Looking for Synergies in Healthy Upper Limb Motion: A Focus on the Wrist.

Recent studies on human upper limb motion highlighted the benefit of dimensionality reduction techniques to extrapolate informative joint patterns. These techniques can simplify the description of upper limb kinematics in physiological conditions, serving as a baseline for the objective assessment of movement alterations, or to be implemented in a robotic joint. However, the successful description of kinematic data requires a proper alignment of the acquisitions to correctly estimate kinematic patterns and their motion variability. Here, we propose a structured methodology to process and analyze upper limb kinematic data, considering time warping and task segmentation to register task execution on a common normalized completion time axis. Functional principal component analysis (fPCA) was used to extract patterns of motion of the wrist joint from the data collected by healthy participants performing activities of daily living. Our results suggest that wrist trajectories can be described as a linear combination of few functional principal components (fPCs). In fact, three fPCs explained more than 85% of the variance of any task. Wrist trajectories in the reaching phase of movement were highly correlated among participants and significantly more than trajectories in the manipulation phase ( [Formula: see text]). These findings may be useful in simplifying the control and design of robotic wrists, and could aid the development of therapies for the early detection of pathological conditions.

A biphasic daily pattern of slow wave activity during a two-day 90-minute sleep wake schedule.

Twenty-four hour sleep patterns were measured in six healthy male volunteers during a 90-minute short sleep-wake (SW 30:60) cycle protocol for 48 hours. Sleep pressure estimates (amount of Slow Wave Sleep [SWS], SWA, and Rate of Synchronization [RoS: the rate of SWA build-up at the beginning of the NREM period]) were compared with the 24-hour patterns of body temperature (Tb24) and sleep propensity. A moderate sleep debt was incurred over the 48 hour study as indicated by decreased levels of 24 hour sleep. On day 1, ultradian patterns of REM and SWS sleep were prominent; on day 2, more prominent were circadian patterns of REM sleep, SWS, Sleep Latency, TST and Tb24. Also on Day 2, biphasic patterns of SWA and RoS were expressed, with peaks occurring during the falling and rising limbs of Tb24. The biphasic peaks in SWA and RoS may be associated with phase-specific interactions of the circadian pacemaker with the sleep homeostat during conditions of moderate sleep pressure. Further research is needed to replicate the finding and to identify biological factors that may underlie the twelve hour pattern in SWA.

Rapid eye movement activity before spontaneous awakening in elderly subjects.

Previous research in young subjects found that rapid eye movement (REM) density is higher in those REM phases which are followed by an awakening (REM-W) than in those preceding NREM (REM-N), suggesting a 'gating role' of REM sleep toward the awakening. It is not yet known whether this evidence is maintained in elderly subjects, who display, relative to young subjects, more awakenings, different sleep states from which the awakenings come (NREM in a high proportion of cases) and a general impairment of rapid eye movement activity (REMA). To investigate this issue, we have compared in three different age groups (young, old and 'old old' subjects) the features of REMA, including REM density and the amount and duration of REM bursts, between REM-W and REM-N. Whereas in the young REM density is higher in REM-W than in REM-N, this difference is already reduced in the old group and fully cancelled in the old old subjects. The evidence that old individuals spontaneously wake up despite the absence of an increase of REMA could imply that in the aged awakening is not preceded by an increase of the arousal level (expressed in REM sleep by the REMA). The similar duration of REM bursts for REM-W and REM-N in both groups of old subjects suggests that with age a marked impairment occurs in the organizational aspects of REMs, independently from the following state.

Preterm infants prefer to be awake at night.

Wakefulness distribution during a 24-h period was studied in ten low-risk preterm and near term infants through video-recording. The highest amount of wakefulness was found in the night-time period between 02:00 and 05:00 h. This result is different from what was observed in infants during the first year of life, and similar to what was found in the foetus.

Polygraphic investigation of 24-h waking distribution in infants.

