >~ ,,I ~ a: t~

2 6242.22.0-

1.8-

1.61.4-

...0-:,--~'" ~ / .

/

t"

...-'"

I i

...""

/I I ,." / .i..." 6.1. :.

~

/!" .p

.

Stage I r e i n

1.21.0O 806040.20

; ,T,MULus

i; NTENS,T

2'5

3'5

/d0/

Fig. 4 Effect of stimulus intensity on the EER (recovery).

fact. However, Fig. 3 shows that subtracting Kcomplexes from the E E R score has no significant effect on the slopes. Stages 2 and 3 show greater E E R responses than stages 4 and lrem at all db levels.

The effect of stimulus intensity on the EER during the recovery period Fig. 4 shows the relation between the average E E R and stimulus intensity in the ten subjects during R1 and R2, the nights of recovery from 64 h of sleep loss. Although, as on B1 and B2, EER increases with db level, the slopes are markedly reduced. In nine of the ten subjects, the regressions of the E E R on stimulus intensity in the four E E G stages could be accounted for by a single slope coefficient. A three way analysis of variance (subjects × conditions × stimulus intensity) was performed within each E E G stage to compare the baseline slopes with those seen after sleep loss. The decreases in the E E R - d b slopes were found to be significant for stages 2 and 3. For stages 4 and lrem the small decreases in slope were not quite significant at the 0.05 level. Electroenceph. clin. Neurophysiol., 1964, 16:269-279

275

RESPONSES TO AUDITORY STIMULI DURING SLEEP

There is a possibility that this decrease in the E E R - d b slope is due to habituation. If there were such an effect, one would expect to see a sharp reduction in the effect of db level on the EER from B1 to Be. However, analysis of variance comparing B1 and Be revealed no significant difference. Even though, following sleep deprivation, the slope of the line relating the EER to stimulus intensity was greatly reduced, the near-threshold level of sound required to evoke a visible response was apparently unchanged. A comparison of mean scores from the null intervals and the 5 db points over the ten subjects revealed that there was a significant increase in the E E R score at 5 db in stages 2 and 3. The increase of the E E R in stages 4 and lrem w a s not significant. It will be recalled that this is the same result found during the baseline period. In summary, the 64 h of sleep loss generally resulted in reduction of the sensitivity of the E E R to increasing db intensities at suprathreshold levels. The high slopes of E E G stages 2 and 3 were lowered to near equality with stages 4 and lrem. After sleep deprivation, sleep levels appeared to be deeper and less variable throughout the night.

The effect of stimulus intensity on the BR during various stages of sleep Individual differences in the frequency of behavioral responses during the baseline period were large. One subject failed to press his microswitch at any time after the onset of sleep, and another responded 62 times (out of about 400 stimuli) during B1 and Be. The latter subject pressed the switch on a number o f stimulus occasions without evidence of awakening in the EEG record. The upper half of Fig. 5, based on B1 and Be, shows the relation between the average percent of BRs and db level during four stages of sleep. For each E E G stage, as db level increases, the percent of BRs increases significantly. Generally speaking, at each d b level, the percent of BRs is significantly greater for stages 2 and 3 than for stages 4 and lrem. This is similar to the results for the EER. Thus, behavioral responses to auditory stimulation during sleep are a joint function of the" intensity of the stimulus and the EEG stage of sleep. A comparison was made of the percentage of responses recorded during the null periods and

Bi + Ba Q Stage 2

22

.." o.

20.

"

18.

~"

16. b.l

(r) z no (t)

o ......... ..'

z

bJo 6" 2" O-

.:

"

n. hi >~ rr" El

/

.. ."

':" J~'~" " i t ° " ~

.

.

0

I08 6

/

-~

Stage I rem

/

A//"

'"

~

Stoge,

//

'4"

R,+

4

Rz

..O Stage 2

2

~ ,-~

0

t

t

/

I,,.0 s .,.."

stage 3

I

.-"

12-

e: , o 8-

(.9

to

.-"

14.

, .....

0

" ........ c, .....

Stage I rern

. ..0"" ....

