Integration of information across the senses is critical for perception and is a common
property of neurons in the cerebral cortex, where it is thought to arise primarily
from corticocortical connections. Much less is known about the role of subcortical
circuits in shaping the multisensory properties of cortical neurons. We show that
stimulation of the whiskers causes widespread suppression of sound-evoked activity
in mouse primary auditory cortex (A1). This suppression depends on the primary somatosensory
cortex (S1), and is implemented through a descending circuit that links S1, via the
auditory midbrain, with thalamic neurons that project to A1. Furthermore, a direct
pathway from S1 has a facilitatory effect on auditory responses in higher-order thalamic
nuclei that project to other brain areas. Crossmodal corticofugal projections to the
auditory midbrain and thalamus therefore play a pivotal role in integrating multisensory
signals and in enabling communication between different sensory cortical areas. In
the primary auditory cortex, visual or tactile stimuli can modulate acoustically-driven
activity. Here, the authors show that circuits linking the primary somatosensory cortex
to both the auditory midbrain and thalamus allow tactile inputs to modulate auditory
thalamocortical processing.
