Ingenious Devices — Getting a Handle on Time

Man is a poor experimental animal, and at present, it would seem that a more complete understanding of the internal processes responsible for diurnal rhythms would come first from study of the lower animals.
— John H. Welsh, "Diurnal Rhythms," Quarterly Review of Biology, 1938.

In the early years of circadian research, scientists created ingenious devices to quantify circadian behavior. Plant researchers duplicated Darwin's method of tying plant leaves to plotting devices. Researchers, using a wide range of laboratory animals, routinely used activity wheels to obtain graphs of the animals' resting and active states. Scientists also created unique devices to monitor such circadian variables as the periodic movement of goldfish and the respiration of Gonyaulax.



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Neurospora Race Tubes. Neurospora, a form of bread mold, is a favored organism for circadian study because it is a simple organism with well-understood genetics. These "race tubes" show the circadian growth patterns of normal Neurospora and of mutant Neurospora, whose circadian functioning is impaired. Can you tell which is which?

Can YOU "Read" a Neurospora Race Tube? When the biological clock of Neurospora functions normally, the growth patterns exhibit a consistent circadian period. By contrast, the clock mutants shown on the right have erratic growth patterns. They should be easy to spot.




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Roaches Rule.
Despite a widespread popular aversion to cockroaches, these nocturnal insects have helped circadian researchers understand the biological clock.

Do nocturnal animals have circadian rhythms? Though they are active at night rather than in the daytime, nocturnal animals show the same sorts of circadian rhythms as other animals. In addition, cockroaches are ideal laboratory animals for circadian research because their activity levels are so easily monitored with activity wheels, and because their relatively large-size makes it easy to study their nervous systems.


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A Drosophila Olympiad.
This system uses a beam of infrared light to time the movement of the fruit flies. The same principle of a disrupted light beam is used in Olympic timing devices to determine the winner of a race.



The "Actiwatch" — Device Measuring Human Locomotor Activity.
The Actiwatch is a miniaturized device, known as an accelerometer, that records movement as a function of time. Data from the Actiwatch are downloaded into a computer for analysis through radio signals, which go from the Actiwatch to an interface reader. This wristwatch-like device, which monitors activity levels in subjects, is useful in studying sleep and circadian rhythms.

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