Mechatronics and Phenomics: a case-study on tremor detection during locomotion in small-sized animals

Movement and behaviour analysis is a key research area in the domain of biomedical engineering and in many other medical research domains aiming at the understanding of physiological motor and cognitive basic mechanisms. The systematic application of robotic and mechatronic technologies to realize new tools and measurement methods for quantitatively assessing motor and cognitive functions in humans as well as in animal models is gaining an increasing popularity. This paper focuses on behavioral analysis of small animal such as mice and rats, and specifically on the design, development and application of a novel system for tremor analysis in reeler mice, a very promising animal model for anatomical and behavioural traits observed in autism. Ground Reaction Force (GRF) sensing is indeed the most direct means of measuring tremor. Under the hypothesis that in-plane GRF components are directly connected to tremor, a dedicated small size, low cost, 2-axis force sensor for measuring the in-plane components of GRF was designed and developed. Special care was paid to design a mechanical structure that would allow self-aligned assembly, so that repeatability and modularity can be easily guaranteed even when combining multiple platforms for implementing a larger sensorised floor embedding multiple sensors. Preliminary testing was performed with both reeler and control (wildtype) mice. A novel measurement method was also identified, applied and verified against experimental data: first Fourier analysis was deployed to extract information due to tremor and to validate the hypothesis of a direct connection between tremor and in-plane GRFs. Secondly, a 2-nd order filter equivalent to an analogical active filter has been implemented in Matlab environment. Data analyzed and filtered highlight a peculiar spectrum frequency in Reeler mice tremor, centered at about 23 Hz. This tremor, which was never quantitatively observed and measured before, is completely absent in wildtype mice