Proceedings of The Physiological Society

University of Bristol (2005) J Physiol 567P, C127

Oral Communications

'What' and 'where' in the auditory system – 'where' and 'when' in the human brain?

Anurova, Irina; Artchakov, Denis; Korvenoja, Antti; Ilmoniemi, Risto; Aronen, Hannu; Carlson, Synnove;

1. Inst. Biomed./Physiology, University of Helsinki, Helsinki, Finland. 2. Dep. Radiology, Helsinki University Central Hospital, Helsinki, Finland. 3. Nexstim Ltd., Helsinki, Finland. 4. Cognitive Brain Res. Unit, University of Helsinki, Helsinki, Finland.

The present research project was focused on neuronal mechanisms underlying the processing of sound content and its spatial location. In recent years, the idea of segregation of spatial and non-spatial auditory processing into separate pathways has gained support from psychophysical (Clarke et al. 1998), electrophysiological (Alain et al. 2001; Anourova et al. 2001) and neuroimaging studies (Alain et al. 2001; Warren & Griffiths, 2003). Results from our earlier experiments (Anourova et al. 2001, 2003) suggest that the dissociation between spatial and non-spatial auditory information processing occurs within the supratemporal plane as early as at about 100 ms from stimulus onset. In the present study we employed the whole-head electro- and magnetoencephalographic recordings in order to investigate the spatiotemporal dynamics during location and pitch auditory information processing in the higher-order associative areas. We analyzed slow evoked responses (the P3 and positive slow wave (PSW), the prominent positive deflection following the P3) elicited by probe stimuli in location and pitch working memory tasks. The number of successive trials averaged for each experimental condition (match and non-match, either location or pitch) was about 200. Minimum current estimates suggested that associative temporal areas in the posterior and middle parts of the superior temporal sulcus were sensitive to sound attribute. The occipito-temporal generator of the P3 was activated more during the spatial than nonspatial task, and the left temporal generator of the PSW tended to be more strongly activated during the non-spatial task. Furthermore, analysis of the source coordinates (2-way ANOVA) revealed a structural segregation in the location of the center of active area within the occipito-temporal cortex: in the location task, the right-hemispheric occipito-temporal source was situated significantly more medially than in the pitch task (p < 0.05). These findings provide evidence for segregation of spatial and non-spatial auditory information processing in associative areas beyond the supratemporal auditory cortex and support the dual-stream model for auditory information processing.

Where applicable, experiments conform with Society ethical requirements