Biomedical subjects

Aage R Møller

Publications and source records attributed to Aage R Møller.

6 recordsLinked to original sources

PubMed2006

Neural plasticity in tinnitus.

Two distinctly different kinds of tinnitus occur: objective and subjective tinnitus. Objective tinnitus is caused by sounds generated in the body while subjective tinnitus is caused by abnormal neural activity that is not evoked by sound. This chapter discusses subjective tinnitus. Subjective tinnitus has many forms. In most forms of tinnitus the anatomical location of the physiological abnormality is in the central nervous system, although the sensation is often referred to one ear or both ears. The cause of most forms of subjective tinnitus is the changes that have occurred as a result of expression of neural plasticity, thus a form of reprogramming of the brain that is not to the benefit of the individual person. Tinnitus often occurs together with hearing loss, indicating that the expression of neural plasticity has been evoked by deprivation of input. Tinnitus is often accompanied by hyperacusis, and sometimes phonophobia and depression, indicating altered processing of auditory information or rerouting of information. Several studies have brought evidence that some forms of tinnitus are associated with an abnormal involvement of the nonclassical (extralemniscal, diffuse, or polysensory) auditory pathways that bypass the primary auditory cerebral cortex and provide subcortical connections to limbic structures among others. There is no general treatment for tinnitus, but there are several treatments that can alleviate or reduce the tinnitus in some patients.

Humans↗

PubMed2006

History of cochlear implants and auditory brainstem implants.

Cochlear implants have evolved during the past 30 years from the single-electrode device introduced by Dr. William House, to the multi-electrode devices with complex digital signal processing that are in use now. This paper describes the history of the development of cochlear implants and auditory brainstem implants (ABIs). The designs of modern cochlear and auditory brainstem implants are described, and the different strategies of signal processing that are in use in these devices are discussed. The primary purpose of cochlear implants was to provide sound awareness in deaf individuals. Modern cochlear implants provide much more, including good speech comprehension, and even allow conversing on the telephone. ABIs that stimulate the cochlear nucleus were originally used only in patients with neurofibromatosis type 2 who had lost hearing due to removal of bilateral vestibular schwannoma. In such patients, ABIs provided sound awareness and some discrimination of speech. Recently, similar degrees of speech discrimination as achieved with cochlear implants have been obtained when ABIs were used in patients who had lost function of their auditory nerve on both sides for other reasons such as trauma and atresia of the internal auditory meatus.

Auditory Brain Stem Implants↗

PubMed2006

Physiological basis for cochlear and auditory brainstem implants.

Cochlear implants bypass functions of the cochlea that have been regarded to be fundamental for discrimination of the frequency (or spectrum). Frequency discrimination is essential for discrimination of sounds, including speech sounds, and the normal auditory system is assumed to make use of both (power) spectral and temporal information for frequency discrimination. Spectral information is represented by the place on the basilar membrane that generates the largest amplitude of vibration on the basilar membrane. Evidence has been presented that the temporal representation of frequency is more robust than the place representation and thus regarded more important for speech discrimination. The fact that some cochlear implants provide good speech discrimination using only information about the energy in a few spectral bands seems to contradict these studies. In that way, frequency discrimination may be similar to trichromatic color vision, which is based on the energy in only three different spectral bands of light, accomplished by different color-sensitive pigments in the cones of the retina. Cochlear nucleus implants (ABIs) also bypass the auditory nerve, which does not perform any processing. Therefore, it may be expected that ABIs are equally efficient as cochlear implants. However, experience from the use of ABIs in patients with bilateral vestibular schwannoma has not been encouraging, but recent studies of the use of ABIs in patients with other causes of injuries to the auditory nerve have shown similar speech discrimination as achieved with modern cochlear implants. Cochlear implants and ABIs are successful in providing speech discrimination because of redundancy in the processing in the ear, redundancy of the speech signal and because the auditory nervous system has a high degree of plasticity. Expression of neural plasticity makes the auditory nervous system adapt to the change in demands of processing of the information provided by cochlear implants.

