Abstract
Audio-visual stimuli typically yield faster responses than isolated modality-specific ones. This crossmodal speed advantage depends upon efficient multisensory integration mechanisms in the brain. Here, we used repetitive transcranial magnetic stimulation (rTMS) to address the role of the posterior parietal cortex, in particular of the inferior parietal lobule (IPL), in speeding up responses to crossmodal stimuli. The results show that rTMS over IPL impairs the response to contralateral modality-specific visual and auditory targets without affecting the response speed advantage following audio-visual targets. Furthermore, this speed advantage is subserved by a neural coactivation mechanism suggesting a summation in a given neural site. Control rTMS over V1 impaired only contralateral visual responses without affecting the response to auditory or audio-visual targets. These results suggest that the response speed advantage for crossmodal targets is maintained in spite of the IPL interference that impairs modality-specific responses. The possible role of alternative sites for the audio-visual advantage, such as the superior colliculus, is discussed.
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Notes
In fact, there was even a tendency towards a greater violation of the race inequality after degrading the response to unimodal with parietal rTMS. This finding could suggest a stronger multisensory effect, although, as such, it has not been demonstrated that a greater violation of the inequality implies a change of any precise neural response.
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Acknowledgments
This research was supported by grants from the Ministero Italiano dell’Università e della Ricerca Scientifica (MIUR) to AM. We thank A. Pascual-Leone and B.E. Stein for insightful discussions and Carlo Toneatto for technical assistance.
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Bolognini, N., Miniussi, C., Savazzi, S. et al. TMS modulation of visual and auditory processing in the posterior parietal cortex. Exp Brain Res 195, 509–517 (2009). https://doi.org/10.1007/s00221-009-1820-7
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DOI: https://doi.org/10.1007/s00221-009-1820-7