Sleep restriction and emotion, electroencephalography (EEG) and dream recall, and insomnia and punctuality
The impact of sleep on the quality of our lives is often referred to, but which aspect of our life is most affected? Is it our performance, or our experience of the world, or the way in which we interact with our social or non-social environment? We all, now and then or perhaps even often, blame our not-so-cheerful mood and irritability on a bad night’s sleep. The influence of our sleep on how we interact with our social environment and respond to stimuli in a non-social environment is, however, rarely investigated in a quantitative and interventional manner and hardly ever in children. In the current issue of the Journal of Sleep Research, Berger et al. (2011) present interesting data on the effects of acute sleep restriction on emotion responses in approximately 3-year-old children. The researchers restricted sleep by preventing a nap in these children. They then assessed their response to pictures with a different emotional value (e.g. a picture of an ice cream or shark) and their response to working on a solvable or non-solvable puzzle. In the no-nap conditions children expressed more negativity in response to neutral and negative stimuli and less positivity to positive images. In the puzzle task, sleep restriction led to a less positive response when solving the solvable puzzle and a more negative response during the non-solvable puzzle task. We all recognize these effects of sleep restriction. The big question is, of course, how does sleep change the brain so that we and our children can enjoy our positive experiences more and be less affected by challenging and frustrating conditions?
Dream Recall and Sleep Electroencephalography (EEG)
Waking up and recalling a vivid dream is another much-discussed and often emotional and pleasant aspect of sleep. It is likely that the brain is different during those last minutes of sleep prior to awakening with a successful dream recall compared to no dream recall, but can we actually measure this? How does the EEG during sleep differ between awakenings with and without dream recall, and does this change with age?
Chellappa et al. (2011) used a 40-h multiple nap protocol and after each nap asked young and older volunteers whether they recalled dreams. Older people recall fewer dreams, especially during daytime naps. The surprising finding of the present study is that when the EEG of naps with dream recall is compared to the EEG of naps with no dream recall, the results are very different for young and older people and especially so for non-rapid eye movement (NREM) sleep. Whereas in younger people, dream recall is associated with less delta activity during NREM sleep, in older people it is associated with more frontal delta power. Although an adequate explanation for these findings is missing, the study may lead to more research on age-related and other individual differences in dream recall and its association with EEG or other imaging approaches.
Age-Related Changes in Muscle Tone During REM Sleep
The submental electromyography (EMG) is recorded in every polysomnographic recording and used for the identification of REM sleep in particular. We look at the EMG, but we hardly ever really quantify this variable. Interest in the behaviour of the EMG during sleep and age-related changes therein has increased in recent years, not least because of REM sleep behaviour disorder and REM sleep without muscle atonia. Ferri et al. (2012) have introduced a method to quantify the EMG and in the present issue apply this method to describe changes in the muscle atonia index across the lifespan (Ferri et al., 2011). In the same subjects, they also quantify EMG-identified movements or activations. This and other EMG approaches may also be useful to describe the effects of hypnotic and other drugs that may affect muscle atonia which, after all, is a key characteristic of an important part of sleep.
Insomnia and Punctuality
To some extent, insomnia is associated with personality characteristics such as ‘perfectionism’ and ‘neuroticism‘, but few studies have attempted to quantify these associations using behaviour-based measures. Spiegelhalder et al. (2011) used punctuality as an indicator of these characteristics. Punctuality was assessed by measuring the difference between the actual and scheduled arrival time of all patients coming to a sleep clinic in Germany. On average, patients arrived 1.7 min before the scheduled time. Punctuality was then compared between primary insomnia and other sleep disorders and was also correlated with polysomnographic (PSG) measures. The punctuality data provide some support for the notion that primary insomnia patients display behavioural signs of perfectionism and neuroticism. Thus, the insomnia patients arrived approximately 4 min earlier. Furthermore, in the full sample, including all patients independent of diagnosis, punctuality correlated with several PSG measures, indicating that those who were punctual had poorer sleep. In these analyses the effects of age, sex and other potential confounders were controlled for. One wonders how the results of similar assessments of punctuality may appear in other countries. Overall, these data demonstrate that simple behaviour-based assessments of personality traits may be predictors of individual differences in sleep.
Floppy Eyelid Syndrome and Sleep Apnoea, Bruxism and Serotonin and Nocturnal Epilepsy
Other papers in this issue provide evidence for an association between floppy eyelid syndrome and sleep apnoea (Chambe et al., 2011), the association between bruxism and a polymorphism in the 5HT2A receptor in a Japanese population (Abe et al., 2012) and a demonstration of a de-novo mutation in a neuronal nicotinic acetylcholine receptor gene in a sporadic patient with nocturnal frontal lobe epilepsy (Sansoni et al., 2011). Progress in the study of the aetiology of sleep disorders goes hand-in-hand with the routine application of genetic screening tools, as well as the availability of large databases.