213

Early Human Development, 1977, I/3,213-225 0 Elsevier/North-Holland Biomedical Press

Responsiveness

J. DITTRICHOVI(,

to stimulation

during paradoxical

sleep in infants

K. PAUL and E. PAVLI/KOVk

Laboratory for the Study of Higher Nervous Activity and Behaviour, Care of Mo ther and Child, 14 7 10 Prague 4 Podoli, Czechoslovakia

Received 15 April 1977

Institute

for the

Accepted 4 August 1977

SUMMARY

11 healthy children were repeatedly studied during 2 sleep cycles in 2 sessions at 2, 6, 12 and 20 wk of life. Three acoustic stimuli, light and tactile stimulus were applied in a randomized order in intervals ranging randomly from 30 to 120 sec. Continuous polygraphic recordings were made of respiration, REMs, EEG and EMG of biceps and triceps brachii. The effect of stimuli on the length of paradoxical sleep, REMs and EMG was assessed. There were age-related changes in the number of REMs after stimuli. At 2 and 6 wk no stimulus elicited any change. At 12 wk the children responded with an increased number of rapid eye movements to acoustic stimuli, at 20 wk they responded to acoustic stimuli and light. The conclusion is that, as far as REMs are concerned, responsiveness during paradoxical sleep changes with age. There was a difference in the incidence of EOG responses and EMG responses. These findings show that it is not possible to assess responsiveness in infants during PS by one measure only. Paradoxical sleep in infancy; rapid eye movements; responses to stimulation; development of sleep in early life ; EMG responses in infants

INTRODUCTION

It is suggested that a systematic study of the infant’s responsiveness to stimulation during different behavioural states might provide clues about the organization of the brain mechanisms which underiine the regulation of states [18]. For this purpose various reflexes [2, 18, 191, evoked EEG responses [1, 4, 7, 12,21, 241 or various behavioural responses [8, 13, 14, 231 in infants have been studied. Findings obtained in newborn human infants frequently differ from those obtained in animals: e.g. during paradoxical

214

sleep (PS) in animals a decrease or abolition of different reflexes is observed [17], whereas in newborn infants many polysynaptic reflexes are clearly present during this state of sleep (summarized in Prechtl) [ 191, Chase [ 31). The discrepancy between these findings, which is still unexplained, stresses the importance of developmental investigations [2,11, 181. We studied the infant’s responsiveness to various stimuli during PS to complete our data on the development of PS during the first months of life. Our previous results showed that this state of sleep changed during the first months of life: there were age-related changes in individual parameters of PS (REMs, EEG, EMG of the chin muscles, body movements, respiratory frequency) as well as in the length of the state [5, 6, 151. In the present study the infant’s responsiveness to stimulation during PS in the course of the first months of life was investigated. The effect of stimulation on the length of the PS was assessed. Since REMs and phasic EMG discharges are taken as characteristic phasic events of PS [lo], the effect of stimulation on these events was analysed.

METHOD

11 mature healthy infants were repeatedly observed at 2, 6, 12 and 20 wk of life. 23 control infants were examined at the same ages. All the infants were born at term and the pregnancies and deliveries were uncomplicated. During the first 6 mth of life the infants were in the special residential unit in which behavioural studies of higher nervous functions and behaviour have been made. The mothers lived in the residential unit during the whole period of breast feeding and regularly visited the infants afterwards. Apart from the specially trained ward nurses who looked after the infants, a special research nurse acted as substitute ‘mother’ during the day. An eight-channel EEG apparatus was used for the polygraphic recordings of EEG, respiration, rapid eye movements and EMG discharges. Paper speed was 7.5 mm/set. The EEG was recorded by means of four bipolar leads (pFI -Cg , C3 -01, pF2 -C4, C4 -02 ); the time constant was 0.3 sec. Respiratory movements were recorded by a strain gauge on the abdomen. Rapid eye movements were recorded using two electrodes placed at the outer canthi. The amplification was 2 mm = 50 pV. This was sufficiently high to obtain clearly visible pen deflections from the eye movements and low enough to keep out EEG potentials. Every sharp pen deflection from the isoelectric line was considered as eye movement. Surface EMG of biceps and triceps brachii was recorded; the bursts of increased activity on the background EMG were assessed. Two states of sleep have been distinguished in the polygrams: paradoxical sleep and quiet sleep (QS). Their characteristics are given in Figure 1. A more detailed description of our assessment of paradoxical sleep has been published elsewhere [5, 161. Five different stimuli were applied in a randomized sequence: (1) a 125

215



______~__-__>

. . waking

____ -

states transition quiet sleep paradoxical sleep stimulation

Fig. 1. Scheme of experiments. Behavioural states during which stimulation was applied were characterized in polygraphic records by the following patterns: Quiet sleep: pneumogram - regular respiration; EEG - continual high amplitude activity or high amplitude bursts of trace alternant; EOG - straight baseline. Paradoxical sleep: pneumogram - irregular respiration; EEG - low to middle amplitude activity with rhythmic components; EOG - potentials of rapid eye movements.

