Changes of sleep EEG slow-wave activity in response to sleep manipulations: to what extent are they related to changes in REM sleep latency?

Sleep interventions may have direct effects on slow-wave activity (SWA, i.e. power of the sleep EEG signal in the 0.75-4.5 Hz range) as well as indirect ones caused by changes in REM sleep (REMS) latency. The effects of changes in REMS latency on SWA were investigated by analysing simulations with a mathematical model. Mean SWA in the first non-REMS episode shows an initial increase and a later decline as a function of REMS latency. In the second non-REMS episode, mean SWA decreases with increasing REMS latency. These results of the simulations were validated with experimental data. In the evaluation of the effects of sleep interventions on SWA the effects of the timing of REMS have to be accounted for. The analysis of SWA over a sufficiently long constant amount of time spent in non-REMS proves to be relatively independent of REMS latency, which allows conclusions about the effects of sleep interventions on SWA per se.

Changes in EEG power density of NREM sleep in depressed patients during treatment with citalopram.

According to a recent hypothesis the therapeutic effects of antidepressants might be related to acute or cumulative suppression of NREM sleep intensity. This intensity has been proposed to be expressed in the EEG power density in NREM sleep. In the present study the relationship was examined between the changes of EEG power density in NREM sleep and the changes in clinical state in 16 depressed patients during treatment with citalopram, a highly specific serotonin uptake inhibitor. A one-week wash-out period was followed by 1 week of placebo administration, a medication period of 5 weeks, and a one-week placebo period. In order to minimize systematic influences of sleep duration and NREM-REM sleep alterations, EEG power was measured over the longest common amount of NREM sleep stages 2, 3 and 4 (91.5 min). During the last treatment week and the week after withdrawal, a significant decrease of EEG power as compared to baseline was found in the 8-9 Hz frequency range. No clear-cut change, however, was observed in the EEG power of the delta frequency range (1-4 Hz), which is considered to be the principle manifestation of NREMS intensity. Furthermore, no relationship between changes in EEG power density and changes in clinical state could be demonstrated.

Self-rated arousal concurrent with the antidepressant response to total sleep deprivation of patients with a major depressive disorder: a disinhibition hypothesis.

In view of the opposing theories regarding the arousing or de-arousing action of total sleep deprivation (TSD) in producing antidepressant effects, 23 patients with a major depressive disorder were deprived of a night's sleep twice weekly for two weeks, and self-rated their condition 38 times using von Zerssen's scale for depression and, concurrently, Thayer's Activation Deactivation Adjective Check List (AD ACL). Transient relief of depression after TSD, indicated by eight patients, was mimicked by their AD ACL scores, which revealed the same underlying factors as were found in Thayer's studies. TSD appears to be simultaneously arousing (giving more energy) and de-arousing (leading to less tension), while this response takes place against a background of increased tiredness/sleepiness. It is argued that TSD sets off a psychological disinhibition process on the basis of cerebral fatigue; in particular the prefrontal (orbital?) areas of the cerebral cortex may be implicated, possibly in relation to a dampening down of subcortical arousal systems.

Selective SWS suppression does not affect the time course of core body temperature in men.

In eight healthy middle-aged men, sleep and core body temperature were recorded under baseline conditions, during all-night SWS suppression by acoustic stimulation, and during undisturbed recovery sleep. SWS suppression resulted in a marked reduction of sleep stages 3 and 4 but did not affect the time course of core body temperature. These data suggest that sleep stages 3 and 4 of nonREM sleep (i.e. SWS) do not play a major role in the regulation of core body temperature in humans.

A single pacemaker can produce different rates of reentrainment in different overt rhythms.

Using a simple Van der Pol oscillator, we show that periodic events triggered by different states of the oscillator can reentrain at different rates following a phase shift of the Zeitgeber. Such differences can emerge due to waveform distortion during reentrainment, due to masking and due to fitting procedures (e.g. acrophase determination). Therefore, different rates of reentrainment are consistent with single pacemaker models of circadian systems. Likewise, "Fractional Desynchronization" can yield different "ranges of entrainment" in different overt rhythms generated by the same pacemaker.

Generation of activity-rest patterns by dual circadian pacemaker systems: a model.

Activity-rest patterns displayed by an animal under various circumstances are suggested to result from the combined influences of two virtually identical circadian pacemaker components. Increased output of each component proportionally increases the probability of activity of the animal. Such a dual circadian pacemaker model explains much of the phenomenology of activity-rest records. Under normal light-dark schedules, the two components of the model have a similar phase relationship to the Zeitgeber. Differential synchronization of the components to dawn and dusk is not assumed.