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.

Decrease of slow-wave sleep in children with prolonged absence of essential lipids intake.

Sleep measures of eight children fed by total parenteral nutrition (TPN) without essential lipids were compared to those of seven children fed by TPN receiving a daily supplementation of essential lipids. Slow wave sleep (SWS) is significantly decreased in the former group, particularly in the second half of the night, thus suggesting that lipids could be involved in sleep regulation.

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.

The thematic continuity of mental sleep experience in the same night.

It has been found that the contents of mental sleep experience (MSE) in rapid eye movement (REM) sleep are often interrelated. The aim of this study was to see whether this interrelatedness is better accounted for by the hypothesis that the mental sleep experience interrupted by provoked awakening is resumed when the subject returns to sleep (resumption), or by the hypothesis that the same contents are elaborated repeatedly throughout the night (iterative processing). We also aimed to gain some information as to the processes by which contents previously stored in memory are retrieved and inserted into the current MSE. Ten subjects were awakened 4 times on each of 4 nights after 9 min of REM sleep, and the contents of all the possible pairings of reports were scored and compared with respect to the factors "night" (same/different), "report continguity" (contiguous/noncontinguous reports), "unit interrelated" (lexical/propositional), and "interrelationship" (paradigmatic/syntagmatic). Both the occurrences and the frequencies of interrelations were greater for same night pairs than for different night pairs, but without significant differences between contiguous and noncontiguous pairs: these data provide support for the iterative processing hypothesis. The units interrelated in pairs of reports are more frequently at a lexical than a propositional level and show more paradigmatic than syntagmatic interrelationships: these data suggest that the reelaboration of contents of previous MSEs occurs mainly at a local level, making for the coherence, rather than the thematic, progression of the MSE narrative.

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.

Bizarreness effect in dream recall.

This study aimed to ascertain a) whether morning reports of dream experience more frequently reproduce bizarre contents of night reports than nonbizarre ones and b) whether this effect depends on the rarity of bizarre contents in the dream or on their richer encoding in memory. Ten subjects were awakened in rapid eye movement (REM) sleep three times per night for 4 nonconsecutive nights and asked to report their previous dream experiences. In the morning they were asked to re-report those dreams. Two separate pairs of judges scored the reports: the former identified the parts in each report with bizarre events, characters or feelings and the latter parsed each report into content units using transformational grammar criteria. By combining the data of the two analyses, content units were classified as bizarre or nonbizarre and, according to whether present in both the night and corresponding morning reports, as semantically equivalent or nonequivalent. The proportion of bizarre contents common to night and morning reports was about twice that of nonbizarre contents and was positively correlated to the quantity of bizarre contents present in the night report. These findings support the view that bizarreness enhances recall of dream contents and that this memory advantage is determined by a richer encoding at the moment of dream generation. Such a view would seem to explain why dreams in everyday life, which are typically remembered after a rather long interval, appear more markedly bizarre than those recalled in the sleep laboratory.

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.

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.

The role of slow-wave sleep on the duration of quiet sleep in infants.

The duration of quiet sleep (QS) phases has been shown to increase during the first year of life. Slow-wave sleep (SWS) appears in about half of the QS phases beyond 20 weeks. In order to evaluate the role of SWS in the lengthening of QS phase duration during the first year of life, we looked at 48 normal full-term infants (aged between 1 and 54 weeks), recorded for a whole-night period. Records included electro-encephalogram (EEG) and other polygraphic parameters. Infants were separated into two groups: (1) those who did not show SWS episodes at all, and (2) those who show both QS phases with (QS SWS+) and without (QS SWS-) SWS episodes. In group 2 the duration of QS SWS+ was longer than that of QS SWS, as well as longer than that of QS of group 1. Group 1 had a duration of QS phases similar to that of QS SWS-. The duration of QS SWS+ depended both on the SWS latency and SWS duration. The lengthening of QS phases with age is accounted for by those phases containing SWS episodes, reflecting a maturational restructuring of QS.

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.

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.

Oxygen consumption during sleep in children under continuous and cyclic nutrition.

