Figure 5.

L6 CT neurons are involved in the behavioral switch between sound detection and discrimination. This scheme summarizes the findings by Guo et al. (2017) who demonstrate the participation of L6 CT neurons (Ntsr1+), via both their intracortical and corticothalamic connections to perceptual modes of enhanced detection or discrimination. Left column, in a baseline condition with low activity in L6 CT neurons and fast-spiking interneurons (FS resetters), the sound-evoked activity in MGV and L4 cortical neurons is moderate. FS resetters are activated following intense firing of L6 CT neurons. Activity of FS resetters increases the power and resets the phase of low frequency rhythms. Middle column, at a short delay period following intense activity of L6 CT and FS resetter neurons, the delta-theta rhythm is at a positive, low excitability phase, and sound-evoked activity is suppressed in A1 but not in the MGV, which favors tone discrimination at the expense of sound sensitivity (the reduced excitability of cortical neurons sharpens frequency tuning). Right column, at longer delays following L6 CT activity, the phase of the cortical rhythm has rotated to a negative, high excitability phase, and sound-evoked activity is enhanced both in A1 and MGV. The enhanced excitability of cortical neurons is expected to increase the overlap in sensory tuning between neighboring tuning regions, which favors tone detection at the expense of reduced tone discrimination. A1, primary auditory cortex; CT, corticothalamic; L6, cortical layer 6; L4, cortical layer 4; MGV, ventral subdivision of the medial geniculate body; FS, fast-spiking interneurons. Reproduced, with permission, from Guo et al. (2017).