Kerstin Hoedlmoser

Slow sleep spindle activity, declarative memory, and general cognitive abilities in children.

STUDY OBJECTIVES Functional interactions between sleep spindle activity, declarative memory consolidation, and general cognitive abilities in school-aged children. DESIGN Healthy, prepubertal children (n = 63; mean age 9.56 ± 0.76 y); ambulatory all-night polysomnography (2 nights); investigating the effect of prior learning (word pair association task; experimental night) versus nonlearning (baseline night) on sleep spindle activity; general cognitive abilities assessed using the Wechsler Intelligence Scale for Children-IV (WISC-IV). MEASUREMENTS AND RESULTS Analysis of spindle activity during nonrapid eye movement sleep (N2 and N3) evidenced predominant peaks in the slow (11-13 Hz) but not in the fast (13-15 Hz) sleep spindle frequency range (baseline and experimental night). Analyses were restricted to slow sleep spindles. Changes in spindle activity from the baseline to the experimental night were not associated with the overnight change in the number of recalled words reflecting declarative memory consolidation. Children with higher sleep spindle activity as measured at frontal, central, parietal, and occipital sites during both baseline and experimental nights exhibited higher general cognitive abilities (WISC-IV) and declarative learning efficiency (i.e., number of recalled words before and after sleep). CONCLUSIONS Slow sleep spindles (11-13 Hz) in children age 8-11 y are associated with inter-individual differences in general cognitive abilities and learning efficiency.

Consolidation of temporal order in episodic memories.

Highlights ► Performance in temporal order memory deteriorates with sleep deprivation. ► REM early in the night is associated with delayed temporal order recall. ► Participants who improve during sleep overnight show more fast spindle activity. ► Spindle-related alpha power at frontal locations may indicate “offline” memory access. ► Distinct sleep mechanisms subserve different aspects of episodic memory consolidation.

Event-related activity and phase locking during a psychomotor vigilance task over the course of sleep deprivation

There is profound knowledge that sleep restriction increases tonic (event‐unrelated) electroencephalographic (EEG) activity. In the present study we focused on time‐locked activity by means of phasic (event‐related) EEG analysis during a psychomotor vigilance task (PVT) over the course of sleep deprivation. Twenty healthy subjects (10 male; mean age ± SD: 23.45 ± 1.97 years) underwent sleep deprivation for 24 h. Subjects had to rate their sleepiness hourly (Karolinska Sleepiness Scale) and to perform a PVT while EEG was recorded simultaneously. Tonic EEG changes in the δ (1–4 Hz), θ (4–8 Hz) and α (8–12 Hz) frequency range were investigated by power spectral analyses. Single‐trial (phase‐locking index, PLI) and event‐related potential (ERP) analyses (P1, N1) were used to examine event‐related changes in EEG activity. Subjective sleepiness, PVT reaction times and tonic EEG activity (delta and theta spectral power) significantly increased over the night. In contrast, event‐related EEG parameters decreased throughout sleep deprivation. Specifically, the ERP component P1 diminished in amplitude, and delta and theta PLI estimates decreased progressively over the night. It is suggested that event‐related EEG measures (such as the amplitude of the P1 and especially delta/theta phase‐locking) serve as a complimentary method to track the deterioration of attention and performance during sleep loss. As these measures actually reflect the impaired response to specific events rather than tonic changes during sleep deprivation they are a promising tool for future sleep research.

Susceptibility to declarative memory interference is pronounced in primary insomnia.

Sleep has been shown to stabilize memory traces and to protect against competing interference in both the procedural and declarative memory domain. Here, we focused on an interference learning paradigm by testing patients with primary insomnia (N = 27) and healthy control subjects (N = 21). In two separate experimental nights with full polysomnography it was revealed that after morning interference procedural memory performance (using a finger tapping task) was not impaired in insomnia patients while declarative memory (word pair association) was decreased following interference. More specifically, we demonstrate robust associations of central sleep spindles (in N3) with motor memory susceptibility to interference as well as (cortically more widespread) fast spindle associations with declarative memory susceptibility. In general the results suggest that insufficient sleep quality does not necessarily show up in worse overnight consolidation in insomnia but may only become evident (in the declarative memory domain) when interference is imposed.

Sleeping on the motor engram: The multifaceted nature of sleep-related motor memory consolidation

HIGHLIGHTSSleep‐related motor memory consolidation depends on multiple boundary conditions.Sleep consolidates explicit, abstract and complex motor sequence information.Sleep consolidates hippocampal‐mediated motor sequence memory traces.Sleep spindles and slow waves are crucial for motor sequence memory consolidation.Sleep can be manipulated to optimize motor sequence memory consolidation. ABSTRACT For the past two decades, it has generally been accepted that sleep benefits motor memory consolidation processes. This notion, however, has been challenged by recent studies and thus the sleep and motor memory story is equivocal. Currently, and in contrast to the declarative memory domain, a comprehensive overview and synthesis of the effects of post‐learning sleep on the behavioral and neural correlates of motor memory consolidation is not available. We therefore provide an extensive review of the literature in order to highlight that sleep‐dependent motor memory consolidation depends upon multiple boundary conditions, including particular features of the motor task, the recruitment of relevant neural substrates (and the hippocampus in particular), as well as the specific architecture of the intervening sleep period (specifically, sleep spindle and slow wave activity). For our field to continue to advance, future research must consider the multifaceted nature of sleep‐related motor memory consolidation.

