Fatigue in the executive cortical network demonstrated in narcoleptics using functional magnetic resonance imaging--a preliminary study.
OBJECTIVE
To demonstrate dynamic changes in cerebral functional activation during a working memory task in a state of severe excessive daytime sleepiness.


METHODS
Omitting the usual morning dose of stimulants in three narcoleptics induced sleepiness. Functional magnetic resonance imaging (fMRI) was used to map cerebral activation during the performance of a 2-back verbal working memory task. Repeated 9.5 min scans were performed, until the subjects felt they could not continue. This was the functional imaging equivalent of the maintenance of wakefulness test.


RESULTS
Bilateral and widespread activation in known nodes of the executive network were seen during the first scan in all subjects, including the lateral prefrontal, posterior parietal and anterior cingulate cortex. There was a reduction in cerebral activation, especially but not exclusively in the prefrontal cortex, associated with slowing of performance from the first to the last tolerated scan. On stimulants, subjective alertness, activation and objective performance were readily maintained.


CONCLUSIONS
This preliminary study suggests that fatigue in the executive cortical network may be demonstrated by a progressive reduction in regional cerebral activation across scans, which may be prevented by stimulant use. Averaging multiple scan runs, a typical practice in fMRI, could blur important dynamic components of activation.
Division of Pulmonary Critical Care and Sleep Medicine, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA. rthomas1@caregroup.harvard.edu
Robert J
RJ
Thomas
D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology*; D005222:Mental Fatigue / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D009290:Narcolepsy / Q000473:pathology / Q000503:physiopathology* / Q000523:psychology; D009483:Neuropsychological Tests