The overnight red-eye flight from New York to London may leave you feeling groggy and 'jet lagged'- sometimes for several days until your circadian rhythms synchronize with the new time cues-but does frequent time-zone travel have even longer-lasting effects?
In a previous study, Kwangwook Cho (now at the University of Bristol) and colleagues found evidence of impaired cognitive abilities in airline cabin crew who had been subjected to repeated jet lag. Those workers also had higher levels of cortisol-an adrenal hormone secreted during stress-following flights that involved crossing many time zones, as compared with flights over domestic routes. In work reported in this issue (Nature Neuroscience, Vol. 4, No. 6, 01 Jun 2001), Cho now uses structural MRI to measure the volume of the temporal lobes-brain regions critically involved in memory-in airline cabin workers subjected to disruption of circadian rhythms for several years. He found that such workers had smaller temporal lobe structures when compared with airline crew with a similar amount of flight time, but longer intervals between transmeridian flights, and thus presumably more time to recover between episodes of jet lag. Furthermore, higher cortisol levels were correlated with a greater reduction of temporal lobe volume. The results are generally consistent with previous work showing that chronic high cortisol levels, such as those associated with severe depression and post-traumatic stress syndrome, for example, are correlated with a reduced volume of temporal lobe structures and memory impairment. Nevertheless, Cho's data may have broad implications, given that, of course, it is not just airline workers who are subjected to frequent disruptions of circadian rhythms, but also many others, including shift workers and parents of young children. It remains to be determined how long such changes in hippocampal volume persist-and the degree to which they and the associated cognitive impairments are reversible.
Dr. Kwangwook Cho
University of Bristol
MRC Centre for Synaptic Plasticity
Department of Anatomy
BS8 1TD Bristol
tel: +44 117 928 8383
fax: +44 117 929 1687
(C) Nature Neuroscience press release.
Message posted by: Trevor M. D'Souza
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