Figure 1. Evidence for order: Large-scale tonotopy within the middle cortical layers of the mouse auditory cortex.

A) Auditory thalamocortical slice immunoreacted for parvalbumin (blue). Retrograde tracers (Cholera toxin β subunit) conjugated to a green or red fluorophore were injected into a low- (7 kHz) or mid-frequency (22.6 kHz) region of the A1 map, respectively. The A1 injection sites appear at the left of the image, the labeled thalamocortical axons in the middle of the image, and the retrogradely labeled MGBv cell bodies to the right of the image. Scale bar = 0.25 mm. B) A tessellated best frequency (frequency that elicits the most spikes across all levels) map delineated from 300 multiunit recording sites in the middle layers of the area identified in (A). Note the clear tonotopic gradient within A1 and AAF compared to the non-tonotopic organization of the remaining fields. Right, Tonal receptive fields from A1 (top and middle) and A2 (bottom) measured at the numbered locations shown on the tessellated map. C) Best frequency distribution along the caudal-to-rostral axis through A1 and AAF. Distance is relative to the mirror reversal in best frequency that indicates the boundary between each field. Data from individual mice are represented by different colors. Solid black lines indicate the linear fit of the A1 and AAF data. See [25] for further details regarding data in A–C