Piero Salzarulo

Morning recall of verbal material depends on prior sleep organization

Despite the evidence that sleep may facilitate memory, controversial findings concern the role of sleep states (NREM, REM). We put forward the hypothesis that sleep organization, i.e. the regular occurrence of NREM-REM cycles, more than sleep states per se, may be crucial for the retention of verbal material presented before sleep. An experiment was performed in which recall of verbal material was requested of young subjects after three different kinds of night sleep: undisturbed sleep, fragmented sleep without sleep cycles disorganization, and fragmented sleep interrupted with sleep disorganization. Morning recall of verbal material was impaired after the night with disturbed sleep cycles, whereas it was not after the night with preserved sleep cycles; the amount of REM was similar in both cases. We conclude that the recall of verbal material is greatly affected by sleep cycle disorganization.

Word recall correlates with sleep cycles in elderly subjects

Morning recall of words presented before sleep was studied in relation to intervening night sleep measures in elderly subjects. Night sleep of 30 elderly subjects aged 61–75 years was recorded. Before sleep, subjects were presented with a list of paired non‐related words and cued recall was asked immediately after the morning awakening. Recall positively correlated with average duration of NREM/REM cycles, and with the proportion of time spent in cycles (TCT) over total sleep time (TST). No significant correlations were found with other sleep or wake measures. These results suggest the importance of sleep structure for sleep‐related memory processes in elderly adults.

Sleep organization in the first year of life: Developmental trends in the quiet sleep–paradoxical sleep cycle

The night sleep of 48 healthy drug‐free infants, aged 1–54 weeks, was recorded and analysed in order to show how cycles contribute to sleep episode organization and how the balance among different sleep states (i.e. quiet sleep, paradoxical sleep and ambiguous sleep) within cycles changes as a function of age.

Yawning in morning and evening types

Yawning occurs more frequently in the early morning and in the late evening, close to sleep onset and after the awakening, and it might be linked to sleep propensity. We aimed to study yawning and its temporal distribution in morning and evening subjects who display different sleep-wake and sleepiness rhythms. Sixteen healthy young adults (8 evening-types and 8 morning-types, matched for age and gender) have been selected and instructed to keep their habitual sleep schedules and to signal every yawning occurrence for three consecutive days. Results show that evening-types yawn more frequently than morning-types, particularly during morning hours. Yawning frequency decreases across daytime in evening-types reaching its lowest level in the early evening and increases thereafter. Instead, in morning-types, yawning frequency remains quite low during daytime and increases in the evening. Moreover, both morning and evening types show a progressive increase of yawning frequency in the hours preceding sleep onset, whereas they differ after the awakening. Evening-types show a higher yawning frequency that remains quite stable in the hours following the awakening, while morning-types display a decline in yawning frequency. Our findings show that the temporal distribution of yawning frequency differs between chronotypes, supporting the hypothesis that differences in sleep-wake rhythm affect yawning, which could represent a behavioural sign of sleep propensity.

Body movements during night sleep and their relationship with sleep stages are further modified in very old subjects

The night sleep of 12 healthy subjects aged 76-98 was polygraphically investigated in order to analyse body movements and their association with sleep stages at very old age; this group was compared with 11 healthy old subjects aged 61-75 years. In very old subjects sleep is less punctuated by body movements and the association of body movements with each sleep stage is further modified compared to less old subjects. Short-lasting movements emerge indifferently from stage 1, stage 2 and REM sleep, but are significantly less frequent in SWS. Furthermore, in very old subjects the probability of awakening after body movements is higher than in old subjects, suggesting that sleep is more vulnerable to the occurrence of body movements than at previous ages. The difficulty in the elderly to maintain a stable state expresses the inability to sustain and coordinate stable physiological activities characteristic of the old age. In addition, the presence of numerous awakenings, not preceded by movements, supports the hypothesis that the awakening in the very old people may be a sudden event, as should be confirmed by the study of other behavioural and physiological activities preceding awakening.

Spontaneous awakenings from sleep in the first year of life.