?'-

rp

5

15

STIMULUS

t~'~

25

,

Stage

3

Stage

4

35

I N T E N S I T Y (db)

Fig. 5 Upper half of figure: Effect of stimulus intensity on BR during four stages of sleep (baseline). Lower half of figure : Effect of stimulus intensity on BR (recovery).

the 5 db stimulus periods. In all EEG stages more BRs appear at 5 db than during the null periods, but a significant difference between these two sets of proportions was found only in stage 2. Thus, there is evidence that sleep raises the threshold for the BR. 1 The lower half of Fig. 5 shows that 64 h of sleep loss almost eliminates behavioral responding. D u r i n g R1 and Rz the highest percent of BRs is 4 percent for stage 2 at 35 db. Although the percent of BRs tends to increase with db level, the increase is not statistically significant. The effect of E E G sleep stage is also erased. There is no significant difference between the E E G stages in the B R - d b slopes. To summarize, the general effect of sleep loss on the BR was to reduce the BRs so much that it was impossible, within our limited sample, to find statistically significant effects of db level or of E E G stage. 1 All subjects responded at all stimulus levels during waking.

Electroenceph. clin. Neurophysiol., 1964, 16:269-279

H.L. WILLIAMSet al.

276 BI+Bz 6.5-

Stage

6.0-

.~) Stage

5.5-

2

. ....'""

3

5.0/

4.5-

Stage ~.'~'..,0 Stage 4

.'"

/

4.0-

3.5-

....~. 7 ... 1"//I~

3.0g

I rein

2.5-

m

g (~ ~E r,,-

2.01.51.0

Rt + Rz

4.5-

4.03.55.02.52.01.51.0

p Stage 3 4/,,0 Stage 4

--,/~

,-",,.~" , e ~

f J ' / ' "

,

0

g

,

15

St*ge ,,,m stage 2

.f"

,

25

i

35

STIMULUS INTENSITY (db)

Fig. 6 Upper half of figure: Effect of stimulus intensity on VCR during four stages of sleep (baseline). VCR is the duration of the period of vasoconstriction following a stimulus, measured in pulse beats. Lower half of figure: Effect of stimulus intensity on VCR (recovery).

The effect of stimulus intensity on the VCR during various stages of sleep In the upper half of Fig. 6 the relation of the VCR to stimulus intensity in the four E E G stages is shown for the baseline period. In general, there is a linear increase from a finger vasoconstriction lasting one pulse beat at zero db (null period) to a V C R lasting five or six pulse beats at 35 db. Although stage 1rein, on the average, shows longer vasoconstriction at all non-zero db levels, statistically speaking, there are no significant differences between the E E G stages. A single line is sufficient to describe all four V C R - d b functions. During baseline, then, the V C R consistently shows a linear relationship to stimulus intensity. Unlike the E E R and the BR, there is no evidence for a consistent effect of E E G stage. Sign tests showed that the average VCRs from

the 5 db stimulus periods were significantly greater than those found in the null intervals in all four E E G stages of sleep. Thus, as with the EER, the sound level required to trigger the VCR seems to be about the same as for waking. In addition, this level for the VCR is relatively constant for all stages of sleep. The lower half of Fig. 6 shows that after sleep deprivation the relation between the VCR and stimulus intensity remains almost the same for stages 3 and 4, but the slope is considerably lower for stages lrem and 2. These changes tend to bring the stages even closer together than during baseline, and again, a single line is statistically sufficient to describe all four V C R - d b functions. Analysis of variance showed that the decreases in V C R - d b slopes were statistically significant for stages 2, 3 and l rem. For stage 4, the small decrease in slope was not quite significant at the 0.05 level. As is suggested by Fig. 6, the intensity of sound required to trigger the VCR was not substantially increased by sleep loss. The 5 db stimulus results in an average VCR that is significantly greater than the null period VCR in all E E G stages of sleep. In summary, as with the E E R and BR, sleep loss reduced the amount of increase in VCR to increases in auditory intensity. However, the db level necessary to evoke a detectable vasoconstriction was not increased. Unlike EER and BR the vasoconstrictor response was not consistently affected by the E E G stage of sleep either before or after sleep deprivation.

