Objectives: The aim of the clinical study is to evaluate the usability, feasibility and validity of the digital version of the ActionResearchArmTest (d-ARAT) using the YG system as a platform. Additionally, the feasibility and usability of the implementation of two rehabilitation measures that only recently became integral part of neurorehabilitation, e.g. Action Observation (AO) and Motor Imagery (MI), into the YG training software will be evaluated. Patients & methods: This observational study is designed as a single-arm trial for testing the assessment software including pre- to post rehabilitation comparison of a training involving AO and MI. Therefore, 75 adult patients with Parkinson's disease, MS, Stroke, traumatic brain injury or Guillain-Barré syndrome will be included. 30 out of the 75 patients will take part in the 4-week training on the enhanced VR-based system with a total of 16 training sessions of 45 min each. Primary outcomes will be the score on the System Usability Scale (SUS) and the ARAT as well as the d-ARAT scores. Secondary outcomes will be hand dexterity (Box-and-Block Test), upper limb activities of daily living (CAHAI) and quality of life (EQ-5D-5L).