Abstract concept learning in a simple neural network inspired by the insect brain.

The capacity to learn abstract concepts such as 'sameness' and 'difference' is considered a higher-order cognitive function, typically thought to be dependent on top-down neocortical processing. It is therefore surprising that honey bees apparantly have this capacity. Here we report a model of the structures of the honey bee brain that can learn sameness and difference, as well as a range of complex and simple associative learning tasks.

Therapy of circadian rhythm disorders in chronic fatigue syndrome: no symptomatic improvement with melatonin or phototherapy.

Background: Patients with chronic fatigue syndrome (CFS) show evidence of circadian rhythm disturbances. We aimed to determine whether CFS symptoms were alleviated by melatonin and bright-light phototherapy, which have been shown to improve circadian rhythm disorders and fatigue in jet-lag and shift workers.

Design: Thirty patients with unexplained fatigue for > 6 months were initially assessed using placebo and then received melatonin (5 mg in the evening) and phototherapy (2500 Lux for 1 h in the morning), each for 12 weeks in random order separated by a washout period.

Estimates of the daily phase and amplitude of the endogenous component of the circadian rhythm of core temperature in sedentary humans living nychthemerally.

Fifteen healthy female subjects were studied for eight days while living conventionally. Subjects were free to choose the ways they spent their time within a framework of regular times of retiring and rising; in practice, much of the waking time was spent in sedentary activities. Nine of the subjects were aware of the natural light-dark cycle, this approximating to a 12:12 L:D schedule at the time of year when the study took place.

Temperature profiles, and the effect of sleep on them, in relation to morningness-eveningness in healthy female subjects.

There were 15 healthy female subjects, differing in their position on the "morningness-eveningness" scale, studied for 7 consecutive days, first while living a sedentary lifestyle and sleeping between midnight and 08:00 and then while undergoing a "constant routine." Rectal temperature was measured at regular intervals throughout this time, and the results were subjected to cosinor analysis both before and after "purification" for the effects of physical activity. Results showed that there was a phase difference in the circadian rhythm of core temperature that was associated with the morningness score, with calculations that "morning types" would be phased earlier than "evening types" by up to about 3 h.

A comparison of some different methods for purifying core temperature data from humans.

Nine healthy females were studied about the time of the spring equinox while living in student accommodations and aware of the passage of solar time. After 7 control days, during which a conventional lifestyle was lived under a 24h "constant routine," the subjects lived 17 x 27h "days" (9h sleep in the dark and 18h wake using domestic lighting, if required). Throughout the experiment, recordings of wrist activity and rectal (core) temperature were taken.

Diurnal variations in the mood and performance of highly practised young women living under strictly controlled conditions.

The diurnal variation in a range of psychological functions and core body temperature were investigated in a series of studies involving a total of 24 highly practised young women who lived in a controlled environment and on a strictly regimented 24-hour routine for 6 or 7 days. Ten participants were exposed to the natural light/dark cycle (L/Dc) through windows, whereas the 14 remaining participants saw no daylight, but all had access to normal clock time. A battery of mood and performance tests was completed every 2 hours whilst awake (08:00-00:00), resulting in nine equally spaced measures per waking day.

Purification of masked temperature data from humans: some preliminary observations on a comparison of the use of an activity diary, wrist actimetry, and heart rate monitoring.

Fourteen ambulatory subjects, varying in their amount of habitual physical activity, were studied for 24 h during a total of 25 "typical" days. Rectal temperature was recorded every 6 minutes, an activity diary was filled in every half hour, and wrist activity and heart rate were monitored every minute. Actimetry and heart rate data generally showed close parallelism with each other and with the masking effects on body temperature.

The effect of activity on the waking temperature rhythm in humans.

Nine healthy female subjects were studied when exposed to the natural light-dark cycle, but living for 17 "days" on a 27h day (9h sleep, 18h wake). Since the circadian endogenous oscillator cannot entrain to this imposed period, forced desynchronization between the sleep/activity cycle and the endogenous circadian temperature rhythm took place. This enabled the effects of activity on core temperature to be assessed at different endogenous circadian phases and at different stages of the sleep/activity cycle.

