Neurobehavioral Alterations in Occupational Noise Exposure: A Systematic Review

: The psychology of sustainability and sustainable development emphasizes the value to ensure health and well-being in different environments, including workplaces. Chronic exposure to noise can cause several extraordinary effects and involve all the systems of the human organism. In addition to cardiovascular, gastrointestinal, and immune effects, the data in the literature show alterations in behavioral disturbances, memory capacity, and cognitive performance. Through this systematic review, the authors try to ﬁnd out the main neurobehavioral alterations in the case of occupational exposure to noise. The literature review included articles published in the major databases (PubMed, Cochrane Library, Scopus, Embase), using a combination of some relevant keywords. This online search yielded 4434 references; after selection, the authors analyzed 41 articles (4 narrative reviews and 37 original articles). From this analysis, it appears that the main symptoms are related to psychological distress, annoyance, sleep disturbances, and cognitive performance. Regarding tasks, the most frequent employments concern school staff, followed by employees from various industrial sectors and ofﬁce workers. Although the causes are still widely debated, it is essential to protect these workers against chronic exposure to noise. In fact, in addition to a hearing loss, they can manifest many other related discomforts over time and compromise their full working capacity, as well as expose them to a greater risk of accidents or absences from work.


Introduction
The psychology of sustainability and sustainable development [1][2][3] is focused on health and well-being of individual/s in different environments. A healthy workplace, through sustainable culture, climate, and practices, create an environment that protects and boosts workers health and safety, as well as organizational effectiveness. Sustainable development can be considered a primary prevention that fosters well-being of the individual and the society. Considering this framework and the need for the development of sustainable workplaces, this systematic review aims to examine the main neurobehavioral alterations in case of occupational exposure to noise. Environmental exposure to high noise levels has been associated with mental health [4,5]. In fact, anxiety, emotional stress, nausea, headache, instability, sexual impotence, mood swings, increased social conflicts or general sound, occupational, environment, neurobehavioral, psychological, mental, neural. All research fields were considered. The search string used was the following: (((((noise) OR (sound)) OR (sound level)) OR (loud)) AND ((((((((workplace) OR (work)) OR (job)) OR (job task)) OR (occupation)) OR (occupational)) OR (environmental)) OR (environment))) AND (((((((neurobehavioral) OR (behavioral)) OR (behavioral)) OR (neurobehavioral)) OR (psychological)) OR (mental)) OR (neural)).
In particular, we conducted a research strategy in the databases on the effects of noise exposure on workers' health by applying the PICO statement. The population studied was that of workers, with no difference in age, gender, or type of job. The type of intervention concerned any type of noise exposure in the workplace. The health outcomes considered were those related to neurobehavioral changes second the most recent studies. We included short-term effects and medium-to long-term effects, such as insomnia, sleep, fatigue, impaired concentration and memory, changes in work performance, errors, mood changes with irritability, anxiety, aggression, depression, annoyance. If found, physiological measures and work-life balance, such as hormone excretion level or changes in management of social and family life, were included.
The pre-specified search terms of PICO are focused upon in Table 1. Population ((workplace) OR (work*)) OR (job)) OR (job task)) OR (occupation)) OR (occupational)) OR (environmental)) OR (environment) Interventions ((noise) OR (sound)) OR (sound level) OR (loud) Outcomes ((neurobehavioral) OR (behavioral)) OR (behavioral)) OR (neurobehavioral)) OR (psychological)) OR (mental)) OR (neural)) Additionally, we practiced a manual search on reference lists of the selected articles and reviews to carry out a wider analysis. Two independent reviewers read titles and abstracts of the reports identified by the search strategy. They selected relevant reports according to inclusion and exclusion criteria. Doubts or disagreements were solved by discussion with a third researcher.
Subsequently, they independently screened the corresponding full text to decide on final eligibility. Finally, the authors eliminated duplicate studies and articles without full texts.
Data were mainly obtained from the published results but also from any other supplementary sources when these were available. In particular, the authors selected date and country of publication, sample size, involved noise source, exposure decibel, and kind of reported disorders. In addition, the authors highlighted the number of studies included for all reviews and the length of the study in the case of experiment or cohort studies.

