Multisensory Integration And Categorization In Mouse Medial Prefrontal Cortex Neurons

We live in a multisensory environment.Many objects and events around us contain multiple sensory information.To perceive and discriminate them,our brain must integrate these multisensory inputs.However,we do not understand the neural mechanism of how the brain synthesizes multisensory information to affect perception and classification.Here,we studied the influence of multisensory integration of medial prefrontal cortex(m PFC)neurons on cue discrimination and categorization.We first trained head-fixed mice to perform a cue-guided alternative-choice task.When the triggered stimulus is a low-frequency pure tone,a horizontal moving grating,or a combination,the mice must choose a left-side choice and otherwise select the right direction.The results showed that animals acquired a higher performance in the combined condition than in a visual or auditory condition,indicating that multisensory integration can enhance the discrimination ability of mice.Chemogenetic inactivation of bilateral m PFC or optogenetic inhibition of PV neurons in unilateral m PFC could decrease the correct rate of the behavioral task.Using multi-channel recording,we recorded and analyzed the activities of m PFC neurons when mice performed the task.Most m PFC neurons showed perceptual or decision-making responses in visual or auditory trials.One-third of neurons recorded can significantly discriminate stimuli.Most of them favored the stimulus denoting the ipsilateral choice being recorded regardless of modalities.Neurons mainly showed two integrative manners: consistent integration and differentiated integration.The differentiated integration mode significantly enhanced the resolution of auditory &visual combined stimuli.Categorization is a vital process when the brain discriminates objects.We systematically studied how m PFC neurons categorize cues in visual,auditory,and visual-auditory modalities.It is found that the categorization accuracy of mice was higher in the visual-auditory condition than in the unisensory condition.We notice the activity of m PFC neurons exhibited several manners for categorizing cues.Some neurons showed a strong response to one category of stimuli but showed no or weak response for stimuli of the other category;some neurons showed a response just to stimuli at the boundary.We also find that a higher proportion of neurons engaged in visual-auditory categorization.The population decoding analysis demonstrates that neurons have low discrimination between stimuli in the same category but show the strong between stimuli of different categories.In the multisensory condition,the populations show higher decoding accuracy.Taken together,we believe that the high-order cerebral cortices greatly rely on multisensory integration in the process of encoding and discriminating cues.These results enrich our understanding of the role of multisensory integration in the brain.