Effect of sleep loss on core temperature when movement is controlled.

Nine subjects were studied for 16 days in an isolation unit where they lived on normal time, working at a decision-making, computer-driven task during the daytime. Interspersed among these control days were three occasions when sleep was curtailed. Rectal temperature and activity (non-dominant wrist) were measured throughout.

Lack of evidence that feedback from lifestyle alters the amplitude of the circadian pacemaker in humans.

Two groups of healthy subjects were studied indoors, first while living normally for 8 days (control section) and then for 18 x 27 h "days" (experimental section). This schedule forces the endogenous (body clock-driven) and exogenous (lifestyle-driven) components of circadian rhythms to run independently. Rectal temperature and wrist movement were measured throughout and used as markers of the amplitude of the circadian rhythm, with the rectal temperature also "purified" by means of the activity record to give information about the endogenous oscillator.

Diurnal trends in mood and performance do not all parallel alertness.

Objectives: This study examined the hypothesis that alertness can be used to predict time-of-day effects on performance.

Methods: For 6 or 7 days the volunteers (24, highly practiced young women) were required to retire to bed at 0000 and were awakened at 0800. A battery of mood and performance tests was completed every 2 hours while the women were awake; the result was 9 equally spaced measures per day.

Light of domestic intensity produces phase shifts of the circadian oscillator in humans.

Twelve subjects have been studied in a chamber that isolated them from external noise and lighting. After several control days, one group (n = 6) was subjected to 18 x 27-h 'days' and the other to 11 x 30-h 'days'. Sleep was in the dark, and awake times were spent in normal domestic lighting (150-500 lux).

Experimental separation of time of day and homeostatic influences on sleep.

The purpose of the present study was to evaluate the simultaneous effects on sleep of prior time awake (PRW) and time of day (TOD). Eight male subjects spent 13 days in an isolated sleep lab and had three 8-h baseline sleeps and then 18 4-h sleeps, distributed to provide three sleeps starting at 2400, 0400, 0800, 1200, 1600, and 2000. The three sleeps were preceded by 4, 8, and 12 h of PRW, respectively.

The effects of age upon some aspects of lifestyle and implications for studies on circadian rhythmicity.

Background: Most studies on lifestyle changes in old age have been transverse. We have conducted a longitudinal study.

Subjects: 112 non-institutionalized subjects were studied in 1984 and again 10 years later (ages in 1984 ranged from 53-82 years).

Good sleep--its timing and physiological sleep characteristics.

The present study used short sleep episodes to explore the relation between subjective sleep quality, timing and physiological content of sleep. Eight subjects participated in 18 4-h sleep episodes to provide 4, 8, and 12 h of prior time awake before bedtimes at six different times of day in a sleep laboratory insulated from environmental disturbances. The results were analysed by ANOVAs and multiple regression techniques.

Hormonal Secretion of Nurses Engaged in Fast-rotating Shift Systems.

The aim of the study was to assess whether fast-rotating shift systems, including one or two consecutive night shifts, would cause significant disturbances of the normal hormonal patterns of ten young female nurses working in an intensive care unit. Plasma cortisol, serum prolactin, and growth hormone were measured at the start, middle, and end of one morning (07-14), one afternoon (14-21), and two night shifts (21-07); urinary excretion rates of 6-sulfatoxymelatonin (aMT6s), adrenaline (epinephrine) and noradrenaline (norephinephrine) were determined for each half of the four shifts. During the night shifts, the hormones more sensitive to exogenous components, such as catecholamines, prolactin, and growth hormone, showed an immediate response to the shifted sleep/activity cycle, evidencing a "masking effect" due to the work activity.

Chronobiology and meal times: internal and external factors.

