Influence of Outdoor Activity and Indoor Activity on Cognition Decline: Use of an Infrared Sensor to Measure Activity

Objective: The increasing number of dementia patients causes serious social problems. Previously, we reported that elderly individuals with cognitive impairment show a low frequency of activity. This study was designed to investigate the correlation of daily activity to the decline in cognitive function. Methods: The study enrolled 53 elderly who live alone. The cognitive function of subjects was assessed by the mini-mental state examination (MMSE) before the investigation. Passive infrared sensors were installed in the subjects' houses. The subjects' in-house movements were recorded by the sensors for similar to 1 year. The activities of daily life were assessed, based on these records. The subjects' cognitive function was assessed again after the investigation and categorized into two groups: the cognition decline group (MMSE score: <24, n = 6) and the normal group (MMSE score: over 24, n = 44). The activity parameters were compared between the two groups. Results: The subjects in the cognition decline group had a significantly lower number of outings (8.8 vs. 17.3, p < 0.01) and there was no cognition decline in patients in the frequent outings group (over 20 outings per month). In addition, the indoor movement decreased in the cognition decline group during the study period and the indoor movement of the normal group was maintained at the baseline level. Conclusions: This study objectively evaluated the behavior of elderly individuals with infrared sensors and revealed that elderly people who have few occasions to go out tend to show a decrease in cognitive function.