Spontaneous awakenings from nocturnal sleep were studied in a sample of 48 healthy infants (M = 26, F = 22), in four age groups (1 to 7 weeks, 8 to 15 weeks, 17 to 22 weeks, 25 to 54 weeks). Consistent with previous data, the number of awakenings is reported less frequently at later ages, owing to a lower frequency of awakenings out of REM sleep. Like young adults, infants in all age groups awake more often from REM than from quiet sleep (QS); this is particularly evident in the first 6 months of life, less so in the second. The duration of the bouts of wakefulness following awakenings remains stable with age. Awakenings out of QS are followed by longer periods of wakefulness than those out of REM sleep, although in older infants the duration is considerably reduced. Night sleep first shows a decrease in the number of awakenings out of REM sleep and then continues after the sixth month of life with the shortening of the wakefulness after awakenings out of QS. In the two younger groups, the distribution of the awakenings shows two main peaks and one main peak differently located during the night; a polymodal pattern appears in group 3, and is even more evident in group 4. It should be stressed that several changes as a function of age occur in the second 6 months of life, indicating this as a period of intense developmental change in sleep-wake rhythms.

Body movements during night sleep in healthy elderly subjects and their relationships with sleep stages.

In order to enlighten the profile of body movements during sleep at old age, the night sleep of twelve elderly subjects was polygraphically investigated; seven young healthy subjects were the control group. Significantly less body movements during sleep were found in the elderly compared to young subjects, meaning that the decrease in the number of body movements observed from infancy to childhood up to adulthood also continues at later ages. Differently from young adult, whose sleep body movements mainly occur in stage REM, no specific sleep state and/or stage was preferentially associated with the occurrence of body movements in the elderly. These data may point to an age-related modification in the interaction between motor cortex control and subcortical circuits. Furthermore, when body movements occur in elderly individuals, they are significantly more often followed in the next 60 s by a sleep stage change or by a spontaneous behavioural awakening. This might reflect a peculiar inability of elderly subjects to sustain stable states, and could also suggest that body movements may act as a co-factor in a process, comprising other physiological changes, leading to state shifts.

Sleep for development or development for waking ? some speculations from a human perspective

The issue of the relationship between sleep and development could be posed in the following terms: (1) does sleep have a function for development? and (2) which is the specificity of sleep function during development? Is it possible to assess critical ages of emergence and decline of specific sleep functions? The results of recent investigations related to the so-called ontogenetic hypothesis for the function of rapid eye movement (REM) sleep will be reviewed; suggestions are put forward concerning the possible role of non-rapid eye movement (NREM) sleep. Because of the difficulties to provoke long-lasting sleep deprivation in humans during development, two different approaches were used. The results of one set of analyses concerned the secretion of growth hormone during sleep under normal and pathological conditions and the relationship between sleep organization and nutritional supply utilisation in infants and children. The second approach aimed at investigating the long-term development of children suffering from sleep abnormalities at earlier ages. Furthermore, the role of dreaming during development will be discussed. The data summarized here only partly support the function of sleep during development; we would like to underscore the difficulty to dissociate the function of sleep from that of waking.

Activity patterns assessed throughout 24-hour recordings in preterm and near term infants.

The motility of 10 low-risk infants, aged between 34 and 40 weeks of postmenstrual age, has been continuously recorded for 24 h. Four codes were distinguished: code 1 (absence of motility or occasional occurrence of startles), code 2 (presence of small general or isolated body movements, startles, smiles, grimaces, and other facial activity), code 3 (forceful and prolonged general movements, startles, and stretches), code 4 (vigorous and abrupt general body movements accompanied by crying). Changes with age concern mainly the increase of the duration of code 1 (quiescence) episodes. Confrontation between day and night showed higher levels of motility during the night than during the day. The last weeks before term represent a time for increase in the ability to sustain a quiet behavior and to reorganize day-night motility distribution.

Slow wave sleep (SWS) distribution across night sleep episode in the elderly

Slow wave sleep (SWS) distribution across night sleep was shown to be different between infants and young adults. The present research aimed at studying the SWS distribution across night sleep in elderly subjects. Nine healthy elderly subjects, 61–71 years old, were submitted to nocturnal polygraphic sleep recording. Eleven young subjects, 21–23 years old, were the control group. Recordings were visually analyzed according to Rechtschaffen and Kales rules; the method proposed by Webb and Dreblow was used for scoring SWS. An NREM-REM cycle was defined as a sequence of NREM and REM sleep not interrupted by a waking period longer than 15 minutes. SWS percentage was calculated for each successive NREM episode. No significant association between SWS percentage and cycle rank was shown in elderly subjects, whereas a significant association was observed in the young ones. This kind of SWS distribution could be interpreted as reflecting the restructuring of internal organization of sleep in the elderly.