The Role Of Different Multisensory Cortical Areas In Visual And Vestibular Recalibration

In daily life,individuals often need to effectively integrate multiple sensory signals that share a common spatiotemporal context into a unified and coherent perception in order to generate more accurate and faster responses,which is referred to as multisensory integration.However,due to differences in the physical conduction of stimuli and neural transmission,the stimulation of different sensory channels is not entirely matched.Only by recalibrating to minimize the differences between sensory inputs can further multisensory integration be achieved.This phenomenon of multisensory recalibration is a short-term multisensory plasticity that reflects the dynamic processing of multisensory integration.It plays a broad and important role in our dynamic adaptation to the surrounding environment.However,our understanding of the neural mechanisms behind multisensory recalibration is still limited.In this study,vestibular-visual conflict adaptation was used as a behavioral paradigm to explore the neural mechanisms of multisensory recalibration.Each experimental session consisted of three consecutive blocks: pre-recalibration,recalibration(gradually introducing vestibular and visual conflicts,also known as conflict adaptation phase),and post-recalibration.The recalibration behavior of subjects to two modal stimuli was evaluated by calculating the changes in their perception of vestibular and visual stimuli(manifested as shifts in the psychometric curves)in the two modalities before and after recalibration.We found that after a systematic vestibular-visual conflict adaptations,the unisensory perceptual estimates for subsequently presented stimuli were shifted toward each other(in opposite directions)to reduce the conflict.This confirmed the existence of multisensory recalibration and provided a behavioral basis for subsequent studies of the corresponding neural mechanisms.Since we did not provide any feedback to the subjects during the vestibular-visual recalibration,it belonged to an unsupervised recalibration,which was generally considered as a bottom-up information processing process.Therefore,we selected three representative target brain regions at different sites along the visual-vestibular processing pathway to investigate the correlation between neural activity and recalibration behavior.The dorsal medial superior temporal cortex(MSTd)served as the primary visual processing area,the posterior insular vestibular cortex(PIVC)served as the primary vestibular processing area,and the ventral intraparietal cortex(VIP)served as the high-level cortical area in the visual-vestibular integration pathway.To compare the changes in neural response to vestibular and visual stimuli in different brain regions before and after recalibration,we performed the neurometric curves to quantify the shift of neuronal tuning.We found that in MSTd,neuronal responses to vestibular and visual stimuli shifted after recalibration,and the direction of tuning shift was consistent with the direction of perceptual shift under each stimulus.In PIVC,the direction of tuning shift for the vestibular stimuli was also consistent with the direction of perceptual shift for vestibular stimuli,but no tuning shift was found for visual stimuli because the PIVC cells were not robustly tuned to visual stimuli.In contrast,the recalibration of neurons in VIP was significantly different: both vestibular and visual neuronal tuning shifted in the direction of the vestibular perceptual shifts.Thus,visual neuronal tuning shifted,surprisingly,contrary to visual perceptual shifts.These results indicated that neuronal recalibration exhibited large differences between different multisensory cortical areas.The neuronal activity in VIP carried not only the heading signals from stimuli,but also choice signals related to behavioral choices made by monkeys in response to heading stimuli.In order to further explore what signals were involved in recalibration,we used partial correlation analysis to separate the heading and choice signals in VIP neurons.We found that after recalibration,the choice signals in VIP neurons decreased under both visual and vestibular conditions,while in MSTd and PIVC,the choice signals did not significantly change before and after recalibration.This was further confirmed by using the targeted dimensionality reduction method.In summary,during the unsupervised visual-vestibular recalibration,PIVC,MSTd,and VIP all underwent changes related to the recalibration behavior in order to reduce conflicts between different senses.However,there were significant differences between these brain regions,indicating that they played different roles in the visual-vestibular recalibration.