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Ultradian rhythms in waking behavior of rhesus monkeys
Physiology & Behavior, Vol. 21, pp. 929--933. Pergamon Press and Brain Research Publ., 1978. Printed in the U.S.A.
Ultradian Rhythms in Waking Behavior of Rhesus Monkeys I DOUGLAS
M. B O W D E N
Department of Psychiatry and Behavioral Sciences,and Regional Primate Research Center University of Washington, Seattle, WA 98195 AND DANIEL
F . K R I P K E A N D V. G R A N T W Y B O R N E Y
Departments of Psychiatry, University of California, LaJolla, CA 92093 and Veterans' Administration Hospital, San Diego, CA 92161 ( R e c e i v e d 31 M a r c h 1978) BOWDEN, D. M., D. F. KRIPKE A N D V. G. WYBORNEY. Ultradian rhythms in waking behavior of rhesus monkeys. PHYSIOL. BEHAV. 21(6) 929-933, 1978.--The behavior of seven individually housed adult male rhesus monkeys was recorded by time-lapse video, 10 hr per day, for up to 5 days. Recordings were analyzed in 50 see intervals for the presence or absence of 5 behaviors, viz., ingestion, locomotion, exploration, self-grooming, and resting. Analyses were based on the number of 50 sec intervals per 5 rain epoch in which each of these behaviors occurred. Variance spectra were computed on each behavior for each animal, and the significance of a prospectively predicted behavioral cyclicity in the frequency band of 12-18 cycles/day was explored with t tests for the group of monkeys. All 5 behaviors exhibited a statistically significant spectral peak as predicted. Significant cross-spectral relationships were found reflecting temporal relationships between ingestion, locomotion, exploration, and resting. The first 3 were in phase with one another and out-of-phase (reciprocal) with resting. Locomotion tended to precede exploration, and exploration to precede ingestion. These results suggest that the 12-24 cycles/day orality rhythm described earlier in monkeys is not discrete, but is one component of a more general 12-18 cycles/day behavioral cycle involving locomotion, exploration, and rest as well. Self-grooming, while perhaps cyclic, was not significantly related to the orality-locomotion-explorationcomplex.
S E V E R A L studies of humans have demonstrated ultradian rhythms in eating, drinking and gastric contractions [4, 8, 17]. Some investigators have speculated that these rhythms may reflect a cyclical oral drive mechanism. Previously, our group described an oral rhythm in monkeys [14] that included both ingestive and noningestive mouth-touching behaviors. Noningestive mouth activity (contact of the empty hand or other nonfood object with the mouth or perioral area) showed a predicted spectral peak in the 12-24 cycle per day (cpd) range of a magnitude and statistical significance equal to that seen in ingestive behavior. The focal concern of this research was whether the eyclicity of behavior in monkeys is uniquely or primarily oral, or whether there is a more general cyclicity in behavioral patterns of which alimentary behaviors are but one aspect [5, 10, 11, 13]. METHOD
Seven feral-born male rhesus monkeys (Macaca mulatta) ranging in age from 3 to 9 years were observed. All had been adapted to single animal caging for at least one year during
which their basic diet was Purina Monkey Chow. The monkeys were studied individually. One to 3 weeks before recordings commenced, each animal was transferred to an observation cage (2x 1 ×0.5 m) with perches at three levels to encourage activity. A 14 hr light-10 hr dark schedule (lightson at 6:00 a.m.) was maintained. F o o d and water were continuously available from an open hopper and tilt-valve fluid dispenser near the floor. Each animal was studied 10 hr/day for 1-5 days. An Odetics Model TC610 time-lapse videorecorder was used to record two consecutive 5 hr sessions per day, beginning at 9:30 a.m. (3.5 hr after lights-on). In exploring for cyclicity of spontaneous behavior, we attempted to classify behaviors into categories as comparable as possible to those that have served to describe the major activities of nonhuman primates in more natural surroundings. Attention was focused on 5 behavioral classes encompassing the major kinds of time-consuming behaviors observed in field studies [2, 16, 19]. On play back of the videotapes, an observer pressed buttons on a keyboard wired to a Raytheon 704 minicomputer to indicate occurrences of behaviors in four classes: ingestion, exploration,
1This research was supported in part by USPHS Grants RR-00166, RR-05432, MH--42493 and HD--02274 to the University of Washington and KO2-MH00117 to the University of California, and by the Research Service of the Veterans' Administration. Ms. Mary Morgan greatly assisted this research.
