According to Brescia,1 the first civilizations used music in all their rituals, such as during birth and death. Music stimulates people's physical, emotional, cognitive and social status. Imaging exams demonstrate activity in parts of the brain, in areas associated with hearing and emotions, when they come into contact with music,2 and when a musical instrument is played, neural connections are created, connecting the two brain hemispheres, which begin to work together.3

Central auditory processing (CAP) refers to a series of processes involved in the detection of and reaction to the sounds received and predominantly involves the structures of the central nervous system (CNS);4 however, for a correct decoding to occur, it is necessary that the auditory skills be complete and effective.5 It is observed that alterations in this system can lead to difficulties in learning, understanding and language delay.6

The CAP includes sound recognition and localization skills, sharing of attention between two stimuli, selecting an auditory stimulus in the presence of background noise, differentiating the variation of frequency, intensity and duration of the sound, in addition to perceiving differences and similarities between verbal sounds,7 and musical practice is considered to favorably stimulate these skills,8 becoming an ally in the treatment and prevention of some disorders.9,10

The auditory processing integrity is a prerequisite for the development of language skills. It is reported that the musical experience positively contributes to the global development of children, as well as in the metalinguistic skills.10,11 The musical experience that can promote improvement in the auditory processing and phonological awareness skills in children of 5 years stands out.12

Research suggests that brain plasticity is induced by musical practice and, therefore, a functional and structural difference in the musicians’ brain auditory areas when compared to that of non-musicians,13–16 which may indicate a faster processing of auditory stimuli, represented, for instance, by the decreased latency and greater P3 amplitude in that population.17

Recent studies have shown that musical practice and training improve the auditory processing skills,7,18 which have shown to be effective and have potential to be used in children, aiming to assist in the acquisition of auditory skills, as well as to improve them.7

Based on the abovementioned facts, the present study has as its main and guiding objective the verification of the scientific evidence on the implications of musical practice in central auditory processing, aiming to answer the following research question: What are the implications of musical practice in central auditory processing?

The studies admitted in this systematic review agree regarding the effects of music or musical training, inferring that they improve auditory processing skills, in addition to causing cortical changes, which favor the learning and development of language in children and newborns, corroborating what was found in other publications.7,12,26,27

The literature points out that musical practice positively influences the CAP skills 9,18 and may be considered a tool to improve these skills, becoming a protective factor in relation to developmental disorders, especially those related to speech and language development.9

The study samples admitted to this systematic review consisted of adults, children aged 6–7 years and neonates, as the age range did not constitute an exclusion criterion. Other studies carried out to verify the effects of music, as well as musical training on populations of adults17,28–33 and children7,12,26,27,34–36 have been evidenced in the literature, and, overall, studies with children carry out the exposure to music/musical training during the study period, while studies with adults evaluate the effects of music that have been present in the subjects’ daily lives for many years.

The literature on the effects of music, as well as musical training on the auditory processing of adults, is broad, showing a superiority in temporal ordering skills, 29 speech recognition in noise 28 and temporal resolution,31 when compared to the performance of non-musicians, in addition to the fact that musicians show superiority in standardized subtests of visual, phonological and executive memory.17 A study developed with 30 popular band singers compared their performance in auditory skills of temporal resolution and ordering between individuals who sing and play musical instrument(s) (n=15) with the performance of those who only sing (n=15) and verified that popular singers who play musical instruments have a better performance in those skills.33

Another study, carried out with 43 adults aged between 18 and 38 years, divided into three groups, one of which consisted of bilingual non-musician adults (n=15), the other by monolingual English-speaking musicians (n ​​=13) and the control group, consisting of monolingual English speakers (n=15), showed that bilingualism and musical training have differential effects on brain networks.30

When evaluating the P300 latency and amplitude in musicians (n ​​=30; between 20 and 53 years old) and non-musicians (n ​​=25; between 18 and 30 years old), in the absence and presence of contralateral noise, researchers found a greater inhibitory effect on musicians compared to non-musicians, showing that the central auditory nervous system of musicians has characteristic peculiarities due to the musical practice to which they are constantly exposed.32 This potential was also assessed in a study developed with 32 university students aged between 18 and 24 years, divided into musicians and non-musicians, in which musicians should have been practicing a musical instrument for a long period (between 9 and 16 years), with the beginning of the practice occurring initially in childhood (between 5 and 10 years). The musicians demonstrated a faster update of working memory (lower latency P300) in the visual and auditory domains and allocated more neural resources to auditory stimuli (higher amplitude P300), demonstrating that long-term musical training is related to improvements in memory, both auditory and visual.17

In line with that observed in the adult population, as well as with the findings of the study carried out with children aged 6–7 years old included in this research,25 the result of another study carried out with children aged 5 years showed that the musical experience promoted the improvement of auditory and metalinguistic skills,12 and there is evidence that musical training positively influences reading skills and speech perception in noise, in addition to causing faster neural responses.26

Other results show positive effects of music on the transfer between cognitive domains in the pediatric population,34,37 since musical training increases the sensitivity to a specific basic acoustic parameter, the tuning, which is equally important for the prosody of music and speech, improving children’s ability to detect changes in tuning not only in music, but also in language.37 When comparing the performance of 5-year-old children with and without musical practice, it is noteworthy that musical practice had a positive influence on the auditory skills of temporal ordering, sound localization and musical appreciation.9

There is longitudinal evidence that children’s speech perception in noise improves after group musical training for a period of 2 years.27 However, researchers found that 6 months of musical training were already sufficient to significantly improve behavior and influence the development of neural processes in 8-year-old children, strengthening theories about brain plasticity by showing that relatively short periods of training have strong consequences on the functional organization of children’s brains.34

