The importance of the motor system in the development of music-based forms of auditory rehabilitation.

Hearing abilities decline with age, and one of the most commonly reported hearing issues in older adults is a difficulty understanding speech when there is loud background noise. Understanding speech in noise relies on numerous cognitive processes, including working memory, and is supported by numerous brain regions, including the motor and motor planning systems. Indeed, many working memory processes are supported by motor and premotor cortical regions. Interestingly, lifelong musicians and nonmusicians given music training over the course of weeks or months show an improved ability to understand speech when there is loud background noise. These benefits are associated with enhanced working memory abilities, and enhanced activity in motor and premotor cortical regions. Accordingly, it is likely that music training improves the coupling between the auditory and motor systems and promotes plasticity in these regions and regions that feed into auditory/motor areas. This leads to an enhanced ability to dynamically process incoming acoustic information, and is likely the reason that musicians and those who receive laboratory-based music training are better able to understand speech when there is background noise. Critically, these findings suggest that music-based forms of auditory rehabilitation are possible and should focus on tasks that promote auditory-motor interactions.

The relationship between acoustic and musical pitch processing in adolescents.

Amusia is defined as a difficulty processing the tonal pitch structure of music such that an individual cannot tell the difference between notes that are in-key and out-of-key. A fine-grained pitch discrimination deficit is often observed in people with amusia. It is possible that an intervention, early in development, could mitigate amusia; however, one challenge identifying amusia early in development is that identifying in- and out-of-key notes is a metacognitive task. Given the common co-occurrence of difficulties with pitch discrimination, it would be easier to identify amusia in developing children by using a pitch change detection task. The goal of this study was to explore the behavioural and neurophysiological profiles of adolescents with poor pitch processing (Poor PP) abilities compared with those with normal pitch processing (Normal PP) abilities. Neurophysiologically, the Poor PPs exhibited a similar event-related potential (ERP) profile to adult amusics during both acoustic and musical pitch discrimination tasks. That is, early ERPs (ERAN, MMN) were similar in Poor PPs compared with Normal PPs, whereas late positivities (P300, P600) were absent in Poor PPs, but present in Normal PPs. At the same time, behavioural data revealed a double dissociation between the abilities to detect a pitch deviant in acoustic and musical context, suggesting that about a third of the children would be missed by selecting a fine-grained acoustic pitch discrimination task to identify the presence of amusia in early childhood.

Musical training improves the ability to understand speech-in-noise in older adults.

It is well known that hearing abilities decline with age, and one of the most commonly reported hearing difficulties reported in older adults is a reduced ability to understand speech in noisy environments. Older adult musicians have an enhanced ability to understand speech in noise, and this has been associated with enhanced brain responses related to both speech processing and the deployment of attention; however, the causal impact of music lessons in older adults has not yet been demonstrated. To investigate whether a causal relationship exists between short-term musical training and performance on auditory tests in older adults and to determine if musical training can be used to improve hearing in older adult nonmusicians, we conducted a longitudinal training study with random assignment. A sample of older adults was randomly assigned to learn to play piano (Music), to learn to play a visuospatially demanding video game (Video), or to serve as a no-contact control (No-contact). After 6 months, the Music group improved their ability to understand a word presented in loud background noise, whereas the other 2 groups did not. This improvement was related to an increase in positive-going electrical brain activity at fronto-left electrodes 200-1000 ms after the presentation of a word in noise. Source analyses suggest that this activity was due to sources located in the left inferior frontal gyrus and other regions involved in the speech-motor system. These findings support the idea that musical training provides a causal benefit to hearing abilities. Importantly, these findings suggest that musical training could be used as a foundation to develop auditory rehabilitation programs for older adults.

The impact of aging on neurophysiological entrainment to a metronome.

In music, entrainment to the beat allows listeners to make predictions about upcoming events. Previous work has shown that neural oscillations will entrain to the beat of the music or rhythmic stimuli. Despite the fact that aging is known to impact both auditory and cognitive processing, little is known about how aging affects neural entrainment to rhythmic stimuli. In this study, younger and older participants listened to isochronous sequences at a slower and faster rate while EEG data was recorded. Steady-state evoked potentials had amplitude peaks at the stimulus rate and its harmonics. Steady-state evoked potentials at the stimulus rate and the first harmonic was attenuated in older adults compared to younger adults. Additionally, no amplitude difference was found for the second and third harmonics in older adults, while there was a decrease in amplitude in younger adults. This age-related decline in the entrainment specificity of the brain responses to the stimulus rate, suggests that aging may decrease the ability to entrain to stimuli in the environment, and further suggests that older adults may be less able to inhibit neural entrainment that is not directly related to the incoming stimulus.

Attending to pitch information inhibits processing of pitch information: the curious case of amusia.