C o p y r i g h t ~ 1978 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/78/120929-05502.00/0
930
BOWDEN, K R I P K E AND WYBORNEY
locomotion, and self-grooming. Ingestion was recorded whenever the animal ate, drank, or clearly chewed food stored in its cheek pouches. Exploration was scored for postural adjustments to allow peering out of the cage, and for manipulations of inanimate objects including a novel object, such as a brush, bottle or mirror, which was changed daily. Locomotion was scored for walking and climbing. Selfgrooming was scored during manual self-examination, scratching, rubbing, and picking at the body. The computer recorded each behavior as either present or absent during each 50 sec interval, so that approximately 360 intervals were scored per session. The Fifth behavioral class, resting, was scored for all intervals during which none of the other four behaviors occurred. Sleeping was included in the resting category. These scores were then combined into counts of how many 50 sec intervals included each behavior in each 5 min epoch. Based on data from our previous studies [12,14] we predicted that, if nonoral behaviors were related to the alimentary rhythm, they should exhibit a cyclicity in the range of 12-18 cpd. In addition, they should show a consistent temporal relationship to the orality rhythm. To examine these predictions, the 5 min count for each behavior during each session was treated as a separate time-series [7,9]. The variance spectrum (auto-spectrum, or power spectral density) of each time series was computed with a resolution of 6 cpd. This allowed examination of rhythms with periods ranging from 10 min to 4 hr. F o r each behavior, the spectra derived from all tapes of a single animal were averaged to provide an averaged spectrum for that animal. To exclude effects that might theoretically distort statistical estimates of the two lowest spectral frequencies, spectra were also computed with a resolution of 4 cpd. To test for temporal relationships among the different behaviors, cross-spectra were calculated between each pair of behaviors for each tape [9] and were averaged similarly to variance spectra. From the averaged cross-spectra, the phase-angle relationships between behaviors at 12 cpd were derived. Temporally correlated cycles would yield consistent phase angles, whereas, if there were no 12-18 cpd cycles in behaviors or if the cycles in different behaviors were temporally unrelated, these phase-angles would be random among the group of monkeys. The statistical consistency of phase-angle relationships among the monkeys was evaluated with the Rayleigh test as described by Batschelet [1]. RESULTS
graph represents the mean of those averages across animals. The mean spectrum for each behavior had its peak in the 12-18 cpd range. To explore whether the spectral peak for a given behavior could be a chance result, a difference score was computed from the averaged spectrum for each animal by substracting the variance at 6 cpd and 24 cpd from the variance at 12 cpd and 18 cpd. Were the observed behaviors temporally random, all spectral frequencies would be expected to be equal, whereas the presence of a 12-18 cpd behavioral cycle would result in positive difference scores. The Witcoxon Matched-Pair Signed-Ranks test [18] was used to evaluate these difference scores. One-tailed tests were selected prospectively, since only positive differences would support the hypothesis. The results of this analysis are presented in Table 1. Each of the behaviors showed a significant 12-18 cpd cyclicity. Similar tests were computed comparing the mean variance at 12-18 cpd with the mean of all other frequencies to test specifically for randomness, without requiring a peak. These tests rejected a null hypothesis of temporal randomness for each behavior (p<0.01; n--7 for each). Analyses of the same data at higher resolution (4 cpd) produced spectra with peaks at 12 cpd for all behaviors except self-grooming (8 cpd), thus excluding spectral end-effect distortions except possibly for grooming. In short, all behawors with the possible exception of self-grooming showed robust cyclicity in the 12-18 cpd frequency range. The cross-spectral analyses are summarized in Table 2 and Fig. 2. Significant phase-angle relationships were demonstrated between 4 of the behaviors: ingestion, exploration, locomotion, and resting. For example (Table 2), the estimated phase angle between resting and ingestion was 184° with 95% confidence that the actual phase difference lay within -+ 38 ° of that value. The probability that no significant phase relationship existed was less than 0.01. Selfgrooming showed no significantly consistent phase-angle relationship with any other behavior. Because resting was defined as the absence of any other behavior, it was to be expected that it was reciprocal or approximately 180° outof-phase with the other behaviors (Fig. 2). Exploration, locomotion, and ingestion were all significantly temporally related, and there were trends for locomotion to precede exploration and for exploration and locomotion to precede ingestion. The phase-angle relationships between these behaviors, however, could not be significantly distinguished from 0 °, that is, the trends for these cyclic behaviors to occur sequentially did not reach significance.