Although homeostatic mechanisms remain of utmost importance, rhythmic changes are present also. The main ones have a period of 24 h (circadian) or about 2-3 h (ultradian). Circadian rhythms are derived from a body clock, found in the base of the brain, and from the pattern of our sleep-wake cycle, including activity and meal times.

Some comments on the measurement of circadian rhythms after time-zone transitions and during night work.

Adjustment of circadian rhythms to changed sleep/wake schedules, as after time-zone transitions and during night work, is not immediate. Different variables appear to adjust at different rates, and such external and internal dissociation is linked with a general malaise ("jet lag") after a time-zone transition. Work using "constant routines" and "purification" methods indicates that the internal dissociation results from differences between variables in the relative contribution of exogenous ("masking") effects to the measured rhythm.

Complex interaction of the sleep-wake cycle and circadian phase modulates mood in healthy subjects.

Background: Several studies of healthy volunteers have revealed that subjective mood may vary with the duration of prior wakefulness and with the time of day. However, in these studies, the effects of extended wakefulness and circadian phase remained confounded, and the interaction of these 2 processes could not be assessed quantitatively.

Methods: In the present study, a total of 24 healthy young subjects (16 men, 8 women) lived on a 30-hour sleep-wake schedule for 19 to 23 days or on a 28-hour sleep-wake schedule for 33 to 36 days; both schedules induced desynchrony between the subjects' sleep-wake cycle and their endogenous circadian pacemaker.

Interpersonal sensitivity predicts depressive symptom response to the circadian rhythm disruption of nightwork.

This paper reports the results of a study designed to explore the validity of a shiftwork model of affective disorders. Fifty-five student nurses doing nightwork for the first time were recruited to a study designed both to replicate an earlier study of the effects of nightwork on cognitive, emotional and neurovegetative measures and to assess the effects of nightwork on personality measures and the role of personality factors and nightwork induced disturbances in predicting accommodation to nightwork. As in the earlier study, concentration, interest, energy, sleep and appetite were significantly disturbed by nightwork and there was an increased perception of recent criticism from other.

The difference between activity when in bed and out of bed. III. Nurses on night work.

Eight nurses have been studied during rest days and three successive night shifts. Measurements of wrist activity have been made and used to assess the extent to which the pattern of daily activity changes between control (rest) days and days involving night work. One analysis considered wrist activity during time spent in bed; this appears to decrease in parallel with the amount of time in bed that is lost during night work but, when this effect is corrected for, there is greater activity during time spent in bed in the daytime compared with control days (when time in bed is during the night).

The shape of the endogenous circadian rhythm of rectal temperature in humans.

Fourteen healthy subjects have been studied in an isolation unit while living on a 30h "day" (20h awake, 10h asleep) for 14 (solar) days but while aware of real time. Waking activities were sedentary and included reading, watching television, and so forth. Throughout, regular recordings of rectal temperature were made, and in a subgroup of 6 subjects, activity was measured by a wrist accelerometer.

The difference between activity when in bed and out of bed. II. Subjects on 27-hour "days".

Nine healthy subjects have been studied while exposed to the normal alternation of light and dark, but with their sleep and activity pattern adjusted to a 27-h "day" for 17 imposed "days." Rectal temperature showed clearly the competing influences of 27-h and 24-h components, and these were separated by the method of "purification." The method indicated that the endogenous component had a constant amplitude throughout the experiment and remained entrained to solar (24-h) time; by contrast, the exogenous component followed the imposed 27-h "day" and increased rectal temperature in proportion to the amount of subjects' activity.

Dissociation of body-temperature and melatonin secretion circadian rhythms in patients with chronic fatigue syndrome.

Many patients with chronic fatigue syndrome (CFS) display features of hypothalamic dysfunction. We have investigated aspects of circadian rhythmicity, an important hypothalamic function, in 20 CFS patients and in 17 age- and sex-matched healthy control subjects. There were no differences between the two groups in the amplitude, mesor (mean value) or timing of the peak (acrophase) of the circadian rhythm of core temperature, or in the timing of the onset of melatonin secretion.