Quality Assessment
Three different reviewers assessed the methodological quality of the selected studies with specific rating tools, to reduce the risk of introducing any bias. We used the INSA method "International Narrative Systematic Assessment" to judge the quality of narrative reviews [28], AMSTAR to evaluate systematic reviews, and the Newcastle Ottawa Scale to evaluate cross-sectional, cohort studies, and case control studies [29,30], while we applied the Jadad scale for randomized clinical trials [31]. In addition, to reduce the risk of bias, we used RobVis (BARR, Bristol, UK), a specific tool for systematic reviews [32] (see Appendix A Figures A1 and A2).

Eligibility and Inclusion Criteria
As stated by the PICO scheme above, the studies included in this review focus on occupational noise and professional categories exposed to this risk. Studies considering workers exposed to environmental noise in the workplace are also included. The studies included refer to occupational noise, measured through quantitative and qualitative assess-ment. We included studies on principal neurobehavioral consequences to this exposure, in particular annoyance, sleep disorders, short memory, poor concentrations, and working performance. All types of study designs were included. No restrictions were applied for language or country.

Exclusion Criteria
We excluded reports related only to environmental exposure or noise pollution, not specifically conducted in a workplace setting, publications on programmatic interventions, and studies not considering diseases or disturbances linked to noises. We restricted our search to the last 10 years, as explained in the Introduction. We also excluded reports of less academic significance, editorial articles, individual contributions, and purely descriptive studies published in scientific conferences, without any quantitative and qualitative inferences.

Results
The online search yielded 4485 studies: PubMed (3056), Scopus (21), Cochrane Library (13), Embase (115), Google Scholar (1280). Of these, 4434 studies were excluded because they were deemed unrelated to noise-related problems. Among the remaining studies, four articles were also excluded because they were duplicates. Duplicate publications were carefully eliminated in order not to introduce bias, by comparing the names of the authors, the topics addressed, the workers examined, and the results obtained. Another six publications were deleted because the full text was not available. In conclusion, 41 studies were finally included in this analysis ( Figure 1). Of these, 4 are literature reviews (2 systematic; 2 narrative) and 37 are original articles. Among the latter, 16 are cross-sectional studies, 2 cohort studies, 5 case control studies, 2 pilot studies, 1 observational study, 10 experimental studies, and 1 mixed (cross / experimental) study (Table 2). the type of prevalent studies in the selected articles. Moreover, "surveys and questionnaires" seems to be the most used tools in the investigations (cluster red on the right side). "Attention," "short-term memory," and "task performance" are the other keywords shown on the map and linked to "occupational noise" and "transportation noise" (cluster green on the left). Cluster blue on the top groups' keywords related to work environment makes a connection between ergonomics, noise, and work performance.   We used the VosViewer tool to create a bibliographic map of the articles retrieved [33]. Figure 2 shows the keywords' co-occurrence network of the articles in the sample. Node sizes are proportional to how many articles are labeled with the keyword selected. Two nodes are connected if the respective keywords are co-associated in an article. The restriction to generate the network is that each keyword occurs almost three times; 36 terms were identified and the total strength of the co-occurrence links with other keywords were calculated. The term "human" was excluded from the network map because all the studies considered have humans as subjects. The network map shows three clusters of keywords' co-occurrence. The major disturbances linked to noise are "depression," "psychological stress," "hearing loss," which are associated with "occupational disease" and have a link to the keyword "middle aged." The cluster shows keywords such as "cross-sectional studies," "prevalence," and "risk factors," suggesting the type of prevalent studies in the selected articles. Moreover, "surveys and questionnaires" seems to be the most used tools in the investigations (cluster red on the right side). "Attention," "short-term memory," and "task performance" are the other keywords shown on the map and linked to "occupational noise" and "transportation noise" (cluster green on the left). Cluster blue on the top groups' keywords related to work environment makes a connection between ergonomics, noise, and work performance. Selected articles examine various symptoms related to psychological distress and reported by the samples, such as annoyance (11/41; 26.8%), sleep disturbances (9/41 21.9%), and reduced work/cognitive performance (14/41; 34.1%). Taking into consideration the tasks examined, it was found that the most frequent analyses concern school staff (10/41; 24.3%), followed by employees from various industrial sectors (9/41 21.9%) and office workers (6/41; 14.6%).  Selected articles examine various symptoms related to psychological distress and reported by the samples, such as annoyance (11/41; 26.8%), sleep disturbances (9/41; 21.9%), and reduced work/cognitive performance (14/41; 34.1%). Taking into consideration the tasks examined, it was found that the most frequent analyses concern school staff (10/41; 24.3%), followed by employees from various industrial sectors (9/41; 21.9%) and office workers (6/41; 14.6%).

