1/6. A review of objective methods of evaluating auditory neural pathways.OBJECTIVES: review physiological methods of evaluating function of the auditory neural pathways in infants, children, and adults. Present two case studies to demonstrate the usefulness of physiological measures in assessing abnormalities of the auditory neural pathways. STUDY DESIGN: review of applications of physiological measures of auditory neural function. methods: review otoacoustic emissions, auditory evoked potentials, and efferent reflexes, and discuss their use in identifying disorders of the auditory neural pathways from the cochlea to the cortex. RESULTS: Auditory disorders occur from peripheral to central areas of the neural system. patients with disorders of the peripheral nerve and/or the input from the cochlear inner hair cells, such as the patients presently described as having auditory neuropathy, demonstrate abnormal efferent reflexes, including middle ear muscle reflexes and efferent suppression of otoacoustic emissions, as well as grossly abnormal brainstem evoked potentials. In contrast, patients with more central disorders can be differentiated by normal results on tests of the neural periphery and abnormal findings on cortical evoked potentials and other measures of central function. CONCLUSIONS: Physiological measures are sensitive, objective, and less variable in assessing neural disorders than traditional behavioral measures such as pure-tone or speech audiometry.- - - - - - - - - - ranking = 1keywords = cortex (Clic here for more details about this article) |
2/6. Cortical deafness to dissonance.Ordinary listeners, including infants, easily distinguish consonant from dissonant pitch combinations and consider the former more pleasant than the latter. The preference for consonance over dissonance was tested in a patient, I.R., who suffers from music perception and memory disorders as a result of bilateral lesions to the auditory cortex. In Experiment 1, I.R. was found to be unable to distinguish consonant from dissonant versions of musical excerpts taken from the classical repertoire by rating their pleasantness. I.R.'s indifference to dissonance was not due to a loss of all affective responses to music, however, since she rated the same excerpts as happy or sad, as normal controls do. In Experiment 2, I.R.'s lack of responsiveness to varying degrees of dissonance was replicated with chord sequences which had been used in a previous study using PET, in examining emotional responses to dissonance. A CT scan of I.R.'s brain was co-registered with the PET activation data from normal volunteers. Comparison of I.R.'s scan with the PET data revealed that the damaged areas overlapped with the regions identified to be involved in the perceptual analysis of the musical input, but not with the paralimbic regions involved in affective responses. Taken together, the findings suggest that dissonance may be computed bilaterally in the superior temporal gyri by specialized mechanisms prior to its emotional interpretation.- - - - - - - - - - ranking = 1keywords = cortex (Clic here for more details about this article) |
3/6. SPET monitoring of auditory cortex activation by electric stimulation in a patient with auditory brainstem implant.auditory cortex activation following multifrequency acoustic stimulation has been evaluated by means of single photon emission tomography (SPET) in one patient before and after an auditory brainstem implant (ABI). No activation could be observed after acoustic stimulation before ABI. After ABI stimulation in the coronal and axial slices, the activation within the temporal cortex contralateral to the stimulated ear was twice (43.76%) that of normal controls (23.94 /- 2.74%). This marked difference was not present in other selected cortical auditory areas (homolateral temporal, homolateral and contralateral parietal cortices). The temporal cortex was also examined with six consecutive sagittal slices from 18.75 mm up to 56.25 mm lateral to the midline. A very strong activation (51.20%) compared with that of normal controls (9.94 /- 7.45%) was detected in the 25.26-mm sagittal slice of the temporal cortex contralateral to the stimulated side. The remaining sagittal slices showed an almost normal post-stimulatory activation. As the 25.26-mm sagittal slice corresponds to the medial part of the auditory temporal cortex, its activation suggests that electrode stimulation is concentrated on the region of the cochlear nucleus in which the neurons that transduce high frequencies are located. SPET can be considered useful, in combination with electric auditory-evoked potentials, to obtain information on ABI placement and function, effectiveness of acoustic stimulation, degree of cortical stimulation and tonotopic spatial distribution of auditory cortex activation.- - - - - - - - - - ranking = 10keywords = cortex (Clic here for more details about this article) |
4/6. Central auditory deficits associated with compromise of the primary auditory cortex.The subject of this study was a 46-year-old female who had suffered a cerebrovascular accident (CVA). magnetic resonance imaging revealed damage in the area of the distribution of the middle cerebral artery involving most, if not all, of the primary auditory area of the left hemisphere. No auditory problems were noted prior to the CVA; however, following the CVA, the subject reported a number of auditory difficulties. Pure-tone thresholds were normal post-CVA, and performance on speech recognition testing was good in both ears if ample time was provided between a response and the presentation of the next test item. Duration pattern, intensity discrimination, and middle latency response test results were abnormal for both ears, and right ear deficits were evident on an auditory fusion test and two dichotic speech tests (digits and rhymes). This case is significant in that it demonstrates a good correlation between damage to known key auditory regions and central auditory test results.- - - - - - - - - - ranking = 4keywords = cortex (Clic here for more details about this article) |
5/6. Auditory brain stem and middle latency responses in a patient with cortical deafness.Auditory brain stem (ABR) and middle latency responses (MLR) were recorded in a patient with bilateral temporal lobe lesions. Audiological and higher cortical functions were assessed using conventional behavioral methods. Roentgenological findings were presented for localizing the lesions. Initially the patient showed no behavioral response to sound. Subsequently the patient reported inconsistent awareness of environmental sounds and pure tone sensitivity was impaired to a severe degree. Higher cortical function was essentially intact and the patient was not aphasic. ABR and acoustic reflex findings were consistent with normal functioning of the auditory periphery and brain stem pathways. MLR component Pa was absent bilaterally. These findings suggest that MLR component is bilaterally generated in the temporal lobes. auditory cortex appears to play a role in auditory sensitivity in humans.- - - - - - - - - - ranking = 1keywords = cortex (Clic here for more details about this article) |
6/6. Detection v discrimination of brief-duration tones. Findings in patients with temporal lobe damage.Based on earlier experiments with cats, we have developed two new hearing tests to evaluate the ability of patients with temporal lobe damage to discriminate tones of short temporal duration. Earlier published studies suggested that patients exhibit notably increased thresholds for detecting tone pulses shorter than 200 ms in length when the signals are presented to the ear located contralateral to the damaged hemisphere. Our experiments with cats indicated that auditory cortex lesions had no effect on the cats' ability to detect brief tones but did impair their ability to discriminate small changes in the frequency of such signals. In giving the brief-tone tests to seven patients with temporal lobe damage, we found a similar behavioral dissociation. All patients exhibited normal detection thresholds in conjunction with substantially elevated frequency difference limina.- - - - - - - - - - ranking = 1keywords = cortex (Clic here for more details about this article) |