Abstract

Sensory cortices can be affected by stimuli of multiple modalities and are thus increasingly thought to be multisensory. For instance, primary visual cortex (V1) is influenced not only by images but also by sounds. Here we show that the activity evoked by sounds in V1 is highly stereotyped across neurons and even across mice. It resembles activity measured elsewhere in the brain and is independent of projections from auditory cortex. Its low-dimensional nature starkly contrasts the high dimensional code that V1 uses to represent images. Furthermore, this sound-evoked activity can be precisely predicted by small body movements that are elicited by each sound and are highly stereotyped across trials and across mice. Thus, neural activity that is apparently multisensory may simply arise from low-dimensional signals associated with changes in internal state and behavior.