Abstract
Repetitive transcranial magnetic stimulation (rTMS) has been shown to interfere with many components of language processing, including semantic, syntactic, and phonologic. However, not much is known about its effects on nonlinguistic auditory processing, especially its action on Heschl's gyrus (HG). We aimed to investigate the behavioral and neural basis of rTMS during a melody processing task, while targeting the left HG, the right HG, and the Vertex as a control site. Response times (RT) were normalized relative to the baseline-rTMS (Vertex) and expressed as percentage change from baseline (%RT change). We also looked at sex differences in rTMS-induced response as well as in functional connectivity during melody processing using rTMS and functional magnetic resonance imaging (fMRI). fMRI results showed an increase in the right HG compared with the left HG during the melody task, as well as sex differences in functional connectivity indicating a greater interhemispheric connectivity between left and right HG in females compared with males. TMS results showed that 10 Hz-rTMS targeting the right HG induced differential effects according to sex, with a facilitation of performance in females and an impairment of performance in males. We also found a differential correlation between the %RT change after 10 Hz-rTMS targeting the right HG and the interhemispheric functional connectivity between right and left HG, indicating that an increase in interhemispheric functional connectivity was associated with a facilitation of performance. This is the first study to report a differential rTMS-induced interference with melody processing depending on sex. In addition, we showed a relationship between the interference induced by rTMS on behavioral performance and the neural activity in the network connecting left and right HG, suggesting that the interhemispheric functional connectivity could determine the degree of modulation of behavioral performance.
Highlights
Specialization and interhemispheric asymmetries of auditory cortical function have been examined using a variety of techniques
We found a negative correlation between the %Response times (RT) change caused by 10 Hz-Repetitive transcranial magnetic stimulation (rTMS) targeting right HG (rHG) and the functional interhemispheric connectivity between right and left auditory cortices, including bilateral superior temporal gyri (STG), bilateral middle temporal gyri (MTG) and the left Heschl’s gyrus (HG)
Using a melody discrimination task we found differential effects on RT after 10 Hz-rTMS targeting the right HG which interacted with sex; that is, compared with 10 Hz-rTMS applied over the Vertex, 10 Hz-rTMS targeting the right HG decreased RT in the female group but increased RT in the male group
Summary
Specialization and interhemispheric asymmetries of auditory cortical function have been examined using a variety of techniques. It has long been thought that the right auditory cortex is especially important for the processing of melodic information (Zatorre et al, 2002) whereas the left is more critical for speech processing (Hickok and Poeppel, 2007) This asymmetry can be explained on the basis of hemispheric differences in spectral and temporal resolution (Tallal et al, 1993; Zatorre et al, 2002; Poeppel, 2003) and is supported by considerable empirical data from neuroimaging studies (Boemio et al, 2005; Schonwiesner et al, 2005; Jamison et al, 2006; Giraud et al, 2007; Hyde et al, 2008). Lesion studies alone cannot probe the way in which the lesion may have caused reorganization or changes in interhemispheric functional processing
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