Awake Mouse Superior Colliculus Neurons's Response Properties And Discrimination Of Visual-Auditory Cues In A Task

Integrating multiple sensory inputs is a critical function of the brain,but the process is extremely complex.Although more and more laboratories around the world are conducting multisensory integration research,our understanding of it is still limited.Previous studies have shown that there are many neurons in the superior colliculus that can respond to stimuli from multiple sensory modalities,and detailed studies regarding multisensory integration has been carried out on them.It is found that for the majority of superior colliculus neurons,their response to spatiotemporal concordant stimulus is greater than the best unisensory response,and even greater than the sum of unisensory responses.However,in most of previous studies,studies on multisensory integration in neuronal level were conducted in anesthetized animals.It is unclear whether neurons' integrative pattern in awake animals is similar to that in anesthetized animals.At the same time,studies conducted in cerebral cortices of primates showed that in rare cases was neurons' multisensory response much higher than unisensory response,suggesting that enhancement integration may occur only under the anesthetized state.In this project,using multi-channel recording in awake but head-fixed mice as animal models,we studied this issue deeply in the middle and deep layers of superior colliculus.The results showed that,unlike previous results obtained in the cat superior colliculus,both visual and auditory spatial receptive fields of mouse superior colliculus neurons did not exhibit strong spatial orientation selectivity,but there was a contralateral preference,that is,the spatial receptive fields were mainly located in the contralateral space of the recording location of neurons(if the neuron was recorded in the left superior colliculus,then its auditory and visual spatial receptive fields were in the right hemisphere).The results also showed that for most of neurons recorded,their response to spatiotemporal concordant visual-auditory stimuli was much higher than the best unisensory response,even greater than the sum of auditory and visual responses.This result suggests that enhancement integrationstill dominates in the superior colliculus of awake animals.This result,combined with our previous data,suggests that the mode of multisensory integration in superior colliculus neurons is not greatly affected by the state of the brain(anesthetized and awake),suggesting that enhancement integration might be an inherent feature of the superior colliculus.Despite this,the audiovisual information integration in the supper colliculus of awake mice was also greatly affected by the spatial arrangement between visual and auditory stimuli.When both were far away from each other in space,the effect of enhanced integration greatly declined.In addition,we trained animals to complete a go/no-go task according to multisensory cues.Only when auditory-visual stimuli are consistent in space and animals made the behavioral choice correctly,they could get water reward.If auditory and visual stimuli were separated in space,they had no reward.Our main purpose is to study whether coding multisensory stimuli in an awake but passive state is the same as that in the cognitive task.The results showed that superior colliculus neurons had similar encoding pattern to visual-auditory stimuli in both performing tasks and awake but passive state,and showed stronger response to spatially concordant visual-auditory stimuli,but weaker response to visual-auditory stimuli in separate spatially,indicating that cognitive state showed less effectiveness on encoding multisensory cues of superior colliculus neurons.The study conducted in superior colliculus of awake mice can help us better understand the role of the superior colliculus in multisensory integration and localization of external stimuli.Considering superior colliculus receives inputs from many cortical and subcortical areas,the result will also enhance our understanding of the integrative process of multisensory information in the brain.