Involvement of the thalamocortical loop in the spontaneous switching of percepts in auditory streaming.
Perceptual grouping of successive frequency components, namely, auditory streaming, is essential for auditory scene analysis. Prolonged listening to an unchanging triplet-tone sequence produces a series of illusory switches between a single coherent stream (S1) and two distinct streams (S2). The predominant percept depends on the frequency difference (Deltaf) between high and low tones. Here, we combined the use of different Deltafs with an event-related fMRI design to identify whether the temporal dynamics of brain activity differs depending on the direction of perceptual switches. The results demonstrated that the activity of the medial geniculate body (MGB) in the thalamus occurred earlier during switching from nonpredominant to predominant percepts, whereas that of the auditory cortex (AC) occurred earlier during switching from predominant to nonpredominant percepts, regardless of Deltaf. The asymmetry of temporal precedence indicates that the MGB and AC activations play different roles in perceptual switching and depend on perceptual predominance rather than on S1 and S2 percepts per se. Our results suggest that feedforward and feedback processes in the thalamocortical loop are involved in the formation of percepts in auditory streaming.
Kondo
Hirohito M
HM
NTT Communication Science Laboratories, NTT Corporation, Kanagawa, Japan. hkondo@brl.ntt.co.jp
Kashino
Makio
M
D000328:Adult; D000704:Analysis of Variance; D001303:Auditory Cortex / Q000502:physiology*; D001306:Auditory Pathways / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D001931:Brain Mapping; D002531:Cerebellum / Q000502:physiology; D005071:Evoked Potentials; D025461:Feedback, Physiological / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D005829:Geniculate Bodies / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009415:Nerve Net / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D015398:Signal Transduction / Q000502:physiology; D055815:Young Adult