Fig. 4: Top-down projections from the motor cortex influence activity in the auditory cortex.

a A virus expressing GFP was injected into the secondary motor cortex (M2; gray outlined area). Histological image on the right shows the expression of GFP in M2. b GFP-expressing terminals of M2 neurons at the anteroposterior level of the auditory cortex (dash-outlined area). c Higher-magnification view of the auditory cortex (dash-outlined area in b). Scale bar represents 1 mm in (a, b) and 0.5 mm in (c). d GFP expression as a function of depth from the cortical surface. Note the strong expression in lower cortical layers. e A virus expressing Channelrhodopsin-2 (ChR2) was injected into M2 and the terminals of M2 neurons were optogenetically stimulated while at the same time recording the activity of auditory cortical neurons. f–h Raster plots and peri-stimulus time histograms of three auditory cortical neurons responding to optogenetic stimulation of M2 axon terminals. Blue shaded area denotes the time period of light delivery. Note the short-latency excitatory responses in (f) and (g), indicating monosynaptic input from M2. Numbers on the bottom right of the PSTHs indicate the depth of the neurons below the brain surface. i Fraction of neurons showing short-latency excitatory responses (as exemplified by the neurons in (f) and (g)) as a function of their depth below cortical surface. j Fraction of neurons showing inhibitory responses to M2 terminal stimulation (as exemplified by the neuron in h). Fractions in (i) and (j) were calculated relative to the total number of neurons at each depth. Data in (a–d) is from one mouse; similar results were obtained from five additional mice injected with a virus expressing GFP or ChR2 in M2. Data in (i, j) are from 886 neurons recorded from four wild-type mice. Source data are provided as a Source Data file.