Short-term memory, alertness and performance: a reappraisal of their relationship to body temperature

Authors

  • M. P. JOHNSON,

    1. Laboratory for Circadian and Sleep Disorders Medicine, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
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    • *

      Cornell University Medical College, 420 East 70th Street, New York, NY 10021 USA.

  • J. F. DUFFY,

    1. Laboratory for Circadian and Sleep Disorders Medicine, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
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  • D. J. DIJK,

    1. Laboratory for Circadian and Sleep Disorders Medicine, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
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  • J. M. RONDA,

    1. Laboratory for Circadian and Sleep Disorders Medicine, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
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  • C. M. DYAL,

    1. Laboratory for Circadian and Sleep Disorders Medicine, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
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    • **

      Columbia Presbyterian Medical Center, 622 West 168th Street, New York, NY 10032 USA.

  • C. A. CZEISLER

    Corresponding author
    1. Laboratory for Circadian and Sleep Disorders Medicine, Division of Endocrinology, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, MA 02115, USA
      Laboratory for Circadian and Sleep Disorders Medicine, 221 Longwood Avenue, Boston, MA 02115 USA
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Laboratory for Circadian and Sleep Disorders Medicine, 221 Longwood Avenue, Boston, MA 02115 USA

Abstract

SUMMARY  Previous studies have led to the beliefs: (1) that short-term memory is best during the night when the body temperature is at its nadir, and (2) that the circadian rhythms of short-term memory and subjective alertness are driven by oscillators independent from each other and from the body temperature cycle. Unfortunately, these conclusions, which would have major implications for understanding the organization of the human circadian timing system, are largely based on field and laboratory studies, which in many cases sampled data infrequently and/or limited data collection to normal waking hours. In order to investigate these points further, we have monitored behavioural variables in two different protocols under controlled laboratory conditions: (1) during a period of 36–60 h of sustained wakefulness; and (2) during forced desynchrony between the body temperature and sleep/wake cycles, allowing testing of non-sleep-deprived subjects at all circadian phases. Contrary to earlier findings, we report here that the circadian rhythm of short-term memory varies in parallel with the circadian rhythms of subjective alertness, calculation performance, and core body temperature under both these experimental conditions. These results challenge the notion that short-term memory is inversely linked to the body temperature cycle and suggest that the human circadian pacemaker, which drives the body temperature cycle, is the primary determinant of endogenous circadian variations in subjective alertness and calculation performance as well as in the immediate recall of meaningful material.

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