Representation Of Cross-modal Information In Neurons Of Auditory Cortex In The Behavioral Task Of Sensory Discrimination

Each of us lives in a complex world and always perceives sensory cues of different modalities(auditory,visual,and tactile)from the outside world.The brain must filter,process and ultimately integrate those sensory cues.Via this process,things and events were accurately encoded.Although multisensory integration is an important and basic function of the brain,we know little about it.According to the point of traditional view,multisensory information is integrated only in the high-order cortices such as medial prefrontal cortex(mPFC)and posterior parietal cortex rather than in primary sensory cortices such as auditory and visual cortices.These results were mainly derived from the research conducted in anaesthetized animals.Obviously,encoding sensory information in the active brain is completely different from that in anesthetized animals,which indicates that sensory cortex,even primary area,might engage in processing multisensory inputs.Using 32 multi-channels extracellular recording,we recorded and examined auditory neurons' responsiveness to auditory,visual and auditory-visual stimuli when animals performed the behavioral tasks of discriminating different sensory stimuli(auditory,visual or auditory-visual).Comparisons of the responses and integrative manners in different cognitive states(task,anaesthetized,passive)were also investigated.The results showed that neurons in auditory cortex could involve in encoding visual cues and displayed strong integrative capability during the course of performing tasks.However,it is also found that neurons' responses and integrative manners did vary with tasks.Nearly half of these neurons recorded could respond to visual stimulation if a paired auditory-visual stimulus is reward-associated in the task,with an average multisensory enhancement of 53%.Most of them exhibited the strong capability to synthesize visual and auditory inputs.Similar phenomena could not be observed in anaesthetized and passive(awake but not do the task)animals.Under the condition of both states,most neurons failed to show visual responses and also failed to show similar integrative capabilities just as they did in the behavioral task.When an animal performed the task in which only auditory stimulus was reward-associated,the majority of neurons did not respond to visual stimuli,and in some of them,the presence of visual stimuli even inhibited the response to the auditory stimulus.In a task that animals could get the reward according to whether a triggered stimulus is visual or not,64% of recorded neurons showed the response to visual stimuli,and exhibited the inhibitory interaction between visual and auditory inputs.These observations indicate that the traditional sensory cortex can also engage in encoding other sensory information.For example,as is found here,auditory cortex can encode visual cues in an active brain.Those results greatly enrich our understanding regarding multisensory integration of the brain,and deepen our understanding for the structure and function of the sensory cortices.This work provides important experimental evidence for revealing how the brain perceives external information.