Feasible Application of the Digit Span Task to the Dementia Screening Test, due to Significant Correlations between its Outcomes and MMSE Score

Abstract

As a screening test of the dementia, such neuropsychological tests as the mini mental state estimation (MMSE) test are usually employed. A problem in MMSE test is that it takes considerably long time, accompanying substantial loads to subjects. We examined whether a digit span task could be an alternative screening test of easier and less time-consuming means for dementia patients. In this task, participants were asked to remember a series of random digits (from 0 to 9), individually displayed on a screen for 2 sec and thereafter to input them on a touch panel. The number of figures was increased from 3 to 7 by one place and vice versa. We recorded the maximum number of figures correctly recalled (Nmax) and the reaction time (RT) until the first digit input. The experiments were carried out by participants clustered into three groups;(1)the healthy young group (n=15, 22±1.15 years old). (2)the healthy elderly group (n=10, 68.5±4.5) and (3)the senile dementia group (n=13, 76.6±6.9). Only participants in the dementia group took the MMSE test. Nmax of dementia group (4.46±0.94) was significantly lower than that of healthy elderly group (6.10±0.62) and of young group (8.71±0.96) (F(2, 34)=84.00, p<0.01). In all groups, RT was significantly elongated with the increased figures of displayed digits, although the slope of the regression line of the dementia group was 2.5 times as much as those of other groups. Regarding the dementia group, the MMSE scores of individual participants were found to be significantly correlated with Nmax (r=0.82, p<0.01) and with RT of 6 digits number (r=-0.64, p<0.05). These results suggested that the digit span task could be a feasible and reliable screening test for dementia.