Movement-related desynchronization detection in Brain-Computer Interface applications for post-stroke motor rehabilitation

Neurological degenerative diseases like stroke, Alzheimer, Amyothrophic Lateral Sclerosis (ALS), Parkinson and many others are constantly increasing their incidence in the world health statistics as far as the mean age of the global population is getting higher and higher. This leads to a general need for effective, at-home and low-cost rehabilitative and health-daily-care tools. The latter should consist either of technological devices implemented for operating in a remote way, i.e. tele-medicine is quickly spreading around the world, or very-advanced computer-based and robotic systems to realize intense and repetitive trainings. This is the challenge in which Information and Communications Technology (ICT) is asked to play a major role in order to bring medicine to reach further advancements. Indeed, no way to cope with these issues is possible outside a strong and vivid cooperation among multi-disciplinary teams of clinicians, physicians, biologists, neuropsychologists and engineers and without a resolute pushing towards a widespread interoperability between Institutes, Hospitals and Universities all over the world, as recently highlighted during the main International conferences on ICT in healthcare. The establishment of well-defined standards for gathering and sharing data will then represent a key element to enhance the efficacy of the aforementioned collaborations. Among the others, stroke is one of the most common neurological pathologies being the second or third cause of mortality in the world; moreover, it causes more than sixty percent survivors remain with severe cognitive and motor impairments that impede them in living normal lives and require a twenty-four-hours daily care. As a consequent, on one side stroke survivors experience a frustrating condition of being completely dependent on other people even to perform simple daily actions like reach and grasp an object,hold a glass of water to drink it and so on. States, by their side, have to take into account additional costs to provide stroke patients and their families with appropriate cares and supports to cope with their needs. For this reason, more and more fundings are recently made available by means of grants, European and International projects, programs to exchange different expertise among various countries with the aim to study how to accelerate and make more effective the recovery process of chronic stroke patients. The global research about this topic is conducted on several parallel aspects: as regard as the basic knowledge of brain processes, neurophysiologists, biologists and engineers are particularly interested in an in-depth understanding of the so-called neuroplastic changes that brain daily operates in order to adapt individuals to life changes, experiences and to realize more extensively their own potentialities. Neuroplasticity is indeed the corner stone for most of the trainings nowadays adopted by the standard as well as the more innovative methods in the rehabilitative programs for post-stroke recovery. Specifically speaking, motor rehabilitation usually includes longterm, repetitive and intense goal-directed exercises that promote neuroplastic mechanisms such as neural sprouting, synapto-genesis and dendritic branching. These processes are strictly related with motor improvements and their study could - one day - serve as prognostic measures of the recovery. Another aspect of this field of neuroscience research is the number of applications that it makes feasible. One of the most exciting is to connect an injured brain to a computer or a robotic device in a Brain-Computer or Brain-Machine Interface (BCI or BMI) scheme aiming at bypassing the impairments of the patient and make him/her autonomously move again or train his/her motor abilities in a more effective way. This kind of research can already count an amount of literature that provides several proofs of concept that these heterogeneous systems constituted by humans and robots can work at the purpose. A particular application of BCI for restoring or enhancing, at least, the reaching abilities of chronic stroke survivors was implemented and is still currently being improved at I.R.C.C.S. San Camillo Hospital Foundation, an Institute for the rehabilitation from neurological diseases located in Lido of Venice and partially technically supported by the Department of Information Engineering of Padua in range of an agreement signed in 2009. This specific BCI platform allows patients to train and improve their reaching movements by means of a robotic arm that provides a force that helps patients in completing the training exercise, i.e. to hit a predetermined target. This force feedback is however subject to a strict condition: during the movement, the person has to produce the expected pattern of cerebral activity. Whenever this is accomplished, a force is delivered proportionally to the entity of the latter activity, otherwise the patient is obliged to operate without any help. In this way, this platform implements the so-called operant-learning, that is one of the most effective conditioning techniques to make a subject learn or relearn a task. If, on one hand, the primary and explicit task is to improve a movement, on the other side the secondary but most important task is to deploy the perilesional part of the brain - still healthy - in becoming responsible for the control of the movement. It is a popular and widely-accepted opinion within the neuroscience community, indeed, that a healthy region of the sensorimotor area nearby the damaged one - which was previously in charge of performing the (reaching) movement - can optimally accomplish the impaired motor function substituting the original control area. Technically speaking, the main crucial feature that can ensure the effectiveness of the whole system is the precise and in real-time identification and quantification of the cerebral pattern associated with the movement, the worldwide named movement-related desynchronization (MRD). Starting from its original definition, passing through the most used techniques for its recognition, the thesis work presents a series of criticisms of the current signal processing method to detect the MRD and a complete analysis of the possible features that can better represent the movement condition and that can be more easily extracted during the on-line operations. Brain - it is well-known - learns by trials and errors and it needs a slightly-delayed (in the range of fraction of seconds) feedback of its performance to learn a task in the best way. This BCI application was born with the purpose to provide the above-mentioned feedback: however, this is only feasible if a computationally easy and contingent signal processing technique is available. This thesis work would like to cope with the lack of a well-planned real-time signal analysis in the current experimental protocol.