The lasting benefit of musical training was evidenced in a study carried out with children aged between 4 and 6 years, in which it was also possible to verify that new brain hemisphere changes appeared one year after the training.36 Therefore, musical education plays an important role in child development, and musical training is also capable of shaping essential skills in the social and academic development.25

The evidence found in the study carried out with newborns infer that the simultaneous occurrence of exaggerated prosodic cues and items to be learned seems to help newborns to process language input, corroborating what was found in previous studies.38,39 For Schon and Tillmann,40 the rhyme in children’s songs are natural auditory stimuli for newborns, improving phonological processing. The absence of learning evidence in neonates against a song presented as a certain melody, which is not a lullaby, may be due to the fact that the melody does not include sufficient variation in tuning or due to the challenging situation imposed by the simultaneous learning of the melody and phonetic content and not just the phonetic content.24

Although none of the studies selected for this research were carried out with the elderly population, there have been reports in the literature about the benefits of musical training in the auditory processing skills of non-hearing aid 41 and hearing aid elderly users.42–44 A study developed with elderly people randomly assigned to learn how to play the piano (music), learn to play a video game (video) or to be used as a control (non-contact) found that after 6 months, the group that learned how to play the piano improved their ability to understand words presented in the presence of background noise, while the other two groups did not. It is important to observe that these findings suggest that musical training can be used as basis for the development of hearing rehabilitation programs for the elderly.41

Another important effect of music was found in a study that assessed the skills of auditory processing throughout life in musicians (n ​​=74) and non-musicians (n ​​=89), aged between 18 and 91 years old, and demonstrated that musicians experience less age-related decline in auditory tasks, such as gap detection and speech understanding in noise.45 The differences between musicians and non-musicians in relation to behavioral and electrophysiological measures increase the expanding literature on experience-dependent plasticity in musicians.23

Studies indicate that there are structural differences between the brains of musicians and non-musicians, among which are the larger volume of the auditory cortex, greater concentration of gray matter in the motor cortex, and larger anterior corpus callosum. Studies involving neuroplasticity indicate a correlation between time of musical study and structural differences. Additionally, it is possible that there is a critical period related to these changes, indicating a possible correlation between the age at which music started being studied and structural brain changes.46,47

Seeking to understand the correlation between musical study and an increase in the corpus callosum, a research was carried out with children from 5 to 7 years old, who were divided into three groups, one group who had weekly practice of musical instrument from 1 to 2h, one group who had weekly practice from 2 to 5h and a control group that did not have music lessons. At the beginning of the study, there were no differences between the volumes of the subjects’ corpus callosum. After 29 weeks of practice, there was a significant difference between the size of the corpus callosum in the children from the three groups, with a greater increase in the corpus callosum being observed in children with a longer time of exposure to musical practice.48

Another similar study carried out with 31 children divided into two groups, one of which (n=15) had keyboard lessons for 15 months and the control group, which did not receive instrumental musical training, but only participated in weekly group music classes at school, found differences in regions such as the right precentral gyrus (motor area related to hand movement), corpus callosum and Heschl gyrus (primary auditory area),49 findings that indicate a strong possibility of music-induced brain plasticity.

Structural brain alterations after musical training in early childhood, for a short period of time (15 months), were correlated with improved motor and auditory skills. These findings shed light on brain plasticity and suggest that structural brain differences evidenced in adult specialists are likely due to training-induced brain plasticity.49 Putkinen et al.35 upon finding an increase in the amplitudes of mismatch negativity (MMN) and P3a with the increase in age in musically trained children, with these increases not being evident in the initial stages of training, suggested that the superior neural auditory discrimination in adult musicians is due to training and not to pre-existing differences between musicians and non-musicians.

Regarding the procedures used to assess auditory processing in the studies chosen for this research, it was found that two of them used only electrophysiological assessment (ERP), 21,24 while the other three used behavioral procedures associated with electrophysiological assessment.22,23,25 Therefore, ERPs were assessed in all studies, which constitute a valuable tool for the study of the neuronal activity generated during new information processing.50

Corroborating these findings, several studies that investigated the effects of music and musical training, found in the literature, also used electrophysiological procedures alone, by recording and analyzing event-related potentials,30,32,35,36 while other studies used behavioral assessment associated with electrophysiological evaluation.17,37,41 However, it was possible to verify that many studies were developed using only behavioral methods,9,12,27–29,31,33 which were shown to be effective and represent the positive effects of music on the participants’ auditory skills. Although the stimuli used to evoke the ERP were different, all of them were able to demonstrate the superiority of the musicians regarding their auditory skills.

The mean time of exposure to music in the studies selected for this systematic review varied considerably and none of them aimed to compare the performance in auditory processing skills according to the time of exposure; however, there is an agreement in the literature that points out that the longer the time of exposure, the more evident are the improvements in auditory processing skills.7,17,18 However, there is evidence that shows that relatively short periods of musical training have strong effects on the brain functional organization in the child population, consolidating theories about brain plasticity.34

Considering the scientific evidence, it was found that the musical experience can improve specific skills of the central auditory processing, regardless of age, optimizing children’s linguistic development. Moreover, individuals exposed to musical experiences are able to discriminate spectrally complex acoustic signals, in addition to experiencing an improvement in short-term cognitive processing and speech recognition in noise.

Therefore, musical practice plays an important role in the development of auditory skills, also shaping skills that are indispensable in the social and academic development.

The authors declare no conflicts of interest.