Effects of superior olivary complex lesions on binaural responses in rat auditory cortex

Unilateral or bilateral lesions of the superior olivary complex (SOC) were made by local injection of kainic acid through a micropipette lowered stereotaxically into the rat's auditory brain stem. The lesions had the effect of destroying cell bodies in the superior olive without disrupting fibers of passage. After a recovery period of approximately one month, physiological recordings were made with tungsten microelectrodes from the auditory cortex of normal animals with SOC lesions. For animals with unilateral SOC lesions recordings were made either ipsilateral or contralateral to the site of damage. Monaural and binaural tone bursts (110 ms duration) were presented dichotically through a sealed sound delivery system and binaural interaction patterns were determined by comparison of monaural and binaural responses. Some cells were excited by stimulation of either ear and facilitated by binaural stimulation (binaural summation or EE cells), whereas others were excited by contralateral stimulation and inhibited by simultaneous ipsilateral stimulation (binaural suppression or EI cells). Both binaural summation and suppression responses were still present following unilateral SOC lesions. Interaural intensity difference thresholds were within the normal range and no differences were found between animals with lesions placed ipsilateral or contralateral to the recording site. Following a bilateral lesion in one case, both binaural summation and suppression responses were still present. The bilateral lesion had the effect of shifting the average interaural intensity difference thresholds in favor of the contralateral ear. These data suggest that binaural interactions above the level of the superior olive contribute to physiological responses in auditory cortex and the binaural responses in the rat's auditory cortex are shaped by both olivary and supraolivary interactions.     

An auditory localization model based on high-frequency spectral cues

We present in this paper a connectionist model that extracts interaural intensity differences (IID) from head-related transfer functions (HRTF) in the form of spectral cues to localize broadband high-frequency auditory stimuli, in both azimuth and elevation. A novel discriminative matching measure (DMM) is defined and optimized to characterize matching this IID spectrum. The optimal DMM approach and a novel backpropagation-based fuzzy model of localization are shown to be capable of localizing sources in azimuth, using only spectral IID cues. The fuzzy neural network model is extended to include localization in elevation. The use of training data with additive noise provides robustness to input errors. Outputs are modeled as two-dimensional Gaussians that act as membership functions for the fuzzy sets of sound locations. Error back-propagation is used to train the network to correlate input patterns and the desired output patterns. The fuzzy outputs are used to estimate the location of the source by detecting Gaussians using the max-energy paradigm. The proposed model shows that HRTF-based spectral IID patterns can provide sufficient information for extracting localization cues using a connectionist paradigm. Successful recognition in the presence of additive noise in the inputs indicates that the computational framework of this model is robust to errors made in estimating the IID patterns. The localization errors for such noisy patterns at various elevations and azimuths are compared and found to be within limits of localization blurs observed in humans.     

Shortened silent period produced by magnetic cortical stimulation in patients with Parkinson's disease

Magnetic cortical stimulation can produce silent periods (SP) following excitatory motor responses. In patients with Parkinson's disease (PD), a shorter SP was observed. The shortened SP in PD patients improved after levodopa administration. This shortened SP in PD patients may be related to the hyperactivity of the motor cortex, and to the dopaminergic system. In control subjects, sound stimulation produced prolongation of the SP at a time interval of 100 ms between sound and magnetic cortical stimulation-increase in the inhibitory function. However, the prolongation of the SP after sound stimulation was not observed in PD patients lack of an increase in the inhibitory function. Even after levodopa administration, sound did not prolong the SP in PD patients. The change of the auditory effects on the SP may be due to the abnormal function of the reticular formation in PD. This change might be independent of the dopaminergic system.     

Optimal boundary impedance for the minimization of reflection: (I) Asymptotic solutions by the geometrical optics method

In the design of surfaces which absorb waves, the impedance boundary condition is used as an effective means of diminishing the reflection. In this paper, we use the geometrical optics method to approximate the optimal impedance value which minimizes the reflected field for the scalar wave equation with a monochromatic source. Our treatment yields good results for optimal impedance in the asymptoticity region of the geometrical optics solution.     