In normal listeners, the tonal rules of music guide musical expectancy. In a minority of individuals, known as amusics, the processing of tonality is disordered, which results in severe musical deficits. It has been shown that the tonal rules of music are neurally encoded, but not consciously available in amusics. Previous neurophysiological studies have not explicitly controlled the level of attention in tasks where participants ignored the tonal structure of the stimuli. Here, we test whether access to tonal knowledge can be demonstrated in congenital amusia when attention is controlled. Electric brain responses were recorded while asking participants to detect an individually adjusted near-threshold click in a melody. In half the melodies, a note was inserted that violated the tonal rules of music. In a second task, participants were presented with the same melodies but were required to detect the tonal deviation. Both tasks required sustained attention, thus conscious access to the rules of tonality was manipulated. In the click-detection task, the pitch deviants evoked an early right anterior negativity (ERAN) in both groups. In the pitch-detection task, the pitch deviants evoked an ERAN and P600 in controls but not in amusics. These results indicate that pitch regularities are represented in the cortex of amusics, but are not consciously available. Moreover, performing a pitch-judgment task eliminated the ERAN in amusics, suggesting that attending to pitch information interferes with perception of pitch. We propose that an impaired top-down frontotemporal projection is responsible for this disorder.

The impact of musicianship on the cortical mechanisms related to separating speech from background noise.

Musicians have enhanced auditory processing abilities. In some studies, these abilities are paralleled by an improved understanding of speech in noisy environments, partially due to more robust encoding of speech signals in noise at the level of the brainstem. Little is known about the impact of musicianship on attention-dependent cortical activity related to lexical access during a speech-in-noise task. To address this issue, we presented musicians and nonmusicians with single words mixed with three levels of background noise, across two conditions, while monitoring electrical brain activity. In the active condition, listeners repeated the words aloud, and in the passive condition, they ignored the words and watched a silent film. When background noise was most intense, musicians repeated more words correctly compared with nonmusicians. Auditory evoked responses were attenuated and delayed with the addition of background noise. In musicians, P1 amplitude was marginally enhanced during active listening and was related to task performance in the most difficult listening condition. By comparing ERPs from the active and passive conditions, we isolated an N400 related to lexical access. The amplitude of the N400 was not influenced by the level of background noise in musicians, whereas N400 amplitude increased with the level of background noise in nonmusicians. In nonmusicians, the increase in N400 amplitude was related to a reduction in task performance. In musicians only, there was a rightward shift of the sources contributing to the N400 as the level of background noise increased. This pattern of results supports the hypothesis that encoding of speech in noise is more robust in musicians and suggests that this facilitates lexical access. Moreover, the shift in sources suggests that musicians, to a greater extent than nonmusicians, may increasingly rely on acoustic cues to understand speech in noise.

Turning down the noise: the benefit of musical training on the aging auditory brain.

Age-related decline in hearing abilities is a ubiquitous part of aging, and commonly impacts speech understanding, especially when there are competing sound sources. While such age effects are partially due to changes within the cochlea, difficulties typically exist beyond measurable hearing loss, suggesting that central brain processes, as opposed to simple peripheral mechanisms (e.g., hearing sensitivity), play a critical role in governing hearing abilities late into life. Current training regimens aimed to improve central auditory processing abilities have experienced limited success in promoting listening benefits. Interestingly, recent studies suggest that in young adults, musical training positively modifies neural mechanisms, providing robust, long-lasting improvements to hearing abilities as well as to non-auditory tasks that engage cognitive control. These results offer the encouraging possibility that musical training might be used to counteract age-related changes in auditory cognition commonly observed in older adults. Here, we reviewed studies that have examined the effects of age and musical experience on auditory cognition with an emphasis on auditory scene analysis. We infer that musical training may offer potential benefits to complex listening and might be utilized as a means to delay or even attenuate declines in auditory perception and cognition that often emerge later in life.

Enhanced attention-dependent activity in the auditory cortex of older musicians.

Musical training improves auditory processing abilities, which correlates with neuro-plastic changes in exogenous (input-driven) and endogenous (attention-dependent) components of auditory event-related potentials (ERPs). Evidence suggests that musicians, compared to non-musicians, experience less age-related decline in auditory processing abilities. Here, we investigated whether lifelong musicianship mitigates exogenous or endogenous processing by measuring auditory ERPs in younger and older musicians and non-musicians while they either attended to auditory stimuli or watched a muted subtitled movie of their choice. Both age and musical training-related differences were observed in the exogenous components; however, the differences between musicians and non-musicians were similar across the lifespan. These results suggest that exogenous auditory ERPs are enhanced in musicians, but decline with age at the same rate. On the other hand, attention-related activity, modeled in the right auditory cortex using a discrete spatiotemporal source analysis, was selectively enhanced in older musicians. This suggests that older musicians use a compensatory strategy to overcome age-related decline in peripheral and exogenous processing of acoustic information.

Neuroplastic effects of music lessons on hippocampal volume in children with congenital hypothyroidism.

Children with congenital hypothyroidism (CH) who experience a neonatal thyroid hormone deficiency have reduced hippocampal volumes compared with healthy controls. Interestingly, evidence suggests that musical training can contribute to structural plasticity in a number of brain areas, including the hippocampus. Therefore, we investigated whether taking music lessons could ameliorate the volumetric reductions of the hippocampus in children with CH. Left and right hippocampal volumes were measured in four groups of children: children with CH with and without music lessons, and healthy controls with and without music lessons. We found that the volume of the right hippocampus was comparable between children with CH who had taken music lessons and the healthy controls. Children with CH who had not taken music lessons had reduced hippocampal volumes compared with the other three groups. These results suggest that music lessons may induce structural neuroplasticity in children with atypical hippocampal development because of early thyroid hormone deficiencies.

