Plasticity in the adult human auditory brainstem following short-term linguistic training

& Peripheral and central structures along the auditory path-way contribute to speech processing and learning. However, because speech requires the use of functionally and acousti-cally complex sounds which necessitates high sensory and cog-nitive demands, long-term exposure and experience using these sounds is often attributed to the neocortex with little emphasis placed on subcortical structures. The present study examines changes in the auditory brainstem, specifically the frequency following response (FFR), as native English-speaking adults learn to incorporate foreign speech sounds (lexical pitch patterns) in word identification. The FFR presumably origi-nates from the auditory midbrain and can be elicited pre-attentively. We measured FFRs to the trained pitch patterns before and after training. Measures of pitch tracking were then derived from the FFR signals. We found increased accuracy in pitch tracking after training, including a decrease in the num-ber of pitch-tracking errors and a refinement in the energy devoted to encoding pitch. Most interestingly, this change in pitch-tracking accuracy only occurred in the most acoustically complex pitch contour (dipping contour), which is also the least familiar to our English-speaking subjects. These results not only demonstrate the contribution of the brainstem in lan-guage learning and its plasticity in adulthood but also dem-onstrate the specificity of this contribution (i.e., changes in encoding only occur in specific, least familiar stimuli, not all stimuli). Our findings complement existing data showing cor-tical changes after second-language learning, and are consis-tent with models suggesting that brainstem changes resulting from perceptual learning are most apparent when acuity in encoding is most needed. &amp