Integrating Visual Information into the Auditory Cortex Promotes Sound Discrimination through Choice-Related Multisensory Integration.

An increasing number of studies have shown that cross-modal interaction can occur in early sensory cortices. Yet, how neurons in sensory cortices integrate multisensory cues in perceptual tasks and to what extent this influences behavior is largely unclear. To investigate, we examined visual modulation of auditory responses in the primary auditory cortex (A1) in a two-alternative forced-choice task. During the task, male rats were required to make a behavioral choice based on the pure tone frequency (low vs high) of the self-triggered stimulus to get a water reward. The result showed that the presence of a noninformative visual cue did not uniformly influence auditory response, with frequently enhancing just one of them. Closely correlated with behavioral choice, the visual cue mainly enhanced responsiveness to the auditory cue indicating a movement direction contralateral to A1 being recorded. Operating in this fashion provided A1 neurons a superior capability to discriminate sound during multisensory trials. Concomitantly, behavioral data and decoding analysis revealed that visual cue presence could speed the process of sound discrimination. We also observed this differential multisensory integration effect in well-trained rats when tested with passive stimulation and under anesthesia, albeit to a much lesser extent. We did not see this differentially integrative effect while recording in A1 in another similar group of rats performing a free-choice task. These data suggest that auditory cortex can engage in meaningful audiovisual processing, and perceptual learning can modify its multisensory integration mechanism to meet task requirements. In the natural environment, visual stimuli are frequently accompanied by auditory cues. Although multisensory integration has traditionally been seen as a feature of associational cortices, recent studies have shown that cross-modal inputs can also influence neuronal activity in primary sensory cortices. However, exactly how neurons in sensory cortices integrate multisensory cues to guide behavioral choice is still unclear. Here, we describe a novel model of multisensory integration used by A1 neurons to shape auditory representations when rats performed a cue-guided task. We found that a task-irrelevant visual cue could specifically enhance the response of neurons in sound guiding to the contralateral choice. This differentially integrative model facilitated sound discrimination and behavioral choice. This result indicates that task engagement can modulate multisensory integration.