Decoding emotional prosody: resolving differences in functional neuroanatomy from fMRI and lesion studies using TMS

Background: Prosody conveys information about the emotional state and intention of others. Lesion studies have shown that damage to the right posterior temporal region is associated with prosody decoding deficits. Dissimilarly to findings from lesion studies, neuroimaging data show substantial bilateral peri-Sylvian activation.

Objective: This study aimed to investigate the involvement of the left and right superior temporal gyrus (STG) in prosodic and semantic processing using transcranial magnetic stimulation (TMS). These two regions of interest were chosen for their correspondence to Wernicke's area in the left hemisphere and its analog in the right.

Methods: Offline TMS with a stimulation frequency of 1 Hz and intensity of 60% of stimulator output (approximately 1.1 Tesla) with one pulse applied per second for 10 minutes (600 pulses) was performed. Directly after TMS on the right STG, the left STG or sham-stimulation, participants completed a prosody decoding or a semantic judgment task (whether the tone/meaning was happy or sad).

Results: Reaction times (RT) for the prosodic task were significantly slower when TMS was applied in the right STG in comparison to left STG and sham conditions. TMS over both right and left STG delayed RT in the semantic task, significantly when the tone of voice was incongruent with the meaning.

Conclusions: Our data strongly suggests that left temporal regions are not crucial to the basic task of prosody decoding per se; however, the analogous region on the right is. Hence, involvement of the left STG in prosodic decoding revealed in previous imaging data is incidental.