The effect of time of night on the EER, BR and VCR The second baseline night was chosen for study, and because the E E G stages of sleep are not equally distributed through the night, the analysis was confined to stage 2. Stage 2 is usually present to some extent during each hour of the night. For each hour of sleep, the scores for the four db levels were averaged. Fig. 7 shows that the three response variables behave differently through the 7 h of stimulation. The E E R shows no consistent change with time Of night. The BRs start at about 35 percent during the 1st h and approach zero after about 4 h of stimulation, somewhat like an exponentially deElectroenceph. clin. Neurophysiol., 1964, 16:269-279

RESPONSES TO AUDITORY STIMULI DURING SLEEP

277

DISCUSSION

5.0 2.8 2.6 :~ nW W

2.4 2.2

2.0 1.8 6O 50

~ 4o ~_ 30 ~

20

8.5 m

8.0

g

7.5

~-

7.0

~ >

6.5 6.0

I I

1 2 Hours

I 3

I 4

I 5

I 6

I 7

of Stimulation

Fig. 7 Effect o f time o f night on the three response m e a s u r e s during stage 2 (baseline). B R a n d V C R decline as a function o f the n u m b e r o f h o u r s o f stimulation, b u t E E R rem a i n s relatively c o n s t a n t t h r o u g h o u t the night.

creasing curve. The VCRs were also a decreasing function of hours of stimulation. The average Spearman rank-order correlation (Lyerly 1952) between hourly scores for each response variable, and number of hours was computed over the ten subjects. The average correlation was 0.07 for the EER (not significant), 0.40 for the BR (p < 0.01), and 0.46 for the VCR (p < 0.01). The correlations were nearly identical for the group receiving the periodic stimulus series and the group receiving the aperiodic stimulus series. It seems, therefore, that stage 2 does not denote the same state of responsivity of the subject to auditory stimulation for V C R and BR throughout the night. On the other hand the responsivity of the EER is apparently constant for all stage 2 periods throughout the night.

One clear result of the present study (noted previously by Derbyshire and McDermott 1958) is that the human is capable of perceiving graded auditory stimuli and responding proportionately to the intensity of the stimulus in all stages of sleep. Even in stages 3 and 4, all three response variables, EER, BR and VCR increased in amount as the db level increased. This result does not agree precisely with the conclusions of Fischgold and Schwartz (1961). They made a careful study of the percent of motor responses to a single light flash from a stroboscope during Nembutal-induced daytime sleep. Their subjects showed 85-100 percent responses to the light flash during stages A and 1, dropped to 27 percent during stage 2, and did not respond at all during stage 3. Naturally Fischgold and Schwartz concluded that the sensory-motor link is lost and instructions are no longer carried out during Loomis' et al. stage C (stage 2 of this paper). We suspect that if they had used increasing intensities of light, a detectable percent of motor responses would have been elicited from Loomis' stages D and E (stages 3 and 4 of this paper). This certainly occurs for the 35 db stimulus administered to our subjects, as can be seen from Fig. 5. A second clear result is that the various EEG patterns cannot be called "light" or "deep" stages of sleep unless one specifies the response variable being studied. If electrocortical changes and motor responses are used as criteria, then on the baseline nights, stages 2 and 3 are "lighter" than stages 4 and 1rem. But if duration of finger vasoconstriction is used as a criterion of "lightness" there are no significant differences between the EEG stages. Those research workers who, like Zung and Wilson (1961) have decided that response to auditory stimulation is a decreasing function of the Loomis' et al. stages A, B, C, D and E (in that order) have overlooked the presence of the emergent REM stage, and have not recorded autonomic responses like finger vasoconstriction. If they had scored [he REM periods separately, Zung and Wilson would probably have noted periods of very low reactivity as Coleman et al. (1959) did. The latter investigators began with a simple logical deduction: EEG amplitude Electroenceph. clin. Neurophysiol., 1964, 16:269-279

