Reverberation impairs brainstem temporal representations of voiced vowel sounds: challenging "periodicity-tagged" segregation of competing speech in rooms.

The auditory system typically processes information from concurrently active sound sources (e.g., two voices speaking at once), in the presence of multiple delayed, attenuated and distorted sound-wave reflections (reverberation). Brainstem circuits help segregate these complex acoustic mixtures into "auditory objects." Psychophysical studies demonstrate a strong interaction between reverberation and fundamental-frequency (F0) modulation, leading to impaired segregation of competing vowels when segregation is on the basis of F0 differences. Neurophysiological studies of complex-sound segregation have concentrated on sounds with steady F0s, in anechoic environments. However, F0 modulation and reverberation are quasi-ubiquitous. We examine the ability of 129 single units in the ventral cochlear nucleus (VCN) of the anesthetized guinea pig to segregate the concurrent synthetic vowel sounds /a/ and /i/, based on temporal discharge patterns under closed-field conditions. We address the effects of added real-room reverberation, F0 modulation, and the interaction of these two factors, on brainstem neural segregation of voiced speech sounds. A firing-rate representation of single-vowels' spectral envelopes is robust to the combination of F0 modulation and reverberation: local firing-rate maxima and minima across the tonotopic array code vowel-formant structure. However, single-vowel F0-related periodicity information in shuffled inter-spike interval distributions is significantly degraded in the combined presence of reverberation and F0 modulation. Hence, segregation of double-vowels' spectral energy into two streams (corresponding to the two vowels), on the basis of temporal discharge patterns, is impaired by reverberation; specifically when F0 is modulated. All unit types (primary-like, chopper, onset) are similarly affected. These results offer neurophysiological insights to perceptual organization of complex acoustic scenes under realistically challenging listening conditions.This work was supported by a grant from the BBSRC to Ian M. Winter. Mark Sayles received a University of Cambridge MB/PhD studentship. Tony Watkins (University of Reading, UK) provided the real-room impulse responses. Portions of the data analysis and manuscript preparation were performed by Mark Sayles during the course of an Action on Hearing Loss funded UK–US Fulbright Commission professional scholarship held in the Auditory Neurophysiology and Modeling Laboratory at Purdue University, USA. Mark Sayles is currently supported by a post-doctoral fellowship from Fonds Wetenschappelijk Onderzoek—Vlaanderen, held in the Laboratory of Auditory Neurophysiology at KU Leuven, Belgium.This paper was originally published in Frontiers in Systems Neuroscience (Sayles M, Stasiak A, Winter IM, Frontiers in Systems Neuroscience 2015, 8, 248, doi:10.3389/fnsys.2014.00248)

Co-modulation Masking Release Begins in the Auditory Periphery

Understanding speech in noisy environments can be difficult, especially for people with hearing loss. The background noise can cover up the sounds of interest. Normally, the auditory system works to alleviate this problem by tagging and then cancelling the noise. Our experiments are aimed at understanding the mechanism of this noise cancellation process. We hypothesize that non-linear signal processing in the mammalian cochlea (the most peripheral part of the auditory system) is the basis of noise cancellation. To test this hypothesis, we measured the responses of auditory-nerve fibers (ANFs) to sounds embedded in background noise with different statistical properties. ANFs are typically categorized according to their spontaneous firing rate (SR) which co-varies with many other aspects of their neural coding properties. We found that low-SR ANFs showed strong neural correlates of noise cancellation, whereas in high-SR ANFs the effect was much weaker. ANF responses support the hypothesis that cochlear non-linearities underlie noise cancellation in complex listening environments. The weakened non-linearities characteristic of the hearing-impaired cochlea could negatively impact listening in noisy places. Future improvements in the signal-processing algorithms for auditory prostheses may help restore better hearing in background noise