Auditory Brain Stem Implants↗

PubMed2005

Are the non-classical auditory pathways involved in autism and PDD?

OBJECTIVE: To test the hypothesis that some of the abnormal sensory perceptions that characterize autism may be explained by an abnormal activation of non-classical (extra-lemniscal) sensory pathways. METHODS: Twenty-one individuals, 18--45 years of age who were diagnosed with autism participated in the study. Sounds (clicks presented at a rate of 40 per second and 65 dB above the normal threshold) were applied through earphones. Electrical stimulation (100 microS rectangular impulses at a rate of 4 per second) was applied through electrodes placed on the skin over the median nerve at the wrist. The participants were asked to match the loudness of the sound with and without the electrical stimulation applied to the median nerve. RESULTS: Electrical stimulation of the median nerve at the wrist in individuals with autism could change the perception of loudness of sounds presented to one ear through an earphone showing a statistically significant abnormal sensory cross-modal interaction. DISCUSSION: We interpreted our results to support the hypothesis that some individuals with autism have an abnormal cross-modal interaction between the auditory and the somatosensory systems. Cross-modal interaction between senses such as hearing and the somatosensory system does not occur normally in adults. As only the non-classical (extralemniscal) ascending auditory pathways receive somatosensory input, the presence of cross-modal interaction in autistic individuals is a sign that autism is associated with abnormal involvement of the non-classical auditory pathways, implying that sensory information is processed by different populations of neurons than in non-autistic individuals.

Acoustic Stimulation↗

PubMed2004

Functional anatomy of the human cochlear nerve and its role in microvascular decompressions for tinnitus.

OBJECTIVE: The functional anatomy (i.e., tonotopy) of the human cochlear nerve is unknown. A better understanding of the tonotopy of the central nervous system segment of the cochlear nerve and of the pathophysiology of tinnitus might help to ameliorate the disappointing results obtained with microvascular decompressions in patients with tinnitus. METHODS: We assume that vascular compression of the cochlear nerve can induce a frequency-specific form of hearing loss and that when the nerve is successfully decompressed, this hearing loss can recuperate. Thirty-one patients underwent a microvascular decompression of the vestibulocochlear nerve for vertigo or tinnitus. Preoperative audiograms were subtracted from postoperative audiograms, regardless of the surgical result with regard to the tinnitus and vertigo, because the hearing improvement could be the only sign of the vascular compression. The frequency of maximal improvement was then correlated to the site of vascular compression. A tonotopy of the cochlear nerve was thus obtained. RESULTS: A total of 18 correlations can be made between the site of compression and postoperative maximal hearing improvement frequency when 5-dB hearing improvement is used as threshold, 13 when 10-dB improvement is used as threshold. A clear distribution can be seen, with clustering of low frequencies at the posterior and inferior side of the cochlear nerve, close to the brainstem, and close to the root exit zone of the facial nerve. High frequencies are distributed closer to the internal acoustic meatus and more superiorly along the posterior aspect of the cochlear nerve. CONCLUSION: The tonotopic organization of the cisternal segment of the cochlear nerve has an oblique rotatory structure as a result of the rotatory course of the cochlear nerve in the posterior fossa. Knowledge of this tonotopic organization of the auditory nerve in its cisternal course might benefit surgeons who perform microvascular decompression operations for the vestibulocochlear compression syndrome, especially in the treatment of unilateral severe tinnitus.

Adult↗

PubMed2003

Pathophysiology of tinnitus.

Tinnitus is not a single entity but a rather diverse group of disorders. Despite symptoms that indicate the ear is the site of the pathology, there is strong evidence that most forms of severe tinnitus are caused by functional changes in the central nervous system. The changes are induced through expression of neural plasticity, some of which may have been caused initially by abnormalities in the ear or the auditory nerve. The involvement of the nonclassical ascending auditory pathway with its subcortical connections to limbic structures (the amygdala) may explain some of the symptoms of some forms of tinnitus including hyperacusis and affective disorders, such as phonophobia and depression, which often accompany severe tinnitus.

Auditory Pathways↗