An evening forbidden zone for sleep has been shown for adults. This research was aimed to ascertain the prevalence of waking in the evening in early development. Twelve infants, aged between 2 weeks and 11 months 3 weeks, were each recorded once over a 24-h period. Recordings included EEG, EOG, EMG, respiration, ECG, and behavioural observation. Four states were defined by combining behavioural and electrophysiological data. Wakefulness was defined by the presence of eyes open, eye movements and additionally body movements, and irregular respiration. In infants younger than 12 months and a half, a greater amount of wakefulness was observed in the time interval between 17 and 20. Older infants show uniform high amount of wakefulness during daytime. Our data corroborate the hypothesis that evening hours are those most frequently characterised by the behavioural waking state, suggesting that a forbidden zone for sleep exists in development and that its time placement corresponds to the one observed in the adult.

Dynamics of electroencephalographic slow wave activity and body temperature during monophasic and biphasic human sleep.

Dynamics of electroencephalographic (EEG) slow wave activity (0.5-4.5 Hz) and body temperature, as estimates, respectively, of the process S and process C, regulating sleep and waking alternate occurrence, were measured during monophasic and biphasic sleep patterns that occurred spontaneously in a 35-year-old woman who lived for 105 days in a winter-type photoperiod (10-14 h light-dark). In monophasic nights, rate of EEG synchronization showed a decreasing trend across the first three non-rapid eye movement (NREM) periods. In biphasic nights, rate of EEG synchronization increased during the third NREM period which precedes the nocturnal awakening. Temperature cycle was not different between biphasic and monophasic nights. Those results confirm that EEG dynamics reflects homeostatic sleep regulatory mechanism, and suggest that the period of prolonged wakefulness in the middle of biphasic night is pre-programmed.

Active processing of declarative knowledge during REM-sleep dreaming.

The ability to process recently acquired knowledge is clearly maintained during sleep. Here we assess whether and how far the sleeper controls this processing (in a non-volitional and non-conscious manner). We posit that during sleep, the cognitive concerns of previous waking may guide access to, and processing of, items of declarative knowledge with which those concerns are associated. In a delayed recall task, before each of three sleep onsets in the same night, 12 subjects heard a different nonsense sentence. When awakened in rapid eye movement (REM) sleep, they were asked to report their dream experience and to recall the last sentence heard. Occurrences of incorporation into dream content were more frequent for this sentence than for the sentences heard before previous sleep onsets, and also more frequent than occurrences of similar contents in reports from a control night. However, the modalities of elaboration of dream contents did not vary. These findings indicate that cognitive concern can affect the accessing of recently acquired declarative knowledge during sleep, but not the modalities by which this is inserted into dream content. They also suggest that cognitive concern may help consolidate knowledge by increasing the likelihood of it being processed during sleep.

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. A greater proportion of time spent in cycles (TCT) on total sleep time (TST), as a result of the lengthening of sleep cycles, was found in older infants, whereas sleep out of cycles decreases with age. The internal structure of the sleep cycles also changes with age, because of the increase in the proportion of quiet sleep (QS), the appearance of slow wave sleep (SWS) from the 21st week onwards, and the decrease in ambiguous sleep. The proportion of paradoxical sleep (PS), however, remains stable throughout the first year of age. The improvement of sleep organization across the first year of life is paralleled by an internal restructuring of the cycle, involving mainly changes in QS. We may speculate that both changes, one involving the lengthening of cycle and the other involving the increase in QS component, contribute to the improvement of biological and psychological sleep functions during development.

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.

Delta (0.5-1.5 Hz) and sigma (11.5-15.5 Hz) EEG power dynamics throughout quiet sleep in malnourished infants.

The present study aimed to quantify, through power spectral analysis, the dynamics (temporal pattern and temporal interrelationship) of the EEG power in the low-delta (delta) and in the sigma-spindle (sigma) frequency band during quiet sleep (QS) in 5 malnourished infants (MI), 5.5 to 13.5 months old, and in 5 age-matched, healthy control infants (CI). Malnutrition results in modification of the temporal pattern of delta and sigma band power during QS. The delta band power increases faster in MI than in CI, leading to higher power levels in MI at the same time segment. However, the overall trend of the delta band power throughout QS is similar in MI and CI. The premature ending of QS phases (uninterrupted QS periods), and the reduced total amount of QS which have been reported in MI could result in an increased slow wave sleep (SWS) "pressure". This SWS pressure could account for both the higher level and the faster increase of the delta band power during the QS phase which are found in MI when compared to CI.

