Therefore, we used 30-kHz and 60-kHz tones to obtain response shifts in the DM. A dorsal shift in tonotopy was observed using tones at 30 kHz up to about 60 kHz in the DM 4, 5, 16. The 20- to 30-kHz tones elicited responses in almost the same region close to the ventral border of the AI 4, 5. In the DM, responses to low frequency sounds around 5–20 kHz were weak and diffuse 4, 5, 16. In addition, the tonotopic gradients of these regions are known to be arranged in a logarithmic manner in mammals including mice 4, 5, 16, 25, rats 26, 27 and cats 28, 29, therefore tonal stimuli over 30 kHz elicited weak responses in almost the same locations as those to 30 kHz ( Supplemental Fig. We presented 5- and 30-kHz tones to mice to generate tonotopic shifts in the AAF, AI and AII, that were clearly distinguishable in these regions 4, 5, 16. Precise locations of the six regions were identified in the brain surface view ( Fig. Anesthetized mice were fixed with the head rotated about 75° to bring the surface of the right auditory cortex to the microscope ( Fig. We used flavoprotein fluorescence imaging 15 to reveal tonal responses in the auditory cortex of the C57BL/6 mouse brain. Identification of multiple regions in the mouse auditory cortex using flavoprotein fluorescence imaging ![]() The physiological identification of the auditory cortical regions will contribute to establishing a standard mouse brain database. The mouse model is widely used in neuroscience research due to advantages in its applicability of various experimental tools, genetic tractability 22, 23 and lissencephalic cortex 24. In the current study, we identified stereotaxic coordinates of the six auditory cortical regions of the C57BL/6 mouse by flavoprotein fluorescence imaging and denoted their position in coronal brain slices. However, a fine auditory cortical map with multiple auditory regions is not currently available. There, a visual cortex map with at least 10 higher-order regions elucidated by physiological 9, 10, 12 and neurotracing studies 21 and a comprehensive body surface map of the somatosensory cortex have been portrayed. Furthermore, recent brain mapping projects performed by the Allen Institute have provided a wide range of information about the mouse brain with an elaborate segmentation 18. This atlas is helpful because it covers all brain regions from the pons to the neocortex and users can recognize various brain regions at a glance on a macroscopic scale. The long-standing brain atlas published by Paxinos and Franklin was established according to chemoarchitectonic patterns 19 it has become the standard reference for the anatomy of the C57BL/6 mouse brain and was reconstructed into a 3-D atlas 20. Precise brain atlases illustrating coronal sections are useful for identifying brain regions in slice sections and encourage the use of common nomenclature in neuroscience research 18, 19. World-wide efforts are developing precise, reliable, useful references of the mouse brain. ![]() Thus, endogenous fluorophore imaging is a powerful means of delineating small cortical regions with a width of ~300 μm as it avoids the inhomogeneous staining associated with the use of exogenous chemical fluorescent dyes 5, 16. In mapping the mouse auditory cortex, flavoprotein fluorescence imaging which reveals intrinsic signals coupled with aerobic metabolism 15, or detection of fluorescence in mice expressing the calcium indicator protein GCaMP3 16, has uncovered many important structures, for example the frequency organization in AII 16, 17, a new frequency gradient in the AI 4, 5, 16 and a new region DM 4, 5. Optical imaging has been a useful tool for fine-grained mapping in mouse sensory cortices 9, 10, 11, 12, 13, 14.
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