Habituation during sleeping and waking

Learning during sleep in humans - A historical review

Sleep helps to consolidate previously acquired memories. Whether new information such as languages and other useful skills can also be learned during sleep has been debated for over a century, however, the sporadic studies' different objectives and varied methodologies make it difficult to draw definitive conclusions. This review provides a comprehensive overview of the history of sleep learning research conducted in humans, from its empirical beginnings in the 1940s to the present day. Synthesizing the findings from 51 research papers, we show that several studies support the notion that simpler forms of learning, such as habituation and conditioning, are possible during sleep. In contrast, the findings for more complex, applied learning (e.g., learning a new language during sleep) are more divergent. While there is often an indication of processing and learning during sleep when looking at neural markers, behavioral evidence for the transfer of new knowledge to wake remains inconclusive. We close by critically examining the limitations and assumptions that have contributed to the discrepancies in the literature and highlight promising new directions in the field.

The efficacy and psychophysiological correlates of dual-attention tasks in eye movement desensitization and reprocessing (EMDR)

This study aimed to investigate the psychophysiological correlates and the effectiveness of different dual-attention tasks used during eye movement desensitization and reprocessing (EMDR). Sixty-two non-clinical participants with negative autobiographical memories received a single session of EMDR without eye movements, or EMDR that included eye movements of either varied or fixed rate of speed. Subjective units of distress and vividness of the memory were recorded at pre-treatment, post-treatment, and 1 week follow-up. EMDR-with eye movements led to greater reduction in distress than EMDR-without eye movements. Heart rate decreased significantly when eye movements began; skin conductance decreased during eye movement sets; heart rate variability and respiration rate increased significantly as eye movements continued; and orienting responses were more frequent in the eye movement than no-eye movement condition at the start of exposure. Findings indicate that the eye movement component in EMDR is beneficial, and is coupled with distinct psychophysiological changes that may aid in processing negative memories.

Sensory processing during early and late nocturnal sleep

The present experiments in 10 healthy men compared auditory evoked potentials (AEPs) and heart rate (HR) indicators of stimulus processing during early and late phases of nocturnal stage 2 sleep. Definition of early and late sleep relied on endocrine pituitary-adrenal secretory activity which is known to be inhibited during early nocturnal sleep but sharply increases during late sleep. AEPs and HR responses were recorded to trains of 10 tone pips (1000 Hz; interstimulus interval 15 s; intertrain interval > 3 min). On one night, tone pips were presented in the first part of sleep, on the other night tone presentation took place in the second part, with the order of conditions balanced across subjects. Amplitudes of N150 and N550 components of the AEP, and of acceleratory and deceleratory HR responses, were higher during the first than second part of nocturnal sleep (P < 0.05). Moreover, habituation of P240 and N550 amplitudes was slower during the first than second part of sleep (P < 0.05). In supplementary experiments, AEP and HR responses to the same stimuli did not differ between the first and second part of the night when subjects were waking during stimulation. Results indicate a reduced inhibitory control over cortical stimulus processing during early nocturnal sleep. This diminished inhibition of cortical processing together with other concomitant changes during early sleep (such as the enhanced inhibition of pituitary-adrenal secretion) may reflect a coordinated regulatory function of sleep possibly mediated by hippocampal mechanisms.

Behavioral, event-related potential, and EEG/FFT changes at sleep onset

Behavioral, event-related potential (ERP), and EEG measures were obtained to describe more fully the relationship between brain activity and arousal level during the process of falling asleep. In addition to standard polysomnographic measures, tones were presented at random intervals throughout two nights to each of nine subjects. Subjects were instructed to respond to the tones whenever they heard them. Initial sleep onset was disrupted five times following zero through four successive response failures. Sampling of EEG was initiated 5 s prior to tone onset (EEG analyses) and continued for 5 s following tone onset (ERP data). With EEG ordered as a function of response rate, significant increases in power were found across all standard frequency bands for the pretone data at sleep onset. Significant changes in amplitude were related to decreasing responsivity for all late ERP components except P2. Inasmuch as virtually all EEG frequencies and ERP components were strongly influenced by momentary changes in arousal, arousal must be considered a (possibly the) primary determinant of the characteristics of the overall electrical output of the brain. Response cessation coupled with sharp increases in EEG synchronization mark the point of sleep onset.

Sleep, brain activation and cognition

Some data have shown the presence of time-of-day effects in learning processes. We explore here whether the same phenomenon occurs during the night and how it relates to REM sleep. In an initial approach to the question, this paper points out the relationships between: 1) REM sleep and brain activation, and 2) REM sleep and information processing. The data are discussed in terms of a REM sleep implication on information processing and we examine the possibility of modifying this processing by acting on REM sleep.

Effects of a change in tone frequency on the habituated orienting response of the sleeping rat

EEG arousal and heart rate responses to change in tone frequency following habituation training were studied during slow wave sleep in the rat. Rats were exposed to sequences of 12 tone pulses. Habituation stimuli (trials 1-7) had a frequency of 16 kHz. The frequency of the following (test) trials was changed to either 5, 12, 14, 22, or 40 kHz. Hearing level was held constant for all frequencies. Test trials were repeated five times to study rehabituation. The results indicate that heart rate deceleration is an indicator of the orienting reflex and its magnitude is a positive function of the amount of frequency change of the stimulus. Large frequency changes in either direction relative to the habituation frequency lead to re-evocation of the habituated EEG arousal and heart rate deceleration, with subsequent rehabituation. Small tone-frequency changes do not result in EEG arousal or heart rate deceleration responses that differ from the responses to the habituated frequency. Heart rate acceleration shows neither short-term habituation nor significant reaction to any of the test frequencies.

