Biomedical subjects
Publications and source records attributed to Robert Stickgold.
The development of mathematical insight, the knack for discovering novel solutions to mathematical problems, might be one of the most erudite forms of learning that we can hope to achieve. However, Wagner and his colleague now report that a night of sleep after being exposed to a class of mathematical problems more than doubles the likelihood of discovering just such a novel solution.
A precipitous decline in eyelid movements (ELMs) has been shown to be a highly reliable indicator of sleep onset. While ELMs correlate well with eye movements during waking and rapid eye movement (REM) sleep, the eye sensor remains silent during the period of slow eye movements (SEMs) typical of sleep onset. If the ELM density (e.g. ELMs per minute) dropped simultaneously with the appearance of SEMs prior to sleep onset, it could be a promising tool for identifying decreases in alertness prior to overt sleep onset. The present study was designed to determine whether the presence of SEMs in the transitional period preceding stage 1 sleep is reflected in decreases in ELM density. ELM densities were computed for 2.5-s epochs with and without SEMs, as well as for 15-s epochs. Decreases in ELM density not only were an excellent correlate of the appearance of SEMs during wakefulness with closed eyes, but also a good predictor of their occurrence (c. 82% accuracy) at a time resolution of 2.5 s. Based on these results, we conclude that ELM density reliably predicts moderate changes in the level of alertness during quiet wakefulness.
The authors report the occurrence of visual hallucinations of varying complexity in 13 normal subjects after sudden, complete, and prolonged visual deprivation. The subjects were all healthy individuals with no history of cognitive dysfunction, psychosis, or ocular pathology. They wore a specially designed blindfold for a period of five consecutive days (96 hours) and were asked to record their daily experiences using a hand-held microcassette recorder. Ten (77%) of the subjects reported visual hallucinations, which were both simple (bright spots of light) and complex (faces, landscapes, ornate objects). The onset of hallucinations was generally after the first day of blindfolding. Subjects were insightful as to their unreal nature. These results indicate that rapid and complete visual deprivation is sufficient to induce visual hallucinations in normal subjects.
Internal deliberations (focused thoughts) and endogenous percepts (hallucinations) vary in a reciprocal manner across the states of waking and sleep, paralleling changes in regional brain activation. As subjects go from waking through sleep onset to NREM sleep and then to REM sleep, they report progressively more hallucinoid imagery and progressively less thinking. We have investigated whether this reciprocity in cognition between NREM and REM is maintained throughout the night. To do so, we analyzed 229 REM and 165 NREM reports collected with the Nightcap sleep monitoring system from 16 participants in their homes over 14 nights. The reports were scored for the presence of hallucinations and directed thinking by external judges. As predicted, hallucinations were more frequent in REM than in NREM for each segment of the night, and directed thinking was more frequent in NREM in the first 5 h of the night. Late in the night, directed thinking was equally infrequent in NREM and REM. At the same time, hallucinations increased within both NREM and REM as the night progressed, whereas directed thinking decreased in NREM and remained at a stable, low level in REM. These findings suggest that a reciprocal shift in focused thinking and hallucinating is a general property of cognitive activity across the wake-sleep cycle. Biological evidence supports the hypothesis that these cognitive changes are governed by specific state regulatory and neurocognitive processes at several levels of the brain.
Hippocampal theta waves recorded during rapid eye movement (REM) sleep are thought to play a critical role in memory consolidation in lower mammals, but previous attempts to detect similar theta oscillations in the human hippocampus have been unsuccessful. Using subdural and depth recordings from epileptic patients, we now report the first evidence of state-dependent hippocampal theta waves (4-7 Hz) in humans. Unlike the continuous theta in rodents, however, these oscillations were consistently observed during REM sleep in short (approximately 1 sec) bursts and during transitions to wake in longer epochs. Theta waves were also observed in the basal temporal lobe and frontal cortex during transitions from sleep to wake and in quiet wakefulness but not in REM, and they were not coherent with hippocampal theta oscillations. The absence of functional coupling between neocortex and hippocampus during theta periods indicates that multiple theta generators exist in the human brain, and that they are dynamically regulated by brain state. Gamma oscillations were also present during REM theta bursts, but the fluctuations in gamma power were not associated with theta phase, pointing out another significant difference between rodent and human theta properties. Together, these findings suggest that the generation mechanisms of theta oscillations in humans might have evolved from tonic to phasic in hippocampus during REM sleep and extended from hippocampus to cortex, where they appear in certain wakefulness-related states.
Historically, the term 'memory consolidation' refers to a process whereby a memory becomes increasingly resistant to interference from competing or disrupting factors with the continued passage of time. Recent findings regarding the learning of skilled sensory and motor tasks ('procedural learning') have refined this definition, suggesting that consolidation can be more strictly determined by time spent in specific brain states such as wake, sleep or certain stages of sleep. There is also renewed interest in the possibility that recalling or 'reactivating' a previously consolidated memory renders it once again fragile and susceptible to interference, therefore requiring periods of reconsolidation. Using a motor skill finger-tapping task, here we provide evidence for at least three different stages of human motor memory processing after initial acquisition. We describe the unique contributions of wake and sleep in the development of different forms of consolidation, and show that waking reactivation can turn a previously consolidated memory back into a labile state requiring subsequent reconsolidation.