Narrative and Systematic Reviews
Regarding the methodological quality of the systematic reviews, the AMSTAR scores show an average, a median, and a modal value of 9, indicating the high quality of the studies (Table 3). Regarding narrative reviews scores, the INSA score shows an average and a median value of 5.5, indicating an intermediate quality. Table 3. Reviews included in this article, with their relative score.

First Author
Included Articles Results Score Freiberg 20 Exposure to onshore wind turbine noise leads to annoyance, sleep disorders, and lowered general health. A.9 Horsten 20 Effect of noise on sleep in the ICU seems to have a significant effect on the arousals in six studies performed with healthy volunteers. The majority of the observed arousals remain unexplained because they did not occur within 3 s of a sound peak. A.9

Mahendra Prashanth narrative
The data suggest that significant adverse health effects due to industrial noise include auditory and heart-related problems. The study provides strong evidence for the claims that noise with a major frequency characteristic of around 4 kHz has auditory effects and being deficient in data fails to show any influence of noise frequency components on non-auditory effects.

I.5
Yuen narrative Results from the survey, monitoring, short-term, and longitudinal studies have positioned the noise pollution scenario in Malaysia at a critical level. This highlighted the resurgent need of practical solutions by the government, non-governmental organizations, and educational institutions to generate a healthy working and living environment.
However, each of these reviews analyzed different work environments, with different complaints reported by workers.
For example, topics covered by Freiberg et al. [34] included some job duties involving wind turbines (manufacturing, transportation, installation, operation, and maintenance). The study population, however, was composed not only of workers in the wind industry, but also of others who worked around wind farms. The literature showed how the noise of wind turbines had a significant influence on the development of annoyance, daytime sleepiness, and general health problems among workers; moreover, even the workers in other sectors but within 3 km of the turbines show a certain prevalence of disorders attributable to this source of noise [35].
Horsten et al., on the other hand, analyzed the scientific evidence of the effect of noise in ICUs on sleep quality. They showed that such noise in the ICU has a significant negative effect, with increased arousals in six studies performed with healthy volunteers; however, there is a high risk of bias due to the multifactorial nature of sleep disorders in intensive care, the different protocols implemented by the different experiments, the sound levels not always measured, and finally the administration of questionnaires not always standardized with subjective symptoms [35].
Mahendra's review focuses on studies published between 1988 and 2009 on the effects of industrial noise, analyzing auditory and non-auditory effects. Some of his included studies have shown that with lasting exposures between 43 and 73 Hz, particular disturbances can occur, such as lack of visual acuity, a drop in IQ scores, distortion of spatial orientation, poor muscle coordination, loss of balance, and confused speech. However, specific noise levels in terms of frequencies that predict health impacts have not yet been validated [25].
Finally, in the case of exposure to vehicular traffic, Yuen highlighted how the discomfort associated with continuous exposure to traffic noise can create an unpleasant condition in highway toll workers and residential communities in the surrounding areas. Traffic noise levels are typically between 75 and 85 dBA and occasionally reach 90 dBA. Respondents wake up more often, have had poorer sleep quality, and feel sleepy during their day work. In addition, they negatively assessed the installation of the so-called TRS "crossroad strips," as they generate excessive vibrations and pulsating or impulsive noises, similar to the sound of hammers, firecrackers, or small explosions [36].

