Beyond motor: a systematic review of multisensory integration deficits in Parkinson's disease.

Parkinson's disease (PD) is primarily characterized by motor symptoms, but non-motor issues, including sensory, perceptual, and cognitive impairment, common, significantly impacting daily functioning. Multisensory integration (MSI), the brain's ability to combine sensory information, is crucial for effective navigation and interaction with the world. In PD, disruptions in MSI can lead to various functional difficulties. This systematic review, conducted by PRISMA guidelines, analyses 40 studies with 2070 participants to investigate MSI in PD. The findings indicate significant deficits in MSI, especially in audiovisual temporal discrimination, body ownership perceptions, and visual-vestibular integration. These deficits negatively affect movement accuracy and verticality perception. The review highlights a strong focus on balance and postural control, with multiple studies reporting issues in visual-vestibular integration and vestibular dysfunction. These impairments, along with cholinergic deficits, contribute to postural instability and increased fall risk in individuals with PD. Studies using virtual reality and portable monitors further emphasize the role of vestibular and proprioceptive dysfunction in maintaining balance. Perceptual integration is also disrupted, with altered body ownership perceptions and impaired audiovisual processing manifesting at the perceptual level, linked to subcortical structures, such as the subthalamic nucleus. These deficits extend to motor imagery and body representation, affecting both hand movement accuracy and visual-vestibular perception. This review underscores the critical role of MSI deficits in PD, highlighting the importance of understanding sensory integration in the management of the disease. Understanding these deficits can lead to more precise diagnostic tools and highly targeted rehabilitation strategies, thereby improving patient outcomes and guiding clinical practice.