Neural Coding of an Auditory Pitch Illusion

Pitch is an important perceptual dimension in audition, supporting auditory object segregation, melody recognition and lexical distinction. Huggins’ pitch, for example, is a phenomenon evoked by two sources of broadband noise presented binaurally with an inter-aural phase shift over a narrow frequency band. Huggins’ pitch and other dichotic pitches have been studied extensively using perceptual experiments. Several models have been proposed to explain and predict the perception of pitch; however, no studies have tried to record in vivo neuron responses to Huggins’ pitch (HP) nor have tried to explain how the HP is coded by neurons. The existence of pitches arising from the detection of binaural temporal cues may suggests that at least some of the “pitch neurons” involved must be linked to binaural unmasking: a phenomenon whereby binaural processing enhances the perceptual signal-to-noise ratio in noisy environments. To evaluate the neural coding of HP, in vivo recordings of chinchilla auditory nerve fibers (ANFs) and medial superior olivary (MSO) axons were made. Monoaurally and binaurally spike trains were gathered from ANFs and MSO axons respectively. Computational simulation using cross-correlation was used to predict the output of HP using ANFs as input and then it was compared to the recorded output (MSO). A decrease in the firing rate near the MSO neuron center frequency was found in the computation model and in the MSO neurons output. Therefore, by recording from single ANFs and single MSO fibers, we provide evidence for a de-correlation based neural coding of an auditory illusion: Huggins’ pitch

Transcriptional profiling of mycobacterial antigen-induced responses in infants vaccinated with BCG at birth

BACKGROUND: Novel tuberculosis (TB) vaccines recently tested in humans have been designed to boost immunity induced by the current vaccine, Mycobacterium bovis Bacille Calmette-Guérin (BCG). Because BCG vaccination is used extensively in infants, this population group is likely to be the first in which efficacy trials of new vaccines will be conducted. However, our understanding of the complexity of immunity to BCG in infants is inadequate, making interpretation of vaccine-induced immune responses difficult. METHODS: To better understand BCG-induced immunity, we performed gene expression profiling in five 10-week old infants routinely vaccinated with BCG at birth. RNA was extracted from 12 hour BCG-stimulated or purified protein derivative of tuberculin (PPD)-stimulated PBMC, isolated from neonatal blood collected 10 weeks after vaccination. RNA was hybridised to the Sentrix(R) HumanRef-8 Expression BeadChip (Illumina) to measure expression of >16,000 genes. RESULTS: We found that ex vivo stimulation of PBMC with PPD and BCG induced largely similar gene expression profiles, except that BCG induced greater macrophage activation. The peroxisome proliferator-activated receptor (PPAR) signaling pathway, including PPAR-gamma, involved in activation of the alternative, anti-inflammatory macrophage response was down-regulated following stimulation with both antigens. In contrast, up-regulation of genes associated with the classic, pro-inflammatory macrophage response was noted. Further analysis revealed a decrease in the expression of cell adhesion molecules (CAMs), including integrin alpha M (ITGAM), which is known to be important for entry of mycobacteria into the macrophage. Interestingly, more leukocyte genes were down-regulated than up-regulated. CONCLUSION: Our results suggest that a combination of suppressed and up-regulated genes may be key in determining development of protective immunity to TB induced by vaccination with BCG

Perfidious synaptic transmission in the guinea-pig auditory brainstem

The presence of ‘giant’ synapses in the auditory brainstem is thought to be a specialization designed to encode temporal information to support perception of pitch, frequency, and sound-source localisation. These ‘giant’ synapses have been found in the ventral cochlear nucleus, the medial nucleus of the trapezoid body and the ventral nucleus of the lateral lemniscus. An interpretation of these synapses as simple relays has, however, been challenged by the observation in the gerbil that the action potential frequently fails in the ventral cochlear nucleus. Given the prominence of these synapses it is important to establish whether this phenomenon is unique to the gerbil or can be observed in other species. Here we examine the responses of units, thought to be the output of neurons in receipt of ‘giant’ synaptic endings, in the ventral cochlear nucleus and the medial nucleus of the trapezoid body in the guinea pig. We found that failure of the action-potential component, recorded from cells in the ventral cochlear nucleus, occurred in ~60% of spike waveforms when recording spontaneous activity. In the medial nucleus of the trapezoid body, we did not find evidence for action-potential failure. In the ventral cochlear nucleus action-potential failures transform the receptive field between input and output of bushy cells. Additionally, the action-potential failures result in “non-primary-like” temporal-adaptation patterns. This is important for computational models of the auditory system, which commonly assume the responses of ventral cochlear nucleus bushy cells are very similar to their “primary like” auditory-nerve-fibre input

Reverberation impairs brainstem temporal representations of voiced vowel sounds: challenging "periodicity-tagged" segregation of competing speech in rooms