Original Articles
The scores assigned to the original articles have an average value of 5.16, a mode of 7, and a median of 6; this indicates an intermediate quality of the studies (Tables 4 and 5).
Researchers from Iran, China, Japan, Sweden, Korea, Denmark, Serbia, Brazil, Thailand, Zimbabwe, and USA have obtained the highest values (NEW CASTLE Scale = 7). Sweden remains the country where the most articles related to the topic have been published in the last 10 years (6/37; 16.2%), followed by Iran (5/37; 13.5%).
To carry out the results and considering the quantity of the selected articles, we proceed with a synthesis of the results based on the main disorders and workers' categories found by the authors.
As for the questionnaire administered to workers, some authors investigate aspects concerning general health, through questionnaires such as General Health Questionnaire (GHQ) and Patient Health Questionnaire (PHQ), or work-related stress, through effortreward imbalance (ERI), Perceived Stress Scale (PSS), and Copenhagen Psychosocial Questionnaire (COPSOQ). Other studies evaluate work performance more specifically, for example, through the Stroop test (ST), reaction time (RT), memory test, and the sustained attention to response test (SART).
Regarding cognitive functions or various logic and memory skills, most authors agree that their quality decreases with exposure to noisy sources. For example, Alimohammadi proved that all the cognitive indicators have a significant relationship with exposure to noise, but in all the cognitive indicators annoyance does not have a significant relationship with cognitive performance [37]. In the study by Monteiro et al., people tested for memory, attention, and serial recall tended to make more mistakes as the noise intensity increased. The participants experienced growing discomfort, stress, and annoyance as the sound pressure levels increased (p < 0.05) [38]. Better cognitive performance can be related to higher education and younger age [39].
For Cheng, the effects of noise can be traced with magnetic resonance imaging. Exposure group scored worse on mental tests, and they had less brain gray matter volumes in the left hippocampus, right middle frontal gyrus, and right inferior parietal lobule compared with the control group (p < 0.002, p < 0.05). The same group showed significantly lower regional homogeneity values in the left amygdala, left hippocampus, left thalamus, and right middle/superior frontal gyrus (p < 0.01) [40].
However, other authors have found conflicting information; for example, Wassermann found that the participants' reaction times are slower in the control condition than in the pink and TV sitcom noise conditions. So, complex television noise does not impair attention, while pink noise, or a signal that combines relevant frequencies, does [41]. For Keller, speech intelligibility has a relevant role in communication; in fact, as the speech intelligibility goes down, missed communication rate and requests for repeat backs increase (p < 0.001). Communication errors in some tests were significant in relation to the decrease in speech intelligibility. However, overall eye behaviors were not overly impacted by the different speech intelligibility levels (eye blink rates, pupil dilation, and basic measures of saccade and fixation metrics showed no difference with increased fatigue, strain, and noise levels) [42].  Attention was significantly improved in pink noise compared to the ambient noise, whereas no differences were found between the ambient and television conditions. Another disorder frequently found in the selected articles is annoyance. Some authors have looked for a correlation between this reported symptom and some individual or work-related factors. For example, Yoon found a difference between gender (ORs 1.58 for men, 1.49 for women with depression, and 1.41 for women with suicidal ideation) and sleep time (ORs 2.95 for workers with less than five hours of sleep) [43].
Moreover, the workplace is important. In fact, Di Biasio showed that workers in shared offices are less annoyed than those who work in open-plan offices. In this last group, he observed a difference between gender (women are more annoyed), year range (51-65+ are more annoyed), and type of workplace (those who work in sales or public affairs sectors or engineering and teaching sectors are more annoyed) [44]. Additionally, a very noisy environment can lead to hearing fatigue and tinnitus, which in turn are related to work-related stress and annoyance [45].
Finally, annoyance is related to individual sensitivity. In fact, for Alihommadi, noise annoyance is significantly related to noise sensitivity (p = 0.0015). People with higher level of noise sensitivity were more annoyed than those with moderate (OR = 11.78) and low sensitivity (OR = 4.88). Moreover, medium level of anxiety seemed to worsen noise annoyance, while in individuals with either low or high level of anxiety, noise annoyance was lower (p = 0.005) [46].
We found many other types of neurobehavioral disorders with noise exposure. For example, Azuma found three more frequent general symptoms, such as "tension, irritability, or nervousness," "feeling depressed," and "unusual tiredness, fatigue, or drowsiness" [47]. Besides, in Sjodin's study, preschool personnel described their occupational fatigue at midday in terms of lack of energy and motivation, physical discomfort, and sleepiness at work. These employees reported being more tired before going to sleep (p < 0.05). Higher levels of depression were related to higher sound fluctuation as perceived subjectively (p < 0.05) and the assessed morning cortisol correlated positively with noise annoyance during work (r = 0.284, p < 0.05) [48].
Mood swings were also found in the Oenning's and Deng's study; in fact, they found an association between chemical substances and noise with depressive symptoms among women belonging to various work categories (p < 0.05). Sometimes, depressive symptoms are secondary to hearing loss caused by exposure to noise and subsequent isolation [49,50].
Insomnia is another ailment reported by workers. In his study, Nari found an increased risk of developing this discomfort in both genders, especially if exposed to vibrations at the same time (1.83/ CI 1.61-2.07 in men and 3.14/ CI 2.76-3.57 in women) [51]. Sleep disturbances appear to be triggered by annoyance, which in turn is related to noise exposure, but they do not appear to be related to the age of workers [52].