278

H.L. WILLIAMSet aL

increases from stage 1 to stage 4. These stages represent increasing depth of sleep. Therefore, "there should be a degree of correspondence between reaction time and E E G amplitude..." But they found that often the reaction time was long when the EEG amplitude was tow, and rapid eye movements were present. Presumably the subject was in stage lrem. The finding (Dement and Kleitman 1957; Dement 1958; Jouvet 1961) that stage l r e m is associated with an elevated auditory threshold in both cats and humans destroyed the notion that in sleep the amplitude of the EEG decreases monotonically with the level of responsivity of the organism. The fact that the VCR durationintensity function is almost constant for all EEG stages similarly destroys the notion that each EEG stage represents a unique "depth of sleep". The effect of sleep loss is to lower the level of reactivity of all three response variables, especially in those EEG stages in which responsiveness is highest during baseline nights. The net result is that after sleep loss there is practically no difference between the E E G stages. Even during the same night, Fig. 7 shows that responsiveness:during stage 2 declines rapidly during the first few hours for BR and VCR so that stage 2 during the 1st h of sleep is quite different from stage 2 during the 6th h of sleep. On the otber hand, EER reactivity during stage 2 is approximately constantAhroughout the night. Thus the EEG stages of sleep do not seem to be an invariant indication of the responsiveness of the organism even when the response variable is specilied. Possibly the variation in responsiveness which is not accounted for by the EEG stage of sleep is linked to some metabolic measure of activation level such as body temperature. Dement (1960) has shown previously that depriving a subject of stage lrem results in a substantial increase in stage 1r(:t,'~during subsequent nights. But if the subject is deprived of all stages of sleep, it seems that stage 4 demonstrates the most significant increase during the first recovery night, and stage lrem then shows an increase on the second recovery night. Our data are in close agreement with those of Berger and Oswald (1962). With four nights of sleep loss they found an increase of stage 4 from 6 percent of total sleep time during baseline nights to 26 percent on

the first recovery night. With two nights of sleep loss, we found an increase of stage 4 from 15 percent during B2 to 24 percent on R1 and 19 percent on R2. Berger and Oswald found a drop in s t a g e l r e m from a baseline percent of 22.5 to 7.4 percent on R1, followed by an increase to 27.5 percent on R~. With two nights of sleep loss, we found a slight drop in stage lrem from a B2 percent of 21.6 to an R1 percent of 19.4, followed by an increase to 26.5 percent on R~. We infer that when the subject has been deprived of all stages of sleep, the "need" for stage 4 dominates over all stages, and tends to depress the amount of stage lrem o n the first recovery night. When the "need" for stage 4 has been partially satisfied, the "need" for stage l rem asserts itself. SUMMARY

Auditory stimulation was used to examine the relation between three response measures and EEG patterns of sleep in human subjects before and after 64 h of acute sleep deprivation. Electroencephalographic responses (EER) behavioral responses (BR) and durations of peripheral vasoconstriction (VCR) increased monotonically as db level increased. The slope of each responsedb line was considerably reduced after sleep deprivation. During the baseline period, before sleep loss, the EER and the BR showed higher thresholds in stages 4 and I rein than in stages 2 and 3. Also the slopes of the EER and the BR on db level were lower in stages 4 and l rem. The VCR, however, was not consistently affected by the EEG stage of sleep. The differential effect of EEG stage tended to disappear for all response variables after sleep deprivation. Near threshold stimuli were sufficient to evoke the EER in EEG stages 2 and 3 both before and after sleep loss. The BR could be reliably evoked by near threshold stimuli only in stages A, 1 and 2 during the baseline period. After sleep loss, very few behavioral responses were evoked at any stimulus intensity. The VCR was consistently evoked by near-threshold stimuli in all stages of sleep both before and after sleep loss. The evidence from this experiment indicates that the EEG stage of sleep is not an invariant indicator of the responsiveness of the organism. For example stage I rem is a "deep" stage of sleep for EER and BR, but not for VCR. Stage 2 is Electroenceph. clin. Neurophysiol., 1964, 16:269-279