The spectral results for each behavior are presented in Fig. 1. Each of the narrow lines represents the averaged spectrum from one animal, while the heavy line in each
DISCUSSION The findings of this study are consistent with previous
TABLE 1 RESULTS OF MATCHED-PAIRSIGNED-RANKSTEST FOR FREQUENCY PEAKSAT 12 AND 18 CPD COMPARED WITH 6 AND 24 CPD IN 7 RHESUS MONKEYS Ingestion No. animals with positive difference
7 <0.010
Exploration
Locomotion
5 <0.050
p indicates probability that group difference=0.
6 <0.025
Self-grooming
6 <0.025
Resting
7 <0.010
ULTRADIAN RHYTHMS IN RHESUS BEHAVIOR
251
931
EXPLORATION
INGESTION
20 ~a
15-
to
IO-
5-
I
I
I
I
l
201 ~
I
I
I
I
I
I
I
f
LOCOMOTION
I
I
I
I
I
I
I
I
SELF-GROOMING
i5
.g
0
i
0
24
48
96
72
i20
0
i
24
4~8
Cycles/ Doys
25
72 96 Cycles/ Doy
T
120
RESTING
20 .m
15
£a
I0 50
.
0
.
.
24
.
.
.
48
.
'
'
72 Cycles / DQy
FIG. 1. Variance spectra of five behaviors. Thin lines represent averaged spectra for one monkey; wide lines represent mean spectrum of the seven animals combined. findings regarding cyclicity of behavior in unrestrained monkeys and with the concept that the cyclities of several behaviors are related, but the data do not prove that a single basic rest activity cycle links all important behavioral and physiological functions in both waking and sleeping conditions.
The period of dominant rhythm observed in this study was somewhat longer than that reported by Delgado-Garcia e t al. [3] in the most nearly comparable study published to date. Here the spectral peak occurred in the 12-18 cpd range, corresponding to an 80-120 min periodicity. Delgado-Garcia
932
BOWDEN, KRIPKE AND WYB()RNEY TABLE 2 PHASIC R E L A T I O N S H I P S B E T W E E N B E H A V I O R A L R H Y T H M S
Resting
Ingestion
Exploration
Locomotion
Self-Grooming
38° p<0.010 NS 22° ± 24° p<0.00l 18° ± 48° p<0.050
164° ± 26° p<0.001 NS 1° ± 4 6 ° p<0.050
145° _+ 29° p <0.005 NS
NS
184 ° ±
Self-Grooming Locomotion Exploration
95 percent confidence limits of phase relationships tested at 12 cpd frequency for all possible pairs of behaviors. 360° corresponds to 120 min; p =probability of no phase difference. See text for further explanation.
0°
/
5 0 0 °,
60 °
90 °
270 °
240 °.
*
150 ° ]80 °
[ ] Locomotion
~] Explorotion
[ ] Incjestion
FIG. 2. Phase-angle relationships of 4 behaviors that showed significant cross-spectral relations with one another. Graph presents a behavioral cycle in which 360°= 120 min. The mean phase angle and 95% angular confidence limits for locomotion, exploration, and ingestion are presented relative to resting, which is referenced to 0°.
et al. [3] observed spectral peaks in their motility measure
corresponding to a 60-90 min period. Several sources of variation may account for this difference. The relationship of the observation period to the light-dark cycle might influence the frequency of the cycles. Delgado-Garcia et al. combined observations throughout their 12-hr light phase, whereas observations in the present study were concentrated in the middle or late 5 or 10 hr o f a 14-hr light phase. In their study, changes in feeding schedules produced shifts in period length by 10-20%, suggesting that differences in this or other aspects of the caretaking schedule may have contributed to the difference. Kleitman [10] noted that age has an influence on the period of the rest-activity cycle that may account for some of the difference. In short, the period of the locomotor
cycle is sensitive to significant modulation by several factors capable of producing the kind of difference in dominant fiequency noted between this study and that of Delgado-Garcia et al. [3]. The nonsignificant trend for locomotion, exploration, and ingestion to occur with progressively wider phase relations to resting is consistent with the sequence most frequently observed by Delgado-Garcia et al. [3], viz., sitting motionless, sitting alert, self-grooming, walking, yawning, picking, and eating. Our previous study [14] indicated that oral cycles were not purely alimentary (eating and drinking), because noningestive, mouth-oriented behaviors were cyclic as well. The present study was based on a more naturalistic categorization of behavior in which noningestive mouth-touching was classified as exploratory or self-grooming behavior. The results demonstrated cycles in exploration, locomotion, and resting to be correlated with ingestion cycles (Table 2, column 1), indicating that the cyclic patterns of behavior in the monkey are not limited to ingestive or mouth-touching behaviors. The fact that the resting state, i.e., the reciprocal of all other behaviors combined, tended to show the greatest concentration of variance in the 12-18 cpd frequency range suggests that ingestive cyclicity is not even