Sleep in hospital

Although sleep has been identified as an activity generally considered necessary for normal functioning, the nursing literature on the subject is relatively scanty. This paper is an attempt to review sleep and its relationship to nursing practice. A discussion of nursing interventions that are likely to ensure that adequate sleep is maintained is included.

Event-related slow potentials evoked during ankle jerk conditioning in wakefulness and NREM sleep

Slow cortical potentials related to the ankle jerk and to its conditioning were studied in 40 adults while awake and during NREM sleep. A weak sound (S) was used as conditioned stimulus, while the ankle jerk, evoked either by Achilles tendon percussion (P) or by electrical stimulation of the sciatic nerve (H), served as unconditioned or 'imperative' stimulus. During waking, responses to simple stimuli (S, P, H) were mostly negative. During S-P and S-H pairs, responses to S were mainly negative, resembling the CNV, while these to P or to H became mostly positive, like the CNV resolution or the positive phase of the motor potential. During NREM sleep, responses to simple as well as to paired stimuli showed mostly a biphasic (negative-positive) morphology resembling the K complex. The conditioned slow potential changes obtained by pairing a sound with the ankle jerk therefore seem to be abolished during NREM sleep. This absence of conditioning can be related to the absence of habituation during NREM sleep. In 35% of the cases, however, positive slow waves were evoked by paired sounds during sleep. The possible significance of these phenomena is discussed.

Evoked K-complexes and cardiovascular responses to spindle-synchronous and spindle-asynchronous stimulus clicks during NREM sleep

The hypothesis that the functional role of the sleep spindle is to preserve sleep by inhibiting sensory input (Yamadori 1971) was examined. Series of 44 dB, 10 msec, 1000 c/sec 'clicks' were presented to 12 subjects at a 30-sec ISI during stage 2 sleep either during spindle bursts (i.e. spindle-synchronous clicks) or during interburst periods (i.e. spindle-asynchronous clicks). Contrary to the spindle inhibitory hypothesis, cortical EEG and cardiovascular responses showed no evidence of spindle 'suppression'. Evoked K-complexes were potentiated by the spindle-synchronous stimulation. A second study with 7 subjects replicated this result and extended the finding to include stage 3--4 sleep. It was suggested that the potentiation of evoked K-complexes was due to phasic reductions in inhibitory action during sleep spindles resulting in increased transmission of sensory events or, perhaps, an increase in the lability of certain EEG response systems.

Feedback control and quantification of the response of EEG alpha to visual stimulation

The response of the posterior EEG alpha thythms to visual stimulation is so variable that it is difficult to obtain reliable on-line measurement of it. Feedback between the EEG alpha and the visual stimulus (1) reduces random variation in the response and (2) facilitates on-line quantification. With feedback EEG, the response to visual stimulation is measured as a series of time durations of alpha and of no-alpha intervals in the EEG. This time series occurs in two stages: an initial disturbance followed by a recovery. The quantification of the series of time durations is achieved by fitting curves to the series of alpha time intervals and of no-alpha time intervals. These functions, computed in each trial of 30 stimulations, are an objective, quantitative definition of EEG response. The utility of the method was demonstrated by testing it with reference to well-known effects. Habituation to a repeated stimulus, dishabituation, habituation to a class of stimuli, dishabituation by changing the class of stimuli, and differences among brain-lesioned, psychiatric patients and normals were shown with a detailed quantification. It was concluded that biofeedback is the method of choice for quantitative research on the EEG component of the human orienting response.

Effect of flurazepam on sleep spindles and K-complexes

In this research, a quantitative study of the EEG from 5 subjects permitted a detailed analysis of the effect of 30 mg of flurazepam administered over 7 nights. Four placebo baseline nights and 3 placebo withdrawal nights were also recorded. For 4 of the subjects, a nondrug and nonplacebo follow-up record was obtained 4 to 6 weeks later. The subjects were 4 females, 1 male, age range 23-42. All complained of either sleep onset greater than 45 min, sleep length of less than 6 h, or two or more sleep awakenings. Compressed spectral analysis yielded a computer-generated somnogram on each of the 15 nights of sleep, and an automated spindle detector was used to count and measure the duration of spindle bursts with frequencies of 12.25-15.5 c/sec on baseline nights 3 and 4, drug nights 1, 2, 3 and 7, on the 3rd withdrawal night, and on the 4-6 week followup record. K-complexes were scored visually on the 4th baseline and 7th drug nights. There were no significant differences in spindle rate per minute among baseline nights and the follow-up record. By the 2nd drug night, spindle rate had significantly increased over the baseline rate. Linear contrast analysis indicated there was a significant increase of spindle rate over drug nights. All 5 subjects showed this pattern of increase. In contrast to the increase in spindle activity, the rate per minute of K-complexes significantly decreased during drug administration.