Botulinum toxin (BT) injections are a painful treatment frequently used to treat spasticity following central neurological damage (stroke, multiple sclerosis, spinal cord injury, head trauma). Tolerance of injections varies from patient to patient. For most patients, the pain experienced during the injection is a major source of stress. Numerous clinical trials have demonstrated the role of music therapy in pain management. Music therapy uses a U shaped technique, allowing the patient to relax in different phases. This system has demonstrated beneficial effects on pain and anxiety in various fields, such as chronic and acute pain, Alzheimer's disease, fibromyalgia and neurological pain. Given the painful nature of spasticity and anxiety treatment, we aim to use a musical intervention to help patients cope better with injections. The primary objective of the study is to investigate the effect of exposure to a musical intervention session during botulinum toxin injections, on injection-induced stress (heart rate variability). Secondary objectives: To study the effect of exposure to a musical intervention session during botulinum toxin injections, during the visit to injections #1, in terms of: * Injection-induced stress for HRV parameters other than LF/HF * Injection-induced pain * Injection anxiety * Patient satisfaction * Effect of musical intervention on the medical procedure performed (botulinum toxin injections) expressed by the doctor at the end of the session. To study the effect of exposure to a musical intervention session, during injections visit n°2, in order to evaluate the effect of repeated exposure to a musical intervention session, in terms of : * Injection-induced stress for HRV parameters other than LF/HF * Injection-induced pain * Injection anxiety * Patient satisfaction * Effect of musical intervention on the medical procedure performed (botulinum toxin injections) expressed by the physician at the end of the session. The hypothesis of this research is that a responsive musical intervention can, in adults, reduce the stress induced by botulinum toxin injections. Patients will be selected from the cohort of patients regularly treated for botulinum toxin injections in the Physical and Rehabilitation Medicine (PRM) department at Clermont-Ferrand University Hospital. Botulinum toxin injections will take place in the PRM department. Each patient will participate in the study for a maximum of 4 months. This study will be carried out in patients receiving regular botulinum toxin injections to treat spasticity. The first injection will be given with (IM-IM) or without musical intervention (CT-IM), depending on the randomization group, followed by the next injection with musical intervention. Patients will be able to choose the style of music (Jazz, Classical, Electronic, R\&B, Ambient, Rock, etc.) that appeals to them in order to benefit from a minimum 20-minute session of musical intervention (duration varying according to the number of injections to be performed).