the most prominent aspect of this behavioral complex. The resting periods very likely included brief sleep episodes which may be cyclic ]12]. The findings of this study are therefore consistent with the view that oral cyclicity is one component of a more general cyclic behavioral pattern. Whether the cycle observed here should be considered a basic rest-activity cycle [10,20] remains an open question. The fact that self-grooming, in this study, and picking [3] and social interaction [15] in other studies have been reported to exhibit cycles of considerably longer periods than the other cycles suggests that there are several behavioral rhythms that may be equally important. The marked contrast between the 12-18 cpd cycles observed in the waking monkey and the 24-36 cpd sleep stage cycles previously described [ 121 leaves doubt whether a single basic cycle underlies both sets of phenomena. It has been shown [6] that several different species exhibiting REM-nonREM cycticity with periods ranging from 10-20 rain up to 90-120 rain show migrating myoelectric complexes in the small intestine and gastric contraction periods with cyclicity close to 12-18 cpd. Thus, it seems clear that these enteric cycles are not related to the REM-nonREM cycle. Based on the resemblance of
U L T R A D I A N R H Y T H M S IN R H E S U S B E H A V I O R
933
frequency, it seems plausible that ingestive and other behavioral cycles might be related to visceral cycles rather than to the REM-nonREM cycle. It would be useful to explore directly whether cycles of waking behavior are related to the REM-nonREM or visceral cycles by carrying out behavioral, sleep, and enteric recordings in the same animals under the same experimental conditions. Most interpretations of the biological significance of ultradian rhythms derive from one of two types of model, adaptive models and servo-error models. In adaptive models, oscillations are regarded as cyclic transitions between two states, each of which is in some sense necessary for the health of the organism, and any factor that disrupts the regular alternation between states threatens its well-being. Among the most commonly recognized rhythms of this sort are hormonal and behavioral aspects of the estrus cycle and the sleep-wake cycle. Females maintained in continuous estrus do not conceive; animals deprived of sleep show a vail-
ety of nonadaptive behavioral changes. In servo-error models, the oscillations are regarded simply as signs of the limits of homeostatic control exercised by the physiological mechanisms that maintain particular variables at a constant level. Knowledge of the frequency and range of oscillation may be important to the physiologist interested in minimizing its contribution to the variance of repeated experimental measurements, determining normal values, or analyzing the mechanisms controlling the variable, but the extremes of oscillation within the normal range are not regarded as representing different biologically significant states. Commonly recognized rhythms of this type are seen in such variables as aortic blood pressure during the cardiac cycle, urine flow rate, and the like. An important goal of future research is to determine whether the adaptive model or the servo-error model is more appropriate for interpreting the kinds of behavioral cyclicity observed in this study.
REFERENCES 1. Batschelet, E. Statistical methods for the analysis of problems in animal orientation and certain biological rhythms. Monograph, American Institute of Biological Sciences, Washington, D.C., 1965. 2. Chivers, D. J. An introduction to the socio-ecology of Malayan forest primates. In: Comparative Ecology and Behaviour of Primates, edited by R. P. Michael and J. H. Crook. London: Academic Press, 1973, pp. 101-146. 3. Delgado-Garcia, J. M., C. Grau, P. DeFeudis, F. del Pozo, J. M. Jimenez and J. M. R. Delgado. Ultradian rhythms in the mobility and behavior of rhesus monkeys. Expl Brain Res. 25: 79-91, 1976. 4. Friedman, S. and C. Fisher. On the presence of a rhythmic, diurnal, oral instinctual drive cycle in man: a preliminary report. J. Am. psychoan. Ass. 15: 317-343, 1967. 5. Globus, G. G., R. L. Drury, E, C. Phoebus and R. Boyd. UItradian rhythms in human performance. Percept. Mot. Skills 33: 1171-1174, 1971. 6. Grivel, M.-L. and Y. Ruckebusch. The propagation of segmental contractions along the small intestine. J. Physiol. 227:611625, 1972. 7. Halberg, F. and H. I. Panofsky. Thermovariance spectra: method and clinical illustrations. II. Thermovariance spectra: simplified computational example and other methodology. Expl reed. Surg. 19: 284-309, 323-338, 1%1. 8. Hiatt, J. F. and D. F. Kripke. Ultradian rhythms in waking gastric activity. Psychosom. Med. 37: 320-325, 1975.