The impact of diurnal sleep on the consolidation of a complex gross motor adaptation task

Diurnal sleep effects on consolidation of a complex, ecological valid gross motor adaptation task were examined using a bicycle with an inverse steering device. We tested 24 male subjects aged between 20 and 29 years using a between‐subjects design. Participants were trained to adapt to the inverse steering bicycle during 45 min. Performance was tested before (TEST1) and after (TEST2) training, as well as after a 2 h retention interval (TEST3). During retention, participants either slept or remained awake. To assess gross motor performance, subjects had to ride the inverse steering bicycle 3 × 30 m straight‐line and 3 × 30 m through a slalom. Beyond riding time, we sophisticatedly measured performance accuracy (standard deviation of steering angle) in both conditions using a rotatory potentiometer. A significant decrease of accuracy during straight‐line riding after nap and wakefulness was shown. Accuracy during slalom riding remained stable after wakefulness but was reduced after sleep. We found that the duration of rapid eye movement sleep as well as sleep spindle activity are negatively related with gross motor performance changes over sleep. Together these findings suggest that the consolidation of adaptation to a new steering device does not benefit from a 2 h midday nap. We speculate that in case of strongly overlearned motor patterns such as normal cycling, diurnal sleep spindles and rapid eye movement sleep might even help to protect everyday needed skills, and to rapidly forget newly acquired, interfering and irrelevant material.

Oscillatory brain responses to own names uttered by unfamiliar and familiar voices

Among auditory stimuli, the own name is one of the most powerful and it is able to automatically capture attention and elicit a robust electrophysiological response. The subject’s own name (SON) is preferentially processed in the right hemisphere, mainly because of its self-relevance and emotional content, together with other personally relevant information such as the voice of a familiar person. Whether emotional and self-relevant information are able to attract attention and can be, in future, introduced in clinical studies remains unclear. In the present study we used EEG and asked participants to count a target name (active condition) or to just listen to the SON or other unfamiliar names uttered by a familiar or unfamiliar voice (passive condition). Data reveals that the target name elicits a strong alpha event related desynchronization with respect to non-target names and triggers in addition a left lateralized theta synchronization as well as delta synchronization. In the passive condition alpha desynchronization was observed for familiar voice and SON stimuli in the right hemisphere. Altogether we speculate that participants engage additional attentional resources when counting a target name or when listening to personally relevant stimuli which is indexed by alpha desynchronization whereas left lateralized theta synchronization may be related to verbal working memory load. After validating the present protocol in healthy volunteers it is suggested to move one step further and apply the protocol to patients with disorders of consciousness in which the degree of residual cognitive processing and self-awareness is still insufficiently understood.

Better than sham? A double-blind placebo-controlled neurofeedback study in primary insomnia

See Thibault et al. (doi:10.1093/awx033) for a scientific commentary on this article. Neurofeedback has been claimed to have therapeutic efficacy in multiple disorders. In a double-blind, placebo-controlled trial in insomnia, Schabus et al. report that sensorimotor rhythm neurofeedback (12–15 Hz) neither changes the EEG nor objectively improves sleep. While patients do report subjective improvements, these do not differ from those seen with placebo feedback.

Slow Oscillation Amplitudes and Up-State Lengths Relate to Memory Improvement

There is growing evidence of the active involvement of sleep in memory consolidation. Besides hippocampal sharp wave-ripple complexes and sleep spindles, slow oscillations appear to play a key role in the process of sleep-associated memory consolidation. Furthermore, slow oscillation amplitude and spectral power increase during the night after learning declarative and procedural memory tasks. However, it is unresolved whether learning-induced changes specifically alter characteristics of individual slow oscillations, such as the slow oscillation up-state length and amplitude, which are believed to be important for neuronal replay. 24 subjects (12 men) aged between 20 and 30 years participated in a randomized, within-subject, multicenter study. Subjects slept on three occasions for a whole night in the sleep laboratory with full polysomnography. Whereas the first night only served for adaptation purposes, the two remaining nights were preceded by a declarative word-pair task or by a non-learning control task. Slow oscillations were detected in non-rapid eye movement sleep over electrode Fz. Results indicate positive correlations between the length of the up-state as well as the amplitude of both slow oscillation phases and changes in memory performance from pre to post sleep. We speculate that the prolonged slow oscillation up-state length might extend the timeframe for the transfer of initial hippocampal to long-term cortical memory representations, whereas the increase in slow oscillation amplitudes possibly reflects changes in the net synaptic strength of cortical networks.

Oscillatory theta activity during memory formation and its impact on overnight consolidation: A missing link?

Sleep has been shown to promote memory consolidation driven by certain oscillatory patterns, such as sleep spindles. However, sleep does not consolidate all newly encoded information uniformly but rather “selects” certain memories for consolidation. It is assumed that such selection depends on salience tags attached to the new memories before sleep. However, little is known about the underlying neuronal processes reflecting presleep memory tagging. The current study sought to address the question of whether event-related changes in spectral theta power (theta ERSP) during presleep memory formation could reflect memory tagging that influences subsequent consolidation during sleep. Twenty-four participants memorized 160 word pairs before sleep; in a separate laboratory visit, they performed a nonlearning control task. Memory performance was tested twice, directly before and after 8 hr of sleep. Results indicate that participants who improved their memory performance overnight displayed stronger theta ERSP during the memory task in comparison with the control task. They also displayed stronger memory task-related increases in fast sleep spindle activity. Furthermore, presleep theta activity was directly linked to fast sleep spindle activity, indicating that processes during memory formation might indeed reflect memory tagging that influences subsequent consolidation during sleep. Interestingly, our results further indicate that the suggested relation between sleep spindles and overnight performance change is not as direct as once believed. Rather, it appears to be mediated by processes beginning during presleep memory formation. We conclude that theta ERSP during presleep memory formation reflects cortico-hippocampal interactions that lead to a better long-term accessibility by tagging memories for sleep spindle-related reprocessing.