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). However, the task dependence of AC activations has not been systematically investigated. In the present study, we applied high-resolution functional magnetic resonance imaging of the AC and adjacent areas to compare activations during pitch discrimination and n-back pitch memory tasks that were varied parametrically in difficulty. We found that anterior AC activations were increased during discrimination but not during memory tasks, while activations in the inferior parietal lobule posterior to the AC were enhanced during memory tasks but not during discrimination. We also found that wide areas of the anterior AC and anterior insula were strongly deactivated during the pitch memory tasks. While these results are consistent with the proposition that the anterior and posterior AC belong to functionally separate auditory processing streams, our results show that this division is present also between tasks using spatially invariant sounds. Together, our results indicate that activations of human AC are strongly dependent on the characteristics of the behavioral task.

Rinne T, Balk MH, Koistinen S, Autti T, Alho K, Sams M. Auditory selective attention modulates activation of human inferior colliculus. J Neurophysiol 100: 3323-3327, 2008. First published October 15, 2008 doi:10.1152/jn.90607.2008. Selective auditory attention powerfully modulates neural activity in the human auditory cortex (AC). In contrast, the role of attention in subcortical auditory processing is not well established. Here, we used functional MRI (fMRI) to examine activation of the human inferior colliculus (IC) during strictly controlled auditory attention tasks. The IC is an obligatory midbrain nucleus of the ascending auditory pathway with diverse internal and external connections. The IC also receives a massive descending projection from the AC, suggesting that cortical processes affect IC operations. In this study, 21 subjects selectively attended to left-ear or right-ear sounds and ignored sounds delivered to the other ear. IC activations depended on the direction of attention, indicating that auditory processing in the human IC is not only determined by acoustic input but also by the current behavioral goals. I N T R O D U C T I O NThere has been a long-lasting debate on whether attention modulates processing of sounds as early as in the subcortical structures of the auditory pathway (Hernández-Peón et al. 1956;Jane et al. 1965;Lukas 1980;Maison et al. 2001;Michie et al. 1996;Näätänen 1992;Oatman and Anderson 1977;Ryan and Miller 1977). Although functional MRI (fMRI) studies in humans have ascertained that attention has a strong effect on cortical activity elicited by sounds (Grady et al. 1997;Jäncke et al. 1999;Johnson and Zatorre 2006;Petkov et al. 2004;Rinne et al. 2005Rinne et al. , 2007, there is no unambiguous evidence that attention modulates subcortical auditory activity. Here we focus on the bilateral inferior colliculus of the midbrain where the ascending parallel auditory pathways converge before continuing to the auditory cortex (AC) via the thalamus. The inferior colliculus (IC) also receives substantial corticofugal projections from the AC (Winer 2006). The functional significance of the corticofugal pathway is not well understood, but stimulation of cortical neurons has been shown to modulate response properties of IC neurons (Suga and Ma 2003). Because the IC has been implicated in attention in some animal studies (Jane et al. 1965;Ryan and Miller 1977), it is possible that the corticofugal projections serve to mediate attention effects to the IC (Suga and Ma 2003).We presented asynchronous left and right ear broadband noise bursts to our human subjects at a rapid rate (Fig. 1A).Temporal regularity of the noise bursts was manipulated so that there was a distinct pitch difference between the left and right ear sounds (Griffiths et al. 2001). Subjects were required to selectively attend to sounds at the designated ear to detect frequent (about once per second) pitch increases or decreases among the attended sounds and to indicate, by pressing one of the two buttons, the direction of ...

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