9. Jenkins, G. M. and D. G. Watts. Special Analysis and Its Applications. San Francisco: Holden-Day, 1%8. 10. Kleitman, N. Sleep and Wakefulness. Chicago: The University of Chicago Press, 1%3. 11. Kripke, D. F. Ultradian rhythms in sleep and wakefulness. In: Advances in Sleep Research, edited by E. Weitzman. New York: Spectrum Publications, 1974, pp. 305--325. 12. Kripke, D. F., F. Halberg, T. Crowley, et al. Ultradian spectra in monkeys. Int. J. Chronobiol. 3: 193-204, 1976. 13. Kripke, D. F., D. J. Mullaney, V. G. Wyborney and S. Messin. There's no basic rest activity cycle. Postgrad Med. J., in press. 14. Lewis, B. D., D. F. Kripke and D. M. Bowden. Ultradian rhythms in hand-mouth behavior of the rhesus monkey. Physiol. Behav. 18: 283-286, 1977. 15. Maxim, P. E., D. M. Bowden and G. P. Sackett. Ultradian rhythms of solitary and social behavior in rhesus monkeys. Physiol. Behav. 17: 337-344, 1976. 16. Neville, M. K. Ecology and activity of Himalayan foothill rhesus monkeys (Macaca mulatta). Ecology 49: 100-123, 1968. 17. Oswald, I., J. Merrington and H. Lewis. Cyclical "on demand" oral intake by adults. Nature 225: 959-960, 1970. 18. Siegel, S. Nonparametric Statistics for the Behavioral Sciences. New York: McGraw-Hill, 1956. 19. Southwick, C. H. An experimental study ofintragroup agonistic behavior in rhesus monkeys (Macaca mulatta). Behaviour 28: 182-209, 1967. 20. Sterman, M. B., E, A. Lucas and L. R. MacDonald. Periodicity within sleep and operant performance in the cat. Brain Res. 38: 327-341, 1972.
Ultradian Rhythms in Waking Behavior of Rhesus Monkeys I DOUGLAS
M. B O W D E N
Department of Psychiatry and Behavioral Sciences,and Regional Primate Research Center University of Washington, Seattle, WA 98195 AND DANIEL
F . K R I P K E A N D V. G R A N T W Y B O R N E Y
Departments of Psychiatry, University of California, LaJolla, CA 92093 and Veterans' Administration Hospital, San Diego, CA 92161 ( R e c e i v e d 31 M a r c h 1978) BOWDEN, D. M., D. F. KRIPKE A N D V. G. WYBORNEY. Ultradian rhythms in waking behavior of rhesus monkeys. PHYSIOL. BEHAV. 21(6) 929-933, 1978.--The behavior of seven individually housed adult male rhesus monkeys was recorded by time-lapse video, 10 hr per day, for up to 5 days. Recordings were analyzed in 50 see intervals for the presence or absence of 5 behaviors, viz., ingestion, locomotion, exploration, self-grooming, and resting. Analyses were based on the number of 50 sec intervals per 5 rain epoch in which each of these behaviors occurred. Variance spectra were computed on each behavior for each animal, and the significance of a prospectively predicted behavioral cyclicity in the frequency band of 12-18 cycles/day was explored with t tests for the group of monkeys. All 5 behaviors exhibited a statistically significant spectral peak as predicted. Significant cross-spectral relationships were found reflecting temporal relationships between ingestion, locomotion, exploration, and resting. The first 3 were in phase with one another and out-of-phase (reciprocal) with resting. Locomotion tended to precede exploration, and exploration to precede ingestion. These results suggest that the 12-24 cycles/day orality rhythm described earlier in monkeys is not discrete, but is one component of a more general 12-18 cycles/day behavioral cycle involving locomotion, exploration, and rest as well. Self-grooming, while perhaps cyclic, was not significantly related to the orality-locomotion-explorationcomplex.
