Processing of auditory motion in inferior parietal lobule: evidence from transcranial magnetic stimulation

The neural substrates of auditory motion processing are, at present, still a matter of debate. It has been hypothesized that motion information is, as in the visual system, processed separately from other aspects of auditory information, such as stationary location. Here we aimed to differentiate the location of auditory motion processing in human cortex using low-frequency repetitive transcranial magnetic stimulation (rTMS) in combination with a psychophysical task of motion discrimination. rTMS was applied offline to right posterior superior temporal gyrus, right inferior parietal lobule, right dorsal premotor cortex, or right primary somatosensory cortex (as reference site). A significant decrease in performance was obtained exclusively for sounds presented in left hemispace after rTMS over the right inferior parietal lobule (BA 40). This finding indicates that the inferior parietal lobule plays a crucial role in the analysis of moving sound, with an apparent contralaterality of cortical processing. Combined with previous studies which have demonstrated effects of rTMS on static sound localization for both inferior parietal and posterior temporal cortices, the results suggest a hierarchical processing of auditory spatial information, with higher-order functions of motion analysis, such as discrimination of motion direction, mainly taking place beyond the temporal lobe.