Enhanced Physiological Tremor in Normal Ageing: Kinematic and Spectral Analysis of Elderly Handwriting

Tremor is a motor phenomenon that occurs in both neurological disorders and normal people. Enhanced physiological tremor can manifest in healthy elderly, as a consequence of age-related normal neurodegeneration, along with an overall decline of motor performance as slowing, decreased coordination, and balance difficulties. Handwriting is a complex neuromotor skill involving fine motor control as well as high-level cognitive processes and its analysis represents a method to investigate motor impairments of the upper limb that occur during the execution of voluntary movements. In this exploratory and preliminary study, has the aim of selecting features and tasks able to characterize handwriting-related kinetic tremor in the elderly by using a digitizing tablet. 11 healthy elderly (over 70 years old) subjects and 17 healthy younger subjects were enrolled in the trial. Participants were asked to perform an accurate drawing task - Archimedes' Spiral, and three fast drawing tasks - overlapped continuous circles and diagonal ascending/descending lines). Data analysis consisted of integrating classical kinematic analysis with spectral analysis. Results of kinematic analysis show the elderly handwriting is overall slower and more fragmented in spiral and diagonal lines tasks but not in overlapped circles compared to younger subjects. The spectral analysis of velocity and acceleration drawing profiles reveals a significant presence of enhanced physiological tremor in the elderly but only in the accurate spiral task. We assess that, beside the Archimedes' spiral already used in previous research works, fast diagonal lines tasks can be employed for kinematic characterization of elderly handwriting but not for tremor identification. The spiral remains the only handwriting exercise able to reveal the presence of age-related enhanced physiological tremor. We conclude that the nature of the handwriting task influences the emergence of involuntary movement and the strength at which motor impairments arise. This aspect must be considered when performing the feature selection of the variables best suited for the characterization of the elderly handwriting.