S E V E R A L studies of humans have demonstrated ultradian rhythms in eating, drinking and gastric contractions [4, 8, 17]. Some investigators have speculated that these rhythms may reflect a cyclical oral drive mechanism. Previously, our group described an oral rhythm in monkeys [14] that included both ingestive and noningestive mouth-touching behaviors. Noningestive mouth activity (contact of the empty hand or other nonfood object with the mouth or perioral area) showed a predicted spectral peak in the 12-24 cycle per day (cpd) range of a magnitude and statistical significance equal to that seen in ingestive behavior. The focal concern of this research was whether the eyclicity of behavior in monkeys is uniquely or primarily oral, or whether there is a more general cyclicity in behavioral patterns of which alimentary behaviors are but one aspect [5, 10, 11, 13]. METHOD
Seven feral-born male rhesus monkeys (Macaca mulatta) ranging in age from 3 to 9 years were observed. All had been adapted to single animal caging for at least one year during
which their basic diet was Purina Monkey Chow. The monkeys were studied individually. One to 3 weeks before recordings commenced, each animal was transferred to an observation cage (2x 1 ×0.5 m) with perches at three levels to encourage activity. A 14 hr light-10 hr dark schedule (lightson at 6:00 a.m.) was maintained. F o o d and water were continuously available from an open hopper and tilt-valve fluid dispenser near the floor. Each animal was studied 10 hr/day for 1-5 days. An Odetics Model TC610 time-lapse videorecorder was used to record two consecutive 5 hr sessions per day, beginning at 9:30 a.m. (3.5 hr after lights-on). In exploring for cyclicity of spontaneous behavior, we attempted to classify behaviors into categories as comparable as possible to those that have served to describe the major activities of nonhuman primates in more natural surroundings. Attention was focused on 5 behavioral classes encompassing the major kinds of time-consuming behaviors observed in field studies [2, 16, 19]. On play back of the videotapes, an observer pressed buttons on a keyboard wired to a Raytheon 704 minicomputer to indicate occurrences of behaviors in four classes: ingestion, exploration,
1This research was supported in part by USPHS Grants RR-00166, RR-05432, MH--42493 and HD--02274 to the University of Washington and KO2-MH00117 to the University of California, and by the Research Service of the Veterans' Administration. Ms. Mary Morgan greatly assisted this research.
C o p y r i g h t ~ 1978 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/78/120929-05502.00/0
930
BOWDEN, K R I P K E AND WYBORNEY
locomotion, and self-grooming. Ingestion was recorded whenever the animal ate, drank, or clearly chewed food stored in its cheek pouches. Exploration was scored for postural adjustments to allow peering out of the cage, and for manipulations of inanimate objects including a novel object, such as a brush, bottle or mirror, which was changed daily. Locomotion was scored for walking and climbing. Selfgrooming was scored during manual self-examination, scratching, rubbing, and picking at the body. The computer recorded each behavior as either present or absent during each 50 sec interval, so that approximately 360 intervals were scored per session. The Fifth behavioral class, resting, was scored for all intervals during which none of the other four behaviors occurred. Sleeping was included in the resting category. These scores were then combined into counts of how many 50 sec intervals included each behavior in each 5 min epoch. Based on data from our previous studies [12,14] we predicted that, if nonoral behaviors were related to the alimentary rhythm, they should exhibit a cyclicity in the range of 12-18 cpd. In addition, they should show a consistent temporal relationship to the orality rhythm. To examine these predictions, the 5 min count for each behavior during each session was treated as a separate time-series [7,9]. The variance spectrum (auto-spectrum, or power spectral density) of each time series was computed with a resolution of 6 cpd. This allowed examination of rhythms with periods ranging from 10 min to 4 hr. F o r each behavior, the spectra derived from all tapes of a single animal were averaged to provide an averaged spectrum for that animal. To exclude effects that might theoretically distort statistical estimates of the two lowest spectral frequencies, spectra were also computed with a resolution of 4 cpd. To test for temporal relationships among the different behaviors, cross-spectra were calculated between each pair of behaviors for each tape [9] and were averaged similarly to variance spectra. From the averaged cross-spectra, the phase-angle relationships between behaviors at 12 cpd were derived. Temporally correlated cycles would yield consistent phase angles, whereas, if there were no 12-18 cpd cycles in behaviors or if the cycles in different behaviors were temporally unrelated, these phase-angles would be random among the group of monkeys. The statistical consistency of phase-angle relationships among the monkeys was evaluated with the Rayleigh test as described by Batschelet [1]. RESULTS