RESPONSES TO AUDITORY STIMULI DURING SLEEP o r d i n a r i l y a " l i g h t " stage o f sleep f o r B R , b u t b e c o m e s " d e e p " a f t e r t h e first few h o u r s o f sleep. O n the first r e c o v e r y n i g h t f o l l o w i n g t w o nights o f sleep loss, the p e r c e n t o f t o t a l sleep t i m e s p e n t in stage 4 i n c r e a s e s s h a r p l y at t h e e x p e n s e o f stages A , lrem a n d 2. O n t h e s e c o n d r e c o v e r y night, stage 1rein i n c r e a s e s significantly. Sleep loss t e n d s to m a k e t h e subject less r e s p o n s i v e in all stages o f sleep. We are indebted to Dr. Murray Glanzer for the generous contribution of his time and advice on interpretation of results, and to Mrs. Ometta F. Kearney and Mrs. Elizabeth O. Engle for the statistical analyses. REFERENCES ACKNER,B. and PAMPIGLIONE,G. Combined EEG, plethysmographic, respiratory and skin resistance studies during sleep. Electroeneeph. clin. Neurophysiol., 1955, 7: 153. BERGER, R. J. Tonus of extrinsic laryngeal muscles during sleep and dreaming. Science, 1961, 134: 840. BERGER, R. J. and OSWALD, I. Effects of sleep deprivation on behavior, subsequent sleep and dreaming. Electroenceph, clin. Neurophysiol., 1962, 14: 297. COLEMAN,P. D., Gray, F.E. and WATANABE,K. EEG amplitude and reaction time during sleep. J. appl. Physiol., 1959, 14: 397. DAVIS, H., DAVIS, P. A., LOOMIS, A. U, HARVEY, E. N. and HOBART, G. Electrical reactions of the human brain to auditory stimulation during sleep. J. Neurophysiol., 1939, 2: 500-514. DEMENT, W. The occurrence of low voltage, fast, electroencephalogram patterns during behavioral sleep in the cat. Electroenceph. clin. Neurophysiol., 1958, 10: 291296. DEMENT, W. The effect of dream deprivation. Science, 1960, 131: 1705. DEMENT, W. and KLEITMAN,N. Cyclic variations in LEG during sleep and their relation to eye movements, body motility, and dreaming. Electroenceph. clin. Neurophysiol., 1957, 9: 673-690. DERBYSHIRE, A. J. and FARLEY, J. C. Sampling auditory responses at the cortical level. Ann. Otol. (St. Louis), 1959, 68: 675-697. DERBYSHIRE,A. J. and MCDERMOTT,M. Further contributions to the LEG method of evaluating auditory func-

279

tion. Laryngoscope International Conference on Audiology, 1958, 68: 558-570. FlSCHGOLD, H. and SCHWARTZ, B. A. A clinical, electroencephalographic and polygraphic study of sleep in the human adult. In G. E. W. WOLSTENHOLMEand M. O'CONNOR (Editors), Ciba Foundation Symposium on The Nature of Sleep. Little, Brown, Boston, 1961, 209-231. GEISLER,C. D. Average responses to clicks in man recorded by scalp electrodes. Armed Services Technical Information Agency Technical Report 380. 1960, AD Number 264724: 1-158. JASPER, H. H. Report of the committee on methods of clinical examination in electroencephalography. Electroenceph, clin. Neurophysiol., 1957, 10: 370-375. JOUVET, M. Telencephalic and rhombencephalic sleep in the cat. In G. E. W. WOLSTENHOLMEand M. O'CoNNOR (Editors), Ciba Foundation ,Symposium on The Nature of Sleep. Little, Brown,~Boston, 1961, 188-208. Loouls, A. L., Harvey, E.,'N. and HOBAm:, G. A., Ill. Cerebral states during sleep, as studied by human brain potentials, J. exp. Psychol., 1937, 21: (2) 127-144. LVERLY, S. B. The average Spearman rank correlation coefficient. Psyehometrika, 1952, 17: 421-428. ROBINSON, R. E., Ill, and EASTWOOD, D. W. :Use of a photo-sphygmometer in indirect blood pressure measurements. Anesthesiology, 1959, 20: 704-707. ROTH, M., SHAW, J. and GREEN, J. The form, voltage distribution and physiological significance of the Kcomplex. Electroeneeph. clin. Neurophysiol., 1956, 8: 385-402. SCHWARTZ, B. A. LEG et mouvements oculaires darts le sommeil de nuit. Electroenceph. olin. Neurophysiol., 1962, 14: 126-128. WILLIAMS,H. U, GRANDA,A. M., JONES, R. C., LUBIN, A. and ARMINGTON,,LI~. LEG frequency and finger pulse volume as predictors of reaction time during sleep loss. Electroenceph. clin. Neurophysiol., 1962a, 14: 64-70. WILLIAMS,H. L., LUBIN, A. and GOODNOW,J. J. Impaired performance with acute sleep loss. Psychol. Monogr., 1959, 73: (14) 1-26. WILLIAMS, H. L., TEPAS, D. I. and MORLOCK, H. C., JR. Evoked responses to clicks and electroencephalographic stages of sleep in man. Science, 1962b, 138: 685-686. ZUNG, W. W. K and WILSON,W. P. Response to auditory stimulation during sleep. Arch. gen. Psychiat., 1961, 4: 548-552.

Reference: WILLIAMS,H. L., HAMMACK,J. T., DALY, R. L., DEMENT, W. C. and LUBIN, A. Responses to auditory stimulation, sleep loss and the LEG stages of sleep. Electroenceph. clin. NeurophysioL, 1964, 16: 269-279.