DIURNAL VARIATION IN LANGUAGE TESTS AND RELEVANCE TO EARLY DETECTION OF DEMENTIA: DISRUPTION OF TIME DEPENDENCY IN DEMENTING SUBJECTS (1996)

To the Editor: In a previous study1 we documented that Word Fluency Measure (WFM) scores2 (used to diagnose dementia levels) of healthy adults exhibited time dependency. It was also documented that aging and dementia alter time-dependent patterns of various human metabolic and cognitive functions.3-6 We recognized that these alterations may affect the evaluation of early dementia in older people and/or stage of dementia in patients. To explore this possibility, we administered the WFM to 19 individuals (5 males and 14 females, age range 68 to 94 years) whose mental test scores7 ranged from 36 to 93. All subjects lived in habitats where the main daily activities (sleep-wake, meals) were similar and controlled. The test required that examinees name, in a 1-minute time period, items related to each of six categories. An examiner was present during the test and used a tape recorder and a stop watch to asses the time. Anova was used to determine time dependency; t test (two-tail), correlation, and χ2 were used for elucidating significant differences between various observations. Analysis of the data detailed in Table 1 did not reveal any correlation between mental test scores and age (correlation coefficient = –.249, R2 = .062, N = 19) or years of education (correlation coefficient = 0.395, R2 = .156, N = 19), and no differences were observed between the mean test scores by gender (t test, P = .908). First day patterns of WFM scores of two subjects, similar in age but differing in their mental test levels, are shown in Figure 1. The WFM patterns monitored for two successive days were similar to the first day pattern for each subject. When the WFM score patterns of all monitored subjects were analyzed, the examined population could be clustered into two groups. In the nine subjects whose mental test scores were lower than 61, no WFM time dependency was found. Among the 10 subjects with mental test scores higher than 73, seven exhibited significant WFM time dependency similar to that exhibited by subject SS (Figure 1). The results indicate that, with regard to cognitive function - WFM, which is used to assess dementia levels, (1) age is not correlated with dementia stage and (2) disruption of time dependency was observed in all subjects whose mental test scores was lower than 61 and was preserved in the majority of subjects with a mental test score of 73 and above. . Representative Patterns of daily WFM Scores in two subjects of similar age and different mental test scores (see text for description of 3-day pattern. It is assumed that changes in patterns of time-dependent (or circadian) rhythms either reflect an alteration of the endogenous component that drives that rhythm or result from the effects of external “masking” signals. It is difficult to decide which of these possibilities relates to the documented alterations in rhythms of aged and demented subjects.3-6 However, it seems that dementia stage and preservation of the time-dependent output of a cognitive function (WFM) are reciprocally correlated. Does such a correlation apply to other physiological and cognitive variables? Does dementia stem from alteration of the endogenous component that controls rhythms, or does the absence of time dependency reflect the inability of dementing people to be entrained by external signals? The answers to the last two questions demand the exposure of demented people to constant and isolated environments, which is neither feasible nor ethical. Yet, as WFM is a test used for assessing dementia stage, it is recommended that its time dependency be examined, rather than relying on one daily measurement. The introduction of such a procedure may be of assistance in the diagnosis of early dementing stages.