graph represents the mean of those averages across animals. The mean spectrum for each behavior had its peak in the 12-18 cpd range. To explore whether the spectral peak for a given behavior could be a chance result, a difference score was computed from the averaged spectrum for each animal by substracting the variance at 6 cpd and 24 cpd from the variance at 12 cpd and 18 cpd. Were the observed behaviors temporally random, all spectral frequencies would be expected to be equal, whereas the presence of a 12-18 cpd behavioral cycle would result in positive difference scores. The Witcoxon Matched-Pair Signed-Ranks test [18] was used to evaluate these difference scores. One-tailed tests were selected prospectively, since only positive differences would support the hypothesis. The results of this analysis are presented in Table 1. Each of the behaviors showed a significant 12-18 cpd cyclicity. Similar tests were computed comparing the mean variance at 12-18 cpd with the mean of all other frequencies to test specifically for randomness, without requiring a peak. These tests rejected a null hypothesis of temporal randomness for each behavior (p<0.01; n--7 for each). Analyses of the same data at higher resolution (4 cpd) produced spectra with peaks at 12 cpd for all behaviors except self-grooming (8 cpd), thus excluding spectral end-effect distortions except possibly for grooming. In short, all behawors with the possible exception of self-grooming showed robust cyclicity in the 12-18 cpd frequency range. The cross-spectral analyses are summarized in Table 2 and Fig. 2. Significant phase-angle relationships were demonstrated between 4 of the behaviors: ingestion, exploration, locomotion, and resting. For example (Table 2), the estimated phase angle between resting and ingestion was 184° with 95% confidence that the actual phase difference lay within -+ 38 ° of that value. The probability that no significant phase relationship existed was less than 0.01. Selfgrooming showed no significantly consistent phase-angle relationship with any other behavior. Because resting was defined as the absence of any other behavior, it was to be expected that it was reciprocal or approximately 180° outof-phase with the other behaviors (Fig. 2). Exploration, locomotion, and ingestion were all significantly temporally related, and there were trends for locomotion to precede exploration and for exploration and locomotion to precede ingestion. The phase-angle relationships between these behaviors, however, could not be significantly distinguished from 0 °, that is, the trends for these cyclic behaviors to occur sequentially did not reach significance.
The spectral results for each behavior are presented in Fig. 1. Each of the narrow lines represents the averaged spectrum from one animal, while the heavy line in each
DISCUSSION The findings of this study are consistent with previous
TABLE 1 RESULTS OF MATCHED-PAIRSIGNED-RANKSTEST FOR FREQUENCY PEAKSAT 12 AND 18 CPD COMPARED WITH 6 AND 24 CPD IN 7 RHESUS MONKEYS Ingestion No. animals with positive difference
7 <0.010
Exploration
Locomotion
5 <0.050
p indicates probability that group difference=0.
6 <0.025
Self-grooming
6 <0.025
Resting
7 <0.010
ULTRADIAN RHYTHMS IN RHESUS BEHAVIOR
251
931
EXPLORATION
INGESTION
20 ~a
15-
to
IO-
5-
I
I
I
I
l
201 ~
I
I
I
I
I
I
I
f
LOCOMOTION
I
I
I
I
I
I
I
I
SELF-GROOMING
i5
.g
0
i
0
24
48
96
72
i20
0
i
24
4~8
Cycles/ Doys
25
72 96 Cycles/ Doy
T
120
RESTING
20 .m
15
£a
I0 50
.
0
.
.
24
.
.
.
48
.
'
'
72 Cycles / DQy
FIG. 1. Variance spectra of five behaviors. Thin lines represent averaged spectra for one monkey; wide lines represent mean spectrum of the seven animals combined. findings regarding cyclicity of behavior in unrestrained monkeys and with the concept that the cyclities of several behaviors are related, but the data do not prove that a single basic rest activity cycle links all important behavioral and physiological functions in both waking and sleeping conditions.
The period of dominant rhythm observed in this study was somewhat longer than that reported by Delgado-Garcia e t al. [3] in the most nearly comparable study published to date. Here the spectral peak occurred in the 12-18 cpd range, corresponding to an 80-120 min periodicity. Delgado-Garcia
932
BOWDEN, KRIPKE AND WYB()RNEY TABLE 2 PHASIC R E L A T I O N S H I P S B E T W E E N B E H A V I O R A L R H Y T H M S
Resting
Ingestion
Exploration
Locomotion
Self-Grooming
38° p<0.010 NS 22° ± 24° p<0.00l 18° ± 48° p<0.050
164° ± 26° p<0.001 NS 1° ± 4 6 ° p<0.050
145° _+ 29° p <0.005 NS
NS
184 ° ±
Self-Grooming Locomotion Exploration
95 percent confidence limits of phase relationships tested at 12 cpd frequency for all possible pairs of behaviors. 360° corresponds to 120 min; p =probability of no phase difference. See text for further explanation.
0°
/
5 0 0 °,
60 °
90 °
270 °
240 °.