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The learning of perceptual skills has been shown in some cases to depend on the plasticity of the visual cortex and to require post-training nocturnal sleep. We now report that sleep-dependent learning of a texture discrimination task can be accomplished in humans by brief (60- 90 min) naps containing both slow-wave sleep (SWS) and rapid eye movement (REM) sleep. This nap-dependent learning closely resembled that previously reported for an 8-h night of sleep in terms of magnitude, sleep-stage dependency and retinotopic specificity, and it was additive to subsequent sleep-dependent improvement, such that performance over 24 h showed as much learning as is normally seen after twice that length of time. Thus, from the perspective of behavioral improvement, a nap is as good as a night of sleep for learning on this perceptual task.
This study examines the individual reproducibility of alterations of subjective, objective, and EEG measures of alertness during 27 h of continuous wakefulness and analyzes their interrelationships. Eight subjects were studied twice under similar constant-routine conditions. Scales and performance tasks were administered at hourly intervals to define temporal changes in subjective and objective alertness. The wake EEG was recorded every 2 h, 2 min with eyes open and 2 min with eyes closed. Plasma glucose and melatonin levels were measured to estimate brain glucose utilization and individual circadian phase, respectively. Decrements of subjective alertness and performance deficits were found to be highly reproducible for a given individual. Remarkably, there was no relationship between the impairments of subjective and objective alertness. With increased duration of wakefulness, EEG activity with eyes closed increased in the delta range and decreased in the alpha range, but the magnitudes of these changes were also unrelated. These findings indicate that sleep deprivation has highly reproducible, but independent, effects on brain mechanisms controlling subjective and objective alertness.
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STUDY OBJECTIVES: To describe emotional experience during sleep-onset rapid-eye-movement [(REM) SOREM] sleep and nighttime REM in narcoleptic patients and to relate any differences in REM emotion to the more general abnormalities of this disorder. DESIGN: Awakenings were performed from SOREM (REM at the onset of daytime naps and nighttime sleep) and nighttime emergent (ascending) REM in 15 patients with narcolepsy and from nighttime REM in 9 normal healthy participants. Subjects rated the occurrence and intensity of discrete emotion types for each line in their REM-mentation reports. Fragmentation of REM was measured and related to emoton. SETTING: Subjects were studied in their own homes over 2 consecutive days and nights (3 nights for normals) and were monitored by ambulatory polysomnography. PARTICIPANTS: Fifteen patients with narcolepsy, aged 17 to 70 years (mean = 45.3) and 9 normal healthy subjects, aged 31 to 60 years (mean = 43.0). RESULTS: Emotions were found more often and were more intense in narcoleptic SOREM than in nighttime REM of either narcoleptic or normal subjects, with anxiety/fear exhibiting the strongest increase, followed by joy/elation. Comparing nighttime REM in narcoleptic and normal subjects, narcoleptics were found to have more intense feelings of anxiety/fear and of joy/elation but to have a less frequent experience of surprise and anger. Positive and negative emotions occurred in a balanced fashion in SOREM and nighttime REM in narcoleptic subjects. In the SOREM of narcoleptic patients, high levels of positive emotions, in particular of joy/elation, were associated with a less fragmented (more stable) REM sleep. CONCLUSION: The REM sleep of patients with narcolepsy affords a unique opportunity to study emotion and to analyze its psychophysiology. Narcolepsy intensifies REM-dream emotion, especially anxiety/fear and joy/elation, and this is most clearly seen during SOREM sleep. The changes in REM emotion of narcoleptic patients could reflect the effect of the fundamental pathology of this disorder upon neurobiologic systems that support cognitive-emotional functions.
Improvement in motor skill performance is known to continue for at least 24 hr following training, yet the relative contributions of time spent awake and asleep are unknown. Here we provide evidence that a night of sleep results in a 20% increase in motor speed without loss of accuracy, while an equivalent period of time during wake provides no significant benefit. Furthermore, a significant correlation exists between the improved performance overnight and the amount of stage 2 NREM sleep, particularly late in the night. This finding of sleep-dependent motor skill improvement may have important implications for the efficient learning of all skilled actions in humans.
