Robust Encoding in the Human Auditory Brainstem: Use It or Lose It?

The human auditory brainstem faithfully represents the acoustic structure of sounds (Galbraith et al., 1995). In musicians, presumably because music training and exposure places high demands on the auditory system, brainstem encoding of both speech and musical sounds is more robust than in non-musicians. It is believed that the corticofugal system, a vast network of efferent connections within the auditory neuroaxis, drives top-down plastic changes underlying the enhancements in brainstem encoding in musicians and other populations with fine-tuned auditory abilities (Wong et al., 2007). Could these same mechanisms lead to impoverished brainstem encoding in those individuals whose musical skill proficiency is below average? Two recent studies on brainstem encoding in amusia, a congenital music disorder, shed a complementary light on this issue (Lehmann et al., 2015; Liu et al., 2015). Together they suggest that a subcortical deficit in auditory processing, which varies as a function of the degree of musical (dis)ability, can emerge as a consequence of limited meaningful interactions with music. We discuss how this notion of auditory detuning fits with the emerging view on top-down induced subcortical plasticity in auditory processing and address its implications for auditory rehabilitation. Musicians are a paradigmatic example of individuals who have benefitted from their interactions with an acoustically enriched environment. From a neural standpoint, lifelong musical training has been linked with enhanced cortical mechanisms of sensory-motor processing (Münte et al. research suggests that musicians with dyslexia might be spared from auditory disabilities associated with dyslexia (Bishop-Liebler et al., 2014; Weiss et al., 2014), providing further support for the claim that enriched musical experience has a beneficial influence on the auditory system by endowing greater resilience when the auditory system is compromised by auditory processing disorders, sensorineural taxation/decline, aging, or disease (Skoe and Kraus, 2014). Similar sensory benefits are purported for bilinguals and tonal language speakers (Krishnan et al., 2005, 2010a; Krizman et al., 2012, 2015). For musicians, training appears to generalize beyond the domain of training (i.e., music), as sensory enhancements are found in the brainstem response to both music and speech stimuli in individuals partaking in lifelong (Musacchia et al., 2007) or short-term musical training (Tierney et al., 2013). This generalization has been theorized to result from shared neural resources for speech and music at a subcortical level (Patel, 2014). An unstated assumption in the literature on experience-dependent plasticity of the subcortical auditory system is that there is some basic, though …