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Poster A18, Thursday, August 16, 10:15 am – 12:00 pm, Room 2000AB

The role of left vs. right superior temporal gyrus in speech perception: An fMRI-guided TMS study

Aurora I Ramos Nunez1, Qiuhai Yue2, Siavash Pasalar2, Randi C Martin2;1College of Coastal Georgia, 2Rice University

A large body of neuroimaging research has implicated the superior temporal gyrus (STG) in speech perception. Price et al.’s (2012) review found that while some studies showed activity only in the left STG for speech stimuli, others showed activity in bilateral STG. However, activity is generally greater on the left and debate continues regarding the necessary role of right STG regions (Turkletaub & Coslett, 2010). The present study employed transcranial magnetic stimulation (TMS) applied to regions activated for speech vs. nonspeech stimuli to directly assess whether both left and right STG regions are causally involved in speech perception. Twenty healthy Rice University students (7 males, 13 females) between the ages of 18 and 22 participated in this fMRI-guided TMS experiment. Participants performed speech and nonspeech discrimination tasks (during the fMRI session) and a speech perception task only (during the TMS session). FMRI was used to detect activity in the STG of each participant which showed greater activation for speech than nonspeech, serving as the landmarks for the Brainsight neuronavigation system for the TMS session. During the fMRI session subjects heard pairs of one-syllable speech sounds and pairs of musical tones and were instructed to make a same or different decision. One anatomical and two functional scans were acquired. During the TMS session, subjects heard pairs of syllables differing in one distinctive feature (one spoken in a male voice and one in a female voice). During the speech discrimination task, three target regions (left anterior and posterior STG and right STG) and one control region (the occipital (V1) cortex) were stimulated via three pulses very 100msec. at onset of the first sound. FMRI analyses were performed on a subject-by-subject basis and were FDR-corrected for multiple comparisons (p level of .001). Consistent with the literature, all 20 subjects showed greater activity in bilateral STG during speech relative to nonspeech perception, but not in the control region (V1). The effects of TMS were analyzed by calculating accuracy difference on speech discrimination between TMS and No TMS in the target and control areas during the speech perception task. There was a 24% accuracy difference between TMS and No TMS in the left anterior STG, which was significantly greater than the 11% difference in the control region; t (1,19) = 2.631, p = 0.016. Neither the accuracy difference in the left posterior STG (15%) nor in the right STG (13%) was significantly different from that in the control region (11%), t (1,19) = .70, p = .49, and t (1,19) = .47, p = .65, respectively. The present study demonstrated a causal relationship between the left anterior STG and speech perception in that TMS disrupted this process. This was not seen in any of the other target areas and suggests that the left anterior STG plays a greater role in speech perception than the right STG. To our knowledge, this is the first study to demonstrate such direct relationship. However, the left posterior STG did not show a TMS effect, thus more research is needed.

Topic Area: Perception: Speech Perception and Audiovisual Integration