Measurements of bone conduction auditory brainstem response with the new audiometric bone conduction transducer Radioear B81<sup/>

OBJECTIVE

To compare recordings of bone conduction (BC) stimulated auditory brainstem response (ABR) obtained using the newer BC transducer Radioear B81 and the conventional BC transducer Radioear B71. Balanced electromagnetic separation transducer (BEST) design found in the B81 may influence the ABR magnitudes and latencies, as well as electrical artefacts.

DESIGN

ABRs to tone burst stimuli of 500 Hz, 2000 Hz, 4000 Hz, click stimulation, and broad-band chirp stimulation at 20 and 50 dB nHL were recorded. For each device, stimulus and intensity level, the ABR Jewett wave V amplitude and latency were obtained. The device-related electrical stimulus artefacts on the ABR recordings were also analysed by calculating the Hilbert envelope of the peri-stimulus recording segments.

STUDY SAMPLE

Twenty-three healthy adults with normal hearing were included in the study.

RESULTS

The ABRs obtained by the B81 were similar to that of the B71 in terms of ABR wave V amplitude and latency. However, the B81 produced smaller electrical artefacts than B71 and this difference was statistically significant.

CONCLUSIONS

The BC transducer Radioear B81 provides ABRs comparable to Radioear B71 while causing smaller artefacts.

Differential effects of temporal regularity on auditory-evoked response amplitude: a decrease in silence and increase in noise

Background

In daily life, we are continuously exposed to temporally regular and irregular sounds. Previous studies have demonstrated that the temporal regularity of sound sequences influences neural activity. However, it remains unresolved how temporal regularity affects neural activity in noisy environments, when attention of the listener is not focused on the sound input.

Methods

In the present study, using magnetoencephalography we investigated the effects of temporal regularity in sound signal sequencing (regular vs. irregular) in silent versus noisy environments during distracted listening.

Results

The results demonstrated that temporal regularity differentially affected the auditory-evoked N1m response depending on the background acoustic environment: the N1m amplitudes elicited by the temporally regular sounds were smaller in silence and larger in noise than those elicited by the temporally irregular sounds.

Conclusions

Our results indicate that the human auditory system is able to involuntarily utilize temporal regularity in sound signals to modulate the neural activity in the auditory cortex in accordance with the surrounding acoustic environment.

Prepulse inhibition of auditory change-related cortical responses

Background

Prepulse inhibition (PPI) of the startle response is an important tool to investigate the biology of schizophrenia. PPI is usually observed by use of a startle reflex such as blinking following an intense sound. A similar phenomenon has not been reported for cortical responses.

Results

In 12 healthy subjects, change-related cortical activity in response to an abrupt increase of sound pressure by 5 dB above the background of 65 dB SPL (test stimulus) was measured using magnetoencephalography. The test stimulus evoked a clear cortical response peaking at around 130 ms (Change-N1m). In Experiment 1, effects of the intensity of a prepulse (0.5 ~ 5 dB) on the test response were examined using a paired stimulation paradigm. In Experiment 2, effects of the interval between the prepulse and test stimulus were examined using interstimulus intervals (ISIs) of 50 ~ 350 ms. When the test stimulus was preceded by the prepulse, the Change-N1m was more strongly inhibited by a stronger prepulse (Experiment 1) and a shorter ISI prepulse (Experiment 2). In addition, the amplitude of the test Change-N1m correlated positively with both the amplitude of the prepulse-evoked response and the degree of inhibition, suggesting that subjects who are more sensitive to the auditory change are more strongly inhibited by the prepulse.

Conclusions

Since Change-N1m is easy to measure and control, it would be a valuable tool to investigate mechanisms of sensory gating or the biology of certain mental diseases such as schizophrenia.

Non-linear laws of echoic memory and auditory change detection in humans

Background

The detection of any abrupt change in the environment is important to survival. Since memory of preceding sensory conditions is necessary for detecting changes, such a change-detection system relates closely to the memory system. Here we used an auditory change-related N1 subcomponent (change-N1) of event-related brain potentials to investigate cortical mechanisms underlying change detection and echoic memory.

Results

Change-N1 was elicited by a simple paradigm with two tones, a standard followed by a deviant, while subjects watched a silent movie. The amplitude of change-N1 elicited by a fixed sound pressure deviance (70 dB vs. 75 dB) was negatively correlated with the logarithm of the interval between the standard sound and deviant sound (1, 10, 100, or 1000 ms), while positively correlated with the logarithm of the duration of the standard sound (25, 100, 500, or 1000 ms). The amplitude of change-N1 elicited by a deviance in sound pressure, sound frequency, and sound location was correlated with the logarithm of the magnitude of physical differences between the standard and deviant sounds.

Conclusions

The present findings suggest that temporal representation of echoic memory is non-linear and Weber-Fechner law holds for the automatic cortical response to sound changes within a suprathreshold range. Since the present results show that the behavior of echoic memory can be understood through change-N1, change-N1 would be a useful tool to investigate memory systems.

Reelin-disabled-1 signaling in the mature rat cochlear nucleus

CONCLUSION

Immunohistochemical detection of Reelin in granular cells and disabled-1 in cochlear nucleus suggests a possible Reelin signaling pathway in mature rat cochlear nucleus.

MATERIALS AND METHODS

Six-week-old Wister rats were used throughout this study. The expression of reelin and disabled-1 were studied by using in situ hybridization technique and immunohistochemistry.

RESULTS

Reelin mRNA expression was observed in granular cell layer of dorsal cochlear nucleus. Immunohistochemistry using anti-reelin monoclonal antibodies confirmed reelin expression in granule cells at protein level. We also examined disabled-1 expression in cochlear nucleus and observed positive immunoreactivity in both ventricular and dorsal cochlear nucleus. In the dorsal cochlear nucleus, fusiform and cartwheel cells were labeled. In the ventricular cochlear nucleus, relatively large cells were labeled with anti-disabled-1 polyclonal antibody but the subtypes of disabled-1 positive cells could not be identified.

Case report: peritonitis by Penicillium spp. in a patient undergoing continuous ambulatory peritoneal dialysis

Even though prominent technical improvements in continuous ambulatory peritoneal dialysis (CAPD) treatments during the last decade, peritonitis keeps its place as an important cause of morbidity and mortality in these patients. Among them fungal peritonitis is happened to be the most difficult one to deal with and comes out serious clinical presentation. It is presented here a case of CAPD related fungal peritonitis caused by Penicillium spp. This case experienced recently relapsing bacterial episodes of peritonitis and received long term antibiotics intraperitoneally and systemically. Eventually, Penicillium spp. was detected in several cultures of peritoneal effluent and also tip of Tenckhoff catheter, therefore it was considered as a causative agent. Then, the catheter was removed and amphotericin B therapy was performed. But the general condition of the patient did not improve till surgically drainage of peritoneal collection which was determined by MR (Magnetic Resonance) examination of abdomen after antifungal treatment was completed and Penicillium spp. in the drainage samples was not determined anymore.