Subjective tinnitus is a common form of tinnitus. It differs from objective tinnitus in that there is no actual, overt sound present. Many researchers believe that subjective tinnitus is associated with changes in the peripheral and/or central auditory system (Moller, 2003; Lockwood et al., 2002; Jastreboff, 1990). Since many patients reported tinnitus in one but not both ears, it was believed for many years that tinnitus may originate from a peripheral source such as the cochlea. However, clinical observations have showed that this cannot account for all forms of subjective tinnitus. Studies found that blocking auditory inputs to the brain did not diminish tinnitus, indicating that central mechanisms must be involved in tinnitus (Berliner et al., 1992; Barrs and Brackman, 1984; House and Brackman, 1981; Kaltenbach et al., 2005).
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The peripheral system consists of the outer, middle, and inner ear. The outer ear includes the external ear (pinna) and ear canal. The middle ear includes the oscicles and the inner ear includes the cochlea. The outer ear and middle ear are separated by the eardrum (tympanic membrane) and the middle and inner ear are separated by the oval window of the cochlea (Silverthorn, 2007). Sounds are directed by the pinna into the ear canal and the waves hit and vibrate the tympanic membrane. The vibrations are then transferred to the oval window through three connected oscicles, the malleus, incus, and stapes, which amplify the signal (Silverthorn, 2007). The vibrations from the oval window create waves within the fluid-filled cochlea causing hairs of hair cells to bend. Hair cells receiving mechanical stimulation (bending of hairs) release neurotransmitters which consequently excite spiral ganglion cells. Action potentials generated by ganglion cells travel by the cochlear nerve to the central auditory system (Silverthorn, 2007).
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A search of the background literature for this review quickly revealed that little systematic neuroethological research has examined age-related hearing loss and its impact on survival in the wild. While the importance of auditory and visual acuity has been shown to have great survival value for a number of different species (Webster and Webster, 1971; Cumming, 1996; Anderson et al., 1998; Sisneros and Bass, 2005; Hollen and Manser, 2006), the impact of sensory aging on predator/prey relationships in a natural habitat has not been well studied. Many years ago, Webster and Webster demonstrated that altering the nature of the middle ear of the kangaroo rat changed hearing sensitivity in such a way that the adult kangaroo rats were more susceptible to predation by snakes in a restricted natural habitat (Webster and Webster, 1971). Similar studies designed to examine the impact of aging in the wild have not been carried out. Studies designed to examine the impact of aging, in species that survive into old age in the wild, are sorely needed. Additional sensory studies might investigate how compensatory plastic changes at one brain nucleus within a circuit would impact on other nuclei, and how homeostatic plasticity of aging might differentially affect changes in temporal reliability relative to changes in the place code. Future studies will need to model the impact of age-related changes across the entire ascending and descending auditory pathways, mapping the plastic adjustments with both positive and negative consequences throughout the system. It is generally assumed that many mammalian species do not survive into old age in the wild. However, few systematic aging studies have been done for most species in the wild. The present studies suggest that it is important to consider the impact of age-related sensory dysfunction on survival, rather than simply focus on the impact of aging on normal adult motor function.
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Central auditory tests can evaluate each auditory processing separately and can determine special processing involved in each one, and therapist can decide which trainings must be chosen based on the results. This specialization leads to an effective and efficient training program . The MAPA test battery was used to evaluate the temporal processing, dichotic listening and monaural low redundancy performance of the central auditory system which they can evaluate the most important parts of auditory processing. There are different test batteries for auditory processing disorder. The MAPA test battery has 90% sensitivity and 100% specificity in diagno- sing (C)APD . As a result, this test battery was selected in this study.
The integrity of the central auditory system is a fundamental condition for language development. Successful language development is related to good learning abilities and academic success (Bishop & Adams, 1990; Ca- povilla & Dias, 2008; Sharma, Purdy, & Kelly, 2009). Individuals with auditory processing deficits tend to present behavioral manifestations occurring in isolated or associated forms, including verbal communication and writing, academic performance, social behavior and hearing (Jorge, 2006). Besides, there seems to be a high frequency of symptoms related to academic and behavioral difficulties in patients with auditory processing dis- orders (Fridlin, Pereira, & Perez, 2014).