Significant Clinical Differences in Primary Hyperparathyroidism Between Patients with and Those Without Concomitant Thyroid Disease

Purpose We evaluated the differences in diagnosis and treatment for primary hyperparathyroidism (pHPT) in patients with and those without concomitant thyroid disease.Methods One hundred and ten patients with pHPT underwent parathyroid localization and thyroid examination by ultrasonography (US) and sestamibi scintigraphy (MIBI). The clinical and biochemical findings, parathyroid localization, and operations performed were compared in 49 patients without thyroid disease and 61 patients with thyroid disease.Results Asymptomatic hypercalcemia was significantly more prevalent in patients with concomitant thyroid disease (88.5%) than in those without thyroid disease (49.0%) (P < 0.01). The mean serum calcium was significantly higher and the inorganic phosphate level was significantly lower in patients without concomitant thyroid disease than in those with concomitant thyroid disease (P < 0.05, P < 0.01, respectively). The pathologic parathyroid gland was identified significantly more often in patients without concomitant thyroid disease than in those with concomitant thyroid disease both by US and MIBI (P < 0.05). Unilateral exploration was performed more often in patients without thyroid disease than in those with thyroid disease (P < 0.01).Conclusion Primary hyperparathyroidism was diagnosed at an earlier stage in patients with concomitant thyroid disease. Thyroid disease concomitant with pHPT influenced parathyroid localization as well as the indication for minimally invasive parathyroidectomy.     

Radio-guided localization of clinically occult breast lesions (ROLL): a DGH experience

AIM: Wire-guided localization (WGL) of clinically occult breast lesions is a well established technique. The aim of this study was to evaluate radio-guided localization (ROLL) within the breast screening service of a district general hospital. METHOD: The study group comprised 70 women who underwent ROLL under US and stereotaxis. This required an injection of Technetium-labelled colloidal albumen into the impalpable breast lesion. The women then proceeded to theatre, where localization was achieved with the use of a gamma probe. The lesion was identified by the presence of a high signal, caused by the injected isotope. The results of 70 consecutive cases in which a breast lesion was localized using ROLL were compared with the results of the latest 70 WGLs. RESULTS: All 140 lesions were successfully localized. However, the change in technique from WGL to ROLL offered significant benefits to patients. CONCLUSION: Our study demonstrated that ROLL is a practical and reliable localization technique. It can be implemented in hospital units without using valuable gamma camera time. The cost compares well with WGL. There is an improved cosmetic outcome for patients, and the very small quantity of radioactivity used is safe for both patients and staff.     

Easy listening to sleep recordings: tools and examples

BACKGROUND AND PURPOSE: To specify a simple conversion of neurophysiological signals contained in sleep recordings into standard audio files and to illustrate how our cerebral audio processor can then detect specific signal characteristics. METHODS: A software package (freely accessible from the Internet) has been developed that converts signals from standard EDF (or EDF+) format to standard audio (WAV) format, a process usually called audification. The software has been applied to sleep EEG, EOG and ECG. The software is easy to apply. RESULTS: A wide range of audified signals is described, stressing the analogy with familiar sounds. Audio properties of EEG in different sleep stages, EOG, ECG and respiration signals are discussed. Auditive presentation of the signals invokes brain processes that differ essentially from the commonly applied visual interpretation, including physiological frequency analysis. CONCLUSIONS: Such auditive interpretation may complement the visual one. The widespread use of EDF+ and multimedia computers makes such audification simple and straightforward.     

Contour interpolation revealed by a dot localization paradigm

Contour interpolation mechanisms allow perception of bounded objects despite incomplete edge information. Here, we introduce a paradigm that maps interpolated contours as they unfold over time. Observers localize dots relative to perceived boundaries of illusory, partly occluded, or control stimuli. Variations in performance with dot position and processing time reveal the location and precision of emerging contour representations. Illusory and occluded contours yielded more proficient dot localization than control stimuli containing only spatial cues, suggesting performance based on low-level representations. Further, illusory contours exhibited a distinct developmental time course, emerging over the first 120 ms of processing. These experiments establish the effectiveness of the dot localization paradigm for examining interpolated edge representations, contour microgenesis, and the underlying processing mechanisms.     

The motion-induced position shift depends on the perceived direction of bistable quartet motion

Motion can influence the perceived position of nearby stationary objects (Nature Neuroscience 3 (2000) 954). To investigate the influence of high-level motion processes on the position shift while controlling for low-level motion signals, we measured the position shift as a function of the motion seen in a bistable quartet. In this stimulus, motion can be seen along either one or the other of two possible paths. An illusory position shift was observed only when the flashes were adjacent to the path where motion was perceived. If the flash was adjacent to the other path, where no motion was perceived, there was no illusory displacement. Thus for the same physical stimulus, a change in the perceived motion path determined the location where illusory position shifts would be seen. This result indicates that high-level motion processes alone are sufficient to produce the position shift of stationary objects. The effect of the timing of the test flash between the onset and offset of the motion was also examined. The position shifts were greatest at the onset of motion, then decreasing gradually, disappearing at the offset of motion. We propose an attentional repulsion explanation for the shift effect.