Letter to the Editor

Specialization among the specialized: Auditory brainstem function is tuned in to timbre

Most listeners have an implicit understanding of the rules that govern how music unfolds over time. This knowledge is acquired in part through statistical learning, a robust learning mechanism that allows individuals to extract regularities from the environment. However, it is presently unclear how this prior musical knowledge might facilitate or interfere with the learning of novel tone sequences that do not conform to familiar musical rules. In the present experiment, participants listened to novel, statistically structured tone sequences composed of pitch intervals not typically found in Western music. Between participants, the tone sequences either had the timbre of artificial, computerized instruments or familiar instruments (piano or violin). Knowledge of the statistical regularities was measured as by a two-alternative forced choice recognition task, requiring discrimination between novel sequences that followed versus violated the statistical structure, assessed at three time points (immediately post-training, as well as one day and one week post-training). Compared to artificial instruments, training on familiar instruments resulted in reduced accuracy. Moreover, sequences from familiar instruments – but not artificial instruments – were more likely to be judged as grammatical when they contained intervals that approximated those commonly used in Western music, even though this cue was non-informative. Overall, these results demonstrate that instrument familiarity can interfere with the learning of novel statistical regularities, presumably through biasing memory representations to be aligned with Western musical structures. These results demonstrate that real-world experience influences statistical learning in a non-linguistic domain, supporting the view that statistical learning involves the continuous updating of existing representations, rather than the establishment of entirely novel ones.

Extinction learning and memory have been broadly investigated at both behavioral and neural levels, but sensory system contributions to extinction processes have been less explored. Using a sound-reward extinction paradigm in male rats, we reveal both cortical and subcortical forms of plasticity associated with the cue-specificity of behavioral extinction memory. In the auditory cortex, frequency tuning narrowed by up to two-thirds of an octave around the remembered extinguished sound cue. Subcortical signals revealed in the auditory brainstem response (ABR) in the same animals developed smaller amplitudes of some (but not all) ABR peaks evoked by the extinguished sound frequency. Interestingly, treatment with an inhibitor of histone deacetylase 3 (HDAC3-i) facilitated both auditory cortical tuning bandwidth changes and changes in subcortical peak amplitude evoked only by the extinguished sound frequency. These neurophysiological changes were correlated to each other, and to the highly precise extinction behavior enabled by HDAC3-i (compared to vehicle controls). Thus, we show for the first time that HDAC3 regulates the specificity of sensory features consolidated in extinction memory. Further, the sensory cortical changes in tuning bandwidth recapitulate known effects of blocking HDAC3 to enhance cue specificity in other behavioral tasks. Therefore, the findings demonstrate how some forms of sensory neuroplasticity may encode specific sensory features of learning experiences in order to enable cue-specific behaviors.

The prevalence of dementia, the most expensive medical condition (Kirschstein, 2000 and Hurd et al., 2013 [1,2]), and its precursor, mild cognitive impairment (MCI) are increasing [3]. Finding effective intervention strategies to prevent or delay dementia is imperative to public health. Prior research provides compelling evidence that central auditory processing (CAP) deficits are a risk factor for dementia [4–6]. Grounded in the information degradation theory [7, 8], we hypothesize that improving brain function at early perceptual levels (i.e., CAP) may be optimal to attenuate cognitive and functional decline and potentially curb dementia prevalence. Piano training is one avenue to enhance cognition [9–13] by facilitating CAP at initial perceptual stages [14–18].

The Keys To Staying Sharp study is a two arm, randomized clinical trial examining the efficacy of piano training relative to music listening instruction to improve CAP, cognition, and everyday function among older adults. In addition, the moderating effects of MCI status on piano training efficacy will be examined and potential mediators of intervention effects will be explored.

We hypothesize that piano training will improve CAP and cognitive performance, leading to functional improvements. We expect that enhanced CAP will mediate cognitive gains. We further hypothesize that cognitive gains will mediate functional improvements.

We plan to enroll 360 adults aged 60 years and older who will be randomized to piano training or an active control condition of music listening instruction and complete pre- and immediate post- assessments of CAP, cognition, and everyday function.

Music training may strengthen auditory skills that help children not only in musical performance but in everyday communication. Comparisons of musicians and non-musicians across the lifespan have provided some evidence for a “musician advantage” in understanding speech in noise, although reports have been mixed. Controlled longitudinal studies are essential to disentangle effects of training from pre-existing differences, and to determine how much music training is necessary to confer benefits. We followed a cohort of elementary school children for 2 years, assessing their ability to perceive speech in noise before and after musical training. After the initial assessment, participants were randomly assigned to one of two groups: one group began music training right away and completed 2 years of training, while the second group waited a year and then received 1 year of music training. Outcomes provide the first longitudinal evidence that speech-in-noise perception improves after 2 years of group music training. The children were enrolled in an established and successful community-based music program and followed the standard curriculum, therefore these findings provide an important link between laboratory-based research and real-world assessment of the impact of music training on everyday communication skills.

Performing musicians invest thousands of hours becoming experts in a range of perceptual, attentional, and cognitive skills. The duration and intensity of musicians’ training – far greater than that of most educational or rehabilitation programs – provides a useful model to test the extent to which skills acquired in one particular context (music) generalize to different domains. Here, we asked whether the instrument-specific and more instrument-general skills acquired during professional violinists’ and pianists’ training would generalize to superior performance on a wide range of analogous (largely non-musical) skills, when compared to closely matched non-musicians. Violinists and pianists outperformed non-musicians on fine-grained auditory psychophysical measures, but surprisingly did not differ from each other, despite the different demands of their instruments. Musician groups did differ on a tuning system perception task: violinists showed clearest biases towards the tuning system specific to their instrument, suggesting that long-term experience leads to selective perceptual benefits given a training-relevant context. However, we found only weak evidence of group differences in non-musical skills, with musicians differing marginally in one measure of sustained auditory attention, but not significantly on auditory scene analysis or multi-modal sequencing measures. Further, regression analyses showed that this sustained auditory attention metric predicted more variance in one auditory psychophysical measure than did musical expertise. Our findings suggest that specific musical expertise may yield distinct perceptual outcomes within contexts close to the area of training. Generalization of expertise to relevant cognitive domains may be less clear, particularly where the task context is non-musical.

Simultaneous recording of brainstem and cortical event-related brain potentials (ERPs) may offer a valuable tool for understanding the early neural transcription of behaviorally relevant sounds and the hierarchy of signal processing operating at multiple levels of the auditory system. To date, dual recordings have been challenged by technological and physiological limitations including different optimal parameters necessary to elicit each class of ERP (e.g., differential adaptation/habitation effects and number of trials to obtain adequate response signal-to-noise ratio).

We investigated a new stimulus paradigm for concurrent recording of the auditory brainstem frequency-following response (FFR) and cortical ERPs. The paradigm is “optimal” in that it uses a clustered stimulus presentation and variable interstimulus interval (ISI) to (i) achieve the most ideal acquisition parameters for eliciting subcortical and cortical responses, (ii) obtain an adequate number of trials to detect each class of response, and (iii) minimize neural adaptation/habituation effects.

Comparison between clustered and traditional (fixed, slow ISI) stimulus paradigms revealed minimal change in amplitude or latencies of either the brainstem FFR or cortical ERP. The clustered paradigm offered over a 3× increase in recording efficiency compared to conventional (fixed ISI presentation) and thus, a more rapid protocol for obtaining dual brainstem–cortical recordings in individual listeners.

We infer that faster recording of subcortical and cortical potentials might allow more complete and sensitive testing of neurophysiological function and aid in the differential assessment of auditory function.