# Dynamic Handwriting Analysis for Neurodegenerative Disease Assessment: A Literary Review
## 3 Research Directions
### Parkinson's Disease
#### 3.1.1 Disease Insight
Patients and controls were requested to write cursive patterns at different sizes (1, 1.5, 2, 3, and 5 cm). Each target pattern was displayed at its required size on the tablet but disappeared as soon as the pen touched the surface of the screen. In contrast to controls, patients with PD undershot the target size of 2 cm and, when required to write as fast as possible, they even undershot the 1.5 cm target size. These findings support the hypothesis that the range in which stroke size can be manipulated without significant changes in stroke duration is smaller in Parkinsonian handwriting than in the healthy handwriting. [PERSON] et al. [68] examined the handwriting dynamics of patients with idiopathic PD, schizophrenia, and drug-induced Parkinsonism (SZ) and of healthy control. Participants were instructed to write the word _hello_ twice at three vertical height scales. The (in)ability to scale movement velocity with increasing movement distance was quantified. Four observations were drawn: (1) both SZ patients with drug-induced Parkinsonism and PD patients exhibited impaired movement velocities and velocity scaling; (2) performance on the velocity scaling measure can distinguish drug-induced Parkinsonism from controls with 90% accuracy; (3) SZ, but not PD, participants displayed abnormalities in movement smoothness; and (4) there was a positive correlation between age and magnitude of the velocity scaling deficit in PD participants. [PERSON] et al. [69] were among the first to analyze handwriting in newly diagnosed, untreated PD patients. The results of the study showed that newly diagnosed patients are impaired in performing complex uni-manual upper limb motor tasks in comparison to healthy subjects. They appeared to be particularly impaired in their handwriting, exhibiting reduced sentence length and writing velocity and a decrease in letter height during writing. Therefore, the authors concluded that impairments in performing tasks involving complex uni-manual upper limb movements are an early characteristic of PD; thus, they could be used for the early disease diagnosis. [PERSON] et al. [70] considered a drawing task instead of handwriting ones to address the hypothesis that PD patients exhibit deficits in controlling acceleration when the task involves an increase in inertial load, specifically under the requirement to increase movement amplitude and/or speed, and in the weight of the pen. Patients showed significantly lower mean velocity, lower acceleration, higher constant error of stroke length, and higher normalized jerk scores than controls. Nevertheless, these effects were not worsened by adding weight to the pen. The observed smaller-than-required movement amplitude suggested a relationship between hypometria and bradykinesia in drawing and/or handwriting. In Reference [71], [PERSON] et al. tested the hypothesis that PD affects differently handwriting movements depending on the coordination pattern of wrist and finger motions. To investigate this hypothesis, the groups under study were requested to perform three types of cyclic wrist and finger movements: drawing two lines and a circle. Although both groups deformed the circle during fast movements, the deformation was more pronounced in patients than in controls. A possible reason for this is that PD patients may be unable to properly regulate the influence of biomechanical factors on wrist and finger motion. In the model of PD handwriting proposed in Reference [59], basal ganglia nuclei is modeled as lumped units, with activity levels represented by rate codes. Basal ganglia dynamics is described in terms of fixed-point behavior; thus, only magnitude-related aspects of handwriting--faster/slower, larger/smaller, etc.--can be captured. [PERSON] et al. [72] presented an alternative model of Parkinsonian handwriting, which produces a stable rhythm in a network of oscillators and resolves the stroke output in a Fourier-style. In the paper, the model predictions were compared to handwriting data obtained by patients and controls.