Actigraphic monitoring of movement and rest-activity rhythms in aging, Alzheimer's disease, and Parkinson's disease

Actigraphy, the long-term assessment of wrist movements, is used in several research fields, among which are included sleep and circadian rhythms. Actigraphs record movements using accelerometers. The present paper addresses some basic problems and their solutions in the actigraphic assessment of movement, motor symptoms, circadian rest-activity rhythms, and nocturnal agitation in healthy elderly and elderly suffering from a neurodegenerative disease (i.e., Parkinson's disease or Alzheimer's disease) and summarizes the results of previous and ongoing research. First, the author has investigated how to filter the accelerometer signal in order to minimize the contribution of accelerations induced by positional changes in the gravitational field-a strong source of artefacts. A bandpass filter from 0.5 to 11 Hz appropriately assesses movement induced accelerations while minimizing gravitational artefact. The application of a bandpass filter from 0.25 to 2 or 3 Hz, as is used in some of the commercially available actigraphs, results in artefacts and moreover biases the slower part of the movement spectrum. It is therefore far from optimal for research on aging, which is associated with a generalized motor slowing. Second, the author has proposed an alternative to traditional methods of signal processing in actigraphy, in order to assess both the duration and intensity of movements, and in order to distinguish Parkinsonian tremor. Based on this algorithm, new types of actigraphs have been designed. Third, the author has proposed sensitive variables in order to quantify rest-activity rhythm disturbances in healthy elderly subjects and Alzheimer patients, who often present with symptoms of nocturnal restlessness. Since, in these subjects, research protocols applying enforced phase shifts or time-free environments are unfeasible and not justifiable from an ethical point of view, the variables were specifically designed to assess the functionality of the circadian timing system from actigraphic recordings made in the natural environment of subjects. Examples of the application of actigraphy are given, including studies on symptom fluctuations and medication responses in Parkinson patients, and studies on circadian rhythm disturbances and possible remedies in elderly and Alzheimer patients.