The insular auditory field receives input from the lemniscal subdivision of the auditory thalamus in mice

• Published in: Journal of comparative neurology (1911) Vol. 522; no. 6; pp. 1373 - 1389
• Main Authors: Takemoto, Makoto, Hasegawa, Kayoko, Nishimura, Masataka, Song, Wen-Jie
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 15.04.2014; Wiley Subscription Services, Inc
• Subjects: Acoustic Stimulation; Amidines - metabolism; Animals; anterior auditory field; Auditory Cortex - cytology; Auditory Pathways - physiology; Calbindins - metabolism; Cholera Toxin - metabolism; Dextrans - metabolism; Geniculate Bodies - cytology; insula; Male; medial geniculate body; Mice; Mice, Inbred C57BL; Neurons - metabolism; Parvalbumins - metabolism; primary auditory cortex; Psychoacoustics; Rhodamines - metabolism; Thalamus - cytology
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23491

ABSTRACT The insular cortex plays important roles in vocal communication, but the origin of auditory input to the insular cortex has not been fully clarified. Here we studied the auditory thalamic input to the insular cortex using mice as a model system. An insular auditory field (IAF) has recently been identified in mice. By using retrograde neuronal tracing, we identified auditory thalamic neurons projecting to the IAF, primary auditory cortex (AI), and anterior auditory field (AAF). After mapping the IAF, AAF, and AI by using optical imaging, we injected a distinct fluorescent tracer into each of the three fields at frequency‐matched locations. Tracer injection into the IAF resulted in retrogradely labeled cells localized ventromedially in the lemniscal division, i.e., the ventral subdivision of the medial geniculate body (MGv). Cells retrogradely labeled by injections into the AAF were primarily found in the medial half of the MGv, whereas those from AI injections were located in the lateral half, although some of these two subsets were intermingled within the MGv. Interestingly, retrogradely labeled cells projecting to the IAF showed virtually no overlap with those projecting to the AAF or the AI. Dual tracer injections into two sites responding to low‐ and high‐frequency tones within each of the three auditory fields demonstrated topographic organizations in all three thalamocortical projections. These results indicate that the IAF receives thalamic input from the MGv in a topographic manner, and that the MGv–IAF projection is parallel to the MGv–AAF and MGv–AI projections. J. Comp. Neurol. 522:1373–1389, 2014. © 2013 Wiley Periodicals, Inc. Injection of retrograde fluorescent tracers of different colors into the insular auditory field (blue), the primary auditory area (green), and the anterior auditory field (red), in the same animal labeled distinct cell populations in the ventral division of the medial geniculate body. Thalamic input to each of the three cortical areas was further shown to be topographically ordered. These results suggest three parallel, topographically organized lemniscal thalamic inputs to the auditory cortices.