The GIN test was performed to assess the auditory ability of temporal resolution (which determines the de- tection threshold gap or very short silent intervals and is identified as an interruption of the sound stimulus) and the physiological mechanism of temporal processing . Previous research observed, healthy subjects aged between 13 and 46 were evaluated and gap thresholds of 4.8 ms for the left ear and 4.9 ms for the right ear were observed . A hundred young healthy adults aged be- tween 18 and 31 years and obtained threshold gaps of 4.19 ms for both ears in a study . A threshold gap of 3.9 ms for 10 adults was observed . The results of the present study, based on our CG, approached the re- sults found in the literature. A comparison of the de- scriptive measures showed that migraineurs had similar performance. Comparing groups of migraine patients and the control group showed different performance amongst the groups, to the detriment of both migraineur group. Previous studies have revealed that the GIN test is sensitive for confirming lesions in the central auditory nervous system . The threshold gap of 18 individuals suffering with Parkinson’s disease was evaluated, which showed a deficit of temporal resolution in these patients and hypothesised that a dysfunction exists in the ce- rebral cortex, especially in the auditory area . The difference in performance on the GIN test between pa- tients with migraine and the control group may denote a central auditory system dysfunction in migraineurs with and without aura. The temporal resolution is essential for speech perception .
The plasticity of the central auditory system has been investigated in various studies and two important factors of time and stimulation (input) in plasticity have been mentioned [23,29-31]. Because sensory and cognitive systems interact with each other at the core level, the highest degree of plasticity is reported in the cortex . In the early years of human development, neuroplasticity reaches its highest levels due to developmental physiological changes. Neu- rons in the area of visual, auditory, and pre- frontal cortex proliferate rapidly in the first 3.5 years of life [32,33]. This growth leads to increased synapses or connections between neu- rons. Rapid myelination of axons occurs during this time as well. Neurotrophins are a family of proteins that play a major role in plasticity in both the peripheral and CNS, and these activity- dependent proteins are largely responsible for molecular changes within the neurons and cha- nges in neuronal connectivity such as axonal branching, dendritic modification, and media- tion of a number of synapses . Once exci- tatory activity (i.e. long-term potentiation) was considered to be the main factor of development and plasticity, now it appears that inhibitory activity in the CANS also plays a role in plasticity . The auditory system plasticity was also found in studies that examined lin- guistic and musical experiences . Plasticity is referred to as changes in neuronal cells for better adaptation to environmental changes, and these changes are usually associated with beh- avioral changes . Auditory training and other behavioral interventions can be justified on the basis of Hebb's (1949) theory  that long-term potentiation (LTP) is the mechanism responsible for learning and memory, leading to
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We employ both modeling approaches, treating them as com- plementary. Exploiting detailed anatomical and physiological knowledge of the peripheral auditory system, the first stage of the simulation is a biologically-faithful model of the trans- duction of sound from the pinna to the mammalian auditory nerve . The second stage is a trainable ANN which mod- els essentially unknown details of central auditory system func- tion at a high level of abstraction. (See Shamma  for ear- lier, similarly-motivated work in this area.) Figure 1(a) shows a schematic representation of this processing scheme and re- lates it to a traditional signal-detection theoretic viewpoint  in which a sensory process produces a (unidimensional) vari- ate X which is the basis for subsequent decisions (Figure 1(b)). Signal detection theory is important and relevant here , , because its clear separation of sensory and decision operations focuses attention on the locus of categorization. That is, does it take place at the sensory stage (so that X is discrete) or at the decision stage (so that X is continuous)?
The study of auditory cortical responses, described thus far, would be incomplete without an examination of how the activity in this area correlates with behavior. The ultimate goal of all neural processing is to allow the organism to better interact with its environment, and so if a neural computation is not used to influence the organism’s behavior then it is in most senses irrelevant. It has been shown, for instance, that animals do not always perform tasks with the level of accuracy that would be predicted from recording their neural activity (Carney et al. 2014). It is therefore necessary to compare our neural studies with behavioral results, in order to fully understand the animals’ ability to process auditory stimuli. To this end, in chapter three of this manuscript, we detail the development of a behavioral training system that will allow us to compare our neural recordings to our animals’ actual ability to perform tasks based on auditory stimuli.
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However, there are some weaknesses in this approach. First, the model performance depends greatly on the accu- racy of an estimated target pitch contour. In fact, the clas- sification of the foreground and the background in the initial segregation stage is mainly based on the objective quality assessment of speech (OQAS) algorithm. But, it is still a machine estimation and the obtained result is more or less different from the subjective mean open score (MOS). In addition, the combination of CASA with OQAS is not the best combination. It is necessary to find an optimal combi- nation method of CASA and OQAS to ameliorate the sepa- ration. Moreover, this system just enables voiced speech segregation based only on pitch. It does not address the problem of unvoiced speech separation.
