To clarify the activity of demented patients cared for with and without artificial nutrition in a care facility, sequential biological observation was applied using electroencephalograms (EEG), electromyograms (EMG) and electro-oculograms (EOG). Awake and sleep patterns and spontaneous swallowing were measured during the daytime in 13 patients with advanced dementia who could orally intake meals (OR patients), and 13 patients with advanced dementia, who received artificial nutrition by percutaneous endoscopic gastrostomy (PEG patients). The awake/sleep pattern fluctuated during daytime in OR and PEG patients, but a fully awake state was relatively preserved around meal times in OR patients. The number of spontaneous swallowing was small in PEG patients (0.1 ± 0.3/h), and the value correlated with the Barthel Index in OR patients. Continuous recording of biological activity in demented patients could be informative in providing an overview of their activities. The present results disclosed that meal times were the limited periods keeping OR patients awake consistently, while there was no opportunity for such periods for PEG patients. The number of spontaneous swallowing was especially small in PEG patients, although low Mini-Mental State Examination and Barthel Index scores and poor awake state during daytime were considerable in those patients.