Another interesting fact is the finding of a greater tendency to develop aggression when exposed to noisy sources. In his study, Alihommadi found that it is present a positive correlation between the daily dose of noise received by the workers and aggressive behavior in terms of verbal and physical aggression, hostility, and anger (p < 0.05) [53]. Furthermore, Milenovic showed that a tendency for reactive aggressiveness increases with noise intensity, in particular between 70 and 90 dB (p < 0.01); he also noted that length of employment did not affect levels of aggressiveness [54]. These conditions can cause workers to show a greater predisposition to addiction. For example, Kim discovered increased intensity of cigarette smoking in noisy and safety-threatening workplace environments [55]. Finally, a higher rate of occupational injuries has been related to greater perceived noise exposure in electronic waste recycling workers of low-income countries [56].
Among school staff, the variable factors that can correlate with a greater manifestation of neurobehavioral disorders are working age, hours of lessons, and workload. For example, in Eysel's study, sleep disturbances in teachers older than 45 years of age were common; tiredness and exhaustion in the evening, after a full day of work, was present in almost all the employees (90%). In this context, 51% of the whole sample consider work as a physical and mental strain; older teachers report a significant worsening in these affectations with increasing years of professional activity in 81% of the cases [57]. Furthermore, in Fredriksson's study, symptoms generally occurred more often in older people (p < 0.05), excepting for hyperacusis and sound-induced auditory fatigue. The prevalence of such disorders increases significantly in people exposed to both noise and stressful working conditions compared to those unexposed (p < 0.05) [58].
The duration of exposure may influence the association between noise and symptoms. In Kristiansen's study, cognitive tests exhibited little changes when teachers with less than four lessons were excluded from the analyses. Moreover, the teachers' average noise exposure was moderately correlated with changes in TBT (two back test) performance, in particular when the analysis was limited to general classrooms (Spearman's rho = −0.35, p = 0.11); instead, the scores in the sustained attention to response test (SART) did not correlate significantly with noise exposure or vocal load [59].
Finally, remaining in the school environment, even students can report related symptoms. Onchang found a difference between two students' cohorts, "the off-campus" (OG) and "inside-campus" (IG); the first suffered more than the others from all community noise categories (traffic, construction, recreation, and advertising; p < 0.001). The largest differences between the two groups in the perception of noise annoyance were consistently found for telephone and personal communication for all the types of community noise; conversely, the smallest differences were for listening to radio and television, reading, and mental tasks. In the group of OG students, reading and mental tasks significantly influenced cumulative grade point average (OR = 2.801, p < 0.05) [60].
In his experimental study, Irgens-Hansen evaluated cognitive performance under exposure to various noise levels among personnel working on board ships in the Royal Norwegian Navy. Reaction times were significantly higher in personnel exposed to values greater than 85.2 dB(A) and in the exposed group in the range of 77.1-85.2 dB(A), compared to personnel exposed to values below 72.6 dB(A). Furthermore, the latter reported a lower workload. Caffeine consumption and nicotine use did not differ significantly between the noise exposure groups [61].
The Molesworth study explored the effect on memory and psychomotor performance in being exposed to 75dBA broadband noise (simulation of an airplane cabin noise). When the performance of reaction times in the presence of noise was compared with conditions in which the volunteers had consumed alcohol, it was found that the impact of alcohol on reaction time was more severe than the noise itself [62].
Jahncke designed an experiment with the exposure of the 47 subjects tested in four different conditions (projecting films on nature, listening to the sounds of nature, with silence and with high/low noise). By testing memory capacity, participants scored lower when exposed to higher noise. Furthermore, the analysis revealed a significant interaction between noise and fatigue/lack of motivation: participants who viewed the film reported more energy than participants exposed to noise only (p < 0.01) and those who listened to the sounds of the nature (p < 0.05). Participants exposed to noise during the rest period ranked as less motivated (i.e., more disinterested) than participants who listened to the sounds of the river (p < 0.05) or watched the film (p < 0.01) [63].
In Smith's study, too, the beneficial role of music is highlighted. In fact, when participants are exposed to office noise, they exhibit lower performance alterations, although after a 10 min habituation period, their performance tends to improve. In the second part of the experiment, the author showed how instead an exposure to Mozart's works improved subsequent performances, especially as regards the visual-spatial reasoning activities [64]. Table 6. Experimental studies included in this review, with their relative score. Increasing sound pressure level from 65 to 95 dB in network "A" increased the speed of work (p < 0.05).
Male participants got annoyed from the noise more than females. Moreover, increase in sound pressure level increased the rate of error (p < 0.05). Response time was significantly increased among personnel exposed to >85.2 dB(A) and 77.1-85.2 dB(A) compared to personnel exposed to <72.6 dB(A). Participants remembered fewer words, rated themselves as more tired, and were less motivated with work in noise compared to low noise; those who saw a nature movie (including river sounds) rated themselves as having more energy after the restoration period in comparison with both the participants who listened to noise and river sounds.
Remaining in office noise during the restoration phase also affected motivation more negatively than listening to river sounds or watching the nature movie.