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This study conducted in two phases. The first phase was to complete and examine the ques- tionnaire and the second one was to perform the speech in noise (SIN) and dichotic digit test (DDT). The research population includes all 8−12 aged male and female students of Oshnavieh, western Iran, from among whom 385 were selected by using the minimum sam- ple size formula. As required coordinated was made with the authorities of Western Azerbaijan Province Education Organization and schools’ principals, 430 questionnaires were distributed randomly among the 8−12 aged students of Oshnavieh and the parents were requested to fill it after studying and signing the letter of cons- tant. After two days, questionnaires were collec- ted from the schools, then reviewed. Out of 430 questionnaires distributed among the schools, 396 ones were filled properly which included 195 male students (37 students with 8 years old, 37 with 9 years old, 46 with 10 years old, 37 with 11 years old, 38 with 12 years old) and 201 female students (38 with 8 years old, 37 with 9 years old, 47 with 10 years old, 41 with 11 years old, 38 with 12 years old). Results obtained for three auditory, language and attention indices were extracted from the questionnaires. 359 students were within the normal range in view of the achieved questionnaire scores and 37 students were in the suspected area to central auditory processing disorder.
BAEP: brainstem auditory evoked potential; BBB: blood – brain barrier; CMS: conventional multiple sclerosis; CNS: central nervous system; CSF: cerebrospinal fluid; DCE-MRI: dynamic contrast-enhanced magnetic resonance imaging; DWI: diffusion-weighted imaging; EDSS: Expanded Disability Status Scale; FLAIR: fluid-attenuated inversion recovery; Gd-DTPA: gadolinium-diethylenetriaminepentaacetic acid; MRI: magnetic resonance imaging; MS: multiple sclerosis; NMO: neuromyelitis optica; OB: oligoclonal band; OSMS: optic-spinal form of multiple sclerosis; SEP: somatosensory evoked potential; VEP: visual evoked potential.
(v) It has also been suggested that the effects o f opioids in the inner ear could be mediated by sympathetic neurones innervating the cochlea (Eybalin et al, 1993). There is evidence that dynorphin-related peptides co-exist with catecholamines within fibres o f the superior cervical ganglion (SCG) that travel through the intraganglionic spiral bundle (Sanchez-Garzon et al, 1990), suggesting that the auditory effects o f opioids m ay be vascularly mediated through catecholamine release in the inner ear. However Sahley and Nodar (1996) report that these dynorphin-containing fibres are devoid o f connections w ith blood vessels and do not appear to be part o f the efferent system. Electrical stimulation o f the SCG causes a catecholamine-mediated decrease in cochlear blood flow, leading to facilitation o f auditory sensitivity (Brechtelsbauer et al, 1990, Ren et al, 1994). It appears unlikely that opioids act through this system, however, as opioid drug agonists inhibit activity within the SCG and therefore have the potential to increase, rather than decrease, cochlear blood flow, leading to a reduction in cochlear sensitivity (Ohlsen et al, 1992: 1993). Furthermore, NC labelling in cochlear blood vessels was not observed.
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Performance is correlated across various rhythm tasks such as entrainment, rhythm discrimination, and amplitude rise time perception, (Thomson et al., 2006; Thomson and Goswami, 2008; Huss et al., 2011), suggesting that these tasks broadly assess a single rhythmic competence. Nevertheless, there is evidence that dramatic impairments in single rhythmic skills can coexist with normal performance in other rhythmic skills. Phillips-Silver et al. (2011), for example, reported a case study of a participant who was able to entrain to a metronome but not to a piece of music. Similarly, Launay et al. (2014) describe a group of participants with difficulties tapping to the beat of rhythmic patterns but with preserved ability to entrain to a metronome. On the other hand, Fries and Swihart (1990) report that a patient with right hemisphere damage was unable to entrain to an acoustic rhythm but was able to entrain to a visual stimulus and could both dis- criminate rhythmic patterns and produce rhythms from memory. Auditory-motor entrainment, therefore, appears to be dissociable from other rhythmic skills.
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Previous intracranial studies, conducted mainly in adults, have indicated that several cortical regions are active at the time o f the scalp recorded N l, the most prominent located to the superior surfaces o f the temporal lobes that can be either negative (Liegeois-Chauvel.C et al., 1993) or positive (Halgren et al., 1995) in polarity when recorded intracranially. These discrepancies in the responses demonstrate that even in adults the major sources contributing to the scalp recorded N l are still unresolved. Other methods have been used to support previous intracranial findings. Dipole source modelling uses scalp recorded data to mathematically estimate the intracerebral sources. In an early study, the responses evoked to tone bursts presented every 0.9 seconds could be explained by three bilateral dipole sources in the temporal lobes (Scherg & Cramon, 1986; Scherg et al., 1989). The first, a vertically orientated dipole located on the STP or near the auditory cortex, was suggested to contribute the scalp recorded wave at 100 ms. A second vertically orientated dipole anterior to the first was suggested to contribute to the N l and the sustained potential. The third was a laterally orientated dipole that was suggested to originate from the magnopyrymidal temporal field and contributed to a negative wave at the lateral scalp locations at 145 ms.
