Temporal pattern of LH secretion: regulation by multiple ultradian oscillators versus a single circadian oscillator.

The possibility that the 24h rhythm output is the composite expression of ultradian oscillators of varying periodicities was examined by assessing the effect of external continuously or pulsed (20-minute) Gonadotropin-releasing hormone (GnRH) infusions on in vitro luteinizing hormone (LH) release patterns from female mouse pituitaries during 38h study spans. Applying stepwise analyses (spectral, cosine fit, best-fit curve, and peak detection analyses) revealed the waveform shape of LH release output patterns over time is composed of several ultradian oscillations of different periods. The results further substantiated previous observations indicating the pituitary functions as an autonomous clock. The GnRH oscillator functions as a pulse generator and amplitude regulator, but it is not the oscillator that drives the ultradian LH release rhythms. At different stages of the estrus cycle, the effect of GnRH on the expression of ultradian periodicities varies, resulting in the modification of their amplitudes but not their periods. The functional output from the system of ultradian oscillators may superimpose a "circadian or infradian phenotype" on the observed secretion pattern. An "amplitude control" hypothesis is proposed: The temporal pattern of LH release is governed by several oscillators that function in conjunction with one another and are regulated by an amplitude-controlled mechanism. Simulated models show that such a mechanism results in better adaptive response to environmental requirements than does a single circadian oscillator.

Circadian pattern of simulated flight performance of pilots is derived from ultradian components.

Studies suggest some physiologic, cognitive, and behavioral 24h rhythms are generated by cyclic components that are shorter in period than circadian. The aim of this study was (1) to examine the hypothesis that 24h human performance rhythms arise from the integration of high-frequency endogenous components and (2) to quantify the contribution of each higher frequency component to the phenotype of the rhythm. We monitored the performance of 9 experienced pilots by employing an array of cognitive-based tests conducted in a flight simulator so that, over the 6-day experiment, data were obtained for each 2h interval of the 24h. The activity-rest schedule of the subjects, no matter the exact clock time schedule of sleep and activity, always consisted of 14h activity (when they carried out regular professional duties) and 10h rest, with at least 8h of sleep. The simulated combat scenarios consisted of simple and complex tasks associated with target interception, aircraft maneuvering, and target shooting and downing. The results yielded two indices: the number of prominent periodicities in the time series and the relative magnitude of the amplitude of each relative to the construction of the composite 24h waveform. Three cyclic components (8h, 12h, and 24h) composed the observed 24h performance pattern. The dominant period and acrophase (peak time) of the compound output rhythm were determined by the interplay between the amplitudes of the various individual ultradian components. Task complexity (workload) increases the expression of the ultradian entities in the 24h pattern. We constructed a model composed of the multiple ultradian components; the composite output defined a "time span" (of 2h-4h duration) as opposed to an exact "time point" of high and low performance, endowing elevated functional capability.

Differences between left- and right-hand reaction time rhythms: indications of shifts in strategies of human brain activity.

Reaction time (RT) measurements serve as quantitative indices for pilots' cognitive processes of the brain. To examine if laterality exists in the brain hemispheres we measured, by the use of a Pilot Evaluation System (PES), right- and left-hand performance rhythms as indicative of RT to audible and visual stimuli. The tests included sets of simple tasks and complex ones to which a secondary task composed of audio signals was added. The accuracy of recorded reaction time was 27 ms. Seven right-handed males, 27-42 years of age, experienced with the PES flight simulator, were tested every 2 h, nine times daily (starting at 08:00 h) during 3 consecutive days. The results indicated that for simple tasks, the 24 h period of RT rhythm is either exclusive or prominent for both hands. For complex tasks the prominent period of RT is 24 h for the right (dominant) hand and 8 h for the left (non-dominant) hand (right-hand 24 h period Fstat = 140, r2 = 0.62 and 8 h period Fstat = 25, r2 = 0.22; left-hand 24 h period Fstat = 44, r2 = 0.34 and 8 h period Fstat = 100, r2 = 0.54). The findings suggest that a laterality exists in the brain hemispheres with regard to differences in rhythm periodicities. The expression of this laterality is dependent on the task-load level and points to a strategy of linkage and integrity in brain activity.

An initial evaluation of work fatigue and circadian changes as assessed by multiplate posturography.

The sensitivity of postural responses to the effects of work fatigue and circadian changes was explored in a pilot study using a specific method of multiplate posturography based on the differential assessment of vertical pressure on four separate platforms for each heel and set of toes of each foot, respectively 8 normal subjects, M.D.s, were given six posturographic examinations immediately before and after three 8-hr. work shifts in the emergency room of a major hospital in Tel-Aviv. 3 posturographic measures (stability, spectral power of postural sway at low frequency of 0.1-0.25 Hz, and unilateral weakening of heel-toe synchronisation) were significantly affected by work fatigue whilst also showing interaction with circadian rhythm. 2 additional measures (power of sway at high frequency of 1.00-3.00 Hz and dysharmonic distribution of weight over the four platforms) were not related to workload but showed significant circadian changes. These effects appeared only on positions involving restricted visual and somatosensory feedback causing vestibular stress. Results justify the application of multiplate posturography as an ancillary tool in measuring objectively the effects of fatigue and circadian changes as well as the interaction between endogenous chronobiological processes and their external conditioning factors (Zeitgebers). Pragmatic implications of the findings in the context of industrial medicine and interdisciplinary efforts to prevent road and air accidents are discussed.