Discussion
The aim of this work was to analyze the most recent scientific literature to identify a correlation between exposure to noisy sources and the development of neurobehavioral disorders, particularly in the workplace. All the studies included defined the exposure to noise as related to the occupational setting, both as noise coming from the work procedures and noise coming from the environment in which the workplace is located.
First of all, our results actually highlighted a not very large number of articles; this could indicate a still current difficulty in approaching this complex issue. A significant amount of data in the scientific literature, in fact, concerns the already known effects of noise on the human body, such as those manifested by the cardiovascular system, and even to a lesser extent the insights into neurobehavioral disorders. After that, in our review, several publications and in particular the experimental studies, concerned working sectors in which they must pay a lot of attention and concentration in every procedure they perform, such as for example military personnel or surgical teams. This observation did not surprise us; in fact, tasks that require continuous and careful monitoring of signals (e.g., warning or alarm systems) can in fact be negatively affected by noise and can be used in experimental studies.
The studies available on the effect of noise in the workplace show how this risk can negatively affect the performance of certain activities, acting in particular on the level of performance and safety; for this reason, even accidents and injuries can be a sentinel indicator of a decline in performance [59,65,66], as well as distraction errors [67] or sickness absence among workers [68].
Exposure to noise can be reduced memory capacity [69][70][71] and short periods of inefficiency/unproductivity [72,73], especially when prolonged visual attention is required [74,75]. However, the evidence of the negative effects of noise on productivity in the workplace is still unclear and controversial. For example, a relationship between sound pressure levels and work productivity has not yet been demonstrated and some publications show opposite results, such as Habibi's experiment, where increasing the exposure noise increased (instead of decreasing) the speed of execution of some works [76].
Other studies indicate that absence from work is also associated with several variables to consider, such as gender, age [77], and smoking behavior [78].
Another working sector most examined in our analysis is that concerning the school staff. The noise in school classrooms originates from external sources, such road traffic, and from internal sources such as operators and pupils [79]. In noisy and reverberating classrooms, school-age children experience greater difficulties in both language perception and listening than adults [80][81][82]. The performance at school of children can be negatively affected by environmental noise, creating interferences in pupils' attention and motivation [83,84], disturbing reading comprehension [85,86], short-term memory [86,87], mathematical skills [88,89], and inducing some kind of hyperactivity [89,90].
These aspects can be decisive in children, as they interfere with language learning processes and phonation: they can favor the onset of dysphonia and dyslexia phenomena due to lack of or reduced control of phonation [91].
Several studies have analyzed the effects of exposure to environmental noise in children, relating to learning, the degree of interest, motivation, and stimulus. For example, research on school-age populations residing near European and international airports showed that they were unable to perform some difficult and complex tasks as well as a control group residing in quiet neighborhoods [92]. There is also some scientific evidence that children exposed to sources of intense noise are more likely to experience impairments in reading and language, especially in the case of pre-existing difficulties.
Considering all this evidence, the World Health Organization Parma Declaration demanded that all the stakeholders get cooperatively involved in reducing the exposure of children to noise to protect them from its harmful effects [93]. The recommended threshold of WHO guidelines for noise level in school classrooms is 35 dB(A): this level should prevent disturbance of communication during class. Actually, it is very common that these noise limits are exceeded and noise intensity in schools can reach as much as 60-80 dB(A) in normal classes; during school workshops and in sport areas, the limit values for workplace can be exceeded [94].
