Circadian preference and cognitive functioning among rehabilitation inpatients.

The influence of circadian preference was examined among 56 morning-oriented rehabilitation inpatients with cognitive (n=28) and noncognitive (n=28) impairments. Each individual was tested twice: morning (preferred time) and evening (nonpreferred time); sessions and test batteries were counterbalanced to control for practice effects. Standard measures assessed attention, language, memory, visuospatial, and executive functions. Persons with cognitive impairment showed disproportionate vulnerability to the effects of circadian preference and time of testing, performing more poorly at nonpreferred than preferred times. Substantial effects (eta2 .12 to .48) were found on tests of executive functioning and tasks incorporating similar higher-order demands (e/g/. complex figure copy). Results are supported by tympanic temperature changes during a vigilance task, and index of cerebral blood flow in response to cognitive challenge. Cognitive reserve theory is suggested as an explanation for the differential effects. These findings may have implications for inpatient therapeutic interventions and discharge planning.