Multisensory integration in ferret auditory cortex: Effects of inactivating visual cortex

Abstract

Neurons in ferret auditory cortex respond to simple visual stimuli such as an LED and auditory responses to white noise can be modulated by the presence of such visual stimuli (Bizley et al., 2007). Visual influences on auditory cortical neurons may result from input connections from a variety of areas — including visual cortex, parietal cortex and the thalamus. Here, we asked whether visual activity in auditory cortex could be abolished by inactivating visual cortex. Multi-unit neural activity was recorded at 13 sites within the auditory cortex of three ferrets before and during inactivation of the visual cortex using cooling loops cooled to between 4 and 7°C. We found numerous auditory cortical units in which cooling significantly reduced visual but not auditory responses (measured as mean firing rate). Furthermore units were found in which visual modulation of auditory responses was reduced by cooling. Both findings support the involvement of visual cortex in multisensory integration within auditory cortex. We also found evidence for the involvement of regions outside of visual cortex: Several units demonstrated visual responses robust to cooling or in which cooling reduced visual responses but only within a circumscribed period of the response. Additionally in rarer cases, cooling led to the emergence of auditory and visual responses or the visual modulation of auditory responses within auditory cortex. Such findings suggest that visual activity in auditory cortex may result from connections to multiple brain regions and that communication from visual to auditory cortex may involve both excitatory and inhibitory mechanisms.