It is also necessary to consider the complexity of the individual factors, involved in the onset of effects and symptoms; some of these seems to be individual sensitivity to noise or coping strategies. For example, from a study conducted on young women [95], it emerged that noise can cause a physiological reaction to stress when they are not effective or there are no suitable strategies to counteract it (for example, the disturbance caused by noise was less annoying for those who knew they could close the windows).
Even how leadership quality is assessed appears to mitigate the negative effects of occupational noise exposure [96], as exposed employees may feel that the problem is recognized and addressed by management; such reassurance could alleviate stress induced by noisy sources. Moreover, it cannot be excluded that some of these individual variables, such as subjective noise sensitivity, paranoia and sleep quality, can be used as positive predictors for the onset of chronic noise exposure impairments [97].
In recent years, as also found in our analysis, many authors are shifting the focus of their research on the neuro-physiological and biochemical alterations suffered by the nervous system and the auditory system, due to noise. In fact, from the data found also through our analysis, it can be hypothesized that noise can directly cause neurobehavioral alterations (through biochemical mechanisms) or indirectly (as a consequence of hearing loss or speech intelligibility or due to its distracting action). Some studies have shown how, with the same sound pressure level, the annoyance increases the more the high frequency content of the noise increases, because such high values interfere with verbal communications [98]. Furthermore, the increased effort of interpretation required to compensate for this discomfort causes tension and psychological fatigue in the exposed subjects, leading to unconscious behavioral modifications [99].
As for the biochemical hypotheses, some experimental studies have shown that noise exposure can cause structural damage to the cochlea and stimulate hyperactivity in the central auditory system, including the cochlear nucleus, inferior colliculus, and auditory cortex. Furthermore, non-classical hearing-sensitive brain areas can (e.g., the lateral amygdala and striatum) can be triggered by noise exposure, which directly activates the brain's emotion-fear system via the thalamus. In this way, noise can activate defense responses involving the mechanisms of the hypothalamus-pituitaryadrenal (HPA) axis. Long-lasting activation of the HPA axis can cause disturbances in hormonal balance as well as morphological and functional changes in the brain, which may be the potential mechanism for subsequent noise-induced cognitive impairment and neurobehavioral manifestations [100][101][102][103].
A strong element of this scientific work is that we have not found another systematic review that addresses this issue in the same way as we do. At the same time, another past systematic review would have given us the opportunity, updating the scientific literature, to compare ourselves with past works and highlight the differences or changes made in the approach to these issues. Other limitations of this review could be the wide variability of samples selected in the various studies, the wide diversity of categories examined, and sometimes a non-standardized and validated methodology regarding questionnaires administered to the exposed or scientific experiments. Additionally, some of the studies lack quantitative measurements and description of the characteristics of noise, thus making it difficult identifying the detrimental and annoying features of noise to plan targeted interventions. Eventually, confounding factors related to the possible extraprofessional noise exposure should be addressed. In fact, even though all the studies refer to occupational noise and its effects, we cannot exclude voluptuary noise exposure of the subjects involved in the studies. However, in all studies, the professional exposure results the main source of noise identified by the investigators, thus making it possible to relate it to the neurobehavioral effects described.

Conclusions
In conclusion, the issue is still widely debated and involves more and more aspects. A greater number of studies will be needed to bring new knowledge on this topic, both as regards the evidence of behavioral disorders and as regards the hormonal and biochemical knowledge underlying these alterations, in order to prevent inconvenience for residents in the areas most exposed and for all those workers who report such disturbances. New opportunities for intervention are desirable in the future, including increased public awareness, worker training programs and education, government intervention addressing health and safety concerns, promotion of regulation, and government funding to enforce higher safety measures, especially in some work sectors such as schools.