Sleep stages preceding spontaneous awakenings in the elderly.

Spontaneous awakenings from sleep were studied in a group of 21 elderly subjects (mean age 69.29+/-3.02 years) free of neurological and somatic diseases. The prevalence of awakenings and the duration of waking bouts were analyzed with regard to the prior sleep state. The results showed an increased frequency of awakenings during Stage 2 NREM in the elderly, who wake out of Stage 2 NREM no less frequently than out of REM sleep. This trend is different from that observed in younger subjects (babies and young adults), where a clear prevalence of REM sleep awakenings has been reported. The duration of Stage 2 interrupted by awakening was shorter than Stage 2 followed by sleep. The duration of waking bouts did not differ according to the preceding sleep stage. It is suggested that the relative inability to sustain Stage 2 may be a mechanism which contributes to the difficulty of sleep maintenance in the elderly.

Prior spontaneous nocturnal waking duration and EEG during quiet sleep in infants: an automatic analysis approach.

To ascertain the role of spontaneous nocturnal waking duration on the EEG dynamics during quiet sleep (QS) periods, we analysed the nocturnal polygraphic recordings of 12 infants aged 9 47 weeks old. Their sleep was characterised by two sleep episodes, separated by spontaneous waking and containing at least two QS-paradoxical sleep (PS) cycles each. Automatic analysis of the EEG activity recorded by the centro-occipital lead and reflecting the degree of synchronisation allowed us to compute a parameter whose values ranged from 0 (maximum of EEG synchronisation) to 10 (maximum of EEG de-synchronisation). Three indicators of the time course of the parameter value were computed during the first QS period of the sleep episode subsequent to nocturnal waking: (i) the parameter range (difference between the EEG parameter value at the QS onset and that at the trough-maximum of EEG synchronisation); (ii) the trough latency (time interval between QS onset and trough); and (iii) rate of synchronisation (range/trough latency). These three indicators were the dependent variables in a multiple regression model, where the independent variables were age and the logarithm of the duration of prior waking. The parameter range was correlated with the duration of prior waking. Both the trough latency and the rate of synchronisation were correlated with age only, respectively, positively and negatively. The marked decline in the rate of synchronisation throughout the first year of life could account for the failure to find a significant correlation between prior waking and the above indicator of the EEG dynamics. The relationship between the duration of prior waking and the parameter range in following sleep in infants supports the hypothesis of the early emergence of the homeostatic regulation of sleep.

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.

Dynamics of EEG background activity level during quiet sleep in multiple nocturnal sleep episodes in infants.

The study reported in this paper investigated the dynamics of EEG background activity during quiet sleep (QS) in the first year of life. These dynamics have been previously shown to follow an intra-sleep trend within a single sleep episode, and the aim of this study was to show whether they were similar in two successive nocturnal sleep episodes interrupted by a waking episode, or whether they exhibited a progressive trend across the two episodes. The polygraphic recordings of two groups of 6 infants aged from 9 to 15 weeks old and from 25 to 47 weeks old, whose nocturnal sleep organisation was spontaneously interrupted, were selected. Three indicators of the time course of the parameter value, obtained from automatic analysis and reflecting the degree of synchronisation of the EEG activity recorded by the centro-occipital lead, were computed for the first two QS periods of two successive sleep episodes: the parameter range (difference between the EEG parameter value at the QS onset and that at the trough); the trough latency (time interval between QS onset and trough); and rate of synchronisation (range/trough latency). All 3 indicators differed between the first and the second QS period of both sleep episodes independently of age. The rate of synchronisation (but not the parameter range and the trough latency) was higher in the first sleep episode than in the second one, showing an over-night decreasing trend. Those results show that, when nocturnal sleep in infants is split into two episodes separated by an intervening waking, also the second sleep episode displays an internal organisation of its EEG dynamics. Moreover, an across-night trend in the rate of synchronisation can be observed from an early age, a finding which suggests, again, the early emergence of homeostatic regulation of sleep.

Delta (0.5-1.5 Hz) and sigma (11.5-15.5 Hz) EEG power dynamics throughout quiet sleep in infants.