The present study investigated the effects of two modalities of parenteral nutrition (continuous nutrition over the 24-hour period vs. cyclic nutrition, i.e., administered only during the night) on O2 consumption during sleep in children affected by severe gastrointestinal diseases. In both feeding modalities O2 consumption was always highest in REM sleep, intermediate in stage 2 and lowest in SWS. The trends during the night of O2 consumption (an increase from the second to the third part of the night) for different sleep stages were comparable in both feeding modalities. These results suggest that O2 consumption is not affected by the feeding modalities investigated, but is dependent on both sleep stages and time of night.

Accessing previous mental sleep experience in REM and NREM sleep.

This study investigated the processes by which contents previously stored in memory are retrieved and inserted into mental sleep experience (MSE). MSE reports were collected from six subjects awakened three times on each of eight nights in two alternate sequences of awakenings (NREM-REM-NREM; REM-REM-REM). The occurrences of interrelations between contents of report pairs were scored using Clark's (1970) feature matching model. These were greater for same night pairs than for different night pairs, and did not differ with respect to sequence of awakenings or order of report pairs (first-second, second-third, first-third). Contents of previous MSEs, therefore, seem to be accessible in both sleep types for insertion into current MSE. The interrelated units were more frequently lexical than propositional, with more paradigmatic than syntagmatic relationships in report pairs from both sequences of awakenings. Thus, the re-elaboration of contents of previous MSEs seems to occur mainly at the level of single contents in both types of sleep, with similar modalities of processing.

Sleep states development in the first year of life assessed through 24-h recordings.

Sleep measures have been evaluated in 13 normal infants aged between 2 weeks and 11 months 3 weeks, with 24 h polygraphic records. Values over the whole 24 h period show that quiet sleep (QS) increases with age while paradoxical sleep (PS) and ambiguous sleep (AmbS) decrease; however, when the 24 h period is split into two periods (day-time, night-time) it can be seen that QS increases only during the night-time while PS and AmbS decrease only during the day-time. The QS in older subjects becomes mainly located at the beginning of the night-time period, when particularly long phases take place. The distribution during the night-time of PS (in terms of the amount and of the mean duration of the phases) does not change with age.

24-hour behavioural states distribution in continuously fed infants.

This study compared the 24-h sleep states distribution in infants fed orally with separate meals with that in infants continuously fed from birth. Sleep was polygraphically recorded for 24 h in 12 infants (aged between 6 weeks and 14 months) continuously fed since birth through an intracaval catheter, and in 12 age-paired control infants. The amount of sleep states in each six 4-h epoch of the 24-h day was evaluated. A clear decrease of the sleep amount, concerning both Paradoxical Sleep and Quiet Sleep, was observed during the day-time in infants older than 4 months, independently from the feeding condition. This result does not support the role of feeding rhythm upon the early development of sleep pattern circadian distribution.

Long term continuously fed infants do not develop heart rate circadian rhythm.

Heart rate (HR) was studied separately for three behavioral states (waking, paradoxical sleep, quiet sleep) at four periods of the nycthemeron, in 8 infants continuously fed from birth. Continuously fed infants show no significant differences for each of the three behavioural states between the HR values of the four periods of the nycthemeron, while controls show a clear decrease during the night-time. Differences between term behavioral states exist both in continuously fed infants and in controls. Long term continuous nutrition does not allow for the establishment of the circadian modulation of HR.

Weight changes and sleep organisation in infants.

We have studied the relationship between weight changes and polygraphically recorded sleep, during a 24 hour period, of 26 infants aged between 2 and 11 months. Weight changes (in percentage within a period of 24 h) have been found to be correlated with the following sleep parameters: total amount of ambiguous sleep, percentage of time spent in cycle of the total sleep time, mean length of the cycles. We speculate that this relationship could be important when weight variations do not proceed as expected only on the basis of the clinical conditions and the caloric intake.

Developmental trend of quiet sleep is altered by early human malnutrition and recovered by nutritional rehabilitation.

Thirteen infants malnourished from birth have been recorded with polygraphic techniques continuously for 24 h. The developmental trend of Quiet Sleep was found to be altered; infants older than 4 months had a diminution of Quiet Sleep with shorter phases. Ambiguous Sleep was increased. These findings reflect the effects of malnutrition on central nervous system development and could have implications for growth and for anabolic processes. Nutritional rehabilitation performed through an intracave catheter led to an increase of Quiet Sleep and to a decrease of Ambiguous Sleep.