There and back again: corticothalamic modulation of cortical sound processing

Beginning with the descriptions of Ramon y Cajal over a century ago, anatomists have noted the massive projection from deep layers of sensory cortex to the thalamus. A functional role for these corticothalamic connections has proven harder to define. Recent work in the primary visual cortex has shown that layer 6 corticothalamic neurons (L6CT) dynamically adjust the gain on cortical sensory processing by engaging local networks of fast-spiking (FS) interneurons. I will present new evidence that L6CT neurons in the mouse auditory cortex can bi-directionally control the gain on cortical and thalamic sensory processing by entraining the phase of low-frequency cortical oscillations. The underlying circuit appears to share several features in common with the visual cortex, including a central role for FS interneurons, though there are also several key differences. The neurophysiological dynamics translate directly to sound perception as L6CT activation can bias the mouse towards heightened detection of faint sounds at the expense of accurate frequency discrimination, or vice versa, depending solely on the relative timing between the sensory trace and L6CT activity. These findings may have interesting implications for the neural underpinnings of adaptive sensory processing.