Distinct pathways involved in sound recognition and localization: A human fMRI study

Evidence from psychophysical studies in normal and brain-damaged subjects s uggests that auditory information relevant to recognition and localization are processed by distinct neuronal populations. We report here on anatomica l segregation of these populations. Brain activation associated with perfor mance in sound identification and localization was investigated in 18 norma l subjects using fMRI. Three conditions were used: (i) comparison of spatia l stimuli simulated with interaural time differences; (ii) identification o f environmental sounds; and (iii) rest. Conditions (i) and (ii) required ac knowledgment of predefined targets by pressing a button. After coregisterin g, images were normalized and smoothed. Activation patterns were analyzed u sing SPM99 for individual subjects and for the whole group. Sound recogniti on and localization activated, as compared to rest, inferior colliculus, me dial geniculate body, Heschl gyrus, and parts of the temporal, parietal, an d frontal convexity bilaterally. The activation pattern on the fronto-tempo ro-parietal convexity differed in the two conditions. Middle temporal gyrus and precuneus bilaterally and the posterior part of left inferior frontal gyrus were more activated by recognition than by localization. Lower part o f inferior parietal lobule and posterior parts of middle and inferior front al gyri were more activated, bilaterally, by localization than by recogniti on. Regions selectively activated by sound recognition, but not those selec tively activated by localization, were significantly larger in women. Passi ve listening paradigm revealed segregated pathways on superior temporal gyr us and inferior parietal lobule. Thus, anatomically distinct networks are i nvolved in sound recognition and sound localization. (C) 2001 Academic Pres s.