Dual compartments of the ventral division of the medial geniculate body projecting to the core region of the auditory cortex in C57BL/6 mice

We investigated precise projection patterns from the ventral division of the medial geniculate body (MGv) projecting to the core region of the auditory cortex in C57BL/6 mice. The core region in mice comprises two different tonotopically organized areas, the anterior auditory field (AAF) and the primary auditory cortex (AI). In the present study, AAF and AI were functionally identified using flavoprotein fluorescence imaging. Biotinylated dextran amine (BDA) was injected iontophoretically into the tonotopic bands to 5 kHz and 20 kHz in AAF, and those to 5 kHz, 10 kHz, and 20 kHz in AI for staining MGv neurons projecting to the injected sites. MGv neurons projecting to AAF were found in the medial part of MGv, while MGv neurons projecting to AI were found in the lateral part. In the medial part of MGv, areas projecting to 5-20 kHz bands in AAF were aligned along the medio lateral axis. In the lateral part of MGv, areas projecting to 5-20 kHz bands in AI were aligned along the dorso ventral axis. These results indicate that AAF and AI receive auditory information via two different MGv compartments with independent tonotopic axes, respectively.