Multisensory integration for self-body motion perception: human brain mechanisms, bayesian modeling approach and adaptive plasticity with aging – Multisense

Perception is multimodal by nature. To perceive one’s own body movements, the central nervous system (CNS) uses multiple sources of sensory information derived from several modalities including vision, touch and muscle proprioception. All these different sources of information have to be efficiently merged to form a coherent percept.
This project aims to better understand the mechanisms that underlie this multisensory integration, including where it takes place in the brain, and to what extent this multisensory processing can be modulated by sensory deficits.
To achieve this general goal, we will utilize multidisciplinary approaches including psychophics, neuro-imaging (fMRI), microneurographic, and computational modelling methods, always using a comparable experimental paradigm. This paradigm will employ specific tools we have already developed and tested to stimulate the visual, proprioceptive and tactile sensory modalities and to induce in the 3 cases illusory sensations of hand movements in motionless participants. Psychophysical methods will be used to quantify the illusory sensations reported by the subject when stimulation is delivered either separately or concurrently, and electromyographic recordings will measure the involuntary motor responses associated with the illusory perceptual responses.
Using these methods, the goals of this proposal are three-fold:
- First, we will attempt to unravel the principles underlying the co-processing and the modulation of the sensory weighting of muscle proprioceptive, visual and tactile information according to their spatial and temporal congruency. On the basis of the psychophysical data acquired, we will test to what extent the rules governing this tri-sensory integration follow statistically-optimal predictions according to a Bayesian modeling approach.
- Second, we will investigate the neural mechanisms underlying multisensory integration from these 3 sensory sources for self-body movement purposes using two complementary techniques: neuro-imaging with fMRI will permit the identification of candidate brain areas for multisensory processing while microneurographic recordings (unit sensory discharge recordings in humans) will permit the examination of possible sensory interactions occurring at the spinal level. Although many studies have shown that the co-processing of various convergent inputs is crucial to properly assess the body configuration and its changes, where these multisensory inputs are integrated by the CNS is not yet fully understood.
- Lastly, we will study whether adaptation of such integrative mechanisms occurs and whether it is correlated with functional plastic changes in the human brain to partly compensate for sensory system decline due to aging. Although there is consensus for the view that aging has a deleterious impact on each sensory system, little is known about how multisensory interactions change as a function of age. One might hypothesize that the decline in the various sensory systems that affects older people may be partly overcome by adaptive changes during the central integration of these sensory inputs. We will compare perceptual performances and cerebral activities between old and young volunteers to study the impact of age on multisensory processing.
The partnership between researchers with expertise in different fields is essential for the multidisciplinary goals of this project, i.e. the study of crossmodal interactions between three sensory modalities, the rules of these interactions and their possible predictions via a Bayesian model, as well as their underlying neural mechanisms from the spinal up to the cerebral level. By analysing the adaptive property of this system as a function of age in healthy elderly persons, insights gained from these studies may also have further implications for the rehabilitation field.