*
150 ° ]80 °
[ ] Locomotion
~] Explorotion
[ ] Incjestion
FIG. 2. Phase-angle relationships of 4 behaviors that showed significant cross-spectral relations with one another. Graph presents a behavioral cycle in which 360°= 120 min. The mean phase angle and 95% angular confidence limits for locomotion, exploration, and ingestion are presented relative to resting, which is referenced to 0°.
et al. [3] observed spectral peaks in their motility measure
corresponding to a 60-90 min period. Several sources of variation may account for this difference. The relationship of the observation period to the light-dark cycle might influence the frequency of the cycles. Delgado-Garcia et al. combined observations throughout their 12-hr light phase, whereas observations in the present study were concentrated in the middle or late 5 or 10 hr o f a 14-hr light phase. In their study, changes in feeding schedules produced shifts in period length by 10-20%, suggesting that differences in this or other aspects of the caretaking schedule may have contributed to the difference. Kleitman [10] noted that age has an influence on the period of the rest-activity cycle that may account for some of the difference. In short, the period of the locomotor
cycle is sensitive to significant modulation by several factors capable of producing the kind of difference in dominant fiequency noted between this study and that of Delgado-Garcia et al. [3]. The nonsignificant trend for locomotion, exploration, and ingestion to occur with progressively wider phase relations to resting is consistent with the sequence most frequently observed by Delgado-Garcia et al. [3], viz., sitting motionless, sitting alert, self-grooming, walking, yawning, picking, and eating. Our previous study [14] indicated that oral cycles were not purely alimentary (eating and drinking), because noningestive, mouth-oriented behaviors were cyclic as well. The present study was based on a more naturalistic categorization of behavior in which noningestive mouth-touching was classified as exploratory or self-grooming behavior. The results demonstrated cycles in exploration, locomotion, and resting to be correlated with ingestion cycles (Table 2, column 1), indicating that the cyclic patterns of behavior in the monkey are not limited to ingestive or mouth-touching behaviors. The fact that the resting state, i.e., the reciprocal of all other behaviors combined, tended to show the greatest concentration of variance in the 12-18 cpd frequency range suggests that ingestive cyclicity is not even the most prominent aspect of this behavioral complex. The resting periods very likely included brief sleep episodes which may be cyclic ]12]. The findings of this study are therefore consistent with the view that oral cyclicity is one component of a more general cyclic behavioral pattern. Whether the cycle observed here should be considered a basic rest-activity cycle [10,20] remains an open question. The fact that self-grooming, in this study, and picking [3] and social interaction [15] in other studies have been reported to exhibit cycles of considerably longer periods than the other cycles suggests that there are several behavioral rhythms that may be equally important. The marked contrast between the 12-18 cpd cycles observed in the waking monkey and the 24-36 cpd sleep stage cycles previously described [ 121 leaves doubt whether a single basic cycle underlies both sets of phenomena. It has been shown [6] that several different species exhibiting REM-nonREM cycticity with periods ranging from 10-20 rain up to 90-120 rain show migrating myoelectric complexes in the small intestine and gastric contraction periods with cyclicity close to 12-18 cpd. Thus, it seems clear that these enteric cycles are not related to the REM-nonREM cycle. Based on the resemblance of
U L T R A D I A N R H Y T H M S IN R H E S U S B E H A V I O R
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frequency, it seems plausible that ingestive and other behavioral cycles might be related to visceral cycles rather than to the REM-nonREM cycle. It would be useful to explore directly whether cycles of waking behavior are related to the REM-nonREM or visceral cycles by carrying out behavioral, sleep, and enteric recordings in the same animals under the same experimental conditions. Most interpretations of the biological significance of ultradian rhythms derive from one of two types of model, adaptive models and servo-error models. In adaptive models, oscillations are regarded as cyclic transitions between two states, each of which is in some sense necessary for the health of the organism, and any factor that disrupts the regular alternation between states threatens its well-being. Among the most commonly recognized rhythms of this sort are hormonal and behavioral aspects of the estrus cycle and the sleep-wake cycle. Females maintained in continuous estrus do not conceive; animals deprived of sleep show a vail-
ety of nonadaptive behavioral changes. In servo-error models, the oscillations are regarded simply as signs of the limits of homeostatic control exercised by the physiological mechanisms that maintain particular variables at a constant level. Knowledge of the frequency and range of oscillation may be important to the physiologist interested in minimizing its contribution to the variance of repeated experimental measurements, determining normal values, or analyzing the mechanisms controlling the variable, but the extremes of oscillation within the normal range are not regarded as representing different biologically significant states. Commonly recognized rhythms of this type are seen in such variables as aortic blood pressure during the cardiac cycle, urine flow rate, and the like. An important goal of future research is to determine whether the adaptive model or the servo-error model is more appropriate for interpreting the kinds of behavioral cyclicity observed in this study.
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