Assessing Motor Abilities in Healthy and Pathological Individuals: A Wearable Sensor-based Analysis Methodology

Millions of individuals worldwide are impacted by neurodegenerative diseases, which are marked by the gradual deterioration of cognitive abilities like memory, attention, language, and problem-solving abilities. Identifying and tracking the symptoms of dementia at an early stage is crucial to facilitating timely interventions that can decelerate its advancement and enhance the overall well-being of patients. One of the key aspects in dementia assessment is understanding neuroplasticity. Neuroplasticity represents the brain's remarkable capacity to adapt and restructure to environmental stimuli, constantly reshaping its neural pathways to enhance movement and function. It reflects ongoing neural pathways and synapse changes due to experiences, environmental shifts, learning, and injury. This adaptability is a continuous, intrinsic part of brain function throughout life. Evaluating neuroplastic changes is essential for understanding learning and memory mechanisms, recovery processes after neural damage, and informing therapeutic interventions for neurological disorders. This evaluation has both academic and clinical implications. Traditional methods include neuroimaging techniques and behavioral assessments. These methods provide valuable information about dysfunctions in brain activity and changes in cognitive and motor abilities. However, their application involves high costs and the use of specialized equipment. Consequently, the need emerges for a specific test, an effective alternative for analyzing motor difficulties. For example, the clinical assessment of bradykinesia in PD emphasizes the importance of the Unified Parkinson's Disease Rating Scale (UPDRS) in clinical trials. However, the UPDRS has limitations, especially in assessing bradykinesia, a central symptom of PD. Bradykinesia, characterized by slowness and decreased amplitude of movements, often accompanied by arrhythmicity, is an important symptom of PD, present from early stages and progressing over time. There is a need for quantitative and objective outcome measures with high sensitivity to change to enable early study of new neuromodulatory therapies. Several studies have explored quantitative approaches to assess index finger tapping using digitized sensors and gyroscopes to measure movements' frequency, amplitude, and rhythmicity. Using inertial sensors on the index finger can provide objective measures of speed, amplitude, and rhythm, overcoming the limitations of clinical rating scales. Studies have shown significant differences in quantitative tapping parameters between patients with PD and healthy controls, suggesting the potential of these measurements to complement clinical analysis. However, whether quantitative measures of tapping can distinguish between different stages of PD and show significant longitudinal changes over time has not yet been fully explored. Another study aimed to compare quantitative measures of tapping among three groups early-stage PD, intermediate-stage PD, and healthy controls and to determine any changes over a 12-month period. While the UPDRS remains the predominant tool for assessing PD in clinical trials, integrating quantitative index finger-tapping measurements through digital technologies offers promising opportunities to improve the accuracy and objectivity of clinical assessment, potentially enabling earlier diagnosis and more sensitive assessments of disease progress and treatment efficacy. In parallel, AD manifests not only with cognitive impairments but also with deficits in fine motor abilities, critical for self-care and daily activities. Patients with AD show impairments not only in higher brain functions but also in motor functions, especially fine motor abilities, crucial for self-care and instrumental activities of daily living (IADLs). Several indicators exist to assess motor dexterity, including finger-tapping tasks and three-dimensional analysis of movements to touch targets. However, many of these tests require complex tasks. They are influenced by language comprehension and memory ability, making them less preferred by patients with mild cognitive impairment or little knowledge of the disease. The FTT has proven to be a quick and simple alternative for assessing fine motor abilities, especially in AD. For example, some studies compared performance on the FTT with other measures of fine motor dexterity in patients with AD at different stages of the disease. The results showed a significant correlation between performance in FTT and the degree of cognitive impairment in patients with advanced AD, suggesting that FTT might be a sensitive indicator of fine motor abilities decline related to disease progression. The FTT appears as a potential assessment tool in this area. This test focuses on the analysis of finger movement to detect any motor abnormalities and concentrate on the accuracy and agility of fine movements of the upper limbs. In addition, variations of the FTT can provide additional detail through movement analysis. Some versions require the simultaneous use of two fingers or both hands, expanding the range of investigation and the ability to gather more complex information about motor function. These variations allow for a more in-depth assessment of coordination, dexterity, and synchronization between hands, thus providing a more comprehensive view of an individual's motor abilities or limitations. As identified in recent studies, this motor challenge arises from the intricate need to shift attention swiftly between different fingers. Such coordination requires precise and timely motor control, a complex process involving various neurological pathways and muscle groups. The brain's adaptability in optimizing these pathways is critical, as it allows for fine-tuning movements necessary for complex tasks. Moreover, these tests underscore that finger coordination is affected by many factors. The specific nature of the task, whether a simple repetitive motion or a complex sequence of movements, plays a significant role. Additionally, the complexity of the required movements themselves can significantly impact coordination. It's not just the task or its complexity; the individual's inherent level of motor control and the amount of practice they have had significantly influence their performance. This highlights the importance of personalized approaches in neuroplasticity assessment and training. The efficiency of brain plasticity is exemplified by the ability of hands and fingers to perform intricate tasks. This efficiency directly results from the brain's ongoing adaptation of neural pathways to improve coordination. Such neuroplastic changes are fascinating and critical for understanding how we can enhance motor abilities through targeted interventions. Despite being simple, the FTT could serve as a preliminary screening tool to detect signs of neuromuscular problems and altered motor abilities in the motor cortex~\cite{delcour2018early}. Performing the test, however, has significant limitations due to its inherent subjectivity. Several methodologies and instruments for performing this test have been developed in the literature, highlighting the challenges in standardizing its application. A critical aspect is that traditional methodology is prone to operator error and provides limited data. In addition, the technologies used are often cumbersome or outdated, further complicating the effectiveness of the test. These constraints highlight the need for a more refined and objective approach to assessing neuroplastic changes, ensuring that the results of the FTT are reliable and complete. A wide range of methodology has been reported in exploring the various device-based methods for performing the FTT. The most common is the traditional tapping lever equipped with a mechanical counter. This simple yet effective device has been a staple in many studies and clinical assessments. The field has also seen innovations like the electronic and software versions provided by Western Psychological Service (WPS). These versions, such as the Digital FTT, consist of a device with an electrical switch and a digital counter, offering more precise measurement capabilities. Even the humble zero key on a numeric keypad has been repurposed as a tapping device in a software-only version of the FTT, demonstrating the creativity in leveraging available technology. The Light Beam Finger Tapper Test, which employs infrared light-sensitive photographic diodes, represents another technological advancement. This method offers a non-intrusive, highly accurate way of measuring finger movements. More recent innovations have embraced the digital era, utilizing keyboards, smartphones, tablets, and even built-in cameras in mobile devices. These methods not only make the FTT more accessible but also allow for a more in-depth analysis of the tapping performance. However, they are often limited by the number of parameters they can monitor. Significant findings have emerged from the use of these various FTT methods. For instance, studies have shown that males generally exhibit quicker single-finger tapping speeds than females, a difference attributed to the proportional development of fast-twitch muscle fibers during puberty. Interestingly, while men's finger-tapping speed shows little decrease with age on average, women's performance tends to decline. These findings provide valuable insights into the gender-specific aspects of motor control and its relation to neuroplasticity. Furthermore, the literature provides normative data with demographic adjustments for a broad age range from 20 to 80 years. This data reflects average performance scores based on gender, with men typically averaging 50 taps per 10-second interval and women averaging 45. These benchmarks are crucial for evaluating motor skill levels and detecting deviations that might indicate neurological issues. In conclusion, the standard FTT has established itself as a widely used method for assessing coordination and cognitive abilities. Its simplicity and the potential for technological enhancement make it a versatile tool in research and clinical settings.