The influence of lifelong musicianship on neurophysiological measures of concurrent sound segregation.

The ability to separate concurrent sounds based on periodicity cues is critical for parsing complex auditory scenes. This ability is enhanced in young adult musicians and reduced in older adults. Here, we investigated the impact of lifelong musicianship on concurrent sound segregation and perception using scalp-recorded ERPs. Older and younger musicians and nonmusicians were presented with periodic harmonic complexes where the second harmonic could be tuned or mistuned by 1-16% of its original value. The likelihood of perceiving two simultaneous sounds increased with mistuning, and musicians, both older and younger, were more likely to detect and report hearing two sounds when the second harmonic was mistuned at or above 2%. The perception of a mistuned harmonic as a separate sound was paralleled by an object-related negativity that was larger and earlier in younger musicians compared with the other three groups. When listeners made a judgment about the harmonic stimuli, the perception of the mistuned harmonic as a separate sound was paralleled by a positive wave at about 400 msec poststimulus (P400), which was enhanced in both older and younger musicians. These findings suggest attention-dependent processing of a mistuned harmonic is enhanced in older musicians and provides further evidence that age-related decline in hearing abilities are mitigated by musical training.

Musicians experience less age-related decline in central auditory processing.

Age-related decline in auditory perception reflects changes in the peripheral and central auditory systems. These age-related changes include a reduced ability to detect minute spectral and temporal details in an auditory signal, which contributes to a decreased ability to understand speech in noisy environments. Given that musical training in young adults has been shown to improve these auditory abilities, we investigated the possibility that musicians experience less age-related decline in auditory perception. To test this hypothesis we measured auditory processing abilities in lifelong musicians (N = 74) and nonmusicians (N = 89), aged between 18 and 91. Musicians demonstrated less age-related decline in some auditory tasks (i.e., gap detection and speech in noise), and had a lifelong advantage in others (i.e., mistuned harmonic detection). Importantly, the rate of age-related decline in hearing sensitivity, as measured by pure-tone thresholds, was similar between both groups, demonstrating that musicians experience less age-related decline in central auditory processing.

Endogenous neuromagnetic activity for mental hierarchy of timing.

The frontal-striatal circuits, the cerebellum, and motor cortices play crucial roles in processing timing information on second to millisecond scales. However, little is known about the physiological mechanism underlying human's preference to robustly encode a sequence of time intervals into a mental hierarchy of temporal units called meter. This is especially salient in music: temporal patterns are typically interpreted as integer multiples of a basic unit (i.e., the beat) and accommodated into a global context such as march or waltz. With magnetoencephalography and spatial-filtering source analysis, we demonstrated that the time courses of neural activities index a subjectively induced meter context. Auditory evoked responses from hippocampus, basal ganglia, and auditory and association cortices showed a significant contrast between march and waltz metric conditions during listening to identical click stimuli. Specifically, the right hippocampus was activated differentially at 80 ms to the march downbeat (the count one) and approximately 250 ms to the waltz downbeat. In contrast, basal ganglia showed a larger 80 ms peak for march downbeat than waltz. The metric contrast was also expressed in long-latency responses in the right temporal lobe. These findings suggest that anticipatory processes in the hippocampal memory system and temporal computation mechanism in the basal ganglia circuits facilitate endogenous activities in auditory and association cortices through feedback loops. The close interaction of auditory, motor, and limbic systems suggests a distributed network for metric organization in temporal processing and its relevance for musical behavior.

Concurrent sound segregation is enhanced in musicians.

The ability to segregate simultaneously occurring sounds is fundamental to auditory perception. Many studies have shown that musicians have enhanced auditory perceptual abilities; however, the impact of musical expertise on segregating concurrently occurring sounds is unknown. Therefore, we examined whether long-term musical training can improve listeners' ability to segregate sounds that occur simultaneously. Participants were presented with complex sounds that had either all harmonics in tune or the second harmonic mistuned by 1%, 2%, 4%, 8%, or 16% of its original value. The likelihood of hearing two sounds simultaneously increased with mistuning, and this effect was greater in musicians than nonmusicians. The segregation of the mistuned harmonic from the harmonic series was paralleled by an object-related negativity that was larger and peaked earlier in musicians. It also coincided with a late positive wave referred to as the P400 whose amplitude was larger in musicians than in nonmusicians. The behavioral and electrophysiological effects of musical expertise were specific to processing the mistuned harmonic as the N1, the N1c, and the P2 waves elicited by the tuned stimuli were comparable in both musicians and nonmusicians. These results demonstrate that listeners' ability to segregate concurrent sounds based on harmonicity is modulated by experience and provides a basis for further studies assessing the potential rehabilitative effects of musical training on solving complex scene analysis problems illustrated by the cocktail party example.