Considering the low incidence of regional lymph node recurrence and the levels with frequent regional recurrence in patients without lymph node metastasis, elective neck dissection in all cases of total thyroidectomy may be immoderate. However, if any risk factors for regional recurrence, including large tumor size, presence of extrathyroid spread, high T stage, and presence of lymph node metastasis, are detected by preoperative and intraoperative evaluation, a systematic compartment-oriented lymphadenectomy should be considered because of the high possibility of regional recurrence.
Electric stimuli can prosthetically excite auditory nerve fibers to partially restore sensory function to individuals impaired by profound or severe hearing loss. While basic response properties of electrically stimulated auditory nerve fibers (ANF) are known, responses to complex, time-changing stimuli used clinically are inadequately understood. We report that forward-masker pulse trains can enhance and reduce ANF responsiveness to subsequent stimuli and the novel observation that sub-threshold (nonspike-evoking) electric trains can reduce responsiveness to subsequent pulse-train stimuli. The effect is observed in the responses of cat ANFs and shown by a computational biophysical ANF model that simulates rate adaptation through integration of external potassium cation (K) channels. Both low-threshold (i.e., Klt) and high-threshold (Kht) channels were simulated at each node of Ranvier. Model versions without Klt channels did not produce the sub-threshold effect. These results suggest that some such accumulation mechanism, along with Klt channels, may underlie sub-threshold masking observed in cat ANF responses. As multichannel auditory prostheses typically present sub-threshold stimuli to various ANF subsets, there is clear relevance of these findings to clinical situations.
The hypothesis of this study was that broader patterns of physiological channel interactions in the local region of the cochlea are associated with poorer spectral resolution in the same region. Electrically evoked compound action potentials (ECAPs) were measured for three to six probe electrodes per subject to examine the channel interactions in different regions across the electrode array. To evaluate spectral resolution at a confined location within the cochlea, spectral-ripple discrimination (SRD) was measured using narrowband ripple stimuli with the bandwidth spanning five electrodes: Two electrodes apical and basal to the ECAP probe electrode. The relationship between the physiological channel interactions, spectral resolution in the local cochlear region, and vowel identification was evaluated. Results showed that (1) there was within- and across-subject variability in the widths of ECAP channel interaction functions and in narrowband SRD performance, (2) significant correlations were found between the widths of the ECAP functions and narrowband SRD thresholds, and between mean bandwidths of ECAP functions averaged across multiple probe electrodes and broadband SRD performance across subjects, and (3) the global spectral resolution reflecting the entire electrode array, not the local region, predicts vowel identification.
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