title: Auditory cortical areas activated by slow frequency-modulated sounds in mice.
abstract: Species-specific vocalizations in mice have frequency-modulated (FM) components slower than the lower limit of FM direction selectivity in the core region of the mouse auditory cortex. To identify cortical areas selective to slow frequency modulation, we investigated tonal responses in the mouse auditory cortex using transcranial flavoprotein fluorescence imaging. For differentiating responses to frequency modulation from those to stimuli at constant frequencies, we focused on transient fluorescence changes after direction reversal of temporally repeated and superimposed FM sweeps. We found that the ultrasonic field (UF) in the belt cortical region selectively responded to the direction reversal. The dorsoposterior field (DP) also responded weakly to the reversal. Regarding the responses in UF, no apparent tonotopic map was found, and the right UF responses were significantly larger in amplitude than the left UF responses. The half-max latency in responses to FM sweeps was shorter in UF compared with that in the primary auditory cortex (A1) or anterior auditory field (AAF). Tracer injection experiments in the functionally identified UF and DP confirmed that these two areas receive afferent inputs from the dorsal part of the medial geniculate nucleus (MG). Calcium imaging of UF neurons stained with fura-2 were performed using a two-photon microscope, and the presence of UF neurons that were selective to both direction and direction reversal of slow frequency modulation was demonstrated. These results strongly suggest a role for UF, and possibly DP, as cortical areas specialized for processing slow frequency modulation in mice.
authors.affiliation: Department of Neurophysiology, Brain Research Institute, Niigata University, Asahi-machi, Niigata, Japan.
authors.forename: Yuusuke
authors.initials: Y
authors.lastname: Honma
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tsukano
authors.forename: Masao
authors.initials: M
authors.lastname: Horie
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Ohshima
authors.forename: Manavu
authors.initials: M
authors.lastname: Tohmi
authors.forename: Yamato
authors.initials: Y
authors.lastname: Kubota
authors.forename: Kuniyuki
authors.initials: K
authors.lastname: Takahashi
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Hishida
authors.forename: Sugata
authors.initials: S
authors.lastname: Takahashi
authors.forename: Katsuei
authors.initials: K
authors.lastname: Shibuki
mesh_terms: D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D005453:Fluorescence; D051379:Mice; D013016:Sound