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With regards to specialised ENT, audiology and speech therapy equipment, few hospitals (6.6%, n = 4) possessed operating microscopes, 6.6% (n = 4) had grommet inser- tion sets, 6.6% (n = 4) had diagnostic audiometers and 4.9% (n = 3) owned at least one of the following equip- ment: a tympanometer, screening audiometer, mastoid drill kit and mastoidectomy instrument set. Only 3.3% (n = 2) hospitals, both located in Lusaka Urban District, had Auditory Brain Response (ABR), Otoacoustic Emis- sion (OAE) and Auditory Steady State Response (ASSR) equipment. Furthermore, 24.6% ( n = 15) and 31.1% ( n = 19) of the participating hospitals had adenotonsillectomy and tracheostomy sets, respectively. The 19 hospitals owning tracheostomy sets were spread across 7 of the 10 provinces of the country. In addition, 4.9% (n = 3) of the hospitals (one FLH and a TLH from Lusaka Province and one SLH from Western Province) were equipped with at least one zero degree endoscope while only 3.3% Table 3 Percentage of surveyed hospitals with at least one of the basic ENT ear equipment according to provinces
Parkinson’s disease (PD) is a progressive neurodegenerative disorder associated with dopamine depletion in the basal ganglia (Benazzouz, Mamad, Abedi, Bouali-Benazzouz, & Chetrit, 2014). In 1817, James Parkinson first described PD as a syndrome that predominantly affected the motor system (Parkinson, 2002). Since then, PD has also been clarified as a syndrome that may also involve abnormalities in behavior, cognition, and emotion (Callesen, Scheel-Krüger, Kringelbach, & Møller, 2013). PD currently affects more than 1% of individuals over the age of 65 years, affecting an estimated 100,000 Canadians (Wong, Gilmour, & Ramage- Morin, 2014) with approximately 5,500 new cases being diagnosed each year (Pringsheim, Jette, Frolkis, & Steeves, 2014). The incidence is similar worldwide (Belin & Westerlund, 2008). This number will continue to increase as the population ages (Bodnar, 2008). Dysfunction of the basal ganglia has been studied intensively as it pertains to motor control (A. Nelson & Kreitzer, 2014), as dopamine decreases, tremors can develop, muscle movements become slower and more rigid, and reflexes become impaired (Wong et al., 2014). These impairments to motor control
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Regarding the inclusion criteria, young adults were selected in order to avoid the influence of age on the behavioral assessment of CAP, as the corresponding tests are influenced by the maturation and degeneration processes of the central au- ditory pathway. Furthermore, right-handed individuals were selected because hand dominance also affects this assessment. Individuals not undergoing any speech, language or occupational therapy intervention before the assessment and with the minimum schooling corresponding to complete secondary education were selected aiming at equal times for a similar formation. Individuals could not have any evident physical, cognitive and psychological problem to avoid that any of these variations affected their capacity to perform the rehabilitation process (FAT).
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Several BICs are seen in middle latency res- ponse (MLR) (20 to 40 ms)  and late latency response (LLR) (63 to 150 ms) [42,43]. BIC in these responses is larger than ABR. This con- dition may indicate that binaural processing is major in thalamocortical and cortical levels, and happens much more than the pontine level . At the level of MLR and LLR, some compo- nents show a larger binaural response than the sum of the monaural responses. In these cases, an underlying facilitation mechanism might be involved. According to studies, these compo- nents belong to non-specific auditory pathways and nuclei, such as medial and dorsal nuclei of the medial geniculate body (MGB). Recordings from the temporal lobe indicate that specific auditory areas show inhibitory patterns, but areas with multisensory processing show facili- tatory patterns [44,45].
The reduction of correct answers in the Q-SIN test can be related to anomalies in these areas, due to the migraine effect. It should be noted that the precise physiological and anatomical mechanism of migraine is still unclear, so it is not possible to certainly relate the anomalies in the cortical and under the cortical regions due to migraine to the inability to speech perception in noise. The results of the Q-SIN test were consis- tent with the results of Ciriaco et al. which con- ducted a computerized test battery to assess speech perception in silence and noise in chil- dren with migraine headache . The results show that SNR loss is not different between normal men and women as well as between men and women with migraine. According to the stu- dies, structural differences between normal men and women as well as men and women with migraine have not been reported so far in the regions involved in the auditory processing. However, indirect effect of sex hormones in men and women on neurotransmitters such as serotonin and gama-Aminobutyric acid (GABA) has been identified, and no difference in their effects on auditory performance has been repor- ted. Shayanmehr et al. , Gheissi et al.  and Bockowski et al.  also achieved the same result in normal individuals, and declared that gender had no effect on the results.