Nearly 300.000 people in the Netherlands and approximately 55 million people worldwide (WHO) suffer from dementia. With 60 - 70% of all cases, Alzheimer's disease (AD) is the most common form of dementia. While AD is mostly associated with cognitive dysfunction, motor symptoms - as acknowledged in DSM-5 - are part of the neurocognitive domain and have shown to precede cognitive decline in people with AD. These data highlight that dementia not only involves cognitive but also motor components. As such, objective screening tools that can detect these motor symptoms are critical yet unavailable.

A prominent and degenerative motor symptom related to AD is paratonia. Paratonia was first described almost two centuries ago and defined as increased muscle tone during passive movements that is proportional to the strength of the stimulus applied up to the production of counter-movements in the later stages of dementia. Paratonia, therefore, is a motor symptom of AD that heavily affects the quality of life and is often misunderstood and mistaken for behavior of a psychosocial nature. However, despite their impact, motor symptoms of AD receive surprisingly little attention. Indirect evidence suggests that paratonia results from central, i.e., frontal lobe disinhibition, as well as peripheral, i.e., impaired skeletal muscle function due to collagen cross-linking and intramuscular inflammation. Based on these data, it can be argued that paratonia can be objectively quantified using non-invasive electrophysiological measurements. Once developed, such accessible and low-cost screening tool provide evidence for the presence and severity of motor symptoms of dementia in clinical settings besides symptoms of cognitive decline.

Currently, the presence and severity of paratonia are assessed with, respectively, the subjective paratonia assessment instrument (PAI) and the subjective Modified Ashworth Scale for Paratonia (MAS-P). However, objective tools to examine paratonia in people with dementia are not available and as such, the diagnosis of paratonia relies solely on subjective interpretation of clinicians. In a recent review, our research group highlighted the various gaps of knowledge in paratonia-research related to the poor recognition of paratonia and the lack of clear guidance for health professionals. Because eExperimental evidence suggested the possibility to measure paratonia through muscle activity. ,This possibility arises from the hypothesis that the increased muscle tone results from lesions in the frontal cortex in people with dementia and consequently increased disinhibition of the motor cortex. In addition, it is also possible that the heightened muscle tone is (partly) caused by disturbed interactions between ascending sensory inputs and descending motor output. As such, it is reasonable to hypothesize paratonia can be objectively characterized by neurophysiological motor and corticomotor parameters. Moreover, there are indications that motor symptoms precede cognitive decline in people with dementia. Therefore, the goals of the proposed project are threefold and focus on (1) examining whether it is possible to the development of an objectively and non-invasively quantifyassessment the development of paratonia with a tool method based on surface electromyography (sEMG) to quantify paratonia, (2) examining the development of the relationship between motor symptoms of AD and cognitive and physical function from preclinical healthy adults to increasing severity of dementia and (3) identifying the contribution of underlying neuromuscular dysfunctions that are associated with the development of paratonia.