Previous studies have demonstrated that the Nightcap home-based sleep-monitoring system can differentiate waking, NREM and REM sleep based on eyelid movements (ELMs) and head movement behavior. The present study aims at determining the reliability of the Nightcap in determining the human sleep onset latency (SOL) as revealed by standard polysomnography (PSG). Four naps were recorded in each of ten normal subjects using both PSG and the Nightcap simultaneously. The Nightcap algorithm scored sleep onset as the first of 4 consecutive 30-sec epochs with less than 5 ELMs. The mean percentage of agreement between the Nightcap and PSG was 93% (k = 0.79), and the average absolute difference was 45 sec (13.3% of SOL(PSG)). SOL(NC) differed by less than 1 min in 85% of onsets. Recordings of EEG activity from 90 sec before and after PSG-identified sleep onsets were subjected to spectral analysis. Changes in spectral power in the theta (4-7 Hz) and alpha (8-12 Hz) frequency bands during the transition into light sleep correlated well with eyelid behavior. However, changes in ELM density predicted sleep onset better than did changes in theta and alpha spectral power. These results suggest that the Nightcap may be a potential alternative to the PSG technique in the assessment of SOL in normal subjects.
Numerous studies have provided evidence for the efficacy of eye movement desensitization and reprocessing therapy (EMDR) in the treatment of posttraumatic stress disorder (PTSD), including recent studies showing it to be more efficient than therapist-directed flooding. But few theoretical explanations of how EMDR might work have been offered. Shapiro, in her original description of EMDR, proposed that its directed eye movements mimic the saccades of rapid eye movement sleep (REM), but provided no clear explanation of how such mimicry might lead to clinical improvement. We now revisit her original proposal and present a complete model for how EMDR could lead to specific improvement in PTSD and related conditions. We propose that the repetitive redirecting of attention in EMDR induces a neurobiological state, similar to that of REM sleep, which is optimally configured to support the cortical integration of traumatic memories into general semantic networks. We suggest that this integration can then lead to a reduction in the strength of hippocampally mediated episodic memories of the traumatic event as well as the memories' associated, amygdala-dependent, negative affect. Experimental data in support of this model are reviewed and possible tests of the model are suggested.
Flexible or 'fluid' cognitive processes are regarded as fundamental to problem solving and creative ability, requiring a specific neurophysiological milieu. REM-sleep dreaming is associated with creative processes and abstract reasoning with increased strength of weak associations in cognitive networks. REM sleep is also mediated by a distinctive neurophysiological profile, different to that of wake and NREM sleep. This study compared the performance of 16 subjects on a test of cognitive flexibility using anagram word puzzles following REM and NREM awakenings across the night, and waking performances during the day. REM awakenings provided a significant 32% advantage in the number of anagrams solved compared with NREM awakenings and was equal to that of wake time trials. Correlations of individual performance profiles suggest that REM sleep may offer a different mode of problem solving compared with wake and NREM. When early and late REM and NREM awakening data were separated, a dissociation was evident, with NREM task performance becoming more REM-like later in the night, while REM performance remained constant. These data suggest that the neurophysiology of REM sleep represents a brain state more amenable to flexible cognitive processing than NREM and different from that in wake, and may offer insights into the neurocognitive properties of REM-sleep dreaming.
Human performance on visual texture discrimination tasks improves slowly (over days) in the absence of additional training. This 'slow learning' requires nocturnal sleep after training and is limited to the region of visual space in which training occurred. Here, we tested human subjects four times in one day and found that with repeated, within-day testing, perceptual thresholds actually increased progressively across the four test sessions. This performance deterioration was prevented either by shifting the target stimuli to an untrained region of visual space or by having the subjects take a mid-day nap between the second and third sessions.
Loneliness predicts morbidity and mortality from broad-based causes, but the reasons for this effect remain unclear. Few differences in traditional health behaviors (e.g., smoking, exercise, nutrition) have been found to differentiate lonely and nonlonely individuals. We present evidence that a prototypic restorative behavior--sleep--does make such a differentiation, not through differences in time in bed or in sleep duration, but through differences in efficacy: In the study we report here, lonely individuals evinced poorer sleep efficiency and more time awake after sleep onset than nonlonely individuals. These results, which were observed in controlled laboratory conditions and were found to generalize to the home, suggest that lonely individuals may be less resilient than nonlonely individuals in part because they sleep more poorly. These results also raise the possibility that social factors such as loneliness not only may influence the selection of health behaviors but also may modulate the salubrity of restorative behaviors.
Growing evidence suggests that sleep plays an important role in the process of procedural learning. Most recently, sleep has been implicated in the continued development of motor-skill learning following initial acquisition. However, the temporal evolution of motor learning before and after sleep, the effects of different training regimens, and the long-term development of motor learning across multiple nights of sleep remain unknown. Here, we report data for subjects trained and retested on a sequential finger-tapping task across multiple days. The findings demonstrate firstly that following initial training, small practice-dependent improvements are possible before, but not following the large practice-independent gains that develop across a night of sleep. Secondly, doubling the quantity of initial training does not alter the amount of subsequent sleep-dependent learning that develops overnight. Thirdly, the amount of sleep-dependent learning does not correlate with the amount of practice-dependent learning achieved during training, suggesting the existence of two discrete motor-learning processes. Finally, whereas the majority of sleep-dependent motor-skill learning develops during the first night of sleep following training, additional nights of sleep still offer continued improvements.