Abstract
Does the brain process the senses independently and then combine them, or are the senses put together early, in putatively “unisensory” areas? Recent studies have found evidence that supposedly unimodal cortical areas are sensitive to multimodal stimuli. This work suggests that multisensory integration begins early, but how early? We investigated visual responses in the inferior colliculus (IC), a midbrain structure in the auditory pathway. While multisensory responses have previously been shown in the IC's external cortex (ICX), the central nucleus (ICC) is typically considered to be a unisensory structure, and would not be expected to have visual responses. We mapped the location of multiunit clusters within the IC and looked at the distribution of activity in the ICX and ICC. We collected data in parallel with a frequency mapping study, such that the location of responses within the IC could be determined. We observed visual or visuo-motor responses in 56 out of 90 (62%) recording locations throughout the IC. Responses were not limited to the ICX, ICC recording sites showed abundant visual activity. These results suggest that visual signals join the auditory pathway in early (in this case, subthalamic) stages of sensory processing.