(A) Sketch of optical imaging of intrinsic signals experimental setup. (B) Localization of AC by intrinsic imaging. Left, 5 mm cranial window on the right hemisphere of an anesthetized mouse under green LED light. Middle and Right, Mean intrinsic signal response map and mean + single trial response traces for White Noise stimulation (WN) from the mouse shown on the left. Responses traces are derived from the region of interest delineated on the left image. (C) Sketch of silicon probe-based electrophysiology experiments in awake mice. (D) Left: Cranial window of the same animal as in B, after placing the probe into AC. Recordings were usually performed at 400, 600 700 and 800 µm in a single penetration for each animal. Middle: A raster plot and a peristimulus histogram of the responses to up- and down-ramp presentations for a sample single unit. Right: Spike waveform and autocorrelogram of spike train for the same unit. (E) Correlation-based, template matching method to detect the six main response types observed in two-photon calcium imaging (onset, offset, tonic response with a quiet or loud intensity tuning). Because of the small number of cells, only these prominent, simple response types were selected. They capture also some of the composite response types (ON, Loud Tonic + OFF) which are more difficult to capture using a binary model. For each unit (n = 410 isolated units in 4 mice and 15 recording locations), the correlation between its average response histogram and the six templates (represented by dashed lines) was computed. Each cell was assigned to the template to which its response was most correlated provided that the correlation was above 0.4 (112 cells passed this threshold). (F) Mean response profiles smoothed with a Gaussian filter, σ = 30 ms) for the different groups of cells identified by template matching. On the right, the heat map depicts the mean response of each unit to up- (left) and down- (right) ramps. Black and white triangles correspond to sound onsets and offsets respectively. Note that a small fraction of neurons classified as Loud or Quiet ON are equally responsive for both types of onset, corresponding to the ON cluster label defined for two-photon calcium imaging data. (G) Histogram of the fractions of neurons that were assigned to each of the six templates shown together with the number of neurons in each group. The plot shows that Loud ON responses types are dominant in layer 5, as seen with two-photon calcium imaging (Figure 1F).