Study of effect of chronic suppurative otitis media on auditory brainstem response latency

<p class="abstract"><strong>Background:</strong> Chronic suppurative otitis media (CSOM) emerging as common hearing problems in the recent years with high prevalence requiring immediate attention. Hence, our study includes assessment of adult patients with CSOM using electrophysiological test, auditory brainstem response (ABR) and analysing the latency of ABR peaks in order to find the effect of CSOM on ABR latency with respect to shift in latency.</p><p class="abstract"><strong>Methods:</strong> The study followed cross sectional study design where data collected from March to September 2019 were used. A total of 50 subjects with unilateral CSOM were analysed. Descriptive statistics and paired t-test was used for statistical analysis of the data. </p><p class="abstract"><strong>Results:</strong> The data was divided into 3 groups based on degree of hearing loss (mild, moderate and moderately severe). The Mean ABR peak latency was analysed and subjects showed a significant latency shift. Also, it was found that the magnitude of latency shift increased with increase in degree of hearing loss.</p><p class="abstract"><strong>Conclusions:</strong> Hence the study concludes that as the amount of conductive component increases the pure tone threshold deteriorates and ABR latency gets affected. Also, the morphology of ABR peaks on comparison to the normal hearing ear gets affected due to constant conductive pathology in the pathological ear.</p><p class="abstract"> </p>

A method for reconstruction of visually evoked potentials from limited amount of sweeps

Visually evoked potentials (VEPs) are signals evoked by a visual stimulus. They consist of brief discrete deflections embedded in background electroencephalographic (EEG) activity, which often has larger amplitude. Background EEG cancelation is a major part of VEPs analysis algorithms often realized by coherent averaging or other methods requiring large minimal amount of registered sweeps. In some cases, especially for pediatric patients, or in poor patient compliance cases, long procedure duration and fatigue might cause impaired attention and non-steady target fixation, affecting the quality of recorded VEPs. The possibility to reconstruct VEPs in every single sweep from limited size ensembles opens new diagnostic possibilities and shortens the registration procedure improving its quality. A proposed method is based on truncated expansion (Karhunen-Loève transform) of VEP signals applying generalized universal basis functions (eigenvectors of covariation matrix) calculated from learning set of sweeps, i.e. an ensemble of collected typical recordings. It realizes the possibility to reconstruct a signal from every single sweep even in limited size ensembles of registered sweeps. Application of adaptively time-shifted basis functions enables optimal reconstruction of the signal with latency shift or jitter.

Footprints of inhibition in the response of cortical delay-tuned neurons of bats

Responses of echo-delay-tuned neurons that encode target distance were investigated in the dorsal auditory cortex of anesthetized short-tailed fruit bats ( Carollia perspicillata). This species echolocates using short downward frequency-modulated (FM) biosonar signals. In response to FM sweeps of increasing level, 60 out of 131 studied neurons (47%) displayed a “paradoxical latency shift,” i.e., longer response latency to loud sounds and shorter latency to faint sounds. In addition, a disproportionately large number of neurons (80%) displayed nonmonotonic responses, i.e., weaker responses to loud sounds and stronger responses to faint sounds. We speculate that the observed paradoxical latency shift and nonmonotonic responses are extracellular footprints of inhibitory processes evoked by loud sounds and that they could represent a specialization for the processing of the emitted loud biosonar pulse. Supporting this idea is the fact that all studied neurons displayed strong response suppression when an artificial loud pulse and a faint echo were presented together at a nonoptimal delay. In 24 neurons, iontophoresis of bicuculline (an antagonist of A-type γ-aminobutyric acid receptors) did not remove inhibitory footprints but did increase the overall spike output, and in some cases it also modified the response bandwidth and shifted the neuron's “best delay.” We suggest that inhibition could play a dual role in shaping delay tuning in different auditory stations. Below the cortex it participates in delay-tuning implementation and leaves a footprint that is measurable in cortical responses, while in the cortex it provides a substrate for an in situ control of neuronal selectivity.

Corticofugal Modulation of the Paradoxical Latency Shifts of Inferior Collicular Neurons

The central auditory system creates various types of neurons tuned to different acoustic parameters other than a specific frequency. The response latency of auditory neurons typically shortens with an increase in stimulus intensity. However, ∼10% of collicular neurons of the little brown bat show a “paradoxical latency-shift (PLS)”: long latencies to intense sounds but short latencies to weak sounds. These neurons presumably are involved in the processing of target distance information carried by a pair of an intense biosonar pulse and its weak echo. Our current studies show that collicular PLS neurons of the big brown bat are modulated by the corticofugal (descending) system. Electric stimulation of cortical auditory neurons evoked two types of changes in the PLS neurons, depending on the relationship in the best frequency (BF) between the stimulated cortical and recorded collicular neurons. When the BF was matched between them, the cortical stimulation did not shift the BFs of the collicular neurons and shortened their response latencies at intense sounds so that the PLS became smaller. When the BF was unmatched, however, the cortical stimulation shifted the BFs of the collicular neurons and lengthened their response latencies at intense sounds, so that the PLS became larger. Cortical electric stimulation also modulated the response latencies of non-PLS neurons. It produced an inhibitory frequency tuning curve or curves. Our findings indicate that corticofugal feedback is involved in shaping the spectrotemporal patterns of responses of subcortical auditory neurons presumably through inhibition.

Temporal dynamics of motion integration for the initiation of tracking eye movements at ultra-short latencies

The perceived direction of a grating moving behind an elongated aperture is biased towards the aperture's long axis. This “barber pole” illusion is a consequence of integrating one-dimensional (1D) or grating and two-dimensional (2D) or terminator motion signals. In humans, we recorded the ocular following responses to this stimulus. Tracking was always initiated at ultra-short latencies (≈ 85 ms) in the direction of grating motion. With elongated apertures, a later component was initiated 15–20 ms later in the direction of the terminator motion signals along the aperture's long axis. Amplitude of the later component was dependent upon the aperture's aspect ratio. Mean tracking direction at the end of the trial (135–175 ms after stimulus onset) was between the directions of the vector sum computed by integrating either terminator motion signals only or both grating and terminator motion signals. Introducing an elongated mask at the center of the “barber pole” did not affect the latency difference between early and later components, indicating that this latency shift was not due to foveal versus peripheral locations of 1D and 2D motion signals. Increasing the size of the foveal mask up to 90% of the stimulus area selectively reduced the strength of the grating motion signals and, consequently, the amplitude of the early component. Conversely, reducing the contrast of, or indenting the aperture's edges, selectively reduced the strength of terminator motion signals and, consequently, the amplitude of the later component. Latencies were never affected by these manipulations. These results tease apart an early component of tracking responses, driven by the grating motion signals and a later component, driven by the line-endings moving at the intersection between grating and aperture's borders. These results support the hypothesis of a parallel processing of 1D and 2D motion signals with different temporal dynamics.