The auditory system typically processes information from concurrently active sound sources (e.g., two voices speaking at once), in the presence of multiple delayed, attenuated and distorted sound-wave reflections (reverberation). Brainstem circuits help segregate these complex acoustic mixtures into "auditory objects." Psychophysical studies demonstrate a strong interaction between reverberation and fundamental-frequency (F0) modulation, leading to impaired segregation of competing vowels when segregation is on the basis of F0 differences. Neurophysiological studies of complex-sound segregation have concentrated on sounds with steady F0s, in anechoic environments. However, F0 modulation and reverberation are quasi-ubiquitous. We examine the ability of 129 single units in the ventral cochlear nucleus (VCN) of the anesthetized guinea pig to segregate the concurrent synthetic vowel sounds /a/ and /i/, based on temporal discharge patterns under closed-field conditions. We address the effects of added real-room reverberation, F0 modulation, and the interaction of these two factors, on brainstem neural segregation of voiced speech sounds. A firing-rate representation of single-vowels' spectral envelopes is robust to the combination of F0 modulation and reverberation: local firing-rate maxima and minima across the tonotopic array code vowel-formant structure. However, single-vowel F0-related periodicity information in shuffled inter-spike interval distributions is significantly degraded in the combined presence of reverberation and F0 modulation. Hence, segregation of double-vowels' spectral energy into two streams (corresponding to the two vowels), on the basis of temporal discharge patterns, is impaired by reverberation; specifically when F0 is modulated. All unit types (primary-like, chopper, onset) are similarly affected. These results offer neurophysiological insights to perceptual organization of complex acoustic scenes under realistically challenging listening conditions.status: publishe

The time course of recovery from suppression and facilitation from single units in the mammalian cochlear nucleus

The responses to two identical, consecutive pure tone stimuli with varying inter-stimulus intervals (?ts) were measured for 89 neurons in the cochlear nucleus of the anaesthetised guinea pig. We observed two main effects; either a decrease (suppression) or an increase (facilitation) in response to the second tone followed by an exponential recovery. Response behaviour correlated with the unit type; primary-like, primary-like with notch and transient-chopper units showed a recovery from suppression that was very similar to that already reported in the auditory nerve. For chopper units the strength of the adaptation was correlated with the units regularity of spike discharge; sustained chopper (CS) units showed less suppression than transient choppers. Onset units showed complete suppression at short ?ts. Pause/Build (PB) units responded with increased activity to the second tone. In contrast to previous studies in the cochlear nucleus the recovery from suppression or facilitation was well described by a single exponential function, enabling us to define a recovery time constant and a maximum suppression/facilitation. There appeared to be a hierarchy in the time constant of recovery with PB and CS units showing the longest recovery times and onset units showing the shortest. <br/

Incidence of Surgical Site Infection Associated With Robotic Surgery

Objective. Robot-assisted surgery is minimally invasive and associated with less blood loss and shorter recovery time than open surgery. We aimed to determine the duration of robot-assisted surgical procedures and the incidence of postoperative surgical site infection (SSI) and to compare our data with the SSI incidence for open procedures according to national data. design. Retrospective cohort study. setting. A 689-bed academic medical center. patients. All patients who underwent a surgical procedure with use of a robotic surgical system during the period from 2000-2007. methods. SSIs were defined and procedure types were classified according to National Healthcare Safety Network criteria. National data for comparison were from 1992-2004. Because of small sample size, procedures were grouped according to surgical site or wound classification. results. Sixteen SSIs developed after 273 robot-assisted procedures (5.9%). The mean surgical duration was 333.6 minutes. Patients who developed SSI had longer mean surgical duration than did patients who did not (558 vs 318 minutes; ). The prostate P \u3c .001 and genitourinary group had 5.74 SSIs per 100 robot-assisted procedures (95% confidence interval [CI], 2.81-11.37), compared with 0.85 SSIs per 100 open procedures from national data. The gynecologic group had 10.00 SSIs per 100 procedures (95% CI, 2.79-30.10), compared with 1.72 SSIs per 100 open procedures. The colon and herniorrhaphy groups had 33.33 SSIs per 100 procedures (95% CI, 9.68-70.00) and 37.50 SSIs per 100 procedures (95% CI, 13.68-69.43), respectively, compared with 5.88 and 1.62 SSIs per 100 open procedures from national data. Patients with a clean-contaminated wound developed 6.1 SSIs per 100 procedures (95% CI, 3.5-10.3), compared with 2.59 SSIs per 100 open procedures. No significant differences in SSI rates were found for other groups. conclusions. Increased incidence of SSI after some types of robot-assisted surgery compared with traditional open surgery may be related to the learning curve associated with use of the robot