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Abstract

The left human auditory thalamus, i.e. the left medial geniculate body (MGB) is top-down modulated by tasks involving speech recognition in contrast to control tasks on the same stimuli [1, 2]. The amount of this task-dependent modulation positively correlates with speech recognition performance [1]. It is to-date unknown which of the three MGB subdivisions (ventral, medial, dorsal) is modulated by speech tasks. The distinction is important, as these subdivisions have very different physiological response properties. Here we hypothesized, that the task-dependent modulation of the left MGB for speech recognition is present in the ventral part, which belongs to the lemniscal auditory pathway and is regarded as the first order thalamic nucleus. Using ultra-high field 7 T fMRI in 33 human participants, we first identified the ventral MGB based on its tonotopical organization and relative spatial location [3]. Within this region, we found a significant positive correlation of the amount of task-dependent modulation (speech vs. speaker task) and the speech recognition performance across participants. The non-tonotopic subdivisions showed no significant response differences between the two experimental tasks nor a correlation of task-dependent modulation with speech recognition performance. These results show that the task-dependent modulation of the MGB is present in the lemniscal subdivision and that the task-dependent modulation of this subdivision plays a role in speech recognition.