Hz sine-wave tone; (2) white noise (both stimuli were generated at a duration of 1 set and an intensity of 75 dB); (3) a female voice addressing the baby by name; (4) a light of intensity 190 lux for 3 set; (5) a tactile stimulus, i.e. pressing the stomach of the baby with a rubber balloon for 3 set; the pressure was 180-220 mm Hg and elicited general motor activity during waking without signs of pain. The interstimuli intervals of 30, 60, 90 and 120 set were administered in randomized order. Stimuli were applied in PS as well as in QS. Two sessions were made to enable us to apply a number of stimuli sufficiently high for purposes of statistical analysis. As indicated in Figure 1, during the first session stimuli were first applied during QS and then during the following PS. During the second session no stimuli were applied during the first QS; stimulation started during PS and continued during the following QS. There were no differences in sleep states and responsiveness between the two sessions. The recordings were made during the day. The length of REM epochs and the REM frequency/min in stimulated infants were compared with those observed in unstimulated infants. In stimulated infants the number of REMs in the 15-set intervals before the stimulus onset was compared with that in the 15-set intervals after the stimulus onset. These data were analysed using a mixed-model, two-way analysis of variance where the effects of the infants and the effects of the stimuli were assessed. In control infants the number of REMs was assessed in the same time-intervals during which stimuli were applied in stimulated infants. An average of 21 stimuli at 2 wk, 18 stimuli at 6 wk, .19 stimuli at 12 wk and 14 stimuli at 20 wk was applied during PS to each subject. Stimuli of all modalities were applied with the exception of one subject at 6 wk (tactile stimulus not applied) and 20 wk (tone not applied). Approximately one stimulus on average at each age period in each subject was not assessed because of artifacts.

216

RESULTS

Length of REM epochs Table I shows the lengths of REM epochs in stimulated and unstimulated infants. The length of REM epoch was assessed in terms of the interval (in minutes) between the first and the last eye movements recorded in EOG. Periods of 2 or more minutes without REMs were not included in the length of the interval There were no significant differences between both groups in the 2nd, 6th and 12th wk of life: average length of one epoch in the 2nd wk lasted approximately 30 min and diminished to 23 min in the 12th week. At 20 wk the difference was significant: one epoch lasted in stimulated infants approximately 12 min, whereas in unstimulated infants one epoch lasted 19 min. Average number of REMs The average number of REMs per minute was not significantly different in stimulated and control infants at different age periods with the exception of the 12th wk of life: at this age the average frequency was significantly higher in stimulated infants as compared to controls (Table II).

REMs before and after stimulation Figure 2 shows two samples of polygrams made during paradoxical sleep 15 set before and 15 set after stimulus (vertical line). The upper part shows a sample of the recording of a 2-wk-old infant, the lower part a sample of the recording in the same infant at the age of 20 wk. At 2 wk an increase in amplitude of the background EMG activity is present after stimulus onset. No rapid eye movements are observable on the EOG. At 20 wk, besides the EMG response, rapid eye movements are apparent. There are also changes in EEG patterns and in respiration. TABLE I The length of REM epochs Infants

2nd wk

6th wk

12th wk

20th wk

Stimulated (N = 11) Control (N = 23)

32.1 f 3.3

23.1 f 3.1

23.4 f 3.5

12.1 f 2.8

30.6 * 3.2

29.9 f 2.7

23.1 f 1.5

19.4 f 1.3

n.s.

n.s.

n.s.

Significance of differences

t= P

Responsiveness to stimulation during paradoxical sleep in infants.

213 Early Human Development, 1977, I/3,213-225 0 Elsevier/North-Holland Biomedical Press Responsiveness J. DITTRICHOVI(, to stimulation during pa...
941KB Sizes 0 Downloads 0 Views