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The Journal of Neuroscience, October 7, 2009, 29(40):12695-12701; doi:10.1523/JNEUROSCI.1549-09.2009

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Behavioral/Systems/Cognitive
Involvement of the Thalamocortical Loop in the Spontaneous Switching of Percepts in Auditory Streaming

Hirohito M. Kondo¹ and Makio Kashino^1,2,3

¹NTT Communication Science Laboratories, NTT Corporation, and ²Exploratory Research for Advanced Technology Shimojo Implicit Brain Function Project, Japan Science and Technology Agency, Atsugi, Kanagawa 243-0198, Japan, and ³Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan

Correspondence should be addressed to Hirohito M. Kondo, NTT Communication Science Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan. Email: hkondo{at}brl.ntt.co.jp

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 (f) between high and low tones. Here, we combined the use of different fs 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 f. 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.

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Received April 1, 2009; revised Aug. 11, 2009; accepted Aug. 29, 2009.

Correspondence should be addressed to Hirohito M. Kondo, NTT Communication Science Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan. Email: hkondo{at}brl.ntt.co.jp

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