Twenty-eight healthy infants, split into 3 groups according to age (group 1: 2-6 weeks, n = 10; group 2: 7-14 weeks, n = 10; and group 3: 4-12 months, n = 8), were recorded during the whole night. For each infant, the longest quiet sleep (QS) phase occurring between 8 p.m. and midnight was selected for EEG power spectral analysis. The power in the frequency band related to low-frequency delta waves (0.5-1.5 Hz, "delta band") and the power in the frequency band related to sigma spindles (11.5-15.5 Hz, "sigma band") were analyzed. Group 1 infants showed no significant modification of the power in the sigma band in the course of the QS phase; the power in the delta band showed a significant increase between the second and the third 5 min segment and a decrease thereafter. Group 2 infants showed a progressive reduction of the power in the sigma band, whereas the power in the delta band increased during the first 15 min. In group 3 infants, the sigma band power significantly decreased between the third and the fifth 5 min segment without further changes. The power in the delta band, on the contrary, increased progressively for the first 20 min and showed a second progressive increase beyond 35 min. For both group 2 and group 3 infants, it appeared that the change in delta power preceded the change in sigma power. The above results provide quantitative evidence that a well-defined temporal inhomogeneity pattern in the EEG of the QS phase may appear between 7 and 14 weeks of age and continues from the fourth month on.

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.

Dynamics of EEG background activity level within quiet sleep in successive cycles in infants.

We investigated in infants the emergence of the trends of the EEG synchronization throughout quiet sleep (QS) as a function of the QS rank. The night sleep of 3 groups with 6 subjects each (aged respectively 9-18 weeks, 21-47 weeks, and 16-45 years) was recorded. A parameter value reflecting the degree of synchronization of the EEG background activity for successive epochs was computed by automatic analysis. For each QS phase 3 indicators of the dynamics of the time course of the EEG parameter activity were determined: the range (difference between the EEG parameter value at the beginning of the QS episode and that at the trough), the trough latency (after QS onset), and the rate of synchronization (range/trough latency). The range and the trough latency increased with age, whereas the rate of synchronization decreased. The range and the rate of synchronization decreased in the successive cycles, whereas the trough latency increased. These results provide further support for the hypothesis of the early emergence of the process S mechanisms and suggest that the framework of the 2-process model could account also for the development of both the EEG background activity dynamics and the sleep-wake organization.

Electromyographic activity and sleep states in infants.

The electromyographic (EMG) activity in infants was studied in relationship to sleep states and age using an automatic method. One night of sleep in 23, healthy, full-term infants was recorded. Based on 10-second measures of chin EMG activity, two parameters were derived: 1) the tonic EMG and 2) the EMG instability (corresponding to phasic events). Age comparisons were made between young (2-11 weeks) and older infants (21-47 weeks) and between two subgroups of young infants (2-3 weeks and 7-11 weeks). State comparisons were made between paradoxical sleep (PS) and quiet sleep (QS) and, for the older infants, between QS with and without slow-wave sleep. QS tonic level did not differ either between age groups or between QS+ and QS- phases. The EMG instability was larger in PS than in QS for all age groups, and larger in the young than in the older infants, although within the group of young infants no differences between age subgroups were found.

Trends in electroencephalographic synchronization across nonrapid eye movement sleep in infants.

The trend of synchronized (high-voltage, low-frequency) electroencephalographic (EEG) activity was determined across nonrapid eye movement (NREM) sleep periods of night sleep in two groups of infants (eight "young infants", age 2-19 weeks; eight "older infants", age 21-54 weeks) and, a reference, in a group of eight adults (age 16-45 years). By automatic analysis of the sleep EEG, a parameter was derived that represents the degree of synchronized (high-amplitude, low-frequency) EEG activity for successive 30-second epochs. For each subject, the average level of EEG synchronization for each NREM period and the time of the NREM period midpoints were determined. In all three groups, synchronized EEG activity tended to decrease across successive NREM periods. This trend was weaker for infants than for adults and, surprisingly, weaker for older than for young infants. This suggests that the decreasing trend typical for adults is already present in the first months after birth. The difference in trend between infants and adults may be caused by differences in the 24-hour sleep-wakefulness distribution, whereas the distinction between young and older infants could be related to a restructuring of sleep in the second semester, in particular to the emergence of slow-wave